From bfcca3a220f2c44d41e7b9a4bd9c50b30c54c2f0 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Thu, 3 Aug 2023 09:26:35 +0200
Subject: [PATCH] gol: Use memory-mapped IO

---
 apps/gol.cpp | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/apps/gol.cpp b/apps/gol.cpp
index 36b13863..02399a7c 100644
--- a/apps/gol.cpp
+++ b/apps/gol.cpp
@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/ioctl.h>
+#include <sys/mman.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -24,6 +25,7 @@ static int g_fb_height;
 static int g_fd;
 
 static Cell* g_cells;
+static char* g_fb;
 
 static Result<void> fill_cells()
 {
@@ -47,27 +49,29 @@ static Cell& find_cell(int row, int column)
 
 static constexpr int BYTES_PER_PIXEL = 4;
 
-static char* g_buf;
-
 static void draw_cells()
 {
-    lseek(g_fd, 0, SEEK_SET);
-
     const int CELL_WIDTH = g_fb_width / g_num_columns;
     const int CELL_HEIGHT = g_fb_height / g_num_rows;
 
     for (int i = 0; i < g_num_rows; i++)
     {
-        memset(g_buf, 0, g_fb_width * BYTES_PER_PIXEL);
 
         for (int j = 0; j < g_num_columns; j++)
         {
-            auto& cell = find_cell(i, j);
-            if (cell.state) memset(g_buf + (j * CELL_WIDTH * BYTES_PER_PIXEL), 0xff, CELL_WIDTH * BYTES_PER_PIXEL);
-        }
+            char* buf = g_fb + (i * g_fb_width * CELL_HEIGHT * BYTES_PER_PIXEL);
 
-        for (int j = 0; j < CELL_HEIGHT; j++) { write(g_fd, g_buf, g_fb_width * BYTES_PER_PIXEL); }
+            auto& cell = find_cell(i, j);
+            u8 color = cell.state ? 0xff : 0x00;
+            for (int k = 0; k < CELL_HEIGHT; k++)
+            {
+                memset(buf + (j * CELL_WIDTH * BYTES_PER_PIXEL), color, CELL_WIDTH * BYTES_PER_PIXEL);
+                buf += g_fb_width * BYTES_PER_PIXEL;
+            }
+        }
     }
+
+    msync(g_fb, g_fb_height * g_fb_width * BYTES_PER_PIXEL, MS_SYNC);
 }
 
 static int find_neighbors(int row, int column)
@@ -137,7 +141,7 @@ Result<int> luna_main(int argc, char** argv)
     else
         srand((unsigned)time(NULL));
 
-    g_fd = open("/dev/fb0", O_WRONLY);
+    g_fd = open("/dev/fb0", O_RDWR);
     if (g_fd < 0)
     {
         perror("gol: cannot open framebuffer for writing");
@@ -149,7 +153,13 @@ Result<int> luna_main(int argc, char** argv)
 
     TRY(fill_cells());
 
-    g_buf = (char*)TRY(calloc_impl(g_fb_width, BYTES_PER_PIXEL));
+    g_fb =
+        (char*)mmap(nullptr, g_fb_height * g_fb_width * BYTES_PER_PIXEL, PROT_READ | PROT_WRITE, MAP_SHARED, g_fd, 0);
+    if (g_fb == MAP_FAILED)
+    {
+        perror("gol: cannot map framebuffer into memory");
+        return 1;
+    }
 
     draw_cells();
 
@@ -162,5 +172,8 @@ Result<int> luna_main(int argc, char** argv)
 
     usleep(delay_at_end * 1000);
 
+    munmap(g_fb, g_fb_height * g_fb_width * BYTES_PER_PIXEL);
+    free(g_cells);
+
     return 0;
 }