From 55f7a99d1bab20b408c8595bb52df2af10c90cae Mon Sep 17 00:00:00 2001
From: Maciej Suminski <maciej.suminski@cern.ch>
Date: Fri, 19 Apr 2013 18:19:50 +0200
Subject: [PATCH] Cairo now renders layers properly (colors are not saturated
 after layer composition), but slower.

---
 common/gal/cairo/cairo_gal.cpp           | 27 +++++++++++++++++-------
 common/gal/opengl/opengl_gal.cpp         |  9 ++++++++
 common/view/view.cpp                     |  2 ++
 include/gal/cairo/cairo_gal.h            |  6 ++++++
 include/gal/graphics_abstraction_layer.h |  6 ++++++
 include/gal/opengl/opengl_gal.h          |  6 ++++++
 6 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/common/gal/cairo/cairo_gal.cpp b/common/gal/cairo/cairo_gal.cpp
index ff0fb47b39..5d72954acb 100644
--- a/common/gal/cairo/cairo_gal.cpp
+++ b/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 );
             }
         }
diff --git a/common/gal/opengl/opengl_gal.cpp b/common/gal/opengl/opengl_gal.cpp
index e75b8265bd..6a23f844d4 100644
--- a/common/gal/opengl/opengl_gal.cpp
+++ b/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()
 {
diff --git a/common/view/view.cpp b/common/view/view.cpp
index d91036cd30..4fc6d92968 100644
--- a/common/view/view.cpp
+++ b/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;
diff --git a/include/gal/cairo/cairo_gal.h b/include/gal/cairo/cairo_gal.h
index 06db9f1f28..36cae06c6e 100644
--- a/include/gal/cairo/cairo_gal.h
+++ b/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 );
 
diff --git a/include/gal/graphics_abstraction_layer.h b/include/gal/graphics_abstraction_layer.h
index 245508b7a2..1940b047ab 100644
--- a/include/gal/graphics_abstraction_layer.h
+++ b/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.
      *
diff --git a/include/gal/opengl/opengl_gal.h b/include/gal/opengl/opengl_gal.h
index ce4ff73c39..d01028112b 100644
--- a/include/gal/opengl/opengl_gal.h
+++ b/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 );