Track the region where text is painted.

Source/core/platform/graphics/skia/PlatformContextSkia.cpp

 /*
  * Copyright (c) 2008, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 171 matching lines @@
     return (c & 0x00FFFFFF) | (a << 24);
 }
 
 // PlatformContextSkia ---------------------------------------------------------
 
 // Danger: canvas can be NULL.
 PlatformContextSkia::PlatformContextSkia(SkCanvas* canvas)
     : m_canvas(canvas)
     , m_deferredSaveFlags(0)
     , m_trackOpaqueRegion(false)
+    , m_trackTextRegion(false)
     , m_printing(false)
     , m_accelerated(false)
     , m_drawingToImageBuffer(false)
     , m_deviceScaleFactor(1)
 {
     m_stateStack.append(State());
     m_state = &m_stateStack.last();
 
     // will be assigned in setGraphicsContext()
     m_gc = 0;
@@ skipping 405 matching lines @@
     // Our layers only have a single alpha channel. This means that subpixel
     // rendered text cannot be composited correctly when the layer is
     // collapsed. Therefore, subpixel text is disabled when we are drawing
     // onto a layer.
     if (isDrawingToLayer())
         return false;
 
     return m_gc->shouldSmoothFonts();
 }
 
+void PlatformContextSkia::trackTextRegion(const SkRect& textRect)
+{
+    if (m_trackTextRegion) {
+        TRACE_EVENT0("skia", "PlatformContextSkia::trackTextRegion");
+        m_textRegion.join(textRect);

[eseidel, 2013/04/18 21:04:38]

I hope this isn't a WebCore::Region (which is abysmally slow)

[alokp, 2013/04/18 22:22:37]

Not WebCore::Region. It is SkRect (for now). I may need a tighter low-cost
region in future, so keeping the name generic.

+    }
+}
+
 } // namespace WebCore