WindowServer: Improvements to support alpha channel in window frames

This fixes some issues handling the alpha channel that may be present
in rendered window frames.

Fixes #5303

Userland/Libraries/LibGfx/ClassicWindowTheme.cpp

@@ -89,11 +89,13 @@ void ClassicWindowTheme::paint_normal_frame(Painter& painter, WindowState window
 
     painter.fill_rect_with_gradient(titlebar_rect, border_color, border_color2);
 
-    int stripe_left = titlebar_title_rect.right() + 5;
     int stripe_right = leftmost_button_rect.left() - 3;
-    if (stripe_left && stripe_right && stripe_left < stripe_right) {
-        for (int i = 2; i <= titlebar_inner_rect.height() - 2; i += 2) {
-            painter.draw_line({ stripe_left, titlebar_inner_rect.y() + i }, { stripe_right, titlebar_inner_rect.y() + i }, stripes_color);
+    if (stripes_color.alpha() > 0) {
+        int stripe_left = titlebar_title_rect.right() + 5;
+        if (stripe_left && stripe_right && stripe_left < stripe_right) {
+            for (int i = 2; i <= titlebar_inner_rect.height() - 2; i += 2) {
+                painter.draw_line({ stripe_left, titlebar_inner_rect.y() + i }, { stripe_right, titlebar_inner_rect.y() + i }, stripes_color);
+            }
         }
     }
 
@@ -145,11 +147,13 @@ void ClassicWindowTheme::paint_notification_frame(Painter& painter, const IntRec
     auto titlebar_rect = title_bar_rect(WindowType::Notification, window_rect, palette);
     painter.fill_rect_with_gradient(Gfx::Orientation::Vertical, titlebar_rect, palette.active_window_border1(), palette.active_window_border2());
 
-    int stripe_top = close_button_rect.bottom() + 4;
-    int stripe_bottom = window_rect.height() - 3;
-    if (stripe_top && stripe_bottom && stripe_top < stripe_bottom) {
-        for (int i = 2; i <= palette.window_title_height() - 2; i += 2) {
-            painter.draw_line({ titlebar_rect.x() + i, stripe_top }, { titlebar_rect.x() + i, stripe_bottom }, palette.active_window_title_stripes());
+    if (palette.active_window_title_stripes().alpha() > 0) {
+        int stripe_top = close_button_rect.bottom() + 4;
+        int stripe_bottom = window_rect.height() - 3;
+        if (stripe_top && stripe_bottom && stripe_top < stripe_bottom) {
+            for (int i = 2; i <= palette.window_title_height() - 2; i += 2) {
+                painter.draw_line({ titlebar_rect.x() + i, stripe_top }, { titlebar_rect.x() + i, stripe_bottom }, palette.active_window_title_stripes());
+            }
         }
     }
 }

Userland/Libraries/LibGfx/ClassicWindowTheme.h

@@ -48,6 +48,10 @@ public:
 
     virtual Vector<IntRect> layout_buttons(WindowType, const IntRect& window_rect, const Palette&, size_t buttons) const override;
     virtual bool is_simple_rect_frame() const override { return true; }
+    virtual bool frame_uses_alpha(WindowState state, const Palette& palette) const override
+    {
+        return compute_frame_colors(state, palette).uses_alpha();
+    }
 
 private:
     struct FrameColors {
@@ -56,6 +60,11 @@ private:
         Color border_color2;
         Color title_stripes_color;
         Color title_shadow_color;
+
+        bool uses_alpha() const
+        {
+            return title_color.alpha() != 0xff || border_color.alpha() != 0xff || border_color2.alpha() != 0xff || title_stripes_color.alpha() != 0xff || title_shadow_color.alpha() != 0xff;
+        }
     };
 
     FrameColors compute_frame_colors(WindowState, const Palette&) const;

Userland/Libraries/LibGfx/Painter.cpp

@@ -206,6 +206,10 @@ void Painter::fill_rect_with_checkerboard(const IntRect& a_rect, const IntSize&
 
 void Painter::fill_rect_with_gradient(Orientation orientation, const IntRect& a_rect, Color gradient_start, Color gradient_end)
 {
+    if (gradient_start == gradient_end) {
+        fill_rect(a_rect, gradient_start);
+        return;
+    }
 
 #ifdef NO_FPU
     return fill_rect(a_rect, gradient_start);
@@ -222,23 +226,31 @@ void Painter::fill_rect_with_gradient(Orientation orientation, const IntRect& a_
     const size_t dst_skip = m_target->pitch() / sizeof(RGBA32);
 
     float increment = (1.0 / ((rect.primary_size_for_orientation(orientation))));
+    float alpha_increment = increment * ((float)gradient_end.alpha() - (float)gradient_start.alpha());
 
     if (orientation == Orientation::Horizontal) {
         for (int i = clipped_rect.height() - 1; i >= 0; --i) {
             float c = offset * increment;
+            float c_alpha = gradient_start.alpha() + offset * alpha_increment;
             for (int j = 0; j < clipped_rect.width(); ++j) {
-                dst[j] = gamma_accurate_blend(gradient_start, gradient_end, c).value();
+                auto color = gamma_accurate_blend(gradient_start, gradient_end, c);
+                color.set_alpha(c_alpha);
+                dst[j] = color.value();
+                c_alpha += alpha_increment;
                 c += increment;
             }
             dst += dst_skip;
         }
     } else {
         float c = offset * increment;
+        float c_alpha = gradient_start.alpha() + offset * alpha_increment;
         for (int i = clipped_rect.height() - 1; i >= 0; --i) {
             auto color = gamma_accurate_blend(gradient_start, gradient_end, c);
+            color.set_alpha(c_alpha);
             for (int j = 0; j < clipped_rect.width(); ++j) {
                 dst[j] = color.value();
             }
+            c_alpha += alpha_increment;
             c += increment;
             dst += dst_skip;
         }

Userland/Libraries/LibGfx/WindowTheme.h

@@ -62,6 +62,7 @@ public:
 
     virtual Vector<IntRect> layout_buttons(WindowType, const IntRect& window_rect, const Palette&, size_t buttons) const = 0;
     virtual bool is_simple_rect_frame() const = 0;
+    virtual bool frame_uses_alpha(WindowState, const Palette&) const = 0;
 
 protected:
     WindowTheme() { }

Userland/Services/WindowServer/WindowFrame.cpp

@@ -221,6 +221,8 @@ Gfx::Bitmap* WindowFrame::window_shadow() const
 
 bool WindowFrame::frame_has_alpha() const
 {
+    if (m_has_alpha_channel)
+        return true;
     if (auto* shadow_bitmap = window_shadow(); shadow_bitmap && shadow_bitmap->format() == Gfx::BitmapFormat::RGBA32)
         return true;
     return false;
@@ -347,12 +349,27 @@ void WindowFrame::render(Gfx::Painter& painter)
     }
 }
 
+void WindowFrame::theme_changed()
+{
+    m_dirty = m_shadow_dirty = true;
+    m_top_bottom = nullptr;
+    m_left_right = nullptr;
+    m_bottom_y = m_right_x = 0;
+
+    layout_buttons();
+    set_button_icons();
+
+    m_has_alpha_channel = Gfx::WindowTheme::current().frame_uses_alpha(window_state_for_theme(), WindowManager::the().palette());
+}
+
 void WindowFrame::render_to_cache()
 {
     if (!m_dirty)
         return;
     m_dirty = false;
 
+    m_has_alpha_channel = Gfx::WindowTheme::current().frame_uses_alpha(window_state_for_theme(), WindowManager::the().palette());
+
     static Gfx::Bitmap* s_tmp_bitmap;
     auto frame_rect = rect();
     auto total_frame_rect = frame_rect;
@@ -387,6 +404,7 @@ void WindowFrame::render_to_cache()
     Gfx::IntPoint update_location(m_shadow_dirty ? Gfx::IntPoint { 0, 0 } : m_shadow_offset);
 
     Gfx::Painter painter(*s_tmp_bitmap);
+
     // Clear the frame area, not including the window content area, which we don't care about
     for (auto& rect : frame_rect_to_update.shatter(window_rect))
         painter.clear_rect({ rect.location() - frame_rect_to_update.location(), rect.size() }, { 255, 255, 255, 0 });

Userland/Services/WindowServer/WindowFrame.h

@@ -88,16 +88,7 @@ public:
         m_shadow_dirty |= re_render_shadow;
     }
 
-    void theme_changed()
-    {
-        m_dirty = m_shadow_dirty = true;
-        m_top_bottom = nullptr;
-        m_left_right = nullptr;
-        m_bottom_y = m_right_x = 0;
-
-        layout_buttons();
-        set_button_icons();
-    }
+    void theme_changed();
 
 private:
     void paint_simple_rect_shadow(Gfx::Painter&, const Gfx::IntRect&, const Gfx::Bitmap&) const;