chrome/browser/thumbnails/simple_thumbnail_crop.cc

   1 // Copyright (c) 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/simple_thumbnail_crop.h"
   6
   7 #include "base/metrics/histogram.h"
   8 #include "content/public/browser/browser_thread.h"
   9 #include "skia/ext/platform_canvas.h"
  10 #include "ui/base/layout.h"
  11 #include "ui/gfx/color_utils.h"
  12 #include "ui/gfx/geometry/size_conversions.h"
  13 #include "ui/gfx/image/image_skia.h"
  14 #include "ui/gfx/screen.h"
  15 #include "ui/gfx/scrollbar_size.h"
  16 #include "ui/gfx/skbitmap_operations.h"
  17
  18 namespace {
  19 static const char kThumbnailHistogramName[] = "Thumbnail.ComputeMS";
  20 }
  21
  22 namespace thumbnails {
  23
  24 SimpleThumbnailCrop::SimpleThumbnailCrop(const gfx::Size& target_size)
  25     : target_size_(target_size) {
  26   DCHECK(!target_size.IsEmpty());
  27 }
  28
  29 ClipResult SimpleThumbnailCrop::GetCanvasCopyInfo(const gfx::Size& source_size,
  30                                                   ui::ScaleFactor scale_factor,
  31                                                   gfx::Rect* clipping_rect,
  32                                                   gfx::Size* copy_size) const {
  33   DCHECK(!source_size.IsEmpty());
  34   ClipResult clip_result = thumbnails::CLIP_RESULT_NOT_CLIPPED;
  35   *clipping_rect = GetClippingRect(source_size, target_size_, &clip_result);
  36   *copy_size = GetCopySizeForThumbnail(scale_factor, target_size_);
  37   return clip_result;
  38 }
  39
  40 void SimpleThumbnailCrop::ProcessBitmap(
  41     scoped_refptr<ThumbnailingContext> context,
  42     const ConsumerCallback& callback,
  43     const SkBitmap& bitmap) {
  44   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  45   if (bitmap.isNull() || bitmap.empty())
  46     return;
  47
  48   SkBitmap thumbnail = CreateThumbnail(
  49       bitmap,
  50       ComputeTargetSizeAtMaximumScale(target_size_),
  51       &context->clip_result);
  52
  53   context->score.boring_score = color_utils::CalculateBoringScore(thumbnail);
  54   context->score.good_clipping =
  55       (context->clip_result == CLIP_RESULT_WIDER_THAN_TALL ||
  56        context->clip_result == CLIP_RESULT_TALLER_THAN_WIDE ||
  57        context->clip_result == CLIP_RESULT_NOT_CLIPPED);
  58
  59   callback.Run(*context.get(), thumbnail);
  60 }
  61
  62 SkBitmap SimpleThumbnailCrop::GetClippedBitmap(const SkBitmap& bitmap,
  63                                                int desired_width,
  64                                                int desired_height,
  65                                                ClipResult* clip_result) {
  66   gfx::Rect clipping_rect =
  67       GetClippingRect(gfx::Size(bitmap.width(), bitmap.height()),
  68                       gfx::Size(desired_width, desired_height),
  69                       clip_result);
  70   SkIRect src_rect = { clipping_rect.x(), clipping_rect.y(),
  71                        clipping_rect.right(), clipping_rect.bottom() };
  72   SkBitmap clipped_bitmap;
  73   bitmap.extractSubset(&clipped_bitmap, src_rect);
  74   return clipped_bitmap;
  75 }
  76
  77 // RenderWidgetHost::CopyFromBackingStore can be costly especially when it is
  78 // necessary to read back the web contents image data from GPU. As the cost is
  79 // roughly proportional to the number of the copied pixels, the size of the
  80 // copied pixels should be as small as possible.
  81 // static
  82 gfx::Size SimpleThumbnailCrop::GetCopySizeForThumbnail(
  83     ui::ScaleFactor scale_factor,
  84     const gfx::Size& thumbnail_size) {
  85   // The copy size returned is the pixel equivalent of |thumbnail_size|, which
  86   // is in DIPs.
  87   if (scale_factor == ui::SCALE_FACTOR_100P) {
  88     // In the case of 1x devices, we get a thumbnail twice as big and reduce
  89     // it at serve time to improve quality.
  90     scale_factor = ui::SCALE_FACTOR_200P;
  91   }
  92   float scale = GetScaleForScaleFactor(scale_factor);
  93   return gfx::ToFlooredSize(gfx::ScaleSize(thumbnail_size, scale));
  94 }
  95
  96 gfx::Rect SimpleThumbnailCrop::GetClippingRect(const gfx::Size& source_size,
  97                                                const gfx::Size& desired_size,
  98                                                ClipResult* clip_result) {
  99   DCHECK(clip_result);
 100
 101   float desired_aspect =
 102       static_cast<float>(desired_size.width()) / desired_size.height();
 103
 104   // Get the clipping rect so that we can preserve the aspect ratio while
 105   // filling the destination.
 106   gfx::Rect clipping_rect;
 107   if (source_size.width() < desired_size.width() ||
 108       source_size.height() < desired_size.height()) {
 109     // Source image is smaller: we clip the part of source image within the
 110     // dest rect, and then stretch it to fill the dest rect. We don't respect
 111     // the aspect ratio in this case.
 112     clipping_rect = gfx::Rect(desired_size);
 113     *clip_result = thumbnails::CLIP_RESULT_SOURCE_IS_SMALLER;
 114   } else {
 115     float src_aspect =
 116         static_cast<float>(source_size.width()) / source_size.height();
 117     if (src_aspect > desired_aspect) {
 118       // Wider than tall, clip horizontally: we center the smaller
 119       // thumbnail in the wider screen.
 120       int new_width = static_cast<int>(source_size.height() * desired_aspect);
 121       int x_offset = (source_size.width() - new_width) / 2;
 122       clipping_rect.SetRect(x_offset, 0, new_width, source_size.height());
 123       *clip_result = (src_aspect >= ThumbnailScore::kTooWideAspectRatio) ?
 124           thumbnails::CLIP_RESULT_MUCH_WIDER_THAN_TALL :
 125           thumbnails::CLIP_RESULT_WIDER_THAN_TALL;
 126     } else if (src_aspect < desired_aspect) {
 127       clipping_rect =
 128           gfx::Rect(source_size.width(), source_size.width() / desired_aspect);
 129       *clip_result = thumbnails::CLIP_RESULT_TALLER_THAN_WIDE;
 130     } else {
 131       clipping_rect = gfx::Rect(source_size);
 132       *clip_result = thumbnails::CLIP_RESULT_NOT_CLIPPED;
 133     }
 134   }
 135   return clipping_rect;
 136 }
 137
 138 // static
 139 gfx::Size SimpleThumbnailCrop::ComputeTargetSizeAtMaximumScale(
 140     const gfx::Size& given_size) {
 141   // TODO(mazda|oshima): Update thumbnail when the max scale factor changes.
 142   // crbug.com/159157.
 143   float max_scale_factor = gfx::ImageSkia::GetMaxSupportedScale();
 144   return gfx::ToFlooredSize(gfx::ScaleSize(given_size, max_scale_factor));
 145 }
 146
 147 SimpleThumbnailCrop::~SimpleThumbnailCrop() {
 148 }
 149
 150 // Creates a downsampled thumbnail from the given bitmap.
 151 // store. The returned bitmap will be isNull if there was an error creating it.
 152 SkBitmap SimpleThumbnailCrop::CreateThumbnail(const SkBitmap& bitmap,
 153                                               const gfx::Size& desired_size,
 154                                               ClipResult* clip_result) {
 155   base::TimeTicks begin_compute_thumbnail = base::TimeTicks::Now();
 156
 157   SkBitmap clipped_bitmap;
 158   if (*clip_result == thumbnails::CLIP_RESULT_UNPROCESSED) {
 159     // Clip the pixels that will commonly hold a scrollbar, which looks bad in
 160     // thumbnails.
 161     int scrollbar_size = gfx::scrollbar_size();
 162     SkIRect scrollbarless_rect =
 163         { 0, 0,
 164           std::max(1, bitmap.width() - scrollbar_size),
 165           std::max(1, bitmap.height() - scrollbar_size) };
 166     SkBitmap bmp;
 167     bitmap.extractSubset(&bmp, scrollbarless_rect);
 168
 169     clipped_bitmap = GetClippedBitmap(
 170         bmp, desired_size.width(), desired_size.height(), clip_result);
 171   } else {
 172     clipped_bitmap = bitmap;
 173   }
 174
 175   // Need to resize it to the size we want, so downsample until it's
 176   // close, and let the caller make it the exact size if desired.
 177   SkBitmap result = SkBitmapOperations::DownsampleByTwoUntilSize(
 178       clipped_bitmap, desired_size.width(), desired_size.height());
 179 #if !defined(USE_AURA)
 180   // This is a bit subtle. SkBitmaps are refcounted, but the magic
 181   // ones in PlatformCanvas can't be assigned to SkBitmap with proper
 182   // refcounting.  If the bitmap doesn't change, then the downsampler
 183   // will return the input bitmap, which will be the reference to the
 184   // weird PlatformCanvas one insetad of a regular one. To get a
 185   // regular refcounted bitmap, we need to copy it.
 186   //
 187   // On Aura, the PlatformCanvas is platform-independent and does not have
 188   // any native platform resources that can't be refounted, so this issue does
 189   // not occur.
 190   //
 191   // Note that GetClippedBitmap() does extractSubset() but it won't copy
 192   // the pixels, hence we check result size == clipped_bitmap size here.
 193   if (clipped_bitmap.width() == result.width() &&
 194       clipped_bitmap.height() == result.height())
 195     clipped_bitmap.copyTo(&result, kN32_SkColorType);
 196 #endif
 197
 198   LOCAL_HISTOGRAM_TIMES(kThumbnailHistogramName,
 199                         base::TimeTicks::Now() - begin_compute_thumbnail);
 200   return result;
 201 }
 202
 203 } // namespace thumbnails