Support browser side thumbnailing for GPU composited pages on Windows.

chrome/browser/tab_contents/thumbnail_generator.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/tab_contents/thumbnail_generator.h"
 
 #include <algorithm>
 #include <map>
 
 #include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
 #include "base/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/history/top_sites.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/thumbnail_score.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_source.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
+#include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "googleurl/src/gurl.h"
 #include "skia/ext/image_operations.h"
 #include "skia/ext/platform_canvas.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/color_utils.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/skbitmap_operations.h"
 
 // Overview
@@ skipping 31 matching lines @@
 // Creates a downsampled thumbnail for the given RenderWidgetHost's backing
 // store. The returned bitmap will be isNull if there was an error creating it.
 SkBitmap GetBitmapForRenderWidgetHost(
     RenderWidgetHost* render_widget_host,
     int desired_width,
     int desired_height,
     int options,
     ThumbnailGenerator::ClipResult* clip_result) {
   base::TimeTicks begin_compute_thumbnail = base::TimeTicks::Now();
 
-  SkBitmap result;
-
   // Get the bitmap as a Skia object so we can resample it. This is a large
   // allocation and we can tolerate failure here, so give up if the allocation
-  // fails.
+  // fails. First try to read from the compositing surface, then to read from
+  // the backing store.
+  content::RenderWidgetHostView* view = render_widget_host->GetView();
   skia::PlatformCanvas temp_canvas;
-  if (!render_widget_host->CopyFromBackingStore(&temp_canvas))
-    return result;
+  bool copy_result = false;
+  // TODO(mazda): Copy the shrinked size of compositing surface instead of the
+  // whole view size.

[vangelis, 2012/03/13 19:40:49]

Don't we want to use the desired_width/height here to do the shrinking on the
gpu since it's already implemented? 

[mazda, 2012/03/14 12:07:46]

Can I resolve the TODO in another CL? Since this size affects performance and
the quality of thumbnail, I'd like to choose optimal value with more
experiments. Just setting desired_width/height can cause the aspect ratio to be
changed. The copied image also needs to be clipped if the aspect ratio is not
equal to that of thumbnail image.

+  if (view) {
+    copy_result = render_widget_host->CopyFromCompositingSurface(
+        view->GetViewBounds().size(),
+        &temp_canvas);
+  }
+  if (!copy_result)
+      copy_result = render_widget_host->CopyFromBackingStore(&temp_canvas);
+  if (!copy_result)
+    return SkBitmap();
+
   const SkBitmap& bmp_with_scrollbars =
       skia::GetTopDevice(temp_canvas)->accessBitmap(false);
   // Clip the edgemost 15 pixels as that will commonly hold a scrollbar, which
   // looks bad in thumbnails.
   SkIRect scrollbarless_rect =
       { 0, 0,
         std::max(1, bmp_with_scrollbars.width() - 15),
         std::max(1, bmp_with_scrollbars.height() - 15) };
   SkBitmap bmp;
   bmp_with_scrollbars.extractSubset(&bmp, scrollbarless_rect);
 
+  SkBitmap result;
   // Check if a clipped thumbnail is requested.
   if (options & ThumbnailGenerator::kClippedThumbnail) {
     SkBitmap clipped_bitmap = ThumbnailGenerator::GetClippedBitmap(
         bmp, desired_width, desired_height, clip_result);
 
     // Need to resize it to the size we want, so downsample until it's
     // close, and let the caller make it the exact size if desired.
     result = SkBitmapOperations::DownsampleByTwoUntilSize(
         clipped_bitmap, desired_width, desired_height);
     // This is a bit subtle. SkBitmaps are refcounted, but the magic
@@ skipping 409 matching lines @@
 
 void ThumbnailGenerator::DidStartLoading() {
   load_interrupted_ = false;
 }
 
 void ThumbnailGenerator::StopNavigation() {
   // This function gets called when the page loading is interrupted by the
   // stop button.
   load_interrupted_ = true;
 }