Added new class gfx::ImageFamily.

ui/gfx/image/image_family.h

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_GFX_IMAGE_IMAGE_FAMILY_H_
+#define UI_GFX_IMAGE_IMAGE_FAMILY_H_
+
+#include <iterator>
+#include <map>
+#include <utility>
+
+#include "ui/base/ui_export.h"
+#include "ui/gfx/image/image.h"
+
+namespace gfx {
+class ImageSkia;
+
+// A collection of images at different sizes. The images should be different
+// representations of the same basic concept (for example, an icon) at various
+// sizes and (optionally) aspect ratios. A method is provided for finding the
+// most appropriate image to fit in a given rectangle.
+class UI_EXPORT ImageFamily {
+ public:
+  // Type for iterating over all images in the family, in order.
+  // Dereferencing this iterator returns a gfx::Image.
+  class const_iterator;
+
+  ImageFamily();
+  ~ImageFamily();
+
+  // Gets an iterator to the first image.
+  const_iterator begin() const { return const_iterator(map_.begin()); }
+  // Gets an iterator to one after the last image.
+  const_iterator end() const { return const_iterator(map_.end()); }
+
+  // Determines whether the image family has no images in it.
+  bool empty() const { return map_.empty(); }
+
+  // Removes all images from the family.
+  void clear() { return map_.clear(); }
+
+  // Adds an image to the family. If another image is already present at the
+  // same size, it will be overwritten.
+  void Add(const gfx::Image& image);
+
+  // Adds an image to the family. If another image is already present at the
+  // same size, it will be overwritten.
+  void Add(const gfx::ImageSkia& image_skia);
+
+  // Gets the best image to use in a rectangle of |width|x|height|.
+  // Gets an image at the same aspect ratio as |width|:|height|, if possible, or
+  // if not, the closest aspect ratio. Among images of that aspect ratio,
+  // returns the smallest image with both its width and height bigger or equal
+  // to the requested size. If none exists, returns the largest image of that
+  // aspect ratio. If there are no images in the family, returns NULL.
+  const gfx::Image* Get(int width, int height) const;
+
+  // An <aspect ratio, DIP width> pair.
+  // A 0x0 image has aspect ratio 1.0. 0xN and Nx0 images are treated as 0x0.
+  struct MapKey : std::pair<float, int> {
+    MapKey(float aspect, int width)
+        : std::pair<float, int>(aspect, width) {}
+
+    float aspect() const { return first; }
+
+    float width() const { return second; }
+  };
+
+  class const_iterator :

[pkotwicz, 2013/03/29 00:25:35]

Is there a way you can avoid creating a custom iterator?
It seems as if you are creating a custom iterator to make the iterator to |map_|
look like a vector iterator.

Would it make sense to have:
std::map<MapKey, size_t> map_; Where the value is an index into |images_|.
std::vector<gfx::Image> images_;

[Matt Giuca, 2013/03/30 00:54:14]

I know it's quite excessive and I feel bad about it, but I couldn't think of a
way.

Note that I originally wrote it to just return the map iterator, but then that
exposed the client to the implementation detail that it is using a map. At one
point I changed the type of the map key and realised that I was exposing the
client to volatility, so I decided to wrap it in an iterator that would just
expose what I needed.
I'd rather not do that, since then I need to manually make sure that the images
in the vector are in the correct order. Unless you think I should just have the
images iterate in their insertion order? That might be acceptable. Note that as
a side-effect, this would make it so that duplicate-sized images are no longer
removed, but they are not accessible in the map. This makes the interface to the
class more complicated, but maybe it is a good thing to preserve all of the
images. What do you think?

(I will wait for further comment by you and possibly rsesek before rewriting
this, because it's a big change to both the code and the interface.)

[pkotwicz, 2013/04/02 16:06:31]

Ok, I am for keeping the iterator.

I think that we should keep the current behavior where we remove duplicate sized
images.

+    std::iterator<std::bidirectional_iterator_tag, const gfx::Image> {
+   public:
+    const_iterator() {}
+
+    const_iterator& operator++() {
+      ++map_iterator_;
+      return *this;
+    }
+
+    const_iterator operator++(int /*unused*/) {
+      const_iterator result(*this);
+      ++(*this);
+      return result;
+    }
+
+    const_iterator& operator--() {
+      --map_iterator_;
+      return *this;
+    }
+
+    const_iterator operator--(int /*unused*/) {
+      const_iterator result(*this);
+      --(*this);
+      return result;
+    }
+
+    bool operator==(const const_iterator& other) const {
+      return map_iterator_ == other.map_iterator_;
+    }
+
+    bool operator!=(const const_iterator& other) const {
+      return map_iterator_ != other.map_iterator_;
+    }
+
+    const gfx::Image& operator*() const {
+      return map_iterator_->second;
+    }
+
+    const gfx::Image* operator->() const {
+      return &**this;
+    }
+
+   private:
+    explicit const_iterator(
+        const std::map<MapKey, gfx::Image>::const_iterator& other);
+
+    std::map<MapKey, gfx::Image>::const_iterator map_iterator_;
+
+    friend class ImageFamily;
+  };
+
+ private:
+  // Find the closest aspect ratio in the map to |desired_aspect|.
+  // Ties are broken by the thinner aspect.
+  // map_ must not be empty.
+  float GetClosestAspect(float desired_aspect) const;
+
+  // Gets an image with aspect ratio |aspect|, at the best size for |width|.
+  // Returns the smallest image of aspect ratio |aspect| with its width bigger
+  // or equal to |width|. If none exists, returns the largest image of aspect
+  // ratio |aspect|. Behavior is undefined if there is not at least one image in
+  // map_ of aspect ratio |aspect|.
+  const gfx::Image* GetWithExactAspect(float aspect, int width) const;
+
+  // Map from (aspect ratio, width) to image.
+  std::map<MapKey, gfx::Image> map_;
+};
+
+}  // namespace gfx
+
+#endif  // UI_GFX_IMAGE_IMAGE_FAMILY_H_