LibGfx: Add a draw_scaled_bitmap() variant that takes a FloatRect as src_rect

Consider

    draw_scaled_bitmap({0, 0, 10, 10}, source, {0, 0, 5, 5}).

Imagine wanting to split that up into two calls, like e.g. the
compositor when redrawing the background with damage rects. You really
want to be able to say

    draw_scaled_bitmap({0, 0, 5, 10}, source, {0, 0, 2.5, 5})

but up to now you couldn't. Now you can.

This makes painting very low-res images (such as tile.png) in mode
"stretch" work much better.

Userland/Demos/LibGfxScaleDemo/main.cpp

@@ -100,8 +100,8 @@ void Canvas::draw(Gfx::Painter& painter)
 
     auto buggie = Gfx::Bitmap::load_from_file("/res/graphics/buggie.png");
     painter.blit({ 25, 39 }, *buggie, { 2, 30, 62, 20 });
-    painter.draw_scaled_bitmap({ 88, 39, 62 * 2, 20 * 2 }, *buggie, { 2, 30, 62, 20 });
-    painter.draw_scaled_bitmap({ 202, 39, 80, 40 }, *buggie, { 2, 30, 62, 20 });
+    painter.draw_scaled_bitmap({ 88, 39, 62 * 2, 20 * 2 }, *buggie, Gfx::IntRect { 2, 30, 62, 20 });
+    painter.draw_scaled_bitmap({ 202, 39, 80, 40 }, *buggie, Gfx::IntRect { 2, 30, 62, 20 });
 }
 
 int main(int argc, char** argv)

Userland/Libraries/LibGfx/Painter.cpp

@@ -783,30 +783,33 @@ ALWAYS_INLINE static void do_draw_integer_scaled_bitmap(Gfx::Bitmap& target, con
 }
 
 template<bool has_alpha_channel, typename GetPixel>
-ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, const IntRect& dst_rect, const IntRect& clipped_rect, const Gfx::Bitmap& source, const IntRect& src_rect, GetPixel get_pixel, float opacity)
+ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, const IntRect& dst_rect, const IntRect& clipped_rect, const Gfx::Bitmap& source, const FloatRect& src_rect, GetPixel get_pixel, float opacity)
 {
-    if (dst_rect == clipped_rect && !(dst_rect.width() % src_rect.width()) && !(dst_rect.height() % src_rect.height())) {
-        int hfactor = dst_rect.width() / src_rect.width();
-        int vfactor = dst_rect.height() / src_rect.height();
+    IntRect int_src_rect = enclosing_int_rect(src_rect);
+    if (dst_rect == clipped_rect && int_src_rect == src_rect && !(dst_rect.width() % int_src_rect.width()) && !(dst_rect.height() % int_src_rect.height())) {
+        int hfactor = dst_rect.width() / int_src_rect.width();
+        int vfactor = dst_rect.height() / int_src_rect.height();
         if (hfactor == 2 && vfactor == 2)
-            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, 2, 2, get_pixel, opacity);
+            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, int_src_rect, source, 2, 2, get_pixel, opacity);
         if (hfactor == 3 && vfactor == 3)
-            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, 3, 3, get_pixel, opacity);
+            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, int_src_rect, source, 3, 3, get_pixel, opacity);
         if (hfactor == 4 && vfactor == 4)
-            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, 4, 4, get_pixel, opacity);
-        return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, src_rect, source, hfactor, vfactor, get_pixel, opacity);
+            return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, int_src_rect, source, 4, 4, get_pixel, opacity);
+        return do_draw_integer_scaled_bitmap<has_alpha_channel>(target, dst_rect, int_src_rect, source, hfactor, vfactor, get_pixel, opacity);
     }
 
     bool has_opacity = opacity != 1.0f;
-    int hscale = (src_rect.width() << 16) / dst_rect.width();
-    int vscale = (src_rect.height() << 16) / dst_rect.height();
+    int hscale = (src_rect.width() * (1 << 16)) / dst_rect.width();
+    int vscale = (src_rect.height() * (1 << 16)) / dst_rect.height();
+    int src_left = src_rect.left() * (1 << 16);
+    int src_top = src_rect.top() * (1 << 16);
 
     for (int y = clipped_rect.top(); y <= clipped_rect.bottom(); ++y) {
         auto* scanline = (Color*)target.scanline(y);
         for (int x = clipped_rect.left(); x <= clipped_rect.right(); ++x) {
-            auto scaled_x = ((x - dst_rect.x()) * hscale) >> 16;
-            auto scaled_y = ((y - dst_rect.y()) * vscale) >> 16;
-            auto src_pixel = get_pixel(source, scaled_x + src_rect.left(), scaled_y + src_rect.top());
+            auto scaled_x = ((x - dst_rect.x()) * hscale + src_left) >> 16;
+            auto scaled_y = ((y - dst_rect.y()) * vscale + src_top) >> 16;
+            auto src_pixel = get_pixel(source, scaled_x, scaled_y);
             if (has_opacity)
                 src_pixel.set_alpha(src_pixel.alpha() * opacity);
             if constexpr (has_alpha_channel) {
@@ -819,8 +822,14 @@ ALWAYS_INLINE static void do_draw_scaled_bitmap(Gfx::Bitmap& target, const IntRe
 
 void Painter::draw_scaled_bitmap(const IntRect& a_dst_rect, const Gfx::Bitmap& source, const IntRect& a_src_rect, float opacity)
 {
-    if (scale() == source.scale() && a_dst_rect.size() == a_src_rect.size())
-        return blit(a_dst_rect.location(), source, a_src_rect, opacity);
+    draw_scaled_bitmap(a_dst_rect, source, FloatRect { a_src_rect }, opacity);
+}
+
+void Painter::draw_scaled_bitmap(const IntRect& a_dst_rect, const Gfx::Bitmap& source, const FloatRect& a_src_rect, float opacity)
+{
+    IntRect int_src_rect = enclosing_int_rect(a_src_rect);
+    if (scale() == source.scale() && a_src_rect == int_src_rect && a_dst_rect.size() == int_src_rect.size())
+        return blit(a_dst_rect.location(), source, int_src_rect, opacity);
 
     auto dst_rect = to_physical(a_dst_rect);
     auto src_rect = a_src_rect * source.scale();

Userland/Libraries/LibGfx/Painter.h

@@ -62,6 +62,7 @@ public:
     void draw_bitmap(const IntPoint&, const CharacterBitmap&, Color = Color());
     void draw_bitmap(const IntPoint&, const GlyphBitmap&, Color = Color());
     void draw_scaled_bitmap(const IntRect& dst_rect, const Gfx::Bitmap&, const IntRect& src_rect, float opacity = 1.0f);
+    void draw_scaled_bitmap(const IntRect& dst_rect, const Gfx::Bitmap&, const FloatRect& src_rect, float opacity = 1.0f);
     void draw_triangle(const IntPoint&, const IntPoint&, const IntPoint&, Color);
     void draw_ellipse_intersecting(const IntRect&, Color, int thickness = 1);
     void set_pixel(const IntPoint&, Color);

Userland/Services/WindowServer/Compositor.cpp

@@ -262,11 +262,12 @@ void Compositor::compose()
             } else if (m_wallpaper_mode == WallpaperMode::Tile) {
                 painter.draw_tiled_bitmap(rect, *m_wallpaper);
             } else if (m_wallpaper_mode == WallpaperMode::Stretch) {
-                float hscale = (float)m_wallpaper->size().width() / (float)ws.size().width();
-                float vscale = (float)m_wallpaper->size().height() / (float)ws.size().height();
+                float hscale = (float)m_wallpaper->width() / (float)ws.width();
+                float vscale = (float)m_wallpaper->height() / (float)ws.height();
 
                 // TODO: this may look ugly, we should scale to a backing bitmap and then blit
-                painter.draw_scaled_bitmap(rect, *m_wallpaper, { rect.x() * hscale, rect.y() * vscale, rect.width() * hscale, rect.height() * vscale });
+                auto src_rect = Gfx::FloatRect { rect.x() * hscale, rect.y() * vscale, rect.width() * hscale, rect.height() * vscale };
+                painter.draw_scaled_bitmap(rect, *m_wallpaper, src_rect);
             } else {
                 ASSERT_NOT_REACHED();
             }