Adding optimization to avoid image copy in SkSurface copy on write when content is discardable

This patch also adds code to SkDeferredCanvas to trigger the optimization.

TEST=DeferredSurfaceCopy bench, Surface unit test
R=reed@google.com

Author: junov@chromium.org

Review URL: https://chromiumcodereview.appspot.com/14063015

git-svn-id: http://skia.googlecode.com/svn/trunk@8797 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 6 insertions, 5 deletions

diff --git a/src/image/SkSurface_Gpu.cpp b/src/image/SkSurface_Gpu.cpp
index 098c92b1b1..687ca6c5ba 100644
--- a/src/image/SkSurface_Gpu.cpp
+++ b/src/image/SkSurface_Gpu.cpp
@@ -23,7 +23,7 @@ public:
     virtual SkImage* onNewImageSnapshot() SK_OVERRIDE;
     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y,
                         const SkPaint*) SK_OVERRIDE;
-    virtual void onCopyOnWrite() SK_OVERRIDE;
+    virtual void onCopyOnWrite(ContentChangeMode) SK_OVERRIDE;
 
 private:
     SkGpuDevice* fDevice;
@@ -86,9 +86,8 @@ void SkSurface_Gpu::onDraw(SkCanvas* canvas, SkScalar x, SkScalar y,
 // Create a new SkGpuDevice and, if necessary, copy the contents of the old
 // device into it. Note that this flushes the SkGpuDevice but
 // doesn't force an OpenGL flush.
-void SkSurface_Gpu::onCopyOnWrite() {
+void SkSurface_Gpu::onCopyOnWrite(ContentChangeMode mode) {
     GrRenderTarget* rt = (GrRenderTarget*) fDevice->accessRenderTarget();
-
     // are we sharing our render target with the image?
     SkASSERT(NULL != this->getCachedImage());
     if (rt->asTexture() == SkTextureImageGetTexture(this->getCachedImage())) {
@@ -96,8 +95,10 @@ void SkSurface_Gpu::onCopyOnWrite() {
             fDevice->createCompatibleDevice(fDevice->config(), fDevice->width(),
             fDevice->height(), fDevice->isOpaque()));
         SkAutoTUnref<SkGpuDevice> aurd(newDevice);
-        fDevice->context()->copyTexture(rt->asTexture(),
-            (GrRenderTarget*)newDevice->accessRenderTarget());
+        if (kRetain_ContentChangeMode == mode) {
+            fDevice->context()->copyTexture(rt->asTexture(),
+                reinterpret_cast<GrRenderTarget*>(newDevice->accessRenderTarget()));
+        }
         SkASSERT(NULL != this->getCachedCanvas());
         SkASSERT(this->getCachedCanvas()->getDevice() == fDevice);
         this->getCachedCanvas()->setDevice(newDevice);