Downsample thumbnail by powers of two before doing lanczos

chrome/renderer/render_view.cc

 // Copyright (c) 2010 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/renderer/render_view.h"
 
 #include <algorithm>
 #include <cmath>
 #include <string>
 #include <vector>
@@ skipping 77 matching lines @@
 #include "chrome/renderer/webgraphicscontext3d_command_buffer_impl.h"
 #include "chrome/renderer/webplugin_delegate_pepper.h"
 #include "chrome/renderer/webplugin_delegate_proxy.h"
 #include "chrome/renderer/websharedworker_proxy.h"
 #include "chrome/renderer/webworker_proxy.h"
 #include "gfx/color_utils.h"
 #include "gfx/favicon_size.h"
 #include "gfx/native_widget_types.h"
 #include "gfx/point.h"
 #include "gfx/rect.h"
+#include "gfx/skbitmap_operations.h"
 #include "grit/generated_resources.h"
 #include "grit/renderer_resources.h"
 #include "media/base/media_switches.h"
 #include "net/base/data_url.h"
 #include "net/base/escape.h"
 #include "net/base/net_errors.h"
 #include "skia/ext/bitmap_platform_device.h"
 #include "skia/ext/image_operations.h"
 #include "third_party/WebKit/WebKit/chromium/public/WebAccessibilityCache.h"
 #include "third_party/WebKit/WebKit/chromium/public/WebAccessibilityObject.h"
@@ skipping 990 matching lines @@
                    static_cast<S16CPU>(src_bmp.width() / dest_aspect));
       score->good_clipping = true;
     }
   }
 
   score->at_top = (view->mainFrame()->scrollOffset().height == 0);
 
   SkBitmap subset;
   device.accessBitmap(false).extractSubset(&subset, src_rect);
 
-  // Resample the subset that we want to get it the right size.
+  // First do a fast downsample by powers of two to get close to the final size.
+  SkBitmap downsampled_subset =
+      SkBitmapOperations::DownsampleByTwoUntilSize(subset, w, h);
+
+  // Do a high-quality resize from the downscaled size to the final size.
   *thumbnail = skia::ImageOperations::Resize(
-      subset, skia::ImageOperations::RESIZE_LANCZOS3, w, h);
+      downsampled_subset, skia::ImageOperations::RESIZE_LANCZOS3, w, h);
 
   score->boring_score = CalculateBoringScore(thumbnail);
 
   HISTOGRAM_TIMES("Renderer4.Thumbnail",
                   base::TimeTicks::Now() - beginning_time);
+
   return true;
 }
 
 bool RenderView::CaptureSnapshot(WebView* view, SkBitmap* snapshot) {
   base::TimeTicks beginning_time = base::TimeTicks::Now();
 
   skia::PlatformCanvas canvas;
   if (!PaintViewIntoCanvas(view, canvas))
     return false;
 
@@ skipping 4354 matching lines @@
       IPC::PlatformFileForTransitToPlatformFile(file_for_transit),
       message_id);
 }
 
 #if defined(OS_MACOSX)
 void RenderView::OnSelectPopupMenuItem(int selected_index) {
   external_popup_menu_->DidSelectItem(selected_index);
   external_popup_menu_.reset();
 }
 #endif