Support browser side thumbnailing for GPU composited pages on Windows.

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 27c6b1811067c059028ad7c20f79f793aa07b18e..47a400653053c657750018cf29b065a2d947b81a 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -32,6 +32,7 @@
 #include "content/public/browser/user_metrics.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/result_codes.h"
+#include "skia/ext/platform_canvas.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebCompositionUnderline.h"
 #include "ui/base/keycodes/keyboard_codes.h"
 #include "webkit/glue/webcursor.h"
@@ -492,10 +493,35 @@ bool RenderWidgetHostImpl::CopyFromBackingStore(skia::PlatformCanvas* output) {
   if (!backing_store)
     return false;
 
+  TRACE_EVENT0("browser", "RenderWidgetHostImpl::CopyFromBackingStore");
   return backing_store->CopyFromBackingStore(
       gfx::Rect(backing_store->size()), output);
 }
 
+bool RenderWidgetHostImpl::CopyFromCompositingSurface(
+    const gfx::Size& size,
+    skia::PlatformCanvas* output) {
+  if (!is_accelerated_compositing_active_)
+    return false;
+
+  TRACE_EVENT0("browser", "RenderWidgetHostImpl::CopyFromCompositingSurface");
+  std::vector<unsigned char> pixels(4 * size.GetArea());
+  if(!GpuSurfaceTracker::Get()->CopySurface(surface_id_,
+                                            size,
+                                            &pixels))

[apatrick_chromium, 2012/03/07 20:39:37]

Is it possible to copy the pixels directly into the SkBitmap rather than copy
them from the vector into the SkBitmap later?

[mazda, 2012/03/08 13:14:28]

Actually SkBitmap::setPixels does not copy the data to SkBitmap and just sets
the pointer, so there should be little difference (I also noticed that
allocPixels is not necessary).
SkCanvas::writePixels does copy the data, but there's no way to write the pixels
directly to SkCanvas with DirectX as far as I know.

[apatrick_chromium, 2012/03/08 20:15:47]

I think you could call SkBitmap::allocPixels before CopySurface, call
SkBitmap::getPixels to get the address of the allocated buffer and pass that as
the pixels argument to CopySurface. That would mean changing the the type of the
pixels argument from std::vector* to void* and the code in AcceleratedPresenter
would just assume that the output buffer was exacly the size implied by the size
argument.

[mazda, 2012/03/10 07:51:37]

Thanks. I changed the AcceleratedSurface::CopyTo to take void*.

+    return false;
+
+  SkBitmap bitmap;
+  bitmap.setConfig(SkBitmap::kARGB_8888_Config, size.width(), size.height());
+  bitmap.allocPixels();
+  bitmap.setPixels(&pixels[0]);

[apatrick_chromium, 2012/03/07 20:39:37]

This won't work if the area of the surface is zero because pixels will not have
an element at index zero to take the address of and will assert in debug builds.

[mazda, 2012/03/08 13:14:28]

I added a check for |size| and also made AcceleratorSurface::CopyTo fail if the
area of surface is zero.

+
+  if (!output->initialize(size.width(), size.height(), true))
+    return false;
+  output->writePixels(bitmap, 0, 0);
+  return true;
+}
+
 #if defined(TOOLKIT_GTK)
 bool RenderWidgetHostImpl::CopyFromBackingStoreToGtkWindow(
     const gfx::Rect& dest_rect, GdkWindow* target) {