wind: Handle ftruncate() and mmap() errors properly

Classic "keeping a pointer to an element inside a vector after the vector is updated" bug, ah yes.

.gitignore

@@ -4,7 +4,14 @@ build/
 initrd/boot/moon
 env-local.sh
 initrd/bin/**
-base/usr/**
+base/usr/bin/**
+base/usr/include/**
+base/usr/lib/**
+base/usr/share/pkgdb/**
+!base/usr/share/fonts/*
+!base/usr/share/icons/*
+base/usr/share/**
+base/usr/x86_64-luna/**
 .fakeroot
 kernel/config.cmake
 ports/out/

CMakeLists.txt

@@ -45,8 +45,10 @@ endif()
 
 add_subdirectory(libluna)
 add_subdirectory(libos)
+add_subdirectory(libui)
 add_subdirectory(libc)
 add_subdirectory(kernel)
 add_subdirectory(apps)
 add_subdirectory(tests)
 add_subdirectory(shell)
+add_subdirectory(wind)

apps/CMakeLists.txt

@@ -47,3 +47,8 @@ luna_app(socket-client.cpp socket-client)
 luna_app(input.cpp input)
 luna_app(shmem-test.cpp shmem-test)
 luna_app(touch.cpp touch)
+luna_app(free.cpp free)
+luna_app(gclient.cpp gclient)
+target_link_libraries(gclient PUBLIC ui)
+luna_app(taskbar.cpp taskbar)
+target_link_libraries(taskbar PUBLIC ui)

apps/free.cpp

@@ -0,0 +1,50 @@
+#include <luna/Units.h>
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <sys/memstat.h>
+
+Result<int> luna_main(int argc, char** argv)
+{
+    bool reserved { false };
+    bool human_readable { false };
+
+    os::ArgumentParser parser;
+    parser.add_description("Query the amount of memory available and used in the system.");
+    parser.add_system_program_info("free"_sv);
+    parser.add_switch_argument(reserved, 'r', "show-reserved"_sv, "show reserved system memory"_sv);
+    parser.add_switch_argument(human_readable, 'h', "human-readable"_sv, "show output in human-readable units"_sv);
+    parser.parse(argc, argv);
+
+    struct membuf buf;
+    memstat(&buf);
+
+    if (human_readable)
+    {
+        auto total = TRY(to_dynamic_unit(buf.mem_total, 10, false, Unit::Binary, true));
+        auto free = TRY(to_dynamic_unit(buf.mem_free, 10, false, Unit::Binary, true));
+        auto used = TRY(to_dynamic_unit(buf.mem_used, 10, false, Unit::Binary, true));
+
+        os::println("%s total memory, out of which:", total.chars());
+        os::println("%s used", used.chars());
+        os::println("%s free", free.chars());
+    }
+    else
+    {
+        os::println("%lu total memory, out of which:", buf.mem_total);
+        os::println("%lu used", buf.mem_used);
+        os::println("%lu free", buf.mem_free);
+    }
+
+    if (reserved)
+    {
+        if (human_readable)
+        {
+            auto reserved_string = TRY(to_dynamic_unit(buf.mem_reserved, 10, false, Unit::Binary, true));
+
+            os::println("%s reserved", reserved_string.chars());
+        }
+        else { os::println("%lu reserved", buf.mem_reserved); }
+    }
+
+    return 0;
+}

apps/gclient.cpp

@@ -0,0 +1,75 @@
+#include <ui/App.h>
+#include <ui/Layout.h>
+
+struct ColorWidget : public ui::Widget
+{
+  public:
+    ColorWidget(ui::Color first, ui::Color second) : m_color(first), m_first_color(first), m_second_color(second)
+    {
+    }
+
+    Result<ui::EventResult> handle_mouse_move(ui::Point) override
+    {
+        m_color = m_second_color;
+        return ui::EventResult::DidHandle;
+    }
+
+    Result<ui::EventResult> handle_mouse_leave(ui::Point) override
+    {
+        m_color = m_first_color;
+        return ui::EventResult::DidHandle;
+    }
+
+    Result<ui::EventResult> handle_mouse_down(ui::Point, int) override
+    {
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<ui::EventResult> handle_mouse_up(ui::Point, int) override
+    {
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<void> draw(ui::Canvas& canvas) override
+    {
+        canvas.fill(m_color);
+        return {};
+    }
+
+  private:
+    ui::Color m_color;
+    ui::Color m_first_color;
+    ui::Color m_second_color;
+};
+
+Result<int> luna_main(int argc, char** argv)
+{
+    ui::App app;
+    TRY(app.init(argc, argv));
+
+    auto* window = TRY(ui::Window::create(ui::Rect { 200, 200, 400, 300 }));
+    app.set_main_window(window);
+
+    window->set_title("Main Window");
+    window->set_background(ui::CYAN);
+
+    ui::HorizontalLayout layout;
+    window->set_main_widget(layout);
+
+    ColorWidget green(ui::GREEN, ui::WHITE);
+    layout.add_widget(green);
+    ColorWidget blue(ui::BLUE, ui::GRAY);
+    layout.add_widget(blue);
+
+    ui::VerticalLayout sublayout;
+    layout.add_widget(sublayout);
+
+    ColorWidget red(ui::RED, ui::CYAN);
+    sublayout.add_widget(red);
+    ColorWidget white(ui::WHITE, ui::GREEN);
+    sublayout.add_widget(white);
+
+    window->draw();
+
+    return app.run();
+}

apps/taskbar.cpp

@@ -0,0 +1,49 @@
+#include <os/Process.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <ui/App.h>
+#include <ui/Button.h>
+#include <ui/Container.h>
+#include <ui/Image.h>
+#include <ui/Layout.h>
+
+void sigchld_handler(int)
+{
+    wait(nullptr);
+}
+
+Result<int> luna_main(int argc, char** argv)
+{
+    ui::App app;
+    TRY(app.init(argc, argv));
+
+    signal(SIGCHLD, sigchld_handler);
+
+    ui::Rect screen = app.screen_rect();
+
+    ui::Rect bar = ui::Rect { ui::Point { 0, screen.height - 50 }, screen.width, 50 };
+
+    auto window = TRY(ui::Window::create(bar, false));
+    app.set_main_window(window);
+    window->set_background(ui::GRAY);
+
+    ui::HorizontalLayout layout(ui::AdjustHeight::Yes, ui::AdjustWidth::No);
+    window->set_main_widget(layout);
+
+    ui::Button button({ 0, 0, 50, 50 });
+    layout.add_widget(button);
+
+    ui::Container container({ 0, 0, 50, 50 }, ui::VerticalAlignment::Center, ui::HorizontalAlignment::Center);
+    button.set_widget(container);
+    button.set_action([] {
+        StringView args[] = { "/usr/bin/gclient" };
+        os::Process::spawn("/usr/bin/gclient", Slice<StringView> { args, 1 }, false);
+    });
+
+    auto image = TRY(ui::ImageWidget::load("/usr/share/icons/32x32/start-icon.tga"));
+    container.set_widget(*image);
+
+    window->draw();
+
+    return app.run();
+}

base/etc/init/01-motd

@@ -1,4 +0,0 @@
-Name=motd
-Description=Show the message of the day to the user.
-Command=/usr/bin/cat /etc/motd
-Wait=true

base/etc/init/98-listen

@@ -1,6 +0,0 @@
-Name=listen
-Description=Start a Unix domain socket test server.
-Command=/usr/bin/socket-test
-StandardOutput=/dev/uart0
-StandardError=/dev/uart0
-Restart=true

base/etc/init/99-login

@@ -1,4 +1,6 @@
 Name=login
-Description=Start the command-line login program.
+Description=Start the display server.
-Command=/usr/bin/login
+Command=/usr/bin/wind --user=selene
+StandardOutput=/dev/uart0
+StandardError=/dev/uart0
 Restart=true

base/etc/user/00-taskbar

@@ -0,0 +1,4 @@
+Name=taskbar
+Description=Start the taskbar.
+Command=/usr/bin/taskbar
+Restart=true

base/etc/user/01-gclient

@@ -0,0 +1,3 @@
+Name=gclient
+Description=Sample user application.
+Command=/usr/bin/gclient

kernel/CMakeLists.txt

@@ -47,6 +47,7 @@ set(SOURCES
     src/sys/poll.cpp
     src/sys/alarm.cpp
     src/sys/pledge.cpp
+    src/sys/memstat.cpp
     src/fs/VFS.cpp
     src/fs/Pipe.cpp
     src/fs/Mount.cpp

kernel/src/arch/x86_64/PS2Mouse.cpp

@@ -43,8 +43,8 @@ static void process_mouse_event(u8 data)
     packet.buttons = 0;
 
     u8 flags = g_mouse_packet[0];
-    if (flags & PS2_MOUSE_X_SIGN) packet.xdelta = -packet.xdelta;
+    if (flags & PS2_MOUSE_X_SIGN) packet.xdelta = -(256 - packet.xdelta);
-    if (flags & PS2_MOUSE_Y_SIGN) packet.ydelta = -packet.ydelta;
+    if (flags & PS2_MOUSE_Y_SIGN) packet.ydelta = -(256 - packet.ydelta);
 
     if (flags & PS2_MOUSE_MIDDLE_BTN) packet.buttons |= moon::MouseButton::Middle;
     if (flags & PS2_MOUSE_RIGHT_BTN) packet.buttons |= moon::MouseButton::Right;

kernel/src/fs/StorageCache.cpp

@@ -1,5 +1,6 @@
 #include "fs/StorageCache.h"
 #include "Log.h"
+#include <luna/Heap.h>
 #include <luna/ScopeGuard.h>
 
 static LinkedList<StorageCache> g_storage_caches;
@@ -23,9 +24,13 @@ Result<StorageCache::CacheEntry*> StorageCache::fetch_entry(u64 block)
 
 void StorageCache::clear()
 {
-    ScopedKMutexLock<100> lock(m_mutex);
+    m_mutex.lock();
 
+    kdbgln("cache: clearing %lu entries, out of %lu buckets", m_cache_entries.size(), m_cache_entries.capacity());
     m_cache_entries.clear();
+    kdbgln("cache: done");
+
+    m_mutex.unlock();
 }
 
 StorageCache::StorageCache()

kernel/src/main.cpp

@@ -31,6 +31,16 @@ void reap_thread()
     }
 }
 
+void oom_thread()
+{
+    while (true)
+    {
+        kernel_wait_for_event();
+        // OOM! Do everything we can to recover memory.
+        StorageCache::clear_caches();
+    }
+}
+
 [[noreturn]] void init()
 {
     {
@@ -58,6 +68,10 @@ void reap_thread()
                                   "Failed to create the process reaper kernel thread");
         Scheduler::set_reap_thread(reap);
 
+        auto oom = mark_critical(Scheduler::new_kernel_thread(oom_thread, "[oom]"),
+                                 "Failed to create the out-of-memory kernel thread");
+        Scheduler::set_oom_thread(oom);
+
 #ifdef ARCH_X86_64
         ATA::Controller::scan();
 #endif

kernel/src/memory/MemoryManager.cpp

@@ -146,9 +146,9 @@ namespace MemoryManager
         bool ok = frame_bitmap->find_and_toggle(false, start_index).try_set_value(index);
         if (!ok)
         {
-            kwarnln("OOM alert! Trying to free caches...");
+            kwarnln("OOM alert! Scheduling the OOM thread...");
-            StorageCache::clear_caches();
+            Scheduler::signal_oom_thread();
-            if (!frame_bitmap->find_and_toggle(false, start_index).try_set_value(index)) return err(ENOMEM);
+            return err(ENOMEM);
         }
 
         start_index = index + 1;

kernel/src/net/Socket.h

@@ -65,6 +65,12 @@ class Socket : public VFS::FileInode
         m_metadata.nlinks--;
     }
 
+    virtual bool can_accept_connections() const = 0;
+
+    virtual bool can_read_data() const = 0;
+
+    virtual bool peer_disconnected() const = 0;
+
     virtual ~Socket() = default;
 
   protected:

kernel/src/net/UnixSocket.h

@@ -17,6 +17,21 @@ class UnixSocket : public Socket
         return (m_state == Connected || m_state == Reset) && !m_data.size();
     }
 
+    bool can_read_data() const override
+    {
+        return (m_state == Connected || m_state == Reset) && m_data.size();
+    }
+
+    bool can_accept_connections() const override
+    {
+        return !m_listen_queue.is_empty();
+    }
+
+    bool peer_disconnected() const override
+    {
+        return m_state == Reset;
+    }
+
     Result<usize> send(const u8*, usize, int) override;
     Result<usize> recv(u8*, usize, int) const override;
 

kernel/src/sys/memstat.cpp

@@ -0,0 +1,21 @@
+#include "Pledge.h"
+#include "memory/MemoryManager.h"
+#include "sys/Syscall.h"
+#include "thread/Scheduler.h"
+#include <bits/memstat.h>
+
+Result<u64> sys_memstat(Registers*, SyscallArgs args)
+{
+    auto* current = Scheduler::current();
+    TRY(check_pledge(current, Promise::p_stdio));
+
+    struct membuf buf;
+    buf.mem_total = MemoryManager::total();
+    buf.mem_used = MemoryManager::used();
+    buf.mem_free = MemoryManager::free();
+    buf.mem_reserved = MemoryManager::reserved();
+
+    if (!MemoryManager::copy_to_user_typed((struct membuf*)args[0], &buf)) return err(EFAULT);
+
+    return 0;
+}

kernel/src/sys/poll.cpp

@@ -2,6 +2,7 @@
 #include "Pledge.h"
 #include "fs/VFS.h"
 #include "memory/MemoryManager.h"
+#include "net/Socket.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
 #include <bits/poll.h>
@@ -45,10 +46,30 @@ Result<u64> sys_poll(Registers*, SyscallArgs args)
             auto& inode = inodes[i];
             if (!inode) continue;
 
-            if (kfds[i].events & POLLIN && !inode->will_block_if_read())
+            if (kfds[i].events & POLLIN)
             {
-                fds_with_events++;
+                if (inode->type() == VFS::InodeType::Socket)
-                kfds[i].revents |= POLLIN;
+                {
+                    auto socket = (Socket*)inode.ptr();
+                    if (socket->can_read_data() || socket->can_accept_connections())
+                    {
+                        fds_with_events++;
+                        kfds[i].revents |= POLLIN;
+                    }
+                    if (socket->peer_disconnected())
+                    {
+                        fds_with_events++;
+                        kfds[i].revents |= POLLHUP;
+                    }
+                }
+                else
+                {
+                    if (!inode->will_block_if_read())
+                    {
+                        fds_with_events++;
+                        kfds[i].revents |= POLLIN;
+                    }
+                }
             }
         }
 

kernel/src/thread/Scheduler.cpp

@@ -13,6 +13,7 @@ static Thread g_idle;
 static Thread* g_current = nullptr;
 static Thread* g_init = nullptr;
 static Thread* g_reap = nullptr;
+static Thread* g_oom = nullptr;
 
 static const usize TICKS_PER_TIMESLICE = 20;
 
@@ -70,6 +71,17 @@ namespace Scheduler
         if (g_reap) g_reap->wake_up();
     }
 
+    void set_oom_thread(Thread* thread)
+    {
+        g_oom = thread;
+        g_oom->unrestricted_task = true;
+    }
+
+    void signal_oom_thread()
+    {
+        if (g_oom) g_oom->wake_up();
+    }
+
     Result<Thread*> new_kernel_thread_impl(Thread* thread, const char* name)
     {
         // If anything fails, make sure to clean up.
@@ -154,8 +166,13 @@ namespace Scheduler
         u64 argv = TRY(image->push_string_vector_on_stack(args));
         u64 envp = TRY(image->push_string_vector_on_stack(env));
 
+        const u64 kernel_stack_base = TRY(MemoryManager::alloc_for_kernel(4, MMU::ReadWrite | MMU::NoExecute));
+        Stack kernel_stack { kernel_stack_base, 4 * ARCH_PAGE_SIZE };
+
         guard.deactivate();
 
+        thread->kernel_stack = kernel_stack;
+
         image->apply(thread);
         thread->set_arguments(args.size(), argv, env.size(), envp);
 
@@ -254,8 +271,12 @@ namespace Scheduler
             new_thread->ticks_left = 1; // The idle task only runs for 1 tick so we can check for new runnable tasks
                                         // as fast as possible.
         }
-        else
+        else if (new_thread->unrestricted_task)
-            new_thread->ticks_left = TICKS_PER_TIMESLICE;
+        {
+            check(new_thread->is_kernel);
+            new_thread->ticks_left = -1;
+        }
+        else { new_thread->ticks_left = TICKS_PER_TIMESLICE; }
     }
 
     void switch_task(Registers* regs)

kernel/src/thread/Scheduler.h

@@ -13,6 +13,9 @@ namespace Scheduler
     void set_reap_thread(Thread*);
     void signal_reap_thread();
 
+    void set_oom_thread(Thread*);
+    void signal_oom_thread();
+
     Result<Thread*> new_kernel_thread(u64 address, const char* name);
     Result<Thread*> new_kernel_thread(void (*func)(void), const char* name);
     Result<Thread*> new_kernel_thread(void (*func)(void*), void* arg, const char* name);

kernel/src/thread/Thread.h

@@ -109,6 +109,8 @@ struct Thread : public LinkedListNode<Thread>
     sigset_t pending_signals { 0 };
     bool interrupted { false };
 
+    bool unrestricted_task { false };
+
     FPData fp_data;
 
     ThreadState state = ThreadState::Runnable;

libc/CMakeLists.txt

@@ -33,6 +33,7 @@ set(SOURCES
     src/sys/utsname.cpp
     src/sys/mount.cpp
     src/sys/pstat.cpp
+    src/sys/memstat.cpp
     src/sys/resource.cpp
     src/sys/socket.cpp
     src/sys/poll.cpp

libc/include/bits/memstat.h

@@ -0,0 +1,14 @@
+/* bits/memstat.h: The membuf structure for memstat(). */
+
+#ifndef _BITS_MEMSTAT_H
+#define _BITS_MEMSTAT_H
+
+struct membuf
+{
+    unsigned long mem_total;
+    unsigned long mem_used;
+    unsigned long mem_free;
+    unsigned long mem_reserved;
+};
+
+#endif

libc/include/bits/poll.h

@@ -8,6 +8,7 @@
 #define POLLIN (1 << 0)
 #define POLLERR (1 << 1)
 #define POLLNVAL (1 << 2)
+#define POLLHUP (1 << 3)
 
 typedef __u64_t nfds_t;
 

libc/include/sys/memstat.h

@@ -0,0 +1,20 @@
+/* sys/memstat.h: Memory usage querying. */
+
+#ifndef _SYS_MEMSTAT_H
+#define _SYS_MEMSTAT_H
+
+#include <bits/memstat.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    /* Query system memory usage. */
+    int memstat(struct membuf* mem);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

libc/src/sys/memstat.cpp

@@ -0,0 +1,13 @@
+#include <bits/errno-return.h>
+#include <sys/memstat.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+extern "C"
+{
+    int memstat(struct membuf* buf)
+    {
+        long rc = syscall(SYS_memstat, buf);
+        __errno_return(rc, int);
+    }
+}

libluna/include/luna/Buffer.h

@@ -11,6 +11,9 @@ class Buffer
     Buffer(Buffer&& other);
     Buffer(const Buffer& other) = delete; // For now.
 
+    Buffer& operator=(Buffer&&);
+    Buffer& operator=(const Buffer&) = delete;
+
     static Result<Buffer> create_sized(usize size);
 
     Result<void> try_resize(usize new_size);

libluna/include/luna/CircularQueue.h

@@ -16,7 +16,7 @@ template <typename T, usize Size> class CircularQueue
     {
     }
 
-    bool is_empty()
+    bool is_empty() const
     {
         return m_tail.load() == m_head.load();
     }
@@ -76,7 +76,7 @@ template <typename T> class DynamicCircularQueue
         if (m_data) free_impl(m_data);
     }
 
-    bool is_empty()
+    bool is_empty() const
     {
         return m_tail.load() == m_head.load();
     }

libluna/include/luna/HashMap.h

@@ -49,6 +49,16 @@ template <typename K, typename V> struct HashMap
         return m_table.try_remove(HashPair<K, V> { key, {} });
     }
 
+    usize capacity() const
+    {
+        return m_table.capacity();
+    }
+
+    usize size() const
+    {
+        return m_table.size();
+    }
+
     void clear()
     {
         m_table.clear();

libluna/include/luna/HashTable.h

@@ -101,10 +101,23 @@ template <typename T> class HashTable
 
     void clear()
     {
-        for (usize i = 0; i < m_capacity; i++) m_buckets[i].~Option();
+        if (m_capacity)
+        {
+            for (usize i = 0; i < m_capacity; i++) m_buckets[i].~Option();
 
-        free_impl(m_buckets);
+            free_impl(m_buckets);
-        m_capacity = m_size = 0;
+            m_capacity = m_size = 0;
+        }
+    }
+
+    usize capacity() const
+    {
+        return m_capacity;
+    }
+
+    usize size() const
+    {
+        return m_size;
     }
 
     ~HashTable()

libluna/include/luna/Syscall.h

@@ -8,7 +8,7 @@
                     _e(umount) _e(pstat) _e(getrusage) _e(symlinkat) _e(readlinkat) _e(umask) _e(linkat) _e(faccessat) \
                         _e(pivot_root) _e(sigreturn) _e(sigaction) _e(kill) _e(sigprocmask) _e(setpgid) _e(isatty)     \
                             _e(getpgid) _e(socket) _e(bind) _e(connect) _e(listen) _e(accept) _e(poll) _e(msync)       \
-                                _e(truncate) _e(ftruncate) _e(utimensat) _e(alarm) _e(pledge)
+                                _e(truncate) _e(ftruncate) _e(utimensat) _e(alarm) _e(pledge) _e(memstat)
 
 enum Syscalls
 {

libluna/src/Buffer.cpp

@@ -15,6 +15,16 @@ Buffer::Buffer(Buffer&& other) : m_data(other.data()), m_size(other.size())
     other.m_data = nullptr;
 }
 
+Buffer& Buffer::operator=(Buffer&& other)
+{
+    if (&other == this) return *this;
+    if (m_data) free_impl(m_data);
+    m_data = other.m_data;
+    m_size = other.m_size;
+    other.m_data = nullptr;
+    return *this;
+}
+
 Buffer::~Buffer()
 {
     if (m_data) free_impl(m_data);

libos/CMakeLists.txt

@@ -14,6 +14,9 @@ set(SOURCES
     src/Mode.cpp
     src/Prompt.cpp
     src/Security.cpp
+    src/LocalServer.cpp
+    src/LocalClient.cpp
+    src/IPC.cpp
 )
 
 add_library(os ${SOURCES})

libos/include/os/IPC.h

@@ -0,0 +1,157 @@
+/**
+ * @file IPC.h
+ * @author apio (cloudapio.eu)
+ * @brief Inter-process communication primitives.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <os/LocalClient.h>
+#include <os/LocalServer.h>
+
+#define IPC_ENUM_SERVER(name) __##name##_SERVER_ERROR = 0
+#define IPC_ENUM_CLIENT(name) __##name##_CLIENT_ERROR = 0
+
+/**
+ * @brief Called to handle IPC events (client-side).
+ *
+ * @param conn The connection object being used.
+ * @param id The ID of the message.
+ * @return Result<void> Whether the operation succeded.
+ */
+extern Result<void> handle_ipc_client_event(os::LocalClient& conn, u8 id);
+
+/**
+ * @brief Called to handle IPC events (server-side).
+ *
+ * @param conn The connection object being used.
+ * @param id The ID of the message.
+ * @return Result<void> Whether the operation succeded.
+ */
+extern Result<void> handle_ipc_server_event(os::LocalServer::Client& conn, u8 id);
+
+namespace os
+{
+    namespace IPC
+    {
+        static constexpr usize IPC_STRING_LENGTH = 256;
+
+#define IPC_STRING(name) char name[os::IPC::IPC_STRING_LENGTH];
+#define COPY_IPC_STRING(name)                                                                                          \
+    TRY(String::from_string_view(StringView::from_fixed_size_cstring(name, os::IPC::IPC_STRING_LENGTH)))
+#define SET_IPC_STRING(name, value) strlcpy(name, value, os::IPC::IPC_STRING_LENGTH)
+
+        /**
+         * @brief Sends an IPC message without waiting for a reply.
+         *
+         * @tparam Client The type of the client interface being used to communicate.
+         * @tparam T The type of the message.
+         * @param client The connection object being used to communicate.
+         * @param message The IPC message.
+         * @return Result<void> Whether the operation succeded.
+         */
+        template <typename Client, typename T> Result<void> send_async(Client& client, const T& message)
+        {
+            u8 id = T::ID;
+            TRY(client.send_typed(id));
+            TRY(client.send_typed(message));
+            return {};
+        }
+
+        /**
+         * @brief Sends an error result to the IPC connection, indicating that an operation could not be performed.
+         *
+         * @tparam Client The type of the client interface being used to communicate.
+         * @param client The connection object being used to communicate.
+         * @param error The error code.
+         * @return Result<void> Whether the operation succeded.
+         */
+        template <typename Client> Result<void> send_error(Client& client, int error)
+        {
+            u8 id = 0;
+            TRY(client.send_typed(id));
+            TRY(client.send_typed(error));
+            return {};
+        }
+
+        /**
+         * @brief Sends an IPC message and waits for a reply (client-only).
+         *
+         * @tparam ResponseType The type of the response.
+         * @tparam T The type of the message.
+         * @param client The connection object being used to communicate.
+         * @param message The IPC message.
+         * @param handler The function used to handle messages that do not match the reply.
+         * @return Result<ResponseType> An error, or the response.
+         */
+        template <typename ResponseType, typename T>
+        Result<ResponseType> send_sync(os::LocalClient& client, const T& message,
+                                       decltype(handle_ipc_client_event) handler = handle_ipc_client_event)
+        {
+            u8 id = T::ID;
+            TRY(client.send_typed(id));
+            TRY(client.send_typed(message));
+
+            // We allow receiving 5 messages of different types, but if those have passed and we still don't have a
+            // reply, fail with ENOMSG.
+            int max_other_messages = 5;
+
+            while (max_other_messages)
+            {
+                u8 response_id;
+                auto rc = client.recv_typed(response_id);
+                if (rc.has_error() && (rc.error() == EAGAIN || rc.error() == EINTR)) continue;
+
+                if (response_id == 0) // Error result
+                {
+                    while (1)
+                    {
+                        int code;
+                        rc = client.recv_typed(code);
+                        if (rc.has_error() && (rc.error() == EAGAIN || rc.error() == EINTR)) continue;
+                        return err(code);
+                    }
+                }
+
+                if (response_id != ResponseType::ID)
+                {
+                    TRY(handler(client, response_id));
+                    max_other_messages--;
+                    continue;
+                }
+
+                while (1)
+                {
+                    ResponseType response;
+                    rc = client.recv_typed(response);
+                    if (rc.has_error() && (rc.error() == EAGAIN || rc.error() == EINTR)) continue;
+                    return response;
+                }
+            }
+
+            return err(ENOMSG);
+        }
+
+        /**
+         * @brief Check for new IPC messages on a connection and handle them appropriately.
+         *
+         * @param client The client connection.
+         * @param handler The function used to handle messages.
+         * @return Result<void> Whether the operation succeded.
+         */
+        Result<void> check_for_messages(os::LocalClient& client,
+                                        decltype(handle_ipc_client_event) handler = handle_ipc_client_event);
+
+        /**
+         * @brief Check for new IPC messages on a connection and handle them appropriately.
+         *
+         * @param server The server connection.
+         * @param handler The function used to handle messages.
+         * @return Result<void> Whether the operation succeded.
+         */
+        Result<void> check_for_messages(os::LocalServer::Client& server,
+                                        decltype(handle_ipc_server_event) handler = handle_ipc_server_event);
+    }
+}

libos/include/os/LocalClient.h

@@ -0,0 +1,99 @@
+/**
+ * @file LocalClient.h
+ * @author apio (cloudapio.eu)
+ * @brief UNIX local domain client class.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/OwnedPtr.h>
+#include <luna/StringView.h>
+
+namespace os
+{
+    /**
+     * @brief A client used to connect to a local server socket.
+     */
+    class LocalClient
+    {
+      public:
+        /**
+         * @brief Create a new client object and connect it to a local server.
+         *
+         * @param path The path of the server socket to connect to.
+         * @param blocking Whether the client should block if no data is available and recv() is called.
+         * @return Result<OwnedPtr<LocalClient>> An error, or a new client object.
+         */
+        static Result<OwnedPtr<LocalClient>> connect(StringView path, bool blocking);
+
+        /**
+         * @brief Return the underlying socket file descriptor used by this object.
+         *
+         * @return int The file descriptor.
+         */
+        int fd() const
+        {
+            return m_fd;
+        }
+
+        /**
+         * @brief Read arbitrary data from the server. The call will block if there is no data and this object has not
+         * been created as non-blocking.
+         *
+         * @param buf The buffer to read data into.
+         * @param length The maximum amount of bytes to read.
+         * @return Result<usize> An error, or the number of bytes read.
+         */
+        Result<usize> recv(u8* buf, usize length);
+
+        /**
+         * @brief Read an object from the server. The call will block if there is no data and this object has not been
+         * created as non-blocking.
+         *
+         * @tparam T The type of the object.
+         * @param out A reference to the object to read data into.
+         * @return Result<void> Whether the operation succeded.
+         */
+        template <typename T> Result<void> recv_typed(T& out)
+        {
+            TRY(recv((u8*)&out, sizeof(T)));
+            return {};
+        }
+
+        /**
+         * @brief Send arbitrary data to the server.
+         *
+         * @param buf The buffer to send data from.
+         * @param length The amount of bytes to send.
+         * @return Result<usize> An error, or the number of bytes actually sent.
+         */
+        Result<usize> send(const u8* buf, usize length);
+
+        /**
+         * @brief Send an object to the server.
+         *
+         * @tparam T The type of the object.
+         * @param out A reference to the object to send data from.
+         * @return Result<void> Whether the operation succeded.
+         */
+        template <typename T> Result<void> send_typed(const T& out)
+        {
+            TRY(send((const u8*)&out, sizeof(T)));
+            return {};
+        }
+
+        /**
+         * @brief Disconnect from the attached server.
+         *
+         * This will make any further reads on this connection return ECONNRESET, and will make this object invalid.
+         */
+        void disconnect();
+
+        ~LocalClient();
+
+      private:
+        int m_fd;
+    };
+}

libos/include/os/LocalServer.h

@@ -0,0 +1,142 @@
+/**
+ * @file LocalServer.h
+ * @author apio (cloudapio.eu)
+ * @brief UNIX local domain server class.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/OwnedPtr.h>
+#include <luna/Result.h>
+#include <luna/StringView.h>
+
+namespace os
+{
+    /**
+     * @brief A local domain server, used to communicate between processes on the same machine.
+     */
+    class LocalServer
+    {
+      public:
+        /**
+         * @brief Create a new server object and bind it to a local address.
+         *
+         * @param path The path to use for the server socket.
+         * @param blocking Whether the server should block if no connections are available when calling accept().
+         * @return Result<OwnedPtr<LocalServer>> An error, or a new server object.
+         */
+        static Result<OwnedPtr<LocalServer>> create(StringView path, bool blocking);
+
+        /**
+         * @brief Activate the server and start listening for connections.
+         *
+         * @param backlog The number of unaccepted connections to keep.
+         * @return Result<void> Whether the operation succeded.
+         */
+        Result<void> listen(int backlog);
+
+        /**
+         * @brief Return the underlying socket file descriptor used by this object.
+         *
+         * @return int The file descriptor.
+         */
+        int fd() const
+        {
+            return m_fd;
+        }
+
+        /**
+         * @brief An interface to communicate with clients connected to a local server.
+         */
+        class Client
+        {
+          public:
+            /**
+             * @brief Read arbitrary data from the client. The call will block if there is no data and the parent server
+             * object has not been created as non-blocking.
+             *
+             * @param buf The buffer to read data into.
+             * @param length The maximum amount of bytes to read.
+             * @return Result<usize> An error, or the number of bytes read.
+             */
+            Result<usize> recv(u8* buf, usize length);
+
+            /**
+             * @brief Read an object from the client. The call will block if there is no data and the parent server
+             * object has not been created as non-blocking.
+             *
+             * @tparam T The type of the object.
+             * @param out A reference to the object to read data into.
+             * @return Result<void> Whether the operation succeded.
+             */
+            template <typename T> Result<void> recv_typed(T& out)
+            {
+                TRY(recv((u8*)&out, sizeof(T)));
+                return {};
+            }
+
+            /**
+             * @brief Send arbitrary data to the client.
+             *
+             * @param buf The buffer to send data from.
+             * @param length The amount of bytes to send.
+             * @return Result<usize> An error, or the number of bytes actually sent.
+             */
+            Result<usize> send(const u8* buf, usize length);
+
+            /**
+             * @brief Send an object to the client.
+             *
+             * @tparam T The type of the object.
+             * @param out A reference to the object to send data from.
+             * @return Result<void> Whether the operation succeded.
+             */
+            template <typename T> Result<void> send_typed(const T& out)
+            {
+                TRY(send((const u8*)&out, sizeof(T)));
+                return {};
+            }
+
+            /**
+             * @brief Disconnect from the attached client.
+             *
+             * This will make any further reads on the client return ECONNRESET, and will make this object invalid.
+             */
+            void disconnect();
+
+            /**
+             * @brief Return the underlying socket file descriptor used by this object.
+             *
+             * @return int The file descriptor.
+             */
+            int fd() const
+            {
+                return m_fd;
+            }
+
+            Client(Client&& other);
+            Client(int fd);
+            ~Client();
+
+          private:
+            int m_fd;
+        };
+
+        /**
+         * @brief Accept a new incoming connection and return a handle to it. If there are no incoming connections,
+         * accept() either blocks until there is one (if the object was created with blocking=true), or returns EAGAIN
+         * (if the object was created with blocking=false).
+         *
+         * @return Result<Client> An error, or a handle to the new connection.
+         */
+        Result<Client> accept();
+
+        ~LocalServer();
+
+      private:
+        int m_fd;
+        bool m_blocking;
+    };
+}

libos/src/IPC.cpp

@@ -0,0 +1,43 @@
+/**
+ * @file IPC.cpp
+ * @author apio (cloudapio.eu)
+ * @brief Inter-process communication primitives.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <os/IPC.h>
+
+namespace os::IPC
+{
+    Result<void> check_for_messages(os::LocalClient& client, decltype(handle_ipc_client_event) handler)
+    {
+        u8 id;
+        auto rc = client.recv_typed(id);
+        if (rc.has_error())
+        {
+            if (rc.error() == EAGAIN) return {}; // No messages, and the caller does not want us to block.
+            if (rc.error() == EINTR)
+                return {}; // Let the caller check for anything having happened because a signal handler ran.
+            return rc.release_error();
+        }
+
+        return handler(client, id);
+    }
+
+    Result<void> check_for_messages(os::LocalServer::Client& client, decltype(handle_ipc_server_event) handler)
+    {
+        u8 id;
+        auto rc = client.recv_typed(id);
+        if (rc.has_error())
+        {
+            if (rc.error() == EAGAIN) return {}; // No messages, and the caller does not want us to block.
+            if (rc.error() == EINTR)
+                return {}; // Let the caller check for anything having happened because a signal handler ran.
+            return rc.release_error();
+        }
+
+        return handler(client, id);
+    }
+}

libos/src/LocalClient.cpp

@@ -0,0 +1,68 @@
+/**
+ * @file LocalClient.cpp
+ * @author apio (cloudapio.eu)
+ * @brief UNIX local domain client class.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <os/LocalClient.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+namespace os
+{
+    Result<OwnedPtr<LocalClient>> LocalClient::connect(StringView path, bool blocking)
+    {
+        auto client = TRY(make_owned<LocalClient>());
+
+        int sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
+        if (sockfd < 0) return err(errno);
+
+        struct sockaddr_un un;
+        un.sun_family = AF_UNIX;
+        strncpy(un.sun_path, path.chars(), sizeof(un.sun_path));
+
+        if (::connect(sockfd, (struct sockaddr*)&un, sizeof(un)) < 0)
+        {
+            close(sockfd);
+            return err(errno);
+        }
+
+        if (!blocking) { fcntl(sockfd, F_SETFL, O_NONBLOCK); }
+
+        fcntl(sockfd, F_SETFD, FD_CLOEXEC);
+
+        client->m_fd = sockfd;
+        return client;
+    }
+
+    LocalClient::~LocalClient()
+    {
+        close(m_fd);
+    }
+
+    Result<usize> LocalClient::recv(u8* buf, usize length)
+    {
+        ssize_t nread = read(m_fd, buf, length);
+        if (nread < 0) return err(errno);
+        return nread;
+    }
+
+    Result<usize> LocalClient::send(const u8* buf, usize length)
+    {
+        ssize_t nwrite = write(m_fd, buf, length);
+        if (nwrite < 0) return err(errno);
+        return nwrite;
+    }
+
+    void LocalClient::disconnect()
+    {
+        close(m_fd);
+        m_fd = -1;
+    }
+}

libos/src/LocalServer.cpp

@@ -0,0 +1,101 @@
+/**
+ * @file LocalServer.cpp
+ * @author apio (cloudapio.eu)
+ * @brief UNIX local domain server class.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <os/FileSystem.h>
+#include <os/LocalServer.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+namespace os
+{
+    Result<OwnedPtr<LocalServer>> LocalServer::create(StringView path, bool blocking)
+    {
+        auto server = TRY(make_owned<LocalServer>());
+
+        (void)os::FileSystem::remove(path); // We explicitly ignore any error here, either it doesn't exist (which is
+                                            // fine), or it cannot be removed, which will make bind() fail later.
+
+        int sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
+        if (sockfd < 0) return err(errno);
+
+        struct sockaddr_un un;
+        un.sun_family = AF_UNIX;
+        strncpy(un.sun_path, path.chars(), sizeof(un.sun_path));
+
+        if (bind(sockfd, (struct sockaddr*)&un, sizeof(un)) < 0)
+        {
+            close(sockfd);
+            return err(errno);
+        }
+
+        if (!blocking) { fcntl(sockfd, F_SETFL, O_NONBLOCK); }
+        server->m_blocking = blocking;
+
+        fcntl(sockfd, F_SETFD, FD_CLOEXEC);
+
+        server->m_fd = sockfd;
+        return server;
+    }
+
+    Result<void> LocalServer::listen(int backlog)
+    {
+        if (::listen(m_fd, backlog) < 0) return err(errno);
+        return {};
+    }
+
+    Result<LocalServer::Client> LocalServer::accept()
+    {
+        int fd = ::accept(m_fd, nullptr, nullptr);
+        if (fd < 0) return err(errno);
+        if (!m_blocking) fcntl(fd, F_SETFL, O_NONBLOCK);
+        return Client { fd };
+    }
+
+    LocalServer::~LocalServer()
+    {
+        close(m_fd);
+    }
+
+    LocalServer::Client::Client(Client&& other) : m_fd(other.m_fd)
+    {
+        other.m_fd = -1;
+    }
+
+    LocalServer::Client::Client(int fd) : m_fd(fd)
+    {
+    }
+
+    LocalServer::Client::~Client()
+    {
+        if (m_fd >= 0) close(m_fd);
+    }
+
+    Result<usize> LocalServer::Client::recv(u8* buf, usize length)
+    {
+        ssize_t nread = read(m_fd, buf, length);
+        if (nread < 0) return err(errno);
+        return nread;
+    }
+
+    Result<usize> LocalServer::Client::send(const u8* buf, usize length)
+    {
+        ssize_t nwrite = write(m_fd, buf, length);
+        if (nwrite < 0) return err(errno);
+        return nwrite;
+    }
+
+    void LocalServer::Client::disconnect()
+    {
+        close(m_fd);
+        m_fd = -1;
+    }
+}

libui/CMakeLists.txt

@@ -0,0 +1,25 @@
+# The UI and graphics library for Luna.
+
+file(GLOB HEADERS include/ui/*.h)
+
+set(SOURCES
+    ${HEADERS}
+    include/ui/ipc/Server.h
+    include/ui/ipc/Client.h
+    src/Canvas.cpp
+    src/Rect.cpp
+    src/Font.cpp
+    src/Image.cpp
+    src/App.cpp
+    src/Window.cpp
+    src/Layout.cpp
+    src/Alignment.cpp
+    src/Container.cpp
+    src/Button.cpp
+)
+
+add_library(ui ${SOURCES})
+target_compile_options(ui PRIVATE ${COMMON_FLAGS} -fno-threadsafe-statics)
+target_include_directories(ui PUBLIC ${CMAKE_CURRENT_LIST_DIR}/include/)
+target_include_directories(ui PUBLIC ${LUNA_BASE}/usr/include)
+target_link_libraries(ui PUBLIC os)

libui/include/ui/Alignment.h

@@ -0,0 +1,30 @@
+/**
+ * @file Alignment.h
+ * @author apio (cloudapio.eu)
+ * @brief UI component alignment.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <ui/Rect.h>
+
+namespace ui
+{
+    enum class VerticalAlignment
+    {
+        Top,
+        Center,
+        Bottom
+    };
+
+    enum class HorizontalAlignment
+    {
+        Left,
+        Center,
+        Right
+    };
+
+    Rect align(Rect container, Rect contained, VerticalAlignment valign, HorizontalAlignment halign);
+}

libui/include/ui/App.h

@@ -0,0 +1,65 @@
+/**
+ * @file App.h
+ * @author apio (cloudapio.eu)
+ * @brief UI application event loop.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/HashMap.h>
+#include <os/LocalClient.h>
+#include <ui/Window.h>
+
+namespace ui
+{
+    class App
+    {
+      public:
+        App();
+        ~App();
+
+        Result<void> init(int, char**);
+        Result<int> run();
+
+        Rect screen_rect();
+
+        os::LocalClient& client()
+        {
+            return *m_client;
+        }
+
+        void set_should_close(bool b)
+        {
+            m_should_close = b;
+        }
+
+        void set_main_window(Window* window)
+        {
+            check(!m_main_window);
+            m_main_window = window;
+        }
+
+        Window* main_window()
+        {
+            return m_main_window;
+        }
+
+        Result<void> register_window(OwnedPtr<Window>&& window, Badge<Window>);
+        void unregister_window(Window* window, Badge<Window>);
+
+        Result<void> handle_ipc_event(u8 id);
+
+        static App& the();
+
+      private:
+        static App* s_app;
+        OwnedPtr<os::LocalClient> m_client;
+        Window* m_main_window { nullptr };
+        HashMap<int, OwnedPtr<Window>> m_windows;
+        bool m_should_close { false };
+
+        Window* find_window(int id);
+    };
+}

libui/include/ui/Button.h

@@ -0,0 +1,35 @@
+/**
+ * @file Button.h
+ * @author apio (cloudapio.eu)
+ * @brief A clickable component that triggers an action when pressed.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <ui/Widget.h>
+
+namespace ui
+{
+    class Button : public Widget
+    {
+      public:
+        Button(Rect rect);
+
+        void set_widget(Widget& widget);
+        void set_action(void (*action)(void));
+
+        Result<EventResult> handle_mouse_move(Point position) override;
+        Result<EventResult> handle_mouse_leave(Point position) override;
+        Result<EventResult> handle_mouse_down(Point position, int buttons) override;
+        Result<EventResult> handle_mouse_up(Point position, int buttons) override;
+        Result<void> draw(Canvas& canvas) override;
+
+      private:
+        bool m_hovered { false };
+        bool m_clicked { false };
+        Widget* m_child;
+        void (*m_action)(void);
+    };
+}

libui/include/ui/Canvas.h

@@ -0,0 +1,73 @@
+/**
+ * @file Canvas.h
+ * @author apio (cloudapio.eu)
+ * @brief Drawable surfaces.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/Result.h>
+#include <luna/Types.h>
+#include <ui/Color.h>
+#include <ui/Point.h>
+#include <ui/Rect.h>
+
+namespace ui
+{
+    /**
+     * @brief A drawable surface.
+     */
+    struct Canvas
+    {
+        int width;
+        int height;
+        int stride;
+        u8* ptr;
+
+        /**
+         * @brief Create a new Canvas object.
+         *
+         * @param ptr The memory to use for the canvas. It must be of at least width * height * 4 bytes of length.
+         * @param width The width of the canvas.
+         * @param height The height of the canvas.
+         * @return Canvas The new Canvas object.
+         */
+        static Canvas create(u8* ptr, int width, int height);
+
+        /**
+         * @brief Return a new Canvas that represents a subsection of the current one.
+         *
+         * @param rect The dimensions of the new canvas. If these exceed the bounds of the current canvas, they will be
+         * clamped.
+         * @return Canvas The new Canvas object.
+         */
+        Canvas subcanvas(Rect rect);
+
+        /**
+         * @brief Return the dimensions of the current canvas.
+         *
+         * @return Rect This canvas's dimensions, as a Rect object.
+         */
+        Rect rect()
+        {
+            return Rect { .pos = { 0, 0 }, .width = width, .height = height };
+        }
+
+        /**
+         * @brief Fill the entire canvas with one color.
+         *
+         * @param color The color to use.
+         */
+        void fill(Color color);
+
+        /**
+         * @brief Fill the canvas with pixels.
+         *
+         * @param pixels The array of pixels (must be at least width*height).
+         * @param stride The number of pixels to skip to go to the next line.
+         */
+        void fill(u32* pixels, int stride);
+    };
+};

libui/include/ui/Color.h

@@ -0,0 +1,113 @@
+/**
+ * @file Color.h
+ * @author apio (cloudapio.eu)
+ * @brief RGBA colors.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/Types.h>
+
+namespace ui
+{
+    /**
+     * @brief A 32-bit ARGB color.
+     */
+    struct Color
+    {
+        union {
+            u32 raw;
+            u8 colors[4];
+        };
+
+        /**
+         * @brief Return the blue value of this color.
+         *
+         * @return constexpr u8 The blue value.
+         */
+        constexpr u8 red() const
+        {
+            return colors[2];
+        }
+
+        /**
+         * @brief Return the green value of this color.
+         *
+         * @return constexpr u8 The green value.
+         */
+        constexpr u8 green() const
+        {
+            return colors[1];
+        }
+
+        /**
+         * @brief Return the blue value of this color.
+         *
+         * @return constexpr u8 The blue value.
+         */
+        constexpr u8 blue() const
+        {
+            return colors[0];
+        }
+
+        /**
+         * @brief Return the alpha value of this color.
+         *
+         * @return constexpr u8 The alpha value.
+         */
+        constexpr u8 alpha() const
+        {
+            return colors[3];
+        }
+
+        /**
+         * @brief Construct a new color from a 32-bit ARGB integer.
+         *
+         * @param raw The integer representing the color.
+         * @return constexpr Color The new color.
+         */
+        static constexpr Color from_u32(u32 raw)
+        {
+            return Color { .raw = raw };
+        }
+
+        /**
+         * @brief Construct a new color from its separate RGBA values (from 0 to 255).
+         *
+         * @param red The red value.
+         * @param green The green value.
+         * @param blue The blue value.
+         * @param alpha The alpha value.
+         * @return constexpr Color The new color.
+         */
+        static constexpr Color from_rgba(u8 red, u8 green, u8 blue, u8 alpha)
+        {
+            return Color { .colors = { blue, green, red, alpha } };
+        }
+
+        /**
+         * @brief Construct a new color from its separate RGB values (from 0 to 255).
+         *
+         * @param red The red value.
+         * @param green The green value.
+         * @param blue The blue value.
+         * @return constexpr Color The new color.
+         */
+        static constexpr Color from_rgb(u8 red, u8 green, u8 blue)
+        {
+            return from_rgba(red, green, blue, 0xff);
+        }
+    };
+
+    static constexpr Color WHITE = Color::from_rgb(0xff, 0xff, 0xff);
+    static constexpr Color BLACK = Color::from_rgb(0x00, 0x00, 0x00);
+    static constexpr Color GRAY = Color::from_rgb(0x80, 0x80, 0x80);
+
+    static constexpr Color BLUE = Color::from_rgb(0x00, 0x00, 0xff);
+    static constexpr Color GREEN = Color::from_rgb(0x00, 0xff, 0x00);
+    static constexpr Color RED = Color::from_rgb(0xff, 0x00, 0x00);
+
+    static constexpr Color CYAN = Color::from_rgb(0x00, 0xff, 0xff);
+};

libui/include/ui/Container.h

@@ -0,0 +1,34 @@
+/**
+ * @file Container.h
+ * @author apio (cloudapio.eu)
+ * @brief A container widget to pad and align objects inside it.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <ui/Alignment.h>
+#include <ui/Widget.h>
+
+namespace ui
+{
+    class Container : public Widget
+    {
+      public:
+        Container(Rect rect, VerticalAlignment valign, HorizontalAlignment halign);
+
+        void set_widget(Widget& widget);
+
+        Result<EventResult> handle_mouse_move(Point position) override;
+        Result<EventResult> handle_mouse_leave(Point position) override;
+        Result<EventResult> handle_mouse_down(Point position, int buttons) override;
+        Result<EventResult> handle_mouse_up(Point position, int buttons) override;
+        Result<void> draw(Canvas& canvas) override;
+
+      private:
+        Widget* m_widget;
+        VerticalAlignment m_valign;
+        HorizontalAlignment m_halign;
+    };
+}

libui/include/ui/Font.h

@@ -0,0 +1,120 @@
+/**
+ * @file Font.h
+ * @author apio (cloudapio.eu)
+ * @brief PSF font loading and rendering.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/Buffer.h>
+#include <luna/SharedPtr.h>
+#include <os/Path.h>
+#include <ui/Canvas.h>
+
+#define PSF_FONT_MAGIC 0x864ab572
+
+namespace ui
+{
+    /**
+     * @brief A class holding PSF font data, used for direct rendering of glyphs into a canvas.
+     */
+    class Font : public Shareable
+    {
+      public:
+        /**
+         * @brief An enum used to select a font weight when loading a font.
+         */
+        enum FontWeight
+        {
+            Regular,
+            Bold,
+        };
+
+        /**
+         * @brief Load a Font object from a font file.
+         *
+         * @param path The full path to the font file.
+         * @return Result<SharedPtr<Font>> An error, or the loaded Font object.
+         */
+        static Result<SharedPtr<Font>> load(const os::Path& path);
+
+        /**
+         * @brief Load a system font by name.
+         *
+         * @param name The name of the font to load (the default system font is "Tamsyn").
+         * @param weight The weight of the font (regular or bold).
+         * @return Result<SharedPtr<Font>> An error, or the loaded Font object.
+         */
+        static Result<SharedPtr<Font>> load_builtin(StringView name, FontWeight weight);
+
+        /**
+         * @brief Return a pointer to the system's default font.
+         *
+         * @return SharedPtr<Font> The default font.
+         */
+        static SharedPtr<Font> default_font();
+
+        /**
+         * @brief Return a pointer to the system's default bold font.
+         *
+         * @return SharedPtr<Font> The default bold font.
+         */
+        static SharedPtr<Font> default_bold_font();
+
+        /**
+         * @brief Render a single Unicode code point onto a canvas, using this font's glyphs.
+         *
+         * @param codepoint The code point to render.
+         * @param color The color to draw the code point in.
+         * @param canvas The canvas to use.
+         */
+        void render(wchar_t codepoint, ui::Color color, ui::Canvas& canvas);
+
+        /**
+         * @brief Render a Unicode text string onto a canvas, using this font's glyphs.
+         *
+         * @param text The string to render (must be null-terminated).
+         * @param color The color to draw the code point in.
+         * @param canvas The canvas to use.
+         */
+        void render(const wchar_t* text, ui::Color color, ui::Canvas& canvas);
+
+        /**
+         * @brief Return the width of this font's glyphs.
+         *
+         * @return int The width.
+         */
+        int width() const
+        {
+            return m_psf_header.width;
+        }
+
+        /**
+         * @brief Return the height of this font's glyphs.
+         *
+         * @return int The height.
+         */
+        int height() const
+        {
+            return m_psf_header.height;
+        }
+
+      private:
+        struct PSFHeader
+        {
+            u32 magic;
+            u32 version; // zero
+            u32 headersize;
+            u32 flags; // 0 if there's no unicode table
+            u32 numglyph;
+            u32 bytesperglyph;
+            int height;
+            int width;
+        };
+
+        PSFHeader m_psf_header;
+        Buffer m_font_data;
+    };
+};

libui/include/ui/Image.h

@@ -0,0 +1,96 @@
+/**
+ * @file Image.h
+ * @author apio (cloudapio.eu)
+ * @brief TGA image loading and rendering.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/Buffer.h>
+#include <luna/SharedPtr.h>
+#include <os/Path.h>
+#include <ui/Widget.h>
+
+namespace ui
+{
+    /**
+     * @brief An image in the TGA file format.
+     */
+    class Image : public Shareable
+    {
+      public:
+        /**
+         * @brief Load a new TGA image from a file.
+         *
+         * @param path The path to open.
+         * @return Result<SharedPtr<Image>> An error, or a new Image object.
+         */
+        static Result<SharedPtr<Image>> load(const os::Path& path);
+
+        /**
+         * @brief Return the array of pixels contained in the image.
+         *
+         * @return u32* The array of pixels.
+         */
+        u32* pixels()
+        {
+            return (u32*)m_image_data.data();
+        }
+
+        /**
+         * @brief Return the width of the image.
+         *
+         * @return u16 The width.
+         */
+        u16 width()
+        {
+            return m_tga_header.w;
+        }
+
+        /**
+         * @brief Return the height of the image.
+         *
+         * @return u16 The height.
+         */
+        u16 height()
+        {
+            return m_tga_header.h;
+        }
+
+      private:
+        struct [[gnu::packed]] TGAHeader
+        {
+            u8 idlen;
+            u8 colormap;
+            u8 encoding;
+            u16 cmaporig, cmaplen;
+            u8 cmapent;
+            u16 x;
+            u16 y;
+            u16 w;
+            u16 h;
+            u8 bpp;
+            u8 pixeltype;
+        };
+
+        TGAHeader m_tga_header;
+        Buffer m_image_data;
+    };
+
+    class ImageWidget final : public Widget
+    {
+      public:
+        static Result<OwnedPtr<ImageWidget>> load(const os::Path& path);
+
+        Result<EventResult> handle_mouse_move(Point position) override;
+        Result<EventResult> handle_mouse_leave(Point position) override;
+        Result<EventResult> handle_mouse_down(Point position, int buttons) override;
+        Result<EventResult> handle_mouse_up(Point position, int buttons) override;
+        Result<void> draw(Canvas& canvas) override;
+
+      private:
+        SharedPtr<Image> m_image;
+    };
+}

libui/include/ui/Layout.h

@@ -0,0 +1,69 @@
+/**
+ * @file Layout.h
+ * @author apio (cloudapio.eu)
+ * @brief Layout widgets to organize content.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/Vector.h>
+#include <ui/Widget.h>
+
+namespace ui
+{
+    enum class AdjustHeight
+    {
+        No,
+        Yes
+    };
+
+    enum class AdjustWidth
+    {
+        No,
+        Yes
+    };
+
+    class HorizontalLayout final : public Widget
+    {
+      public:
+        HorizontalLayout(AdjustHeight adjust_height = AdjustHeight::Yes, AdjustWidth adjust_width = AdjustWidth::Yes);
+
+        Result<EventResult> handle_mouse_move(Point position) override;
+        Result<EventResult> handle_mouse_leave(Point position) override;
+        Result<EventResult> handle_mouse_down(Point position, int buttons) override;
+        Result<EventResult> handle_mouse_up(Point position, int buttons) override;
+
+        Result<void> draw(Canvas& canvas) override;
+
+        Result<void> add_widget(Widget& widget);
+
+      private:
+        Vector<Widget*> m_widgets;
+        AdjustHeight m_adjust_height;
+        AdjustWidth m_adjust_width;
+        int m_used_width;
+    };
+
+    class VerticalLayout final : public Widget
+    {
+      public:
+        VerticalLayout(AdjustHeight adjust_height = AdjustHeight::Yes, AdjustWidth adjust_width = AdjustWidth::Yes);
+
+        Result<EventResult> handle_mouse_move(Point position) override;
+        Result<EventResult> handle_mouse_leave(Point position) override;
+        Result<EventResult> handle_mouse_down(Point position, int buttons) override;
+        Result<EventResult> handle_mouse_up(Point position, int buttons) override;
+
+        Result<void> draw(Canvas& canvas) override;
+
+        Result<void> add_widget(Widget& widget);
+
+      private:
+        Vector<Widget*> m_widgets;
+        AdjustHeight m_adjust_height;
+        AdjustWidth m_adjust_width;
+        int m_used_height;
+    };
+}

libui/include/ui/Mouse.h

@@ -0,0 +1,21 @@
+/**
+ * @file Mouse.h
+ * @author apio (cloudapio.eu)
+ * @brief Mouse buttons.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <moon/Mouse.h>
+
+namespace ui
+{
+    enum MouseButtons
+    {
+        LEFT = moon::Left,
+        MIDDLE = moon::Middle,
+        RIGHT = moon::Right,
+    };
+}

libui/include/ui/Point.h

@@ -0,0 +1,22 @@
+/**
+ * @file Point.h
+ * @author apio (cloudapio.eu)
+ * @brief 2D space points.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+
+namespace ui
+{
+    /**
+     * @brief A point in 2D space.
+     */
+    struct Point
+    {
+        int x { 0 };
+        int y { 0 };
+    };
+}

libui/include/ui/Rect.h

@@ -0,0 +1,81 @@
+/**
+ * @file Rect.h
+ * @author apio (cloudapio.eu)
+ * @brief A simple 2D rectangle representation.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <ui/Point.h>
+
+namespace ui
+{
+    /**
+     * @brief A simple rectangle.
+     */
+    struct Rect
+    {
+        Point pos;
+        int width;
+        int height;
+
+        /**
+         * @brief Check if a point is contained in this rectangle.
+         *
+         * @param point The point to check.
+         * @return true The point is contained inside the rectangle.
+         * @return false The point is not contained inside the rectangle.
+         */
+        bool contains(Point point);
+
+        /**
+         * @brief Check if another rectangle is contained in this one.
+         *
+         * @param point The rectangle to check.
+         * @return true The other rectangle is contained inside this one.
+         * @return false The other rectangle is not contained inside this one.
+         */
+        bool contains(Rect rect);
+
+        /**
+         * @brief Normalize a point to fit inside this rectangle.
+         *
+         * @param point The original point.
+         * @return Point The normalized point.
+         */
+        Point normalize(Point point);
+
+        /**
+         * @brief Transform an absolute position to a position relative to this rectangle.
+         *
+         * @param pos The original absolute position.
+         * @return Point The position relative to this rectangle.
+         */
+        Point relative(Point pos);
+
+        /**
+         * @brief Transform a position relative to this rectangle to an absolute position.
+         *
+         * @param pos The original relative position.
+         * @return Point The absolute position.
+         */
+        Point absolute(Point pos);
+
+        /**
+         * @brief Transform another rectangle relative to this one to an absolute rectangle.
+         *
+         * @param rect The original relative rectangle.
+         * @return Point The absolute rectangle.
+         */
+        Rect absolute(Rect rect);
+
+        /**
+         * @brief Return a copy of this rectangle with no negative values (normalized to 0).
+         *
+         * @return Rect The new rectangle.
+         */
+        Rect normalized();
+    };
+}

libui/include/ui/Widget.h

@@ -0,0 +1,68 @@
+/**
+ * @file Widget.h
+ * @author apio (cloudapio.eu)
+ * @brief Abstract widget class.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/Result.h>
+#include <ui/Canvas.h>
+#include <ui/Point.h>
+#include <ui/Rect.h>
+
+namespace ui
+{
+    class Window;
+
+    enum class EventResult
+    {
+        DidHandle,
+        DidNotHandle,
+    };
+
+    class Widget
+    {
+      public:
+        virtual Result<EventResult> handle_mouse_move(Point position);
+        virtual Result<EventResult> handle_mouse_down(Point position, int buttons);
+        virtual Result<EventResult> handle_mouse_up(Point position, int buttons);
+        virtual Result<EventResult> handle_mouse_leave(Point position);
+
+        virtual Result<void> draw(Canvas& canvas);
+
+        void set_window(Window* window, Rect rect, Badge<Window>)
+        {
+            m_window = window;
+            m_rect = rect;
+        }
+
+        void set_parent(Widget* parent)
+        {
+            m_parent = parent;
+            m_window = parent->m_window;
+        }
+
+        Widget* parent()
+        {
+            return m_parent;
+        }
+
+        Window* window()
+        {
+            return m_window;
+        }
+
+        Rect& rect()
+        {
+            return m_rect;
+        }
+
+      protected:
+        Widget* m_parent { nullptr };
+        Window* m_window;
+        Rect m_rect { 0, 0, 50, 50 };
+    };
+}

libui/include/ui/Window.h

@@ -0,0 +1,66 @@
+/**
+ * @file Window.h
+ * @author apio (cloudapio.eu)
+ * @brief UI windows.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <luna/OwnedPtr.h>
+#include <luna/StringView.h>
+#include <ui/Canvas.h>
+#include <ui/Mouse.h>
+#include <ui/Rect.h>
+#include <ui/Widget.h>
+
+namespace ui
+{
+    class Window
+    {
+      public:
+        static Result<Window*> create(Rect rect, bool decorated = true);
+
+        void set_title(StringView title);
+
+        void set_background(Color color)
+        {
+            m_background = color;
+        }
+
+        void set_main_widget(Widget& widget)
+        {
+            check(!m_main_widget);
+            widget.set_window(this, m_canvas.rect(), {});
+            m_main_widget = &widget;
+        }
+
+        Canvas& canvas()
+        {
+            return m_canvas;
+        }
+
+        void update();
+
+        void close();
+
+        Result<void> draw();
+        Result<void> handle_mouse_move(ui::Point position);
+        Result<void> handle_mouse_buttons(ui::Point position, int buttons);
+
+        int id() const
+        {
+            return m_id;
+        }
+
+        ~Window();
+
+      private:
+        int m_id;
+        Canvas m_canvas;
+        Widget* m_main_widget { nullptr };
+        Color m_background { ui::BLACK };
+        Option<int> m_old_mouse_buttons;
+    };
+}

libui/include/ui/ipc/Client.h

@@ -0,0 +1,55 @@
+/**
+ * @file ipc/Client.h
+ * @author apio (cloudapio.eu)
+ * @brief IPC message definitions for UI messages sent to the client.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <os/IPC.h>
+#include <ui/Point.h>
+
+namespace ui
+{
+    enum ClientMessages : u8
+    {
+        IPC_ENUM_CLIENT(ui),
+        CREATE_WINDOW_RESPONSE_ID,
+        WINDOW_CLOSE_REQUEST_ID,
+        MOUSE_EVENT_REQUEST_ID,
+        GET_SCREEN_RECT_RESPONSE_ID
+    };
+
+    struct CreateWindowResponse
+    {
+        static constexpr u8 ID = CREATE_WINDOW_RESPONSE_ID;
+
+        int window;
+        IPC_STRING(shm_path);
+    };
+
+    struct WindowCloseRequest
+    {
+        static constexpr u8 ID = WINDOW_CLOSE_REQUEST_ID;
+
+        int window;
+    };
+
+    struct MouseEventRequest
+    {
+        static constexpr u8 ID = MOUSE_EVENT_REQUEST_ID;
+
+        int window;
+        Point position;
+        int buttons;
+    };
+
+    struct GetScreenRectResponse
+    {
+        static constexpr u8 ID = GET_SCREEN_RECT_RESPONSE_ID;
+
+        Rect rect;
+    };
+}

libui/include/ui/ipc/Server.h

@@ -0,0 +1,66 @@
+/**
+ * @file ipc/Server.h
+ * @author apio (cloudapio.eu)
+ * @brief IPC message definitions for UI messages sent to the server.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#pragma once
+#include <os/IPC.h>
+#include <ui/Color.h>
+#include <ui/Rect.h>
+#include <ui/ipc/Client.h>
+
+namespace ui
+{
+    enum ServerMessages : u8
+    {
+        IPC_ENUM_SERVER(ui),
+        CREATE_WINDOW_ID,
+        SET_WINDOW_TITLE_ID,
+        INVALIDATE_ID,
+        CLOSE_WINDOW_ID,
+        GET_SCREEN_RECT_ID,
+    };
+
+    struct CreateWindowRequest
+    {
+        using ResponseType = CreateWindowResponse;
+        static constexpr u8 ID = CREATE_WINDOW_ID;
+
+        ui::Rect rect;
+        bool decorated;
+    };
+
+    struct SetWindowTitleRequest
+    {
+        static constexpr u8 ID = SET_WINDOW_TITLE_ID;
+
+        int window;
+        IPC_STRING(title);
+    };
+
+    struct InvalidateRequest
+    {
+        static constexpr u8 ID = INVALIDATE_ID;
+
+        int window;
+    };
+
+    struct CloseWindowRequest
+    {
+        static constexpr u8 ID = CLOSE_WINDOW_ID;
+
+        int window;
+    };
+
+    struct GetScreenRectRequest
+    {
+        using ResponseType = GetScreenRectResponse;
+        static constexpr u8 ID = GET_SCREEN_RECT_ID;
+
+        int _shadow; // Unused.
+    };
+}

libui/src/Alignment.cpp

@@ -0,0 +1,40 @@
+/**
+ * @file Alignment.cpp
+ * @author apio (cloudapio.eu)
+ * @brief UI component alignment.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <ui/Alignment.h>
+
+namespace ui
+{
+    Rect align(Rect container, Rect contained, VerticalAlignment valign, HorizontalAlignment halign)
+    {
+        Rect result;
+        result.width = contained.width;
+        result.height = contained.height;
+        result.pos.y = container.pos.y;
+        result.pos.x = container.pos.x;
+
+        switch (valign)
+        {
+        case VerticalAlignment::Top: break;
+        case VerticalAlignment::Center: result.pos.y += (container.height - contained.height) / 2; break;
+        case VerticalAlignment::Bottom: result.pos.y += container.height - contained.height; break;
+        default: break;
+        }
+
+        switch (halign)
+        {
+        case HorizontalAlignment::Left: break;
+        case HorizontalAlignment::Center: result.pos.x += (container.width - contained.width) / 2; break;
+        case HorizontalAlignment::Right: result.pos.x += container.width - contained.width; break;
+        default: break;
+        }
+
+        return result;
+    }
+}

libui/src/App.cpp

@@ -0,0 +1,128 @@
+/**
+ * @file App.cpp
+ * @author apio (cloudapio.eu)
+ * @brief UI application event loop.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <os/IPC.h>
+#include <ui/App.h>
+#include <ui/ipc/Client.h>
+#include <ui/ipc/Server.h>
+
+Result<void> handle_ipc_client_event(os::LocalClient&, u8 id)
+{
+    return ui::App::the().handle_ipc_event(id);
+}
+
+namespace ui
+{
+    App* App::s_app { nullptr };
+
+    App::App()
+    {
+        s_app = this;
+    }
+
+    App::~App()
+    {
+        s_app = nullptr;
+    }
+
+    Result<void> App::init(int argc, char** argv)
+    {
+        StringView socket_path = "/tmp/wind.sock";
+
+        os::ArgumentParser parser;
+        parser.add_description("A UI application."_sv);
+        parser.add_system_program_info(argv[0]);
+        parser.add_value_argument(socket_path, 's', "socket"_sv, "the path for the local IPC socket"_sv);
+        parser.parse(argc, argv);
+
+        m_client = TRY(os::LocalClient::connect(socket_path, true));
+
+        return {};
+    }
+
+    Result<int> App::run()
+    {
+        check(m_main_window);
+        while (!m_should_close) { TRY(os::IPC::check_for_messages(*m_client)); }
+        return 0;
+    }
+
+    App& App::the()
+    {
+        check(s_app);
+        return *s_app;
+    }
+
+    Rect App::screen_rect()
+    {
+        ui::GetScreenRectRequest request {};
+        auto response = os::IPC::send_sync<ui::GetScreenRectResponse>(*m_client, request).release_value();
+        return response.rect;
+    }
+
+    Result<void> App::register_window(OwnedPtr<Window>&& window, Badge<Window>)
+    {
+        int id = window->id();
+        check(TRY(m_windows.try_set(id, move(window))));
+        return {};
+    }
+
+    void App::unregister_window(Window* window, Badge<Window>)
+    {
+        int id = window->id();
+        check(m_windows.try_remove(id));
+    }
+
+    Window* App::find_window(int id)
+    {
+        auto* window = m_windows.try_get_ref(id);
+        check(window);
+        return window->ptr();
+    }
+
+#define READ_MESSAGE(request)                                                                                          \
+    do {                                                                                                               \
+        auto rc = m_client->recv_typed(request);                                                                       \
+        if (rc.has_error())                                                                                            \
+        {                                                                                                              \
+            if (rc.error() == EAGAIN) { continue; }                                                                    \
+            if (rc.error() == EINTR) { continue; }                                                                     \
+            else                                                                                                       \
+                return rc.release_error();                                                                             \
+        }                                                                                                              \
+        break;                                                                                                         \
+    } while (true)
+
+    Result<void> App::handle_ipc_event(u8 id)
+    {
+        switch (id)
+        {
+        case WINDOW_CLOSE_REQUEST_ID: {
+            WindowCloseRequest request;
+            READ_MESSAGE(request);
+            os::eprintln("ui: Window close request from server! Shall comply.");
+            auto* window = find_window(request.window);
+            window->close();
+            return {};
+        }
+        case MOUSE_EVENT_REQUEST_ID: {
+            MouseEventRequest request;
+            READ_MESSAGE(request);
+            auto* window = find_window(request.window);
+            window->handle_mouse_move(request.position);
+            window->handle_mouse_buttons(request.position, request.buttons);
+            window->draw();
+            return {};
+        }
+        default: fail("Unexpected IPC request from server!");
+        }
+    }
+}

libui/src/Button.cpp

@@ -0,0 +1,68 @@
+/**
+ * @file Button.cpp
+ * @author apio (cloudapio.eu)
+ * @brief A clickable component that triggers an action when pressed.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <ui/Button.h>
+#include <ui/Mouse.h>
+
+namespace ui
+{
+    Button::Button(Rect rect)
+    {
+        m_rect = rect;
+    }
+
+    void Button::set_widget(Widget& widget)
+    {
+        widget.rect() = m_rect;
+        m_child = &widget;
+        widget.set_parent(this);
+    }
+
+    void Button::set_action(void (*action)(void))
+    {
+        m_action = action;
+    }
+
+    Result<EventResult> Button::handle_mouse_move(Point position)
+    {
+        m_hovered = true;
+        return m_child->handle_mouse_move(position);
+    }
+
+    Result<EventResult> Button::handle_mouse_leave(Point position)
+    {
+        m_hovered = m_clicked = false;
+        return m_child->handle_mouse_leave(position);
+    }
+
+    Result<EventResult> Button::handle_mouse_down(Point position, int buttons)
+    {
+        auto result = TRY(m_child->handle_mouse_down(position, buttons));
+        if (result == EventResult::DidNotHandle)
+        {
+            if (!m_clicked && (buttons == ui::MouseButtons::LEFT))
+            {
+                m_clicked = true;
+                m_action();
+            }
+        }
+        return EventResult::DidHandle;
+    }
+
+    Result<EventResult> Button::handle_mouse_up(Point position, int buttons)
+    {
+        if (buttons & ui::MouseButtons::LEFT) m_clicked = false;
+        return m_child->handle_mouse_up(position, buttons);
+    }
+
+    Result<void> Button::draw(Canvas& canvas)
+    {
+        return m_child->draw(canvas);
+    }
+}

libui/src/Canvas.cpp

@@ -0,0 +1,62 @@
+/**
+ * @file Canvas.cpp
+ * @author apio (cloudapio.eu)
+ * @brief Drawable surfaces.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <ui/Canvas.h>
+
+namespace ui
+{
+    Canvas Canvas::create(u8* ptr, int width, int height)
+    {
+        return Canvas { .width = width, .height = height, .stride = width, .ptr = ptr };
+    }
+
+    Canvas Canvas::subcanvas(Rect rect)
+    {
+        if (rect.pos.x < 0) rect.pos.x = 0;
+        if (rect.pos.y < 0) rect.pos.y = 0;
+        if (rect.pos.x + rect.width > width) rect.width = width - rect.pos.x;
+        if (rect.pos.y + rect.height > height) rect.height = height - rect.pos.y;
+
+        u8* p = ptr + rect.pos.x * sizeof(Color) + (rect.pos.y * sizeof(Color) * stride);
+
+        return Canvas { .width = rect.width, .height = rect.height, .stride = stride, .ptr = p };
+    }
+
+    void Canvas::fill(Color color)
+    {
+        u8* p = ptr;
+        for (int i = 0; i < height; i++)
+        {
+            u32* colorp = (u32*)p;
+            for (int j = 0; j < width; j++)
+            {
+                *colorp = color.raw;
+                colorp++;
+            }
+            p += stride * sizeof(Color);
+        }
+    }
+
+    void Canvas::fill(u32* pixels, int _stride)
+    {
+        u8* p = ptr;
+        for (int i = 0; i < height; i++)
+        {
+            u32* colorp = (u32*)p;
+            for (int j = 0; j < width; j++)
+            {
+                u32 pix = pixels[j];
+                if (Color::from_u32(pix).alpha() == 0xff) *colorp = pix;
+                colorp++;
+            }
+            pixels += _stride;
+            p += stride * sizeof(Color);
+        }
+    }
+}

libui/src/Container.cpp

@@ -0,0 +1,55 @@
+/**
+ * @file Container.cpp
+ * @author apio (cloudapio.eu)
+ * @brief A container widget to pad and align objects inside it.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <ui/Container.h>
+
+namespace ui
+{
+    Container::Container(Rect rect, VerticalAlignment valign, HorizontalAlignment halign)
+        : m_valign(valign), m_halign(halign)
+    {
+        m_rect = rect;
+    }
+
+    void Container::set_widget(Widget& widget)
+    {
+        m_widget = &widget;
+        widget.rect() = ui::align(m_rect, widget.rect(), m_valign, m_halign);
+        widget.set_parent(this);
+    }
+
+    Result<EventResult> Container::handle_mouse_move(Point position)
+    {
+        return m_widget->handle_mouse_move(position);
+    }
+
+    Result<EventResult> Container::handle_mouse_leave(Point position)
+    {
+        return m_widget->handle_mouse_leave(position);
+    }
+
+    Result<EventResult> Container::handle_mouse_down(Point position, int buttons)
+    {
+        return m_widget->handle_mouse_down(position, buttons);
+    }
+
+    Result<EventResult> Container::handle_mouse_up(Point position, int buttons)
+    {
+        return m_widget->handle_mouse_up(position, buttons);
+    }
+
+    Result<void> Container::draw(Canvas& canvas)
+    {
+        auto rect = ui::Rect { m_widget->rect().pos.x - m_rect.pos.x, m_widget->rect().pos.y - m_rect.pos.y,
+                               m_widget->rect().width, m_widget->rect().height };
+        auto subcanvas = canvas.subcanvas(rect);
+        return m_widget->draw(subcanvas);
+    }
+
+}

libui/src/Font.cpp

@@ -0,0 +1,121 @@
+/**
+ * @file Font.cpp
+ * @author apio (cloudapio.eu)
+ * @brief PSF font loading and rendering.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <luna/String.h>
+#include <os/File.h>
+#include <ui/Font.h>
+
+constexpr static int BYTES_PER_PIXEL = (int)sizeof(ui::Color);
+
+namespace ui
+{
+    Result<SharedPtr<Font>> Font::load(const os::Path& path)
+    {
+        auto font = TRY(make_shared<Font>());
+
+        auto file = TRY(os::File::open(path, os::File::ReadOnly));
+
+        TRY(file->read_typed(font->m_psf_header));
+
+        if (font->m_psf_header.magic != PSF_FONT_MAGIC)
+        {
+            os::eprintln("ui::Font::load(%s) failed: font magic does not match PSF2 magic", path.name().chars());
+            return err(ENOTSUP);
+        }
+
+        if (font->m_psf_header.version != 0)
+        {
+            os::eprintln("ui::Font::load(%s) failed: font version is unsupported", path.name().chars());
+            return err(ENOTSUP);
+        }
+
+        if (font->m_psf_header.flags)
+        {
+            os::eprintln("ui::Font::load(%s) warning: font has a unicode table, which we're ignoring",
+                         path.name().chars());
+            // todo(); // Font has a unicode table, oh no!
+        }
+
+        font->m_font_data = TRY(file->read_all()); // Read the rest of the file into the font data buffer.
+
+        return font;
+    }
+
+    Result<SharedPtr<Font>> Font::load_builtin(StringView name, FontWeight weight)
+    {
+        auto path = TRY(String::format("/usr/share/fonts/%s-%s.psf"_sv, name.chars(),
+                                       weight == FontWeight::Bold ? "Bold" : "Regular"));
+
+        return load(path.view());
+    }
+
+    SharedPtr<Font> Font::default_font()
+    {
+        static SharedPtr<ui::Font> s_default_font = {};
+        if (!s_default_font) s_default_font = load("/usr/share/fonts/Tamsyn-Regular.psf").release_value();
+        return s_default_font;
+    }
+
+    SharedPtr<Font> Font::default_bold_font()
+    {
+        static SharedPtr<ui::Font> s_default_bold_font = {};
+        if (!s_default_bold_font) s_default_bold_font = load("/usr/share/fonts/Tamsyn-Bold.psf").release_value();
+        return s_default_bold_font;
+    }
+
+    void Font::render(wchar_t codepoint, ui::Color color, ui::Canvas& canvas)
+    {
+        const wchar_t str[] = { codepoint, 0 };
+        render(str, color, canvas);
+    }
+
+    void Font::render(const wchar_t* text, ui::Color color, ui::Canvas& canvas)
+    {
+        usize len = wcslen(text);
+
+        int height = m_psf_header.height;
+        int width = m_psf_header.width;
+        int last_char_width = width;
+
+        if (canvas.width < (m_psf_header.width * static_cast<int>(len)))
+        {
+            len = (canvas.width / width) + 1;
+            last_char_width = canvas.width % width;
+        }
+
+        if (canvas.height < height) height = canvas.height;
+
+        const int bytes_per_line = (m_psf_header.width + 7) / 8;
+
+        for (usize i = 0; i < len; i++)
+        {
+            if (i + 1 == len) width = last_char_width;
+            wchar_t codepoint = text[i];
+
+            u8* glyph =
+                m_font_data.data() + (codepoint > 0 && codepoint < (wchar_t)m_psf_header.numglyph ? codepoint : 0) *
+                                         m_psf_header.bytesperglyph;
+
+            u32 offset = (u32)i * m_psf_header.width * BYTES_PER_PIXEL;
+            for (int y = 0; y < height; y++)
+            {
+                u32 line = offset;
+                int mask = 1 << (m_psf_header.width - 1);
+                for (int x = 0; x < width; x++)
+                {
+                    if (*((u32*)glyph) & mask) *(u32*)(canvas.ptr + line) = color.raw;
+                    mask >>= 1;
+                    line += BYTES_PER_PIXEL;
+                }
+                glyph += bytes_per_line;
+                offset += canvas.stride * BYTES_PER_PIXEL;
+            }
+        }
+    }
+}

libui/src/Image.cpp

@@ -0,0 +1,68 @@
+/**
+ * @file Image.cpp
+ * @author apio (cloudapio.eu)
+ * @brief TGA image loading and rendering.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <os/File.h>
+#include <ui/Alignment.h>
+#include <ui/Image.h>
+
+namespace ui
+{
+    Result<SharedPtr<Image>> Image::load(const os::Path& path)
+    {
+        auto image = TRY(make_shared<Image>());
+        auto file = TRY(os::File::open(path, os::File::ReadOnly));
+
+        TRY(file->read_typed(image->m_tga_header));
+
+        if (image->m_tga_header.encoding != 2) todo();
+        if (image->m_tga_header.bpp != 32) todo();
+
+        Buffer image_id;
+        TRY(file->read(image_id, image->m_tga_header.idlen));
+
+        TRY(file->read(image->m_image_data,
+                       image->m_tga_header.w * image->m_tga_header.h * (image->m_tga_header.bpp / 8)));
+
+        return image;
+    }
+
+    Result<OwnedPtr<ImageWidget>> ImageWidget::load(const os::Path& path)
+    {
+        auto widget = TRY(make_owned<ImageWidget>());
+        widget->m_image = TRY(Image::load(path));
+        widget->m_rect = { 0, 0, widget->m_image->width(), widget->m_image->height() };
+        return widget;
+    }
+
+    Result<EventResult> ImageWidget::handle_mouse_move(Point)
+    {
+        return EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> ImageWidget::handle_mouse_leave(Point)
+    {
+        return EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> ImageWidget::handle_mouse_up(Point, int)
+    {
+        return EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> ImageWidget::handle_mouse_down(Point, int)
+    {
+        return EventResult::DidNotHandle;
+    }
+
+    Result<void> ImageWidget::draw(Canvas& canvas)
+    {
+        canvas.subcanvas({ 0, 0, m_image->width(), m_image->height() }).fill(m_image->pixels(), m_image->width());
+        return {};
+    }
+}

libui/src/Layout.cpp

@@ -0,0 +1,192 @@
+/**
+ * @file Layout.cpp
+ * @author apio (cloudapio.eu)
+ * @brief Layout widgets to organize content.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <stdlib.h>
+#include <ui/Layout.h>
+
+namespace ui
+{
+    HorizontalLayout::HorizontalLayout(AdjustHeight adjust_height, AdjustWidth adjust_width)
+        : m_adjust_height(adjust_height), m_adjust_width(adjust_width)
+    {
+    }
+
+    Result<EventResult> HorizontalLayout::handle_mouse_move(Point position)
+    {
+        EventResult result = ui::EventResult::DidNotHandle;
+
+        for (auto widget : m_widgets)
+        {
+            if (widget->rect().contains(position)) result = TRY(widget->handle_mouse_move(position));
+            else
+                TRY(widget->handle_mouse_leave(position));
+        }
+
+        return result;
+    }
+
+    Result<EventResult> HorizontalLayout::handle_mouse_leave(Point position)
+    {
+        for (auto widget : m_widgets) TRY(widget->handle_mouse_leave(position));
+
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> HorizontalLayout::handle_mouse_up(Point position, int buttons)
+    {
+        for (auto widget : m_widgets)
+        {
+            if (widget->rect().contains(position)) return widget->handle_mouse_up(position, buttons);
+        }
+
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> HorizontalLayout::handle_mouse_down(Point position, int buttons)
+    {
+        for (auto widget : m_widgets)
+        {
+            if (widget->rect().contains(position)) return widget->handle_mouse_down(position, buttons);
+        }
+
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<void> HorizontalLayout::draw(Canvas& canvas)
+    {
+        for (auto widget : m_widgets)
+        {
+            ui::Rect rect = { m_rect.relative(widget->rect().pos), widget->rect().width, widget->rect().height };
+            auto subcanvas = canvas.subcanvas(rect);
+            TRY(widget->draw(subcanvas));
+        }
+
+        return {};
+    }
+
+    Result<void> HorizontalLayout::add_widget(Widget& widget)
+    {
+        TRY(m_widgets.try_append(&widget));
+
+        if (m_adjust_width == AdjustWidth::No)
+        {
+            widget.rect().pos.x = m_rect.pos.x + m_used_width;
+            m_used_width += widget.rect().width;
+        }
+        else
+        {
+            int used_width = 0;
+            div_t result = div(m_rect.width, (int)m_widgets.size());
+            for (auto w : m_widgets)
+            {
+                w->rect().pos.x = m_rect.pos.x + used_width;
+                w->rect().width = result.quot;
+                used_width += result.quot;
+            }
+            m_widgets[m_widgets.size() - 1]->rect().width += result.rem;
+        }
+
+        widget.rect().pos.y = m_rect.pos.y;
+
+        if (m_adjust_height == AdjustHeight::Yes) { widget.rect().height = m_rect.height; }
+
+        widget.set_parent(this);
+
+        return {};
+    }
+
+    VerticalLayout::VerticalLayout(AdjustHeight adjust_height, AdjustWidth adjust_width)
+        : m_adjust_height(adjust_height), m_adjust_width(adjust_width)
+    {
+    }
+
+    Result<EventResult> VerticalLayout::handle_mouse_move(Point position)
+    {
+        EventResult result = ui::EventResult::DidNotHandle;
+
+        for (auto widget : m_widgets)
+        {
+            if (widget->rect().contains(position)) result = TRY(widget->handle_mouse_move(position));
+            else
+                TRY(widget->handle_mouse_leave(position));
+        }
+
+        return result;
+    }
+
+    Result<EventResult> VerticalLayout::handle_mouse_leave(Point position)
+    {
+        for (auto widget : m_widgets) TRY(widget->handle_mouse_leave(position));
+
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> VerticalLayout::handle_mouse_up(Point position, int buttons)
+    {
+        for (auto widget : m_widgets)
+        {
+            if (widget->rect().contains(position)) return widget->handle_mouse_up(position, buttons);
+        }
+
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<EventResult> VerticalLayout::handle_mouse_down(Point position, int buttons)
+    {
+        for (auto widget : m_widgets)
+        {
+            if (widget->rect().contains(position)) return widget->handle_mouse_down(position, buttons);
+        }
+
+        return ui::EventResult::DidNotHandle;
+    }
+
+    Result<void> VerticalLayout::draw(Canvas& canvas)
+    {
+        for (auto widget : m_widgets)
+        {
+            ui::Rect rect = { m_rect.relative(widget->rect().pos), widget->rect().width, widget->rect().height };
+            auto subcanvas = canvas.subcanvas(rect);
+            TRY(widget->draw(subcanvas));
+        }
+
+        return {};
+    }
+
+    Result<void> VerticalLayout::add_widget(Widget& widget)
+    {
+        TRY(m_widgets.try_append(&widget));
+
+        if (m_adjust_height == AdjustHeight::No)
+        {
+            widget.rect().pos.y = m_rect.pos.y + m_used_height;
+            m_used_height += widget.rect().height;
+        }
+        else
+        {
+            int used_height = 0;
+            div_t result = div(m_rect.height, (int)m_widgets.size());
+            for (auto w : m_widgets)
+            {
+                w->rect().pos.y = m_rect.pos.y + used_height;
+                w->rect().height = result.quot;
+                used_height += result.quot;
+            }
+            m_widgets[m_widgets.size() - 1]->rect().height += result.rem;
+        }
+
+        widget.rect().pos.x = m_rect.pos.x;
+
+        if (m_adjust_width == AdjustWidth::Yes) { widget.rect().width = m_rect.width; }
+
+        widget.set_parent(this);
+
+        return {};
+    }
+}

libui/src/Rect.cpp

@@ -0,0 +1,62 @@
+/**
+ * @file Rect.cpp
+ * @author apio (cloudapio.eu)
+ * @brief A simple 2D rectangle representation.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <ui/Rect.h>
+
+namespace ui
+{
+    bool Rect::contains(Point point)
+    {
+        return (point.x >= pos.x) && (point.y >= pos.y) && (point.x <= (pos.x + width)) &&
+               (point.y <= (pos.y + height));
+    }
+
+    bool Rect::contains(Rect rect)
+    {
+        if (!contains(rect.pos)) return false;
+        Point rel = relative(rect.pos);
+        if ((rel.x + rect.width) > width) return false;
+        if ((rel.y + rect.height) > height) return false;
+        return true;
+    }
+
+    Point Rect::normalize(Point point)
+    {
+        if (point.x < pos.x) point.x = pos.x;
+        if (point.y < pos.y) point.y = pos.y;
+        if (point.x > pos.x + width) point.x = pos.x + width;
+        if (point.y > pos.y + height) point.y = pos.y + height;
+        return point;
+    }
+
+    Point Rect::relative(Point point)
+    {
+        point = normalize(point);
+        point.x -= pos.x;
+        point.y -= pos.y;
+        return point;
+    }
+
+    Point Rect::absolute(Point point)
+    {
+        point.x += pos.x;
+        point.y += pos.y;
+        return point;
+    }
+
+    Rect Rect::absolute(Rect rect)
+    {
+        return Rect { absolute(rect.pos), rect.width, rect.height };
+    }
+
+    Rect Rect::normalized()
+    {
+        return Rect { ui::Point { pos.x < 0 ? 0 : pos.x, pos.y < 0 ? 0 : pos.y }, width, height };
+    }
+};

libui/src/Window.cpp

@@ -0,0 +1,124 @@
+/**
+ * @file Window.cpp
+ * @author apio (cloudapio.eu)
+ * @brief UI windows.
+ *
+ * @copyright Copyright (c) 2023, the Luna authors.
+ *
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <ui/App.h>
+#include <ui/Window.h>
+#include <ui/ipc/Server.h>
+#include <unistd.h>
+
+static Result<u32*> create_shm_region(const char* path, int* outfd, ui::Rect rect)
+{
+    int fd = shm_open(path, O_RDWR, 0600);
+    shm_unlink(path);
+    if (fd < 0) return err(errno);
+
+    usize size = rect.width * rect.height * 4; // 4 bytes per pixel
+
+    void* p = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (p == MAP_FAILED)
+    {
+        shm_unlink(path);
+        close(fd);
+        return 0;
+    }
+
+    if (outfd) *outfd = fd;
+    else
+        close(fd);
+    return (u32*)p;
+}
+
+namespace ui
+{
+    Result<Window*> Window::create(Rect rect, bool decorated)
+    {
+        auto window = TRY(make_owned<Window>());
+
+        ui::CreateWindowRequest request;
+        request.rect = rect;
+        request.decorated = decorated;
+        auto response = TRY(os::IPC::send_sync<ui::CreateWindowResponse>(App::the().client(), request));
+
+        u32* pixels = TRY(create_shm_region(response.shm_path, nullptr, rect));
+
+        window->m_canvas = ui::Canvas { rect.width, rect.height, rect.width, (u8*)pixels };
+        window->m_id = response.window;
+
+        Window* p = window.ptr();
+
+        App::the().register_window(move(window), {});
+
+        return p;
+    }
+
+    Window::~Window()
+    {
+        if (m_canvas.ptr) munmap(m_canvas.ptr, ((usize)m_canvas.width) * ((usize)m_canvas.height) * 4);
+    }
+
+    void Window::set_title(StringView title)
+    {
+        ui::SetWindowTitleRequest request;
+        request.window = m_id;
+        SET_IPC_STRING(request.title, title.chars());
+        os::IPC::send_async(App::the().client(), request);
+    }
+
+    void Window::update()
+    {
+        ui::InvalidateRequest request;
+        request.window = m_id;
+        os::IPC::send_async(App::the().client(), request);
+    }
+
+    void Window::close()
+    {
+        App& app = App::the();
+
+        ui::CloseWindowRequest request;
+        request.window = m_id;
+        os::IPC::send_async(app.client(), request);
+
+        if (this == app.main_window()) app.set_should_close(true);
+
+        app.unregister_window(this, {});
+    }
+
+    Result<void> Window::draw()
+    {
+        m_canvas.fill(m_background);
+        if (m_main_widget) return m_main_widget->draw(m_canvas);
+        update();
+        return {};
+    }
+
+    Result<void> Window::handle_mouse_move(ui::Point position)
+    {
+        if (!m_main_widget) return {};
+        TRY(m_main_widget->handle_mouse_move(position));
+        return {};
+    }
+
+    Result<void> Window::handle_mouse_buttons(ui::Point position, int buttons)
+    {
+        if (!m_main_widget) return {};
+        if (buttons) TRY(m_main_widget->handle_mouse_down(position, buttons));
+        if (m_old_mouse_buttons.has_value())
+        {
+            int old_buttons = m_old_mouse_buttons.value();
+            int diff = old_buttons & ~buttons;
+            if (diff) TRY(m_main_widget->handle_mouse_up(position, diff));
+        }
+        m_old_mouse_buttons = buttons;
+        return {};
+    }
+}

tools/install-headers.sh

@@ -8,10 +8,12 @@ cd $LUNA_ROOT
 mkdir -p $LUNA_BASE
 mkdir -p $LUNA_BASE/usr/include
 mkdir -p $LUNA_BASE/usr/include/luna
+mkdir -p $LUNA_BASE/usr/include/ui
 mkdir -p $LUNA_BASE/usr/include/os
 mkdir -p $LUNA_BASE/usr/include/moon
 
 cp --preserve=timestamps -RT libc/include/ $LUNA_BASE/usr/include
 cp --preserve=timestamps -RT libluna/include/luna/ $LUNA_BASE/usr/include/luna
+cp --preserve=timestamps -RT libui/include/ui/ $LUNA_BASE/usr/include/ui
 cp --preserve=timestamps -RT libos/include/os/ $LUNA_BASE/usr/include/os
 cp --preserve=timestamps -RT kernel/src/api/ $LUNA_BASE/usr/include/moon

tools/sources.sh

@@ -4,7 +4,7 @@ source $(dirname $0)/env.sh
 
 cd $LUNA_ROOT
 
-FOLDERS=(kernel libc libos libluna apps shell tests)
+FOLDERS=(kernel libc libos libui libluna apps shell tests)
 
 SOURCES=($(find ${FOLDERS[@]} -type f -name "*.cpp"))
 SOURCES+=($(find ${FOLDERS[@]} -type f -name "*.h"))

wind/CMakeLists.txt

@@ -0,0 +1,19 @@
+set(SOURCES
+    main.cpp
+    Screen.h
+    Screen.cpp
+    Mouse.h
+    Mouse.cpp
+    Window.h
+    Window.cpp
+    IPC.cpp
+    IPC.h
+    Client.h
+)
+
+add_executable(wind ${SOURCES})
+target_compile_options(wind PRIVATE -Os ${COMMON_FLAGS} -Wno-write-strings -fno-threadsafe-statics)
+add_dependencies(wind libc)
+target_include_directories(wind PRIVATE ${LUNA_BASE}/usr/include ${CMAKE_CURRENT_LIST_DIR})
+target_link_libraries(wind PRIVATE os ui)
+install(TARGETS wind DESTINATION ${LUNA_BASE}/usr/bin)

wind/Client.h

@@ -0,0 +1,18 @@
+#pragma once
+#include "Window.h"
+#include <os/LocalServer.h>
+
+struct Client
+{
+    os::LocalServer::Client conn;
+    Vector<Window*> windows;
+    bool rpc_in_progress { false };
+    u8 rpc_id { 0 };
+
+    Client(os::LocalServer::Client&& client)
+#ifdef CLIENT_IMPLEMENTATION
+        : conn(move(client)), windows() {}
+#else
+        ;
+#endif
+};

wind/IPC.cpp

@@ -0,0 +1,221 @@
+#include "IPC.h"
+#include "Screen.h"
+#include <errno.h>
+#include <luna/Alignment.h>
+#include <luna/String.h>
+#include <os/File.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <time.h>
+#include <unistd.h>
+
+#define TRY_OR_IPC_ERROR(expr)                                                                                         \
+    ({                                                                                                                 \
+        auto _expr_rc = (expr);                                                                                        \
+        if (!_expr_rc.has_value())                                                                                     \
+        {                                                                                                              \
+            delete window;                                                                                             \
+            os::IPC::send_error(client.conn, _expr_rc.error());                                                        \
+            return {};                                                                                                 \
+        }                                                                                                              \
+        _expr_rc.release_value();                                                                                      \
+    })
+
+static Result<u32*> create_shm_region(const char* path, int* outfd, ui::Rect rect)
+{
+    int fd = shm_open(path, O_RDWR | O_CREAT | O_EXCL, 0600);
+    if (fd < 0)
+    {
+        int olderr = errno;
+        os::eprintln("wind: could not create shared memory region: shm_open failed (%s) - %s", path, strerror(olderr));
+        return err(olderr);
+    }
+
+    usize size = align_up<PAGE_SIZE>(rect.width * rect.height * 4); // 4 bytes per pixel
+
+    if (ftruncate(fd, size) < 0)
+    {
+        int olderr = errno;
+        os::eprintln("wind: could not create shared memory region: ftruncate failed (%d, %zu) - %s", fd, size,
+                     strerror(olderr));
+        shm_unlink(path);
+        close(fd);
+        return err(olderr);
+    }
+
+    void* p = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (p == MAP_FAILED)
+    {
+        int olderr = errno;
+        os::eprintln("wind: could not create shared memory region: mmap failed (%zu, %d) - %s", size, fd,
+                     strerror(olderr));
+        shm_unlink(path);
+        close(fd);
+        return err(olderr);
+    }
+
+    if (outfd) *outfd = fd;
+    else
+        close(fd);
+    return (u32*)p;
+}
+
+#define READ_MESSAGE(request)                                                                                          \
+    do {                                                                                                               \
+        auto rc = client.conn.recv_typed(request);                                                                     \
+        if (rc.has_error())                                                                                            \
+        {                                                                                                              \
+            if (rc.error() == EAGAIN)                                                                                  \
+            {                                                                                                          \
+                client.rpc_in_progress = true;                                                                         \
+                client.rpc_id = decltype(request)::ID;                                                                 \
+                return {};                                                                                             \
+            }                                                                                                          \
+            if (rc.error() == EINTR)                                                                                   \
+            {                                                                                                          \
+                client.rpc_in_progress = true;                                                                         \
+                client.rpc_id = decltype(request)::ID;                                                                 \
+                return {};                                                                                             \
+            }                                                                                                          \
+            else                                                                                                       \
+                return rc.release_error();                                                                             \
+        }                                                                                                              \
+    } while (0)
+
+#define CHECK_WINDOW_ID(request)                                                                                       \
+    do {                                                                                                               \
+        if ((usize)request.window >= client.windows.size() || !client.windows[request.window])                         \
+        {                                                                                                              \
+            os::eprintln("wind: Window id is invalid!");                                                               \
+            return {};                                                                                                 \
+        }                                                                                                              \
+    } while (0)
+
+static Result<void> handle_create_window_message(Client& client)
+{
+    ui::CreateWindowRequest request;
+    READ_MESSAGE(request);
+
+    request.rect = request.rect.normalized();
+
+    if (request.decorated)
+    {
+        request.rect.height +=
+            Window::titlebar_height(); // Make sure we provide the full contents rect that was asked for.
+        request.rect.pos.y -= Window::titlebar_height(); // Adjust it so the contents begin at the expected coordinates.
+    }
+
+    auto name = TRY(String::from_cstring("Window"));
+
+    auto* window = new (std::nothrow) Window(request.rect, move(name), request.decorated);
+    if (!window)
+    {
+        os::IPC::send_error(client.conn, ENOMEM);
+        return {};
+    }
+
+    auto shm_path = TRY_OR_IPC_ERROR(String::format("/wind-shm-%d-%lu"_sv, client.conn.fd(), time(NULL)));
+
+    window->pixels = TRY_OR_IPC_ERROR(create_shm_region(shm_path.chars(), nullptr, window->contents));
+
+    TRY_OR_IPC_ERROR(client.windows.try_append(window));
+    int id = static_cast<int>(client.windows.size() - 1);
+
+    window->client = &client;
+    window->id = id;
+
+    ui::CreateWindowResponse response;
+    response.window = id;
+    SET_IPC_STRING(response.shm_path, shm_path.chars());
+    os::IPC::send_async(client.conn, response);
+    return {};
+}
+
+static Result<void> handle_set_window_title_message(Client& client)
+{
+    ui::SetWindowTitleRequest request;
+    READ_MESSAGE(request);
+
+    auto name = COPY_IPC_STRING(request.title);
+
+    os::println("wind: SetWindowTitle(\"%s\") for window %d", name.chars(), request.window);
+
+    CHECK_WINDOW_ID(request);
+
+    client.windows[request.window]->name = move(name);
+
+    return {};
+}
+
+static Result<void> handle_invalidate_message(Client& client)
+{
+    ui::InvalidateRequest request;
+    READ_MESSAGE(request);
+
+    CHECK_WINDOW_ID(request);
+
+    client.windows[request.window]->dirty = true;
+
+    return {};
+}
+
+static Result<void> handle_close_window_message(Client& client)
+{
+    ui::CloseWindowRequest request;
+    READ_MESSAGE(request);
+
+    CHECK_WINDOW_ID(request);
+
+    auto* window = client.windows[request.window];
+    client.windows[request.window] = nullptr;
+    g_windows.remove(window);
+    delete window;
+
+    return {};
+}
+
+static Result<void> handle_get_screen_rect_message(Client& client)
+{
+    ui::GetScreenRectRequest request;
+    READ_MESSAGE(request); // Kinda pointless, but required.
+
+    ui::GetScreenRectResponse response;
+    response.rect = Screen::the().canvas().rect();
+    os::IPC::send_async(client.conn, response);
+
+    return {};
+}
+
+namespace wind
+{
+    Result<void> handle_ipc_message(Client& client, u8 id)
+    {
+        client.rpc_in_progress = false;
+        switch (id)
+        {
+        case ui::CREATE_WINDOW_ID: return handle_create_window_message(client);
+        case ui::SET_WINDOW_TITLE_ID: return handle_set_window_title_message(client);
+        case ui::INVALIDATE_ID: return handle_invalidate_message(client);
+        case ui::CLOSE_WINDOW_ID: return handle_close_window_message(client);
+        case ui::GET_SCREEN_RECT_ID: return handle_get_screen_rect_message(client);
+        default: os::eprintln("wind: Invalid IPC message from client!"); return err(EINVAL);
+        }
+    }
+
+    Result<void> handle_ipc(Client& client)
+    {
+        if (client.rpc_in_progress) return handle_ipc_message(client, client.rpc_id);
+
+        u8 id;
+        auto rc = client.conn.recv_typed(id);
+        if (rc.has_error())
+        {
+            if (rc.error() == EAGAIN) { return {}; }
+            if (rc.error() == EINTR) { return {}; }
+            else
+                return rc.release_error();
+        }
+
+        return handle_ipc_message(client, id);
+    }
+}

wind/IPC.h

@@ -0,0 +1,10 @@
+#pragma once
+#include "Client.h"
+#include <ui/ipc/Server.h>
+
+namespace wind
+{
+    Result<void> handle_ipc_message(Client& client, u8 id);
+
+    Result<void> handle_ipc(Client& client);
+}

wind/Mouse.cpp

@@ -0,0 +1,98 @@
+#include "Mouse.h"
+#include "Client.h"
+#include <os/File.h>
+#include <os/IPC.h>
+#include <ui/Image.h>
+#include <ui/ipc/Client.h>
+
+static SharedPtr<ui::Image> g_mouse_cursor;
+
+Mouse::Mouse(ui::Canvas& screen)
+{
+    m_position.x = screen.width / 2;
+    m_position.y = screen.height / 2;
+    m_screen_rect = screen.rect();
+
+    g_mouse_cursor = ui::Image::load("/usr/share/cursors/default.tga").value_or({});
+}
+
+void Mouse::draw(ui::Canvas& screen)
+{
+    if (!g_mouse_cursor) return;
+    auto canvas = screen.subcanvas(ui::Rect { m_position, g_mouse_cursor->width(), g_mouse_cursor->height() });
+    canvas.fill(g_mouse_cursor->pixels(), g_mouse_cursor->width());
+}
+
+void Mouse::update(const moon::MousePacket& packet)
+{
+    m_position.x += packet.xdelta;
+    m_position.y -= packet.ydelta;
+    m_position = m_screen_rect.normalize(m_position);
+
+    if (m_dragging_window && !(packet.buttons & moon::MouseButton::Left))
+    {
+        os::println("Stopped drag: window at (%d,%d,%d,%d) with offset (%d,%d)", m_dragging_window->surface.pos.x,
+                    m_dragging_window->surface.pos.y, m_dragging_window->surface.width,
+                    m_dragging_window->surface.height, this->m_initial_drag_position.x,
+                    this->m_initial_drag_position.y);
+        m_dragging_window = nullptr;
+    }
+
+    if (m_dragging_window)
+    {
+        m_dragging_window->surface.pos =
+            ui::Point { m_position.x - m_initial_drag_position.x, m_position.y - m_initial_drag_position.y };
+        m_dragging_window->surface = m_dragging_window->surface.normalized();
+    }
+
+    else if ((packet.buttons & moon::MouseButton::Left) && !m_dragging_window)
+    {
+        // Iterate from the end of the list, since windows at the beginning are stacked at the bottom and windows at the
+        // top are at the end.
+        for (Window* window = g_windows.last().value_or(nullptr); window;
+             window = g_windows.previous(window).value_or(nullptr))
+        {
+            if (window->surface.absolute(window->close_button).contains(m_position))
+            {
+                ui::WindowCloseRequest request;
+                request.window = window->id;
+                auto& client = *window->client;
+                os::IPC::send_async(client.conn, request);
+                break;
+            }
+            else if (window->surface.absolute(window->titlebar).contains(m_position))
+            {
+                m_dragging_window = window;
+                m_initial_drag_position = window->surface.relative(m_position);
+                os::println("Started drag: window at (%d,%d,%d,%d) with offset (%d,%d)", window->surface.pos.x,
+                            window->surface.pos.y, window->surface.width, window->surface.height,
+                            m_initial_drag_position.x, m_initial_drag_position.y);
+                window->focus();
+                break;
+            }
+            else if (window->surface.absolute(window->contents).contains(m_position))
+            {
+                window->focus();
+                break; // We don't want to continue iterating, otherwise this would take into account windows whose
+                       // titlebar is underneath another window's contents!
+            }
+        }
+    }
+
+    for (Window* window = g_windows.last().value_or(nullptr); window;
+         window = g_windows.previous(window).value_or(nullptr))
+    {
+        auto titlebar = window->surface.absolute(window->titlebar);
+        auto contents = window->surface.absolute(window->contents);
+        if (titlebar.contains(m_position)) break;
+        if (contents.contains(m_position))
+        {
+            ui::MouseEventRequest request;
+            request.window = window->id;
+            request.position = contents.relative(m_position);
+            request.buttons = packet.buttons;
+            os::IPC::send_async(window->client->conn, request);
+            break;
+        }
+    }
+}

wind/Mouse.h

@@ -0,0 +1,22 @@
+#pragma once
+#include "Screen.h"
+#include "Window.h"
+#include <moon/Mouse.h>
+#include <ui/Canvas.h>
+
+class Mouse
+{
+  public:
+    Mouse(ui::Canvas& screen);
+
+    void update(const moon::MousePacket& packet);
+
+    void draw(ui::Canvas& screen);
+
+  private:
+    ui::Point m_position;
+    ui::Rect m_screen_rect;
+
+    Window* m_dragging_window = nullptr;
+    ui::Point m_initial_drag_position;
+};

wind/Screen.cpp

@@ -0,0 +1,36 @@
+#include "Screen.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+Screen Screen::s_the;
+
+Result<void> Screen::open()
+{
+    int fd = ::open("/dev/fb0", O_RDWR);
+    if (fd < 0) return err(errno);
+
+    int width = ioctl(fd, FB_GET_WIDTH);
+    int height = ioctl(fd, FB_GET_HEIGHT);
+
+    void* p = mmap(nullptr, width * height * BYTES_PER_PIXEL, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    close(fd);
+
+    if (p == MAP_FAILED) { return err(errno); }
+
+    Screen screen;
+
+    screen.m_canvas = ui::Canvas::create((u8*)p, width, height);
+    screen.m_size = width * height * BYTES_PER_PIXEL;
+
+    s_the = screen;
+
+    return {};
+}
+
+void Screen::sync()
+{
+    msync(m_canvas.ptr, size(), MS_SYNC);
+}

wind/Screen.h

@@ -0,0 +1,34 @@
+#pragma once
+#include <luna/OwnedPtr.h>
+#include <ui/Canvas.h>
+
+constexpr int BYTES_PER_PIXEL = 4;
+
+class Screen
+{
+  public:
+    static Result<void> open();
+
+    ui::Canvas& canvas()
+    {
+        return m_canvas;
+    }
+
+    int size() const
+    {
+        return m_size;
+    }
+
+    static Screen& the()
+    {
+        return s_the;
+    }
+
+    void sync();
+
+  private:
+    ui::Canvas m_canvas;
+    int m_size;
+
+    static Screen s_the;
+};

wind/Window.cpp

@@ -0,0 +1,67 @@
+#include "Window.h"
+#include <luna/Utf8.h>
+#include <os/File.h>
+#include <sys/mman.h>
+#include <ui/Font.h>
+#include <ui/Image.h>
+
+LinkedList<Window> g_windows;
+
+void Window::draw(ui::Canvas& screen)
+{
+    dirty = false;
+
+    auto window = screen.subcanvas(surface);
+    window.subcanvas(contents).fill(pixels, contents.width);
+
+    wchar_t buffer[4096];
+    Utf8StringDecoder decoder(name.chars());
+    decoder.decode(buffer, sizeof(buffer)).release_value();
+
+    auto font = ui::Font::default_font();
+
+    auto titlebar_canvas = window.subcanvas(titlebar);
+    titlebar_canvas.fill(ui::GRAY);
+
+    auto textarea = titlebar_canvas.subcanvas(ui::Rect { 10, 10, titlebar_canvas.width - 10, titlebar_canvas.height });
+    font->render(buffer, ui::BLACK, textarea);
+
+    static SharedPtr<ui::Image> g_close_icon;
+
+    if (!g_close_icon) g_close_icon = ui::Image::load("/usr/share/icons/16x16/app-close.tga").release_value();
+
+    auto close_area = window.subcanvas(close_button);
+    close_area.fill(g_close_icon->pixels(), g_close_icon->width());
+}
+
+void Window::focus()
+{
+    // Bring the window to the front of the list.
+    g_windows.remove(this);
+    g_windows.append(this);
+}
+
+Window::Window(ui::Rect r, String&& n, bool d) : surface(r), name(move(n)), decorated(d)
+{
+    auto font = ui::Font::default_font();
+    if (decorated && surface.width < 36) surface.width = 36;
+    if (decorated && surface.height < (font->height() + 20)) surface.height = font->height() + 20;
+    titlebar = decorated ? ui::Rect { 0, 0, surface.width, font->height() + 20 } : ui::Rect { 0, 0, 0, 0 };
+    close_button = decorated ? ui::Rect { surface.width - 26, 10, 16, 16 } : ui::Rect { 0, 0, 0, 0 };
+    contents = decorated ? ui::Rect { 0, font->height() + 20, surface.width, surface.height - (font->height() + 20) }
+                         : ui::Rect { 0, 0, surface.width, surface.height };
+    g_windows.append(this);
+}
+
+int Window::titlebar_height()
+{
+    auto font = ui::Font::default_font();
+    return font->height() + 20;
+}
+
+Window::~Window()
+{
+    usize size = contents.width * contents.height * 4;
+
+    munmap(pixels, size);
+}

wind/Window.h

@@ -0,0 +1,33 @@
+#pragma once
+#include <luna/LinkedList.h>
+#include <luna/String.h>
+#include <ui/Canvas.h>
+#include <ui/Color.h>
+#include <ui/Rect.h>
+
+struct Client;
+
+struct Window : public LinkedListNode<Window>
+{
+    ui::Rect surface;
+    ui::Rect titlebar;
+    ui::Rect close_button;
+    ui::Rect contents;
+    u32* pixels;
+    String name;
+    bool dirty { false };
+    Client* client;
+    int id;
+    bool decorated;
+
+    static int titlebar_height();
+
+    Window(ui::Rect, String&&, bool);
+    ~Window();
+
+    void focus();
+
+    void draw(ui::Canvas& screen);
+};
+
+extern LinkedList<Window> g_windows;

wind/main.cpp

@@ -0,0 +1,179 @@
+#define CLIENT_IMPLEMENTATION
+#include "Client.h"
+#include "IPC.h"
+#include "Mouse.h"
+#include "Screen.h"
+#include "Window.h"
+#include <errno.h>
+#include <moon/Keyboard.h>
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <os/LocalServer.h>
+#include <os/Process.h>
+#include <os/Security.h>
+#include <pwd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/poll.h>
+#include <time.h>
+#include <unistd.h>
+
+static void debug(const Vector<OwnedPtr<Client>>& clients)
+{
+    os::println("--- wind: DEBUG OUTPUT ---");
+
+    os::println("-- wind: Listing clients --");
+
+    for (const auto& client : clients)
+    {
+        os::println("Client with fd %d, owns %zu windows", client->conn.fd(), client->windows.size());
+    }
+
+    os::println("-- wind: Listing windows --");
+
+    for (const auto& window : g_windows)
+    {
+        os::println("Window of client (fd %d), id %d, %sdecorated, %sdirty (\"%s\") (%d,%d,%d,%d)",
+                    window->client->conn.fd(), window->id, window->decorated ? "" : "not ", window->dirty ? "" : "not ",
+                    window->name.chars(), window->surface.pos.x, window->surface.pos.y, window->surface.width,
+                    window->surface.height);
+    }
+
+    os::println("-- wind: Listing processes --");
+
+    system("ps");
+
+    os::println("--- wind: END DEBUG OUTPUT ---");
+}
+
+Result<int> luna_main(int argc, char** argv)
+{
+    srand((unsigned)time(NULL));
+
+    TRY(os::Security::pledge("stdio rpath wpath cpath unix proc exec tty signal id", NULL));
+
+    StringView socket_path = "/tmp/wind.sock";
+    StringView user;
+
+    os::ArgumentParser parser;
+    parser.add_description("The display server for Luna's graphical user interface."_sv);
+    parser.add_system_program_info("wind"_sv);
+    parser.add_value_argument(socket_path, 's', "socket"_sv, "the path for the local IPC socket"_sv);
+    parser.add_value_argument(user, 'u', "user"_sv, "the user to run as"_sv);
+    parser.parse(argc, argv);
+
+    if (geteuid() != 0)
+    {
+        os::eprintln("error: wind must be run as root to initialize resources, run with --user=<USERNAME> to drop "
+                     "privileges afterwards");
+        return 1;
+    }
+
+    auto mouse = TRY(os::File::open("/dev/mouse", os::File::ReadOnly));
+    mouse->set_buffer(os::File::NotBuffered);
+    mouse->set_close_on_exec();
+
+    auto keyboard = TRY(os::File::open("/dev/kbd", os::File::ReadOnly));
+    keyboard->set_buffer(os::File::NotBuffered);
+    keyboard->set_close_on_exec();
+
+    TRY(Screen::open());
+    auto& screen = Screen::the();
+
+    Mouse mouse_pointer { screen.canvas() };
+
+    ioctl(STDIN_FILENO, TTYSETGFX, 1);
+
+    setpgid(0, 0);
+
+    int fd = open("/dev/null", O_RDONLY);
+    if (fd >= 0)
+    {
+        dup2(fd, STDIN_FILENO);
+        close(fd);
+    }
+
+    clearenv();
+
+    if (!user.is_empty())
+    {
+        auto* pwd = getpwnam(user.chars());
+        if (pwd)
+        {
+            setgid(pwd->pw_gid);
+            setuid(pwd->pw_uid);
+        }
+    }
+
+    auto server = TRY(os::LocalServer::create(socket_path, false));
+    TRY(server->listen(20));
+
+    StringView args[] = { "/usr/bin/init"_sv, "--user"_sv };
+    TRY(os::Process::spawn("/usr/bin/init"_sv, Slice<StringView> { args, 2 }, false));
+
+    ui::Color background = ui::BLACK;
+
+    Vector<OwnedPtr<Client>> clients;
+    Vector<struct pollfd> fds;
+    TRY(fds.try_append({ .fd = mouse->fd(), .events = POLLIN, .revents = 0 }));
+    TRY(fds.try_append({ .fd = keyboard->fd(), .events = POLLIN, .revents = 0 }));
+    TRY(fds.try_append({ .fd = server->fd(), .events = POLLIN, .revents = 0 }));
+
+    TRY(os::Security::pledge("stdio rpath wpath cpath unix signal proc exec", NULL));
+
+    while (1)
+    {
+        screen.canvas().fill(background);
+        for (auto* window : g_windows) window->draw(screen.canvas());
+        mouse_pointer.draw(screen.canvas());
+        screen.sync();
+
+        for (auto& pfd : fds) { pfd.revents = 0; }
+
+        int rc = poll(fds.data(), fds.size(), 1000);
+        if (!rc) continue;
+        if (rc < 0 && errno != EINTR) { os::println("poll: error: %s", strerror(errno)); }
+
+        if (fds[0].revents & POLLIN)
+        {
+            moon::MousePacket packet;
+            TRY(mouse->read_typed(packet));
+            mouse_pointer.update(packet);
+        }
+        if (fds[1].revents & POLLIN)
+        {
+            moon::KeyboardPacket packet;
+            TRY(keyboard->read_typed(packet));
+            os::println("%s key %d", packet.released ? "Released" : "Pressed", packet.key);
+            if (!packet.released && packet.key == moon::K_Tab) debug(clients);
+        }
+        for (usize i = 0; i < clients.size(); i++)
+        {
+            if (fds[i + 3].revents & POLLIN) wind::handle_ipc(*clients[i]);
+            if (fds[i + 3].revents & POLLHUP)
+            {
+                os::println("wind: Client %d disconnected", i);
+                fds.remove_at(i + 3);
+                auto client = clients.remove_at(i);
+                client->conn.disconnect();
+                for (auto& window : client->windows)
+                {
+                    if (window)
+                    {
+                        g_windows.remove(window);
+                        delete window;
+                    }
+                }
+            }
+        }
+        if (fds[2].revents & POLLIN)
+        {
+            auto client = TRY(server->accept());
+            os::println("wind: New client connected!");
+            TRY(fds.try_append({ .fd = client.fd(), .events = POLLIN, .revents = 0 }));
+            OwnedPtr<Client> c = TRY(adopt_owned_if_nonnull(new Client(move(client))));
+            TRY(clients.try_append(move(c)));
+        }
+    }
+}