src/chrome/browser/thumbnails/content_based_thumbnailing_algorithm.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chrome/browser/thumbnails/content_based_thumbnailing_algorithm.h"
   6
   7 #include "base/metrics/histogram.h"
   8 #include "base/threading/sequenced_worker_pool.h"
   9 #include "chrome/browser/thumbnails/content_analysis.h"
  10 #include "chrome/browser/thumbnails/simple_thumbnail_crop.h"
  11 #include "content/public/browser/browser_thread.h"
  12 #include "third_party/skia/include/core/SkBitmap.h"
  13 #include "ui/gfx/scrollbar_size.h"
  14 #include "ui/gfx/size_conversions.h"
  15 #include "ui/gfx/skbitmap_operations.h"
  16 #include "ui/gfx/skia_util.h"
  17
  18 namespace {
  19
  20 const char kThumbnailHistogramName[] = "Thumbnail.RetargetMS";
  21 const char kFailureHistogramName[] = "Thumbnail.FailedRetargetMS";
  22 const float kScoreBoostFromSuccessfulRetargeting = 1.1f;
  23
  24 void CallbackInvocationAdapter(
  25     const thumbnails::ThumbnailingAlgorithm::ConsumerCallback& callback,
  26     scoped_refptr<thumbnails::ThumbnailingContext> context,
  27     const SkBitmap& source_bitmap) {
  28   callback.Run(*context.get(), source_bitmap);
  29 }
  30
  31 }  // namespace
  32
  33 namespace thumbnails {
  34
  35 using content::BrowserThread;
  36
  37 ContentBasedThumbnailingAlgorithm::ContentBasedThumbnailingAlgorithm(
  38     const gfx::Size& target_size)
  39     : target_size_(target_size) {
  40   DCHECK(!target_size.IsEmpty());
  41 }
  42
  43 ClipResult ContentBasedThumbnailingAlgorithm::GetCanvasCopyInfo(
  44     const gfx::Size& source_size,
  45     ui::ScaleFactor scale_factor,
  46     gfx::Rect* clipping_rect,
  47     gfx::Size* target_size) const {
  48   DCHECK(!source_size.IsEmpty());
  49   gfx::Size target_thumbnail_size =
  50       SimpleThumbnailCrop::GetCopySizeForThumbnail(scale_factor, target_size_);
  51
  52   ClipResult clipping_method = thumbnails::CLIP_RESULT_NOT_CLIPPED;
  53   *clipping_rect = GetClippingRect(
  54       source_size, target_thumbnail_size, target_size, &clipping_method);
  55   return clipping_method;
  56 }
  57
  58 void ContentBasedThumbnailingAlgorithm::ProcessBitmap(
  59     scoped_refptr<ThumbnailingContext> context,
  60     const ConsumerCallback& callback,
  61     const SkBitmap& bitmap) {
  62   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  63   DCHECK(context.get());
  64   if (bitmap.isNull() || bitmap.empty())
  65     return;
  66
  67   gfx::Size target_thumbnail_size =
  68       SimpleThumbnailCrop::ComputeTargetSizeAtMaximumScale(target_size_);
  69
  70   SkBitmap source_bitmap =
  71       PrepareSourceBitmap(bitmap, target_thumbnail_size, context.get());
  72
  73   // If the source is same (or smaller) than the target, just return it as
  74   // the final result. Otherwise, send the shrinking task to the blocking
  75   // thread pool.
  76   if (source_bitmap.width() <= target_thumbnail_size.width() ||
  77       source_bitmap.height() <= target_thumbnail_size.height()) {
  78     context->score.boring_score =
  79         SimpleThumbnailCrop::CalculateBoringScore(source_bitmap);
  80     context->score.good_clipping =
  81         (context->clip_result == CLIP_RESULT_WIDER_THAN_TALL ||
  82          context->clip_result == CLIP_RESULT_TALLER_THAN_WIDE ||
  83          context->clip_result == CLIP_RESULT_NOT_CLIPPED ||
  84          context->clip_result == CLIP_RESULT_SOURCE_SAME_AS_TARGET);
  85
  86     callback.Run(*context.get(), source_bitmap);
  87     return;
  88   }
  89
  90   if (!BrowserThread::GetBlockingPool()->PostWorkerTaskWithShutdownBehavior(
  91           FROM_HERE,
  92           base::Bind(&CreateRetargetedThumbnail,
  93                      source_bitmap,
  94                      target_thumbnail_size,
  95                      context,
  96                      callback),
  97           base::SequencedWorkerPool::SKIP_ON_SHUTDOWN)) {
  98     LOG(WARNING) << "PostSequencedWorkerTask failed. The thumbnail for "
  99                  << context->url << " will not be created.";
 100   }
 101 }
 102
 103 // static
 104 SkBitmap ContentBasedThumbnailingAlgorithm::PrepareSourceBitmap(
 105     const SkBitmap& received_bitmap,
 106     const gfx::Size& thumbnail_size,
 107     ThumbnailingContext* context) {
 108   gfx::Size resize_target;
 109   SkBitmap clipped_bitmap;
 110   if (context->clip_result == CLIP_RESULT_UNPROCESSED) {
 111     // This case will require extracting a fragment from the retrieved bitmap.
 112     int scrollbar_size = gfx::scrollbar_size();
 113     gfx::Size scrollbarless(
 114         std::max(1, received_bitmap.width() - scrollbar_size),
 115         std::max(1, received_bitmap.height() - scrollbar_size));
 116
 117     gfx::Rect clipping_rect = GetClippingRect(
 118         scrollbarless,
 119         thumbnail_size,
 120         &resize_target,
 121         &context->clip_result);
 122
 123     received_bitmap.extractSubset(&clipped_bitmap,
 124                                   gfx::RectToSkIRect(clipping_rect));
 125   } else {
 126     // This means that the source bitmap has been requested and at least
 127     // clipped. Upstream code in same cases seems opportunistic and it may
 128     // not perform actual resizing if copying with resize is not supported.
 129     // In this case we will resize to the orignally requested copy size.
 130     resize_target = context->requested_copy_size;
 131     clipped_bitmap = received_bitmap;
 132   }
 133
 134   SkBitmap result_bitmap = SkBitmapOperations::DownsampleByTwoUntilSize(
 135       clipped_bitmap, resize_target.width(), resize_target.height());
 136 #if !defined(USE_AURA)
 137   // If the bitmap has not been indeed resized, it has to be copied. In that
 138   // case resampler simply returns a reference to the original bitmap, sitting
 139   // in PlatformCanvas. One does not simply assign these 'magic' bitmaps to
 140   // SkBitmap. They cannot be refcounted.
 141   //
 142   // With Aura, this does not happen since PlatformCanvas is platform
 143   // idependent.
 144   if (clipped_bitmap.width() == result_bitmap.width() &&
 145       clipped_bitmap.height() == result_bitmap.height()) {
 146     clipped_bitmap.copyTo(&result_bitmap, kN32_SkColorType);
 147   }
 148 #endif
 149
 150   return result_bitmap;
 151 }
 152
 153 // static
 154 void ContentBasedThumbnailingAlgorithm::CreateRetargetedThumbnail(
 155     const SkBitmap& source_bitmap,
 156     const gfx::Size& thumbnail_size,
 157     scoped_refptr<ThumbnailingContext> context,
 158     const ConsumerCallback& callback) {
 159   base::TimeTicks begin_compute_thumbnail = base::TimeTicks::Now();
 160   float kernel_sigma =
 161       context->clip_result == CLIP_RESULT_SOURCE_SAME_AS_TARGET ? 5.0f : 2.5f;
 162   SkBitmap thumbnail = thumbnailing_utils::CreateRetargetedThumbnailImage(
 163       source_bitmap, thumbnail_size, kernel_sigma);
 164   bool processing_failed = thumbnail.empty();
 165   if (processing_failed) {
 166     // Log and apply the method very much like in SimpleThumbnailCrop (except
 167     // that some clipping and copying is not required).
 168     LOG(WARNING) << "CreateRetargetedThumbnailImage failed. "
 169                  << "The thumbnail for " << context->url
 170                  << " will be created the old-fashioned way.";
 171
 172     ClipResult clip_result;
 173     gfx::Rect clipping_rect = SimpleThumbnailCrop::GetClippingRect(
 174         gfx::Size(source_bitmap.width(), source_bitmap.height()),
 175         thumbnail_size,
 176         &clip_result);
 177     source_bitmap.extractSubset(&thumbnail, gfx::RectToSkIRect(clipping_rect));
 178     thumbnail = SkBitmapOperations::DownsampleByTwoUntilSize(
 179         thumbnail, thumbnail_size.width(), thumbnail_size.height());
 180   }
 181
 182   HISTOGRAM_TIMES(
 183       processing_failed ? kFailureHistogramName : kThumbnailHistogramName,
 184       base::TimeTicks::Now() - begin_compute_thumbnail);
 185   context->score.boring_score =
 186         SimpleThumbnailCrop::CalculateBoringScore(source_bitmap);
 187   if (!processing_failed)
 188     context->score.boring_score *= kScoreBoostFromSuccessfulRetargeting;
 189   context->score.good_clipping =
 190       (context->clip_result == CLIP_RESULT_WIDER_THAN_TALL ||
 191        context->clip_result == CLIP_RESULT_TALLER_THAN_WIDE ||
 192        context->clip_result == CLIP_RESULT_NOT_CLIPPED ||
 193        context->clip_result == CLIP_RESULT_SOURCE_SAME_AS_TARGET);
 194   // Post the result (the bitmap) back to the callback.
 195   BrowserThread::PostTask(
 196       BrowserThread::UI,
 197       FROM_HERE,
 198       base::Bind(&CallbackInvocationAdapter, callback, context, thumbnail));
 199 }
 200
 201 ContentBasedThumbnailingAlgorithm::~ContentBasedThumbnailingAlgorithm() {
 202 }
 203
 204 //  static
 205 gfx::Rect ContentBasedThumbnailingAlgorithm::GetClippingRect(
 206     const gfx::Size& source_size,
 207     const gfx::Size& thumbnail_size,
 208     gfx::Size* target_size,
 209     ClipResult* clip_result) {
 210   // Compute and return the clipping rectagle of the source image and the
 211   // size of the target bitmap which will be used for the further processing.
 212   // This function in 'general case' is trivial (don't clip, halve the source)
 213   // but it is needed for handling edge cases (source smaller than the target
 214   // thumbnail size).
 215   DCHECK(target_size);
 216   DCHECK(clip_result);
 217   gfx::Rect clipping_rect;
 218   if (source_size.width() < thumbnail_size.width() ||
 219       source_size.height() < thumbnail_size.height()) {
 220     clipping_rect = gfx::Rect(thumbnail_size);
 221     *target_size = thumbnail_size;
 222     *clip_result = CLIP_RESULT_SOURCE_IS_SMALLER;
 223   } else if (source_size.width() < thumbnail_size.width() * 4 ||
 224              source_size.height() < thumbnail_size.height() * 4) {
 225     clipping_rect = gfx::Rect(source_size);
 226     *target_size = source_size;
 227     *clip_result = CLIP_RESULT_SOURCE_SAME_AS_TARGET;
 228   } else {
 229     clipping_rect = gfx::Rect(source_size);
 230     target_size->SetSize(source_size.width() / 2, source_size.height() / 2);
 231     *clip_result = CLIP_RESULT_NOT_CLIPPED;
 232   }
 233
 234   return clipping_rect;
 235 }
 236
 237 }  // namespace thumbnails