libui: Add Rect::relative

libui/include/ui/Rect.h

@@ -29,6 +29,14 @@ namespace ui
          */
         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 Return a copy of this rectangle with no negative values (normalized to 0).
          *

libui/src/Rect.cpp

@@ -17,6 +17,14 @@ namespace ui
         return point;
     }
 
+    Point Rect::relative(Point point)
+    {
+        point = normalize(point);
+        point.x -= pos.x;
+        point.y -= pos.y;
+        return point;
+    }
+
     Rect Rect::absolute()
     {
         return Rect { ui::Point { pos.x < 0 ? 0 : pos.x, pos.y < 0 ? 0 : pos.y }, width, height };