Refactored-out the code of thumbnaling algorithm from thumbnail_tab_helper.

chrome/browser/thumbnails/thumbnail_tab_helper.cc

Index: chrome/browser/thumbnails/thumbnail_tab_helper.cc
diff --git a/chrome/browser/thumbnails/thumbnail_tab_helper.cc b/chrome/browser/thumbnails/thumbnail_tab_helper.cc
index 64837767c74ea7a67d31279d301d89bf38a5d5bf..40f8d8e998e92c571f48fbb2104d5a4b62a9b2c8 100644
--- a/chrome/browser/thumbnails/thumbnail_tab_helper.cc
+++ b/chrome/browser/thumbnails/thumbnail_tab_helper.cc
@@ -4,12 +4,13 @@
 
 #include "chrome/browser/thumbnails/thumbnail_tab_helper.h"
 
-#include "base/metrics/histogram.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/thumbnails/render_widget_snapshot_taker.h"
 #include "chrome/browser/thumbnails/thumbnail_service.h"
 #include "chrome/browser/thumbnails/thumbnail_service_factory.h"
+#include "chrome/browser/thumbnails/thumbnailing_algorithm.h"
+#include "chrome/browser/thumbnails/thumbnailing_context.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_source.h"
 #include "content/public/browser/notification_types.h"
@@ -45,191 +46,85 @@ using content::RenderViewHost;
 using content::RenderWidgetHost;
 using content::WebContents;
 
-namespace {
-
-// The thumbnail size in DIP.
-static const int kThumbnailWidth = 212;
-static const int kThumbnailHeight = 132;
+using thumbnails::ClipResult;
+using thumbnails::ThumbnailingContext;
+using thumbnails::ThumbnailingAlgorithm;
 
-static const char kThumbnailHistogramName[] = "Thumbnail.ComputeMS";
+namespace {
 
-// Returns the size used by RenderWidgetHost::CopyFromBackingStore.
-//
-// The size is calculated in such a way that the copied size in pixel becomes
-// equal to (f * kThumbnailWidth, f * kThumbnailHeight), where f is the scale
-// of ui::SCALE_FACTOR_200P. Since RenderWidgetHost::CopyFromBackingStore takes
-// the size in DIP, we need to adjust the size based on |view|'s device scale
-// factor in order to copy the pixels with the size above.
-//
-// The copied size was chosen for the following reasons.
-//
-// 1. When the scale factor of the primary monitor is ui::SCALE_FACTOR_200P, the
-// generated thumbnail size is (f * kThumbnailWidth, f * kThumbnailHeight).
-// In order to avoid degrading the image quality by magnification, the size
-// of the copied pixels should be equal to or larger than this thumbnail size.
-//
-// 2. RenderWidgetHost::CopyFromBackingStore can be costly especially when
-// it is necessary to read back the web contents image data from GPU. As the
-// cost is roughly propotional to the number of the copied pixels, the size of
-// the copied pixels should be as small as possible.
-//
-// When the scale factor of the primary monitor is ui::SCALE_FACTOR_100P,
-// we still copy the pixels with the same size as ui::SCALE_FACTOR_200P because
-// the resampling method used in RenderWidgetHost::CopyFromBackingStore is not
-// good enough for the resampled image to be used directly for the thumbnail
-// (http://crbug.com/141235). We assume this is not an issue in case of
-// ui::SCALE_FACTOR_200P because the high resolution thumbnail on high density
-// display alleviates the aliasing.
-// TODO(mazda): Copy the pixels with the smaller size in the case of
-// ui::SCALE_FACTOR_100P once the resampling method has been improved.
-gfx::Size GetCopySizeForThumbnail(content::RenderWidgetHostView* view) {
-  gfx::Size copy_size(kThumbnailWidth, kThumbnailHeight);
-  ui::ScaleFactor scale_factor =
-      ui::GetScaleFactorForNativeView(view->GetNativeView());
-  switch (scale_factor) {
-    case ui::SCALE_FACTOR_100P:
-      copy_size = gfx::ToFlooredSize(gfx::ScaleSize(
-          copy_size, ui::GetScaleFactorScale(ui::SCALE_FACTOR_200P)));
-      break;
-    case ui::SCALE_FACTOR_200P:
-      // Use the size as-is.
-      break;
-    default:
-      DLOG(WARNING) << "Unsupported scale factor. Use the same copy size as "
-                    << "ui::SCALE_FACTOR_100P";
-      copy_size = gfx::ToFlooredSize(gfx::ScaleSize(
-          copy_size, ui::GetScaleFactorScale(ui::SCALE_FACTOR_200P)));
-      break;
-  }
-  return copy_size;
+// Feed the constructed thumbnail to the thumbnail service.
+void UpdateThumbnail(const ThumbnailingContext& context,
+                     const SkBitmap& thumbnail) {
+  gfx::Image image(thumbnail);
+  context.service->SetPageThumbnail(context, image);
+  VLOG(1) << "Thumbnail taken for " << context.url << ": "
+          << context.score.ToString();
 }
 
-// Returns the size of the thumbnail stored in the database in pixel.
-gfx::Size GetThumbnailSizeInPixel() {
-  gfx::Size thumbnail_size(kThumbnailWidth, kThumbnailHeight);
-  // Determine the resolution of the thumbnail based on the maximum scale
-  // factor.
-  // TODO(mazda|oshima): Update thumbnail when the max scale factor changes.
-  // crbug.com/159157.
-  float max_scale_factor =
-      ui::GetScaleFactorScale(ui::GetMaxScaleFactor());
-  return gfx::ToFlooredSize(gfx::ScaleSize(thumbnail_size, max_scale_factor));
-}
+void ProcessCanvas(ThumbnailingContext* context,
+                   ThumbnailingAlgorithm* algorithm,
+                   skia::PlatformBitmap* temp_bitmap,
+                   bool succeeded) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  if (!succeeded)
+    return;
 
-// Returns the clipping rectangle that is used for creating a thumbnail with
-// the size of |desired_size| from the bitmap with the size of |source_size|.
-// The type of clipping that needs to be done is assigned to |clip_result|.
-gfx::Rect GetClippingRect(const gfx::Size& source_size,
-                          const gfx::Size& desired_size,
-                          ThumbnailTabHelper::ClipResult* clip_result) {
-  DCHECK(clip_result);
-
-  float desired_aspect =
-      static_cast<float>(desired_size.width()) / desired_size.height();
-
-  // Get the clipping rect so that we can preserve the aspect ratio while
-  // filling the destination.
-  gfx::Rect clipping_rect;
-  if (source_size.width() < desired_size.width() ||
-      source_size.height() < desired_size.height()) {
-    // Source image is smaller: we clip the part of source image within the
-    // dest rect, and then stretch it to fill the dest rect. We don't respect
-    // the aspect ratio in this case.
-    clipping_rect = gfx::Rect(desired_size);
-    *clip_result = ThumbnailTabHelper::kSourceIsSmaller;
-  } else {
-    float src_aspect =
-        static_cast<float>(source_size.width()) / source_size.height();
-    if (src_aspect > desired_aspect) {
-      // Wider than tall, clip horizontally: we center the smaller
-      // thumbnail in the wider screen.
-      int new_width = static_cast<int>(source_size.height() * desired_aspect);
-      int x_offset = (source_size.width() - new_width) / 2;
-      clipping_rect.SetRect(x_offset, 0, new_width, source_size.height());
-      *clip_result = (src_aspect >= ThumbnailScore::kTooWideAspectRatio) ?
-          ThumbnailTabHelper::kTooWiderThanTall :
-          ThumbnailTabHelper::kWiderThanTall;
-    } else if (src_aspect < desired_aspect) {
-      clipping_rect =
-          gfx::Rect(source_size.width(), source_size.width() / desired_aspect);
-      *clip_result = ThumbnailTabHelper::kTallerThanWide;
-    } else {
-      clipping_rect = gfx::Rect(source_size);
-      *clip_result = ThumbnailTabHelper::kNotClipped;
-    }
-  }
-  return clipping_rect;
+  SkBitmap bitmap = temp_bitmap->GetBitmap();
+  algorithm->ProcessBitmap(context, base::Bind(&UpdateThumbnail), bitmap);
 }
 
-// Creates a downsampled thumbnail from the given bitmap.
-// store. The returned bitmap will be isNull if there was an error creating it.
-SkBitmap CreateThumbnail(
-    const SkBitmap& bitmap,
-    const gfx::Size& desired_size,
-    ThumbnailTabHelper::ClipResult* clip_result) {
-  base::TimeTicks begin_compute_thumbnail = base::TimeTicks::Now();
-
-  SkBitmap clipped_bitmap;
-  if (*clip_result == ThumbnailTabHelper::kUnprocessed) {
-    // Clip the pixels that will commonly hold a scrollbar, which looks bad in
-    // thumbnails.
-    int scrollbar_size = gfx::scrollbar_size();
-    SkIRect scrollbarless_rect =
-        { 0, 0,
-          std::max(1, bitmap.width() - scrollbar_size),
-          std::max(1, bitmap.height() - scrollbar_size) };
-    SkBitmap bmp;
-    bitmap.extractSubset(&bmp, scrollbarless_rect);
-
-    clipped_bitmap = ThumbnailTabHelper::GetClippedBitmap(
-        bmp, desired_size.width(), desired_size.height(), clip_result);
-  } else {
-    clipped_bitmap = bitmap;
+void AsyncProcessThumbnail(content::WebContents* web_contents,
+                           scoped_refptr<ThumbnailingContext> context,
+                           scoped_refptr<ThumbnailingAlgorithm> algorithm) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  RenderWidgetHost* render_widget_host = web_contents->GetRenderViewHost();
+  content::RenderWidgetHostView* view = render_widget_host->GetView();
+  if (!view)
+    return;
+  if (!view->IsSurfaceAvailableForCopy()) {
+#if defined(OS_WIN)
+    // On Windows XP, neither the backing store nor the compositing surface is
+    // available in the browser when accelerated compositing is active, so ask
+    // the renderer to send a snapshot for creating the thumbnail.
+    if (base::win::GetVersion() < base::win::VERSION_VISTA) {
+      gfx::Size view_size =
+          render_widget_host->GetView()->GetViewBounds().size();
+      g_browser_process->GetRenderWidgetSnapshotTaker()->AskForSnapshot(
+          render_widget_host,
+          base::Bind(&ThumbnailingAlgorithm::ProcessBitmap,
+                     algorithm, context, base::Bind(&UpdateThumbnail)),
+          view_size,
+          view_size);
+    }
+#endif
+    return;
   }
 
-  // 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.
-  SkBitmap result = SkBitmapOperations::DownsampleByTwoUntilSize(
-      clipped_bitmap, desired_size.width(), desired_size.height());
-#if !defined(USE_AURA)
-  // This is a bit subtle. SkBitmaps are refcounted, but the magic
-  // ones in PlatformCanvas can't be assigned to SkBitmap with proper
-  // refcounting.  If the bitmap doesn't change, then the downsampler
-  // will return the input bitmap, which will be the reference to the
-  // weird PlatformCanvas one insetad of a regular one. To get a
-  // regular refcounted bitmap, we need to copy it.
-  //
-  // On Aura, the PlatformCanvas is platform-independent and does not have
-  // any native platform resources that can't be refounted, so this issue does
-  // not occur.
-  //
-  // Note that GetClippedBitmap() does extractSubset() but it won't copy
-  // the pixels, hence we check result size == clipped_bitmap size here.
-  if (clipped_bitmap.width() == result.width() &&
-      clipped_bitmap.height() == result.height())
-    clipped_bitmap.copyTo(&result, SkBitmap::kARGB_8888_Config);
-#endif
+  gfx::Rect copy_rect = gfx::Rect(view->GetViewBounds().size());
+  // Clip the pixels that will commonly hold a scrollbar, which looks bad in
+  // thumbnails.
+  int scrollbar_size = gfx::scrollbar_size();
+  gfx::Size copy_size;
+  copy_rect.Inset(0, 0, scrollbar_size, scrollbar_size);
 
-  HISTOGRAM_TIMES(kThumbnailHistogramName,
-                  base::TimeTicks::Now() - begin_compute_thumbnail);
-  return result;
-}
+  if (copy_rect.IsEmpty())
+    return;
 
-}  // namespace
+  context->clip_result = algorithm->GetCanvasCopyInfo(
+      copy_rect.size(),
+      ui::GetScaleFactorForNativeView(view->GetNativeView()),
+      &copy_rect,
+      &copy_size);
 
-ThumbnailTabHelper::ThumbnailingContext::ThumbnailingContext(
-    content::WebContents* web_contents,
-    bool load_interrupted)
-    : browser_context(web_contents->GetBrowserContext()),
-      url(web_contents->GetURL()),
-      clip_result(kUnprocessed) {
-  score.at_top =
-      (web_contents->GetRenderViewHost()->GetLastScrollOffset().y() == 0);
-  score.load_completed = !web_contents->IsLoading() && !load_interrupted;
+  skia::PlatformBitmap* temp_bitmap = new skia::PlatformBitmap;
+  render_widget_host->CopyFromBackingStore(
+      copy_rect,
+      copy_size,
+      base::Bind(&ProcessCanvas, context, algorithm, base::Owned(temp_bitmap)),
+      temp_bitmap);
 }
 
-ThumbnailTabHelper::ThumbnailingContext::~ThumbnailingContext() {
-}
+}  // namespace
 
 ThumbnailTabHelper::ThumbnailTabHelper(content::WebContents* contents)
     : content::WebContentsObserver(contents),
@@ -310,32 +205,6 @@ void ThumbnailTabHelper::RenderViewHostDeleted(
       content::Source<RenderViewHost>(renderer));
 }
 
-double ThumbnailTabHelper::CalculateBoringScore(const SkBitmap& bitmap) {
-  if (bitmap.isNull() || bitmap.empty())
-    return 1.0;
-  int histogram[256] = {0};
-  color_utils::BuildLumaHistogram(bitmap, histogram);
-
-  int color_count = *std::max_element(histogram, histogram + 256);
-  int pixel_count = bitmap.width() * bitmap.height();
-  return static_cast<double>(color_count) / pixel_count;
-}
-
-SkBitmap ThumbnailTabHelper::GetClippedBitmap(const SkBitmap& bitmap,
-                                              int desired_width,
-                                              int desired_height,
-                                              ClipResult* clip_result) {
-  gfx::Rect clipping_rect =
-      GetClippingRect(gfx::Size(bitmap.width(), bitmap.height()),
-                      gfx::Size(desired_width, desired_height),
-                      clip_result);
-  SkIRect src_rect = { clipping_rect.x(), clipping_rect.y(),
-                       clipping_rect.right(), clipping_rect.bottom() };
-  SkBitmap clipped_bitmap;
-  bitmap.extractSubset(&clipped_bitmap, src_rect);
-  return clipped_bitmap;
-}
-
 void ThumbnailTabHelper::UpdateThumbnailIfNecessary(
     WebContents* web_contents) {
   // Destroying a WebContents may trigger it to be hidden, prompting a snapshot
@@ -360,107 +229,14 @@ void ThumbnailTabHelper::UpdateThumbnailIfNecessary(
     return;
   }
 
-  AsyncUpdateThumbnail(web_contents);
-}
-
-void ThumbnailTabHelper::UpdateThumbnail(
-    ThumbnailingContext* context,
-    const SkBitmap& thumbnail) {
-  Profile* profile =
-      Profile::FromBrowserContext(context->browser_context);
-  scoped_refptr<thumbnails::ThumbnailService> thumbnail_service =
-      ThumbnailServiceFactory::GetForProfile(profile);
-
-  if (!thumbnail_service)
-    return;
-
-  context->score.boring_score = CalculateBoringScore(thumbnail);
-  context->score.good_clipping =
-      (context->clip_result == ThumbnailTabHelper::kWiderThanTall ||
-       context->clip_result == ThumbnailTabHelper::kTallerThanWide ||
-       context->clip_result == ThumbnailTabHelper::kNotClipped);
-
-  gfx::Image image(thumbnail);
-  thumbnail_service->SetPageThumbnail(context->url, image, context->score);
-  VLOG(1) << "Thumbnail taken for " << context->url << ": "
-          << context->score.ToString();
-}
-
-void ThumbnailTabHelper::AsyncUpdateThumbnail(
-    WebContents* web_contents) {
-  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
-  RenderWidgetHost* render_widget_host = web_contents->GetRenderViewHost();
-  content::RenderWidgetHostView* view = render_widget_host->GetView();
-  if (!view)
-    return;
-  if (!view->IsSurfaceAvailableForCopy()) {
-#if defined(OS_WIN)
-    // On Windows XP, neither the backing store nor the compositing surface is
-    // available in the browser when accelerated compositing is active, so ask
-    // the renderer to send a snapshot for creating the thumbnail.
-    if (base::win::GetVersion() < base::win::VERSION_VISTA) {
-      scoped_refptr<ThumbnailingContext> context(
-          new ThumbnailingContext(web_contents, load_interrupted_));
-      gfx::Size view_size =
-          render_widget_host->GetView()->GetViewBounds().size();
-      g_browser_process->GetRenderWidgetSnapshotTaker()->AskForSnapshot(
-          render_widget_host,
-          base::Bind(&ThumbnailTabHelper::UpdateThumbnailWithBitmap,
-                     context),
-          view_size,
-          view_size);
-    }
-#endif
-    return;
-  }
-
-  gfx::Rect copy_rect = gfx::Rect(view->GetViewBounds().size());
-  // Clip the pixels that will commonly hold a scrollbar, which looks bad in
-  // thumbnails.
-  int scrollbar_size = gfx::scrollbar_size();
-  copy_rect.Inset(0, 0, scrollbar_size, scrollbar_size);
+  scoped_refptr<thumbnails::ThumbnailingAlgorithm> algorithm(
+      thumbnail_service->GetThumbnailingAlgorithm());
 
   scoped_refptr<ThumbnailingContext> context(
-      new ThumbnailingContext(web_contents, load_interrupted_));
-  copy_rect = GetClippingRect(copy_rect.size(),
-                              gfx::Size(kThumbnailWidth, kThumbnailHeight),
-                              &context->clip_result);
-
-  gfx::Size copy_size = GetCopySizeForThumbnail(view);
-  skia::PlatformBitmap* temp_bitmap = new skia::PlatformBitmap;
-  render_widget_host->CopyFromBackingStore(
-      copy_rect,
-      copy_size,
-      base::Bind(&ThumbnailTabHelper::UpdateThumbnailWithCanvas,
-                 context,
-                 base::Owned(temp_bitmap)),
-      temp_bitmap);
-}
-
-void ThumbnailTabHelper::UpdateThumbnailWithBitmap(
-    ThumbnailingContext* context,
-    const SkBitmap& bitmap) {
-  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
-  if (bitmap.isNull() || bitmap.empty())
-    return;
-
-  SkBitmap thumbnail = CreateThumbnail(bitmap,
-                                       GetThumbnailSizeInPixel(),
-                                       &context->clip_result);
-
-  UpdateThumbnail(context, thumbnail);
-}
-
-void ThumbnailTabHelper::UpdateThumbnailWithCanvas(
-    ThumbnailingContext* context,
-    skia::PlatformBitmap* temp_bitmap,
-    bool succeeded) {
-  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
-  if (!succeeded)
-    return;
-
-  SkBitmap bitmap = temp_bitmap->GetBitmap();
-  UpdateThumbnailWithBitmap(context, bitmap);
+      new ThumbnailingContext(web_contents,
+                              thumbnail_service,
+                              load_interrupted_));
+  AsyncProcessThumbnail(web_contents, context, algorithm);
 }
 
 void ThumbnailTabHelper::DidStartLoading(