Loading/Creating images for mutiple scale factors on the fly

ui/gfx/image/image_skia.cc

Index: ui/gfx/image/image_skia.cc
diff --git a/ui/gfx/image/image_skia.cc b/ui/gfx/image/image_skia.cc
index e5fb8e3c617ce18b81fb4c00aea2918c07cd49d2..3d8acf135fb0b991938abca1660b94229af48897 100644
--- a/ui/gfx/image/image_skia.cc
+++ b/ui/gfx/image/image_skia.cc
@@ -4,30 +4,117 @@
 
 #include "ui/gfx/image/image_skia.h"
 
-#include <limits>
+#include <algorithm>
 #include <cmath>
+#include <limits>
 
 #include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "ui/gfx/image/image_skia_source.h"
 #include "ui/gfx/size.h"
 #include "ui/gfx/skia_util.h"
 
 namespace gfx {
+namespace {
+
+// static
+gfx::ImageSkiaRep& NullImageRep() {
+  CR_DEFINE_STATIC_LOCAL(ImageSkiaRep, null_image_rep, ());
+  return null_image_rep;
+}
+
+}  // namespace
 
 namespace internal {
+namespace {
+
+class Matcher {
+ public:
+  explicit Matcher(ui::ScaleFactor scale_factor) : scale_factor_(scale_factor) {
+  }
+
+  bool operator()(const ImageSkiaRep& rep) const {
+    return rep.scale_factor() == scale_factor_;
+  }
+
+ private:
+  ui::ScaleFactor scale_factor_;
+};
+
+}  // namespace
 
 // A helper class such that ImageSkia can be cheaply copied. ImageSkia holds a
 // refptr instance of ImageSkiaStorage, which in turn holds all of ImageSkia's
 // information.
 class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
  public:
-  ImageSkiaStorage() {
+  ImageSkiaStorage(ImageSkiaSource* source, const gfx::Size& size)
+      : source_(source),
+        size_(size) {
   }
 
   std::vector<gfx::ImageSkiaRep>& image_reps() { return image_reps_; }
 
-  void set_size(const gfx::Size& size) { size_ = size; }
   const gfx::Size& size() const { return size_; }
 
+  // Returns the iterator of the image rep whose density best matches
+  // |scale_factor|. If the image for the |scale_factor| doesn't exist
+  // in the storage and |storage| is set, it fetches new image by calling
+  // |ImageSkiaSource::GetImageForScale|. If the source returns the
+  // image with different scale factor (if the image doesn't exist in
+  // resource, for example), it will fallback to closest image rep.
+  std::vector<ImageSkiaRep>::iterator FindRepresentation(
+      ui::ScaleFactor scale_factor, bool fetch_new_image) const {
+    ImageSkiaStorage* non_const = const_cast<ImageSkiaStorage*>(this);
+
+    float scale = ui::GetScaleFactorScale(scale_factor);
+    ImageSkia::ImageSkiaReps::iterator closest_iter =
+        non_const->image_reps().end();
+    ImageSkia::ImageSkiaReps::iterator exact_iter =
+        non_const->image_reps().end();
+    float smallest_diff = std::numeric_limits<float>::max();
+    for (ImageSkia::ImageSkiaReps::iterator it =
+             non_const->image_reps().begin();
+         it < image_reps_.end(); ++it) {
+      if (it->GetScale() == scale) {
+        // found exact match
+        fetch_new_image = false;
+        if (it->is_null())
+          continue;
+        exact_iter = it;
+        break;
+      }
+      float diff = std::abs(it->GetScale() - scale);
+      if (diff < smallest_diff && !it->is_null()) {
+        closest_iter = it;
+        smallest_diff = diff;
+      }
+    }
+
+    if (fetch_new_image && source_.get()) {
+      ImageSkiaRep image = source_->GetImageForScale(scale_factor);
+
+      // If the source returned the new image, store it.
+      if (!image.is_null() &&
+          std::find_if(image_reps_.begin(), image_reps_.end(),
+                       Matcher(image.scale_factor())) == image_reps_.end()) {
+        non_const->image_reps().push_back(image);
+      }
+
+      // If the result image's scale factor isn't same as the expected
+      // scale factor, create null ImageSkiaRep with the |scale_factor|
+      // so that the next lookup will fallback to the closest scale.
+      if (image.is_null() || image.scale_factor() != scale_factor) {
+        non_const->image_reps().push_back(
+            ImageSkiaRep(SkBitmap(), scale_factor));
+      }
+
+      // image_reps_ must have the exact much now, so find again.
+      return FindRepresentation(scale_factor, false);
+    }
+    return exact_iter != image_reps_.end() ? exact_iter : closest_iter;
+  }
+
  private:
   ~ImageSkiaStorage() {
   }
@@ -35,8 +122,10 @@ class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
   // Vector of bitmaps and their associated scale factor.
   std::vector<gfx::ImageSkiaRep> image_reps_;
 
+  scoped_ptr<ImageSkiaSource> source_;
+
   // Size of the image in DIP.
-  gfx::Size size_;
+  const gfx::Size size_;
 
   friend class base::RefCounted<ImageSkiaStorage>;
 };
@@ -46,6 +135,11 @@ class ImageSkiaStorage : public base::RefCounted<ImageSkiaStorage> {
 ImageSkia::ImageSkia() : storage_(NULL) {
 }
 
+ImageSkia::ImageSkia(ImageSkiaSource* source, const gfx::Size& size)
+    : storage_(new internal::ImageSkiaStorage(source, size)) {
+  DCHECK(source);
+}
+
 ImageSkia::ImageSkia(const SkBitmap& bitmap) {
   Init(ImageSkiaRep(bitmap));
 }
@@ -103,7 +197,8 @@ void ImageSkia::RemoveRepresentation(ui::ScaleFactor scale_factor) {
     return;
 
   ImageSkiaReps& image_reps = storage_->image_reps();
-  ImageSkiaReps::iterator it = FindRepresentation(scale_factor);
+  ImageSkiaReps::iterator it =
+      storage_->FindRepresentation(scale_factor, false);
   if (it != image_reps.end() && it->scale_factor() == scale_factor)
     image_reps.erase(it);
 }
@@ -112,7 +207,8 @@ bool ImageSkia::HasRepresentation(ui::ScaleFactor scale_factor) {
   if (isNull())
     return false;
 
-  ImageSkiaReps::iterator it = FindRepresentation(scale_factor);
+  ImageSkiaReps::iterator it =
+      storage_->FindRepresentation(scale_factor, false);
   return (it != storage_->image_reps().end() &&
           it->scale_factor() == scale_factor);
 }
@@ -122,7 +218,7 @@ const ImageSkiaRep& ImageSkia::GetRepresentation(
   if (isNull())
     return NullImageRep();
 
-  ImageSkiaReps::iterator it = FindRepresentation(scale_factor);
+  ImageSkiaReps::iterator it = storage_->FindRepresentation(scale_factor, true);
   if (it == storage_->image_reps().end())
     return NullImageRep();
 
@@ -137,6 +233,10 @@ int ImageSkia::width() const {
   return isNull() ? 0 : storage_->size().width();
 }
 
+gfx::Size ImageSkia::size() const {
+  return gfx::Size(width(), height());
+}
+
 int ImageSkia::height() const {
   return isNull() ? 0 : storage_->size().height();
 }
@@ -191,36 +291,9 @@ void ImageSkia::Init(const ImageSkiaRep& image_rep) {
     storage_ = NULL;
     return;
   }
-  storage_ = new internal::ImageSkiaStorage();
-  storage_->set_size(gfx::Size(image_rep.GetWidth(), image_rep.GetHeight()));
+  storage_ = new internal::ImageSkiaStorage(
+      NULL, gfx::Size(image_rep.GetWidth(), image_rep.GetHeight()));
   storage_->image_reps().push_back(image_rep);
 }
 
-// static
-ImageSkiaRep& ImageSkia::NullImageRep() {
-  CR_DEFINE_STATIC_LOCAL(ImageSkiaRep, null_image_rep, ());
-  return null_image_rep;
-}
-
-std::vector<ImageSkiaRep>::iterator ImageSkia::FindRepresentation(
-    ui::ScaleFactor scale_factor) const {
-  DCHECK(!isNull());
-
-  float scale = ui::GetScaleFactorScale(scale_factor);
-  ImageSkiaReps& image_reps = storage_->image_reps();
-  ImageSkiaReps::iterator closest_iter = image_reps.end();
-  float smallest_diff = std::numeric_limits<float>::max();
-  for (ImageSkiaReps::iterator it = image_reps.begin();
-       it < image_reps.end();
-       ++it) {
-    float diff = std::abs(it->GetScale() - scale);
-    if (diff < smallest_diff) {
-      closest_iter = it;
-      smallest_diff = diff;
-    }
-  }
-
-  return closest_iter;
-}
-
 }  // namespace gfx