Cairo now renders layers properly (colors are not saturated after layer composition), but slower.

common/gal/cairo/cairo_gal.cpp

@@ -612,6 +612,21 @@ void CAIRO_GAL::Restore()
 }
 
 
+void CAIRO_GAL::BeginLayer()
+{
+    cairo_push_group( cairoImage );
+}
+
+
+void CAIRO_GAL::EndLayer()
+{
+    storePath();
+
+    cairo_pop_group_to_source( cairoImage );
+    cairo_paint_with_alpha( cairoImage, fillColor.a );
+}
+
+
 int CAIRO_GAL::BeginGroup()
 {
     // If the grouping is started: the actual path is stored in the group, when
@@ -693,15 +708,13 @@ void CAIRO_GAL::DrawGroup( int aGroupNumber )
             break;
 
         case CMD_STROKE_PATH:
-            cairo_set_source_rgba( cairoImage, strokeColor.r, strokeColor.g, strokeColor.b,
-                                   strokeColor.a );
+            cairo_set_source_rgb( cairoImage, strokeColor.r, strokeColor.g, strokeColor.b );
             cairo_append_path( cairoImage, it->cairoPath );
             cairo_stroke( cairoImage );
             break;
 
         case CMD_FILL_PATH:
-            cairo_set_source_rgba( cairoImage, fillColor.r, fillColor.g, fillColor.b,
-                                   fillColor.a );
+            cairo_set_source_rgb( cairoImage, fillColor.r, fillColor.g, fillColor.b );
             cairo_append_path( cairoImage, it->cairoPath );
             cairo_fill( cairoImage );
             break;
@@ -779,15 +792,13 @@ void CAIRO_GAL::storePath()
         {
             if( isFillEnabled )
             {
-                cairo_set_source_rgba( cairoImage, fillColor.r, fillColor.g, fillColor.b,
-                                       fillColor.a );
+                cairo_set_source_rgb( cairoImage, fillColor.r, fillColor.g, fillColor.b );
                 cairo_fill_preserve( cairoImage );
             }
 
             if( isStrokeEnabled )
             {
-                cairo_set_source_rgba( cairoImage, strokeColor.r, strokeColor.g, strokeColor.b,
-                                       strokeColor.a );
+                cairo_set_source_rgb( cairoImage, strokeColor.r, strokeColor.g, strokeColor.b );
                 cairo_stroke_preserve( cairoImage );
             }
         }

common/gal/opengl/opengl_gal.cpp

@@ -1283,6 +1283,15 @@ void OPENGL_GAL::Restore()
 }
 
 
+void OPENGL_GAL::BeginLayer()
+{
+}
+
+void OPENGL_GAL::EndLayer()
+{
+}
+
+
 // TODO Error handling
 int OPENGL_GAL::BeginGroup()
 {

common/view/view.cpp

@@ -419,9 +419,11 @@ void VIEW::redrawRect( const BOX2I& aRect )
         {
             drawItem drawFunc( this, l->id );
 
+            m_gal->BeginLayer();
             m_gal->SetLayerDepth( (double) l->renderingOrder );
             l->items->Query( aRect, drawFunc );
             l->isDirty = false;
+            m_gal->EndLayer();
 
             totalItems    += drawFunc.count;
             totalDrawTime += drawFunc.time;

include/gal/cairo/cairo_gal.h

@@ -95,6 +95,12 @@ public:
     /// @copydoc GAL::EndDrawing()
     virtual void EndDrawing();
 
+    /// @copydoc GAL::BeginLayer()
+    virtual void BeginLayer();
+
+    /// @copydoc GAL::EndLayer()
+    virtual void EndLayer();
+
     /// @copydoc GAL::DrawLine()
     virtual void DrawLine( const VECTOR2D& aStartPoint, const VECTOR2D& aEndPoint );
 

include/gal/graphics_abstraction_layer.h

@@ -95,6 +95,12 @@ public:
     /// @brief End the drawing, needs to be called for every new frame.
     virtual void EndDrawing() = 0;
 
+    /// @brief Begin the layer drawing, needs to be called for every new layer.
+    virtual void BeginLayer() = 0;
+
+    /// @brief Finish the layer drawing, needs to be called for every new layer.
+    virtual void EndLayer() = 0;
+
     /**
      * @brief Draw a line.
      *

include/gal/opengl/opengl_gal.h

@@ -102,6 +102,12 @@ public:
     /// @copydoc GAL::EndDrawing()
     virtual void EndDrawing();
 
+    /// @copydoc GAL::BeginLayer()
+    virtual void BeginLayer();
+
+    /// @copydoc GAL::EndLayer()
+    virtual void EndLayer();
+
     /// @copydoc GAL::DrawLine()
     virtual void DrawLine( const VECTOR2D& aStartPoint, const VECTOR2D& aEndPoint );