Efficiently handle image layer scaling

webkit/compositor_bindings/web_layer_impl_fixed_bounds.h

Index: webkit/compositor_bindings/web_layer_impl_fixed_bounds.h
diff --git a/webkit/compositor_bindings/web_layer_impl_fixed_bounds.h b/webkit/compositor_bindings/web_layer_impl_fixed_bounds.h
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index 0000000000000000000000000000000000000000..2e83a4415c02dd114b0d4605a3c9fb57ff369d79
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+++ b/webkit/compositor_bindings/web_layer_impl_fixed_bounds.h
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+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebLayerImplFixedBounds_h
+#define WebLayerImplFixedBounds_h
+
+#include "ui/gfx/size.h"
+#include "ui/gfx/transform.h"
+#include "webkit/compositor_bindings/web_layer_impl.h"
+
+namespace WebKit {
+
+// A special implementation of WebLayerImpl for layers that its contents
+// need to be automatically scaled when the bounds changes. The compositor
+// can efficiently handle the bounds change of such layers if the bounds
+// is fixed to a given value and the change of bounds are converted to
+// transformation scales.
+class WebLayerImplFixedBounds : public WebLayerImpl {
+public:
+    WEBKIT_COMPOSITOR_BINDINGS_EXPORT WebLayerImplFixedBounds();
+    WEBKIT_COMPOSITOR_BINDINGS_EXPORT explicit WebLayerImplFixedBounds(scoped_refptr<cc::Layer>);
+    virtual ~WebLayerImplFixedBounds();
+
+    // WebLayerImpl overrides.
+    virtual void invalidateRect(const WebFloatRect&) OVERRIDE;
+    virtual void setAnchorPoint(const WebFloatPoint&) OVERRIDE;
+    virtual void setBounds(const WebSize&) OVERRIDE;
+    virtual WebSize bounds() const OVERRIDE;
+    virtual void setSublayerTransform(const SkMatrix44&) OVERRIDE;
+    virtual void setSublayerTransform(const WebTransformationMatrix&) OVERRIDE;
+    virtual SkMatrix44 sublayerTransform() const OVERRIDE;
+    virtual void setTransform(const SkMatrix44&) OVERRIDE;
+    virtual void setTransform(const WebTransformationMatrix&) OVERRIDE;
+    virtual SkMatrix44 transform() const OVERRIDE;
+
+    WEBKIT_COMPOSITOR_BINDINGS_EXPORT void setFixedBounds(const gfx::Size& fixedBounds);
+
+protected:
+    void setTransformInternal(const gfx::Transform&);
+    void setSublayerTransformInternal(const gfx::Transform&);
+    void updateLayerBoundsAndTransform();
+
+    gfx::Transform m_originalSublayerTransform;
+    gfx::Transform m_originalTransform;
+    gfx::Size m_originalBounds;
+    gfx::Size m_fixedBounds;
+};
+
+} // namespace WebKit
+
+#endif // WebLayerImplFixedBounds_h