WindowServer: Add wallpaper backing bitmap

Fixes inconsistencies in redrawing the wallpaper when in stretch mode by
first drawing to a backing bitmap. To reduce unnecessary allocations,
the backing bitmap is only used for stretch mode.

Userland/Applications/FileManager/main.cpp

@@ -550,10 +550,14 @@ ErrorOr<int> run_in_desktop_mode()
     } wallpaper_listener;
 
     auto selected_wallpaper = Config::read_string("WindowManager"sv, "Background"sv, "Wallpaper"sv, ""sv);
+    RefPtr<Gfx::Bitmap> wallpaper_bitmap {};
     if (!selected_wallpaper.is_empty()) {
-        auto wallpaper_bitmap = TRY(Gfx::Bitmap::try_load_from_file(selected_wallpaper));
-        GUI::Desktop::the().set_wallpaper(wallpaper_bitmap, {});
+        wallpaper_bitmap = TRY(Gfx::Bitmap::try_load_from_file(selected_wallpaper));
     }
+    // This sets the wallpaper at startup, even if there is no wallpaper, the
+    // desktop should still show the background color. It's fine to pass a
+    // nullptr to Desktop::set_wallpaper.
+    GUI::Desktop::the().set_wallpaper(wallpaper_bitmap, {});
 
     window->show();
     return GUI::Application::the()->exec();

Userland/Services/WindowServer/Compositor.cpp

@@ -121,6 +121,8 @@ void CompositorScreenData::init_bitmaps(Compositor& compositor, Screen& screen)
     m_temp_bitmap = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRx8888, size, screen.scale_factor()).release_value_but_fixme_should_propagate_errors();
     m_temp_painter = make<Gfx::Painter>(*m_temp_bitmap);
     m_temp_painter->translate(-screen.rect().location());
+
+    clear_wallpaper_bitmap();
 }
 
 void Compositor::init_bitmaps()
@@ -303,25 +305,23 @@ void Compositor::compose()
         check_restore_cursor_back(cursor_screen, cursor_rect);
 
     auto paint_wallpaper = [&](Screen& screen, Gfx::Painter& painter, Gfx::IntRect const& rect, Gfx::IntRect const& screen_rect) {
-        // FIXME: If the wallpaper is opaque and covers the whole rect, no need to fill with color!
-        painter.fill_rect(rect, background_color);
         if (m_wallpaper) {
             if (m_wallpaper_mode == WallpaperMode::Center) {
                 Gfx::IntPoint offset { (screen.width() - m_wallpaper->width()) / 2, (screen.height() - m_wallpaper->height()) / 2 };
+
+                // FIXME: If the wallpaper is opaque and covers the whole rect, no need to fill with color!
+                painter.fill_rect(rect, background_color);
                 painter.blit_offset(rect.location(), *m_wallpaper, rect.translated(-screen_rect.location()), offset);
             } 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->width() / (float)screen.width();
-                float vscale = (float)m_wallpaper->height() / (float)screen.height();
-
-                // TODO: this may look ugly, we should scale to a backing bitmap and then blit
-                auto relative_rect = rect.translated(-screen_rect.location());
-                auto src_rect = Gfx::FloatRect { relative_rect.x() * hscale, relative_rect.y() * vscale, relative_rect.width() * hscale, relative_rect.height() * vscale };
-                painter.draw_scaled_bitmap(rect, *m_wallpaper, src_rect);
+                VERIFY(screen.compositor_screen_data().m_wallpaper_bitmap);
+                painter.blit(rect.location(), *screen.compositor_screen_data().m_wallpaper_bitmap, rect);
             } else {
                 VERIFY_NOT_REACHED();
             }
+        } else {
+            painter.fill_rect(rect, background_color);
         }
     };
 
@@ -791,8 +791,10 @@ bool Compositor::set_background_color(String const& background_color)
     wm.config()->write_entry("Background", "Color", background_color);
     bool succeeded = !wm.config()->sync().is_error();
 
-    if (succeeded)
+    if (succeeded) {
+        update_wallpaper_bitmap();
         Compositor::invalidate_screen();
+    }
 
     return succeeded;
 }
@@ -805,6 +807,7 @@ bool Compositor::set_wallpaper_mode(String const& mode)
 
     if (succeeded) {
         m_wallpaper_mode = mode_to_enum(mode);
+        update_wallpaper_bitmap();
         Compositor::invalidate_screen();
     }
 
@@ -817,11 +820,45 @@ bool Compositor::set_wallpaper(RefPtr<Gfx::Bitmap> bitmap)
         m_wallpaper = nullptr;
     else
         m_wallpaper = bitmap;
+    update_wallpaper_bitmap();
     invalidate_screen();
 
     return true;
 }
 
+void Compositor::update_wallpaper_bitmap()
+{
+    Screen::for_each([&](Screen& screen) {
+        auto& screen_data = screen.compositor_screen_data();
+        if (m_wallpaper_mode != WallpaperMode::Stretch || !m_wallpaper) {
+            screen_data.clear_wallpaper_bitmap();
+            return IterationDecision::Continue;
+        }
+        if (!screen_data.m_wallpaper_bitmap)
+            screen_data.init_wallpaper_bitmap(screen);
+
+        auto rect = screen_data.m_wallpaper_bitmap->rect();
+        auto& painter = *screen_data.m_wallpaper_painter;
+
+        painter.draw_scaled_bitmap(rect, *m_wallpaper, m_wallpaper->rect());
+
+        return IterationDecision::Continue;
+    });
+}
+
+void CompositorScreenData::init_wallpaper_bitmap(Screen& screen)
+{
+    m_wallpaper_bitmap = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRx8888, screen.size(), screen.scale_factor()).release_value_but_fixme_should_propagate_errors();
+    m_wallpaper_painter = make<Gfx::Painter>(*m_wallpaper_bitmap);
+    m_wallpaper_painter->translate(-screen.rect().location());
+}
+
+void CompositorScreenData::clear_wallpaper_bitmap()
+{
+    m_wallpaper_painter = nullptr;
+    m_wallpaper_bitmap = nullptr;
+}
+
 void CompositorScreenData::flip_buffers(Screen& screen)
 {
     VERIFY(m_screen_can_set_buffer);
@@ -839,6 +876,7 @@ void Compositor::screen_resolution_changed()
     init_bitmaps();
     invalidate_occlusions();
     overlay_rects_changed();
+    update_wallpaper_bitmap();
     compose();
 }
 

Userland/Services/WindowServer/Compositor.h

@@ -36,9 +36,11 @@ struct CompositorScreenData {
     RefPtr<Gfx::Bitmap> m_front_bitmap;
     RefPtr<Gfx::Bitmap> m_back_bitmap;
     RefPtr<Gfx::Bitmap> m_temp_bitmap;
+    RefPtr<Gfx::Bitmap> m_wallpaper_bitmap;
     OwnPtr<Gfx::Painter> m_back_painter;
     OwnPtr<Gfx::Painter> m_front_painter;
     OwnPtr<Gfx::Painter> m_temp_painter;
+    OwnPtr<Gfx::Painter> m_wallpaper_painter;
     RefPtr<Gfx::Bitmap> m_cursor_back_bitmap;
     OwnPtr<Gfx::Painter> m_cursor_back_painter;
     Gfx::IntRect m_last_cursor_rect;
@@ -60,6 +62,8 @@ struct CompositorScreenData {
     void flip_buffers(Screen&);
     void draw_cursor(Screen&, Gfx::IntRect const&);
     bool restore_cursor_back(Screen&, Gfx::IntRect&);
+    void init_wallpaper_bitmap(Screen&);
+    void clear_wallpaper_bitmap();
 
     template<typename F>
     IterationDecision for_each_intersected_flushing_rect(Gfx::IntRect const& intersecting_rect, F f)
@@ -211,6 +215,7 @@ private:
     void stop_window_stack_switch_overlay_timer();
     void start_window_stack_switch_overlay_timer();
     void finish_window_stack_switch();
+    void update_wallpaper_bitmap();
 
     RefPtr<Core::Timer> m_compose_timer;
     RefPtr<Core::Timer> m_immediate_compose_timer;