Only load theme images for the scale factors that use them

chrome/browser/themes/browser_theme_pack.cc

Index: chrome/browser/themes/browser_theme_pack.cc
diff --git a/chrome/browser/themes/browser_theme_pack.cc b/chrome/browser/themes/browser_theme_pack.cc
index 3a8fb68df6d7987446647d55572ff96063c37d1f..ff1c56ba77ef7f89155f439c643a4763349f0c46 100644
--- a/chrome/browser/themes/browser_theme_pack.cc
+++ b/chrome/browser/themes/browser_theme_pack.cc
@@ -480,6 +480,127 @@ class ThemeImageSource: public gfx::ImageSkiaSource {
   DISALLOW_COPY_AND_ASSIGN(ThemeImageSource);
 };
 
+// An ImageSkiaSouce that delays decoding PNG data into bitmaps until needed
+// and, if necessary, generates bitmaps for scale factors for which no PNG was
+// provided. The first PNG will be used to compute the DIP size and will
+// therefore be decoded when added. Once a PNG is decoded the resulting bitmap
+// is stored for later use.
+class ThemeImagePngSource : public gfx::ImageSkiaSource {
+ public:
+  ThemeImagePngSource() {}

[pkotwicz, 2013/06/14 18:23:05]

Ideally we should not even cache the PNG data for the unused scale factors. You
should be able to do this by passing a weak ptr to BrowserThemePack and the
idr_id (BrowserThemePack does not support weak ptrs so you will have to make it
do so). - There may be a good way of splitting up BrowserThemePack to avoid the
nastiness of it being both ref counted and support weak ptrs but I cannot think
of one right now.

You should be able to use
ImageSkia(ImageSkiaSource* source, ui::ScaleFactor scale_factor);
in BrowserThemePack::GetImageNamed().

+
+  void AddPng(scoped_refptr<base::RefCountedMemory> png_memory,
+              ui::ScaleFactor scale_factor) {
+    png_map_[scale_factor] = png_memory;
+    if (bitmap_map_.empty())
+      init(png_memory, scale_factor);
+  }
+
+  gfx::Size size() const { return dip_size_; }
+
+ private:
+  void init(scoped_refptr<base::RefCountedMemory> png_memory,
+            ui::ScaleFactor scale_factor) {
+    SkBitmap bitmap;
+    if (!gfx::PNGCodec::Decode(png_memory->front(),
+                               png_memory->size(),
+                               &bitmap)) {
+      NOTREACHED();
+      return;
+    }
+    bitmap_map_[scale_factor] = bitmap;
+    dip_size_ = gfx::Size(
+        static_cast<int>(bitmap.width() /
+                         ui::GetScaleFactorScale(scale_factor)),
+        static_cast<int>(bitmap.height() /
+                          ui::GetScaleFactorScale(scale_factor)));
+  }
+
+  virtual gfx::ImageSkiaRep GetImageForScale(
+      ui::ScaleFactor scale_factor) OVERRIDE {
+    // Look up the scale factor in the bitmap map. If found, use the bitmap and
+    // return it.
+    BitmapMap::const_iterator exact_bitmap = bitmap_map_.find(scale_factor);
+    if (exact_bitmap != bitmap_map_.end()) {
+      return gfx::ImageSkiaRep(exact_bitmap->second, scale_factor);
+    }
+
+    // Look up the scale factor in the png map. If found, decode it,
+    // store the result in the bitmap map and return it.
+    PngMap::const_iterator exact_png = png_map_.find(scale_factor);
+    if (exact_png != png_map_.end()) {
+      SkBitmap bitmap;
+      if (!gfx::PNGCodec::Decode(exact_png->second->front(),
+                                 exact_png->second->size(),
+                                 &bitmap)) {
+        NOTREACHED();
+        return gfx::ImageSkiaRep(SkBitmap(), scale_factor);
+      }
+      bitmap_map_[scale_factor] = bitmap;
+      return gfx::ImageSkiaRep(bitmap, scale_factor);
+    }
+
+    // No exact match was found, find the scale factor with highest scale.
+    PngMap::const_iterator available_png = png_map_.end();
+    for (PngMap::const_iterator it = png_map_.begin(); it != png_map_.end();
+         ++it) {
+      if (available_png == png_map_.end() ||
+          (ui::GetScaleFactorScale(it->first) >
+           ui::GetScaleFactorScale(available_png->first))) {
+        available_png = it;
+      }
+    }
+    if (available_png == png_map_.end()) {
+      NOTREACHED();
+      return gfx::ImageSkiaRep(SkBitmap(), scale_factor);
+    }
+
+    // Look up the found scale factor in the bitmap map. If not found, decode
+    // the corresponding png and store the result in bitmap map.
+    BitmapMap::const_iterator available_bitmap =
+        bitmap_map_.find(available_png->first);
+    if (available_bitmap == bitmap_map_.end()) {
+      SkBitmap bitmap;
+      if (!gfx::PNGCodec::Decode(available_png->second->front(),
+                                 available_png->second->size(),
+                                 &bitmap)) {
+        NOTREACHED();
+        return gfx::ImageSkiaRep(SkBitmap(), scale_factor);
+      }
+      bitmap_map_[available_png->first] = bitmap;
+      available_bitmap = bitmap_map_.find(available_png->first);
+    }
+
+    // Use available bitmap to create bitmap for desired scale factor by
+    // scaling, store the result in the bitmap map and return it.
+    gfx::Size scaled_size = gfx::ToCeiledSize(
+        gfx::ScaleSize(gfx::Size(available_bitmap->second.width(),
+                                 available_bitmap->second.height()),
+                       ui::GetScaleFactorScale(scale_factor) /
+                       ui::GetScaleFactorScale(available_bitmap->first)));
+    SkBitmap scaled_bitmap;
+    scaled_bitmap.setConfig(SkBitmap::kARGB_8888_Config,
+                            scaled_size.width(),
+                            scaled_size.height());
+    if (!scaled_bitmap.allocPixels())
+      SK_CRASH();
+    scaled_bitmap.eraseARGB(0, 0, 0, 0);
+    SkCanvas canvas(scaled_bitmap);
+    SkRect scaled_bounds = RectToSkRect(gfx::Rect(scaled_size));
+    canvas.drawBitmapRect(available_bitmap->second, NULL, scaled_bounds);
+    bitmap_map_[scale_factor] = scaled_bitmap;
+    return gfx::ImageSkiaRep(scaled_bitmap, scale_factor);
+  }
+
+ private:
+  typedef std::map<ui::ScaleFactor,
+                   scoped_refptr<base::RefCountedMemory> > PngMap;
+  typedef std::map<ui::ScaleFactor, SkBitmap> BitmapMap;
+  PngMap png_map_;
+  BitmapMap bitmap_map_;
+  gfx::Size dip_size_;
+};
+
 class TabBackgroundImageSource: public gfx::CanvasImageSource {
  public:
   TabBackgroundImageSource(const gfx::ImageSkia& image_to_tint,
@@ -749,34 +870,34 @@ gfx::Image BrowserThemePack::GetImageNamed(int idr_id) {
   if (image_iter != images_on_ui_thread_.end())
     return image_iter->second;
 
-  // TODO(pkotwicz): Do something better than loading the bitmaps
-  // for all the scale factors associated with |idr_id|.
-  // See crbug.com/243831.
-  gfx::ImageSkia source_image_skia;
-  for (size_t i = 0; i < scale_factors_.size(); ++i) {
-    scoped_refptr<base::RefCountedMemory> memory =
-        GetRawData(idr_id, scale_factors_[i]);
-    if (memory.get()) {
-      // Decode the PNG.
-      SkBitmap bitmap;
-      if (!gfx::PNGCodec::Decode(memory->front(), memory->size(),
-                                 &bitmap)) {
-        NOTREACHED() << "Unable to decode theme image resource " << idr_id
-                     << " from saved DataPack.";
+  ThemeImagePngSource* png_source = NULL;
+  for (int pass = 0; pass < 2; ++pass) {
+    // Two passes: In the first pass, we process only scale factor 100%, if
+    // available, and in the second pass all other scale factors. The reason is
+    // that the first png added, determines the DIP size.
+    for (size_t i = 0; i < scale_factors_.size(); ++i) {
+      if ((pass == 0 && scale_factors_[i] != ui::SCALE_FACTOR_100P) ||
+          (pass == 1 && scale_factors_[i] == ui::SCALE_FACTOR_100P)) {
         continue;
       }
-      source_image_skia.AddRepresentation(
-          gfx::ImageSkiaRep(bitmap, scale_factors_[i]));
+      scoped_refptr<base::RefCountedMemory> memory =
+          GetRawData(idr_id, scale_factors_[i]);
+      if (memory.get()) {
+        if (!png_source)
+          png_source = new ThemeImagePngSource;
+        png_source->AddPng(memory, scale_factors_[i]);
+      }
     }
   }
 
-  if (!source_image_skia.isNull()) {
-    ThemeImageSource* source = new ThemeImageSource(source_image_skia);
-    gfx::ImageSkia image_skia(source, source_image_skia.size());
+  if (png_source) {
+    // |image_skia| owns png_source.
+    gfx::ImageSkia image_skia(png_source, png_source->size());
     gfx::Image ret = gfx::Image(image_skia);
     images_on_ui_thread_[prs_id] = ret;
     return ret;
   }
+
   return gfx::Image();
 }