Always select best favicon bitmap

components/favicon/core/favicon_selector.h

+// Copyright (c) 2017 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 COMPONENTS_FAVICON_CORE_FAVICON_SELECTOR_H_
+#define COMPONENTS_FAVICON_CORE_FAVICON_SELECTOR_H_
+
+#include <list>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/optional.h"
+#include "components/favicon/core/favicon_url.h"
+#include "ui/gfx/image/image_skia.h"
+
+namespace favicon {
+
+// Represents a queue contaning favicon bitmaps, sorted by descending score.
+// Candidates can be dequeued one by one and the result of processing candidates
+// can be fed back to the queue, such that it keeps track of the best candidate
+// found so far.
+class FaviconSelector {
+ public:
+  // Used to track a candidate favicon bitmap.
+  struct Candidate {
+    // Builds a scored candidate by selecting the best bitmap size.
+    static Candidate FromFaviconURL(const favicon::FaviconURL& favicon_url,
+                                    int target_pixel_size);
+
+    GURL icon_url;
+    favicon_base::IconType icon_type;
+    float score;
+  };
+
+  struct BestCandidate {
+    Candidate candidate;
+    gfx::Size original_size;
+    SkBitmap bitmap;
+  };
+
+  // Defines the goals or ideal pixel size that a particular
+  // FaviconSelector is looking for.
+  class TargetSizeSpec {
+   public:
+    static TargetSizeSpec ForLargest();
+    // Returns largest pixel sizes first.
+    static std::vector<TargetSizeSpec> For16x16Dips();
+
+    TargetSizeSpec(const TargetSizeSpec&);
+    ~TargetSizeSpec();
+
+    TargetSizeSpec(TargetSizeSpec&&);
+    TargetSizeSpec& operator=(TargetSizeSpec&&);
+
+    // Returns the target pixel size.
+    int pixel_size() const { return pixel_size_; }
+
+    // Returns the target scale factor.
+    float scale_factor() const { return scale_factor_; }
+
+    // Returns whether the spec is requiring the best-matching bitmap only.
+    // TODO(mastiz): Rename this?
+    bool WantsBestBitmapOnly() const;
+
+    // Checks if |bitmap_results| contains a bitmap satistying this spec.
+    bool HasSatisfyingResult(
+        const std::vector<favicon_base::FaviconRawBitmapResult>& bitmap_results)
+        const;
+
+    // Scores and sorts the entries in |favicon_urls|, best icon size matches
+    // first. Pruning means discarding all but the best bitmap per candidate.
+    // Returns the sorted, scored and pruned candidate list.
+    std::list<Candidate> SortAndPruneCandidates(
+        const std::vector<favicon::FaviconURL>& favicon_urls) const;
+
+   private:
+    TargetSizeSpec();
+
+    int pixel_size_;
+    float scale_factor_;
+
+    // If true, FaviconHandler will resample candidates whenever needed to
+    // ensure that bitmaps for all |pixel_sizes| are produced.
+    bool ensure_exact_size_;
+  };
+
+  // Convenience function to construct multiple selectors. |target_size_specs|
+  // must be in descending pixel size order.
+  static std::vector<FaviconSelector> BuildMultiple(
+      const std::vector<TargetSizeSpec>& target_size_specs,
+      const std::vector<favicon::FaviconURL>& candidates);
+
+  // |candidates| must be non-empty.
+  FaviconSelector(const TargetSizeSpec& target_size_spec,
+                  const std::vector<favicon::FaviconURL>& candidates);
+  ~FaviconSelector();
+  FaviconSelector(FaviconSelector&&);
+  FaviconSelector& operator=(FaviconSelector&&);
+
+  const TargetSizeSpec& target_size_spec() const { return target_size_spec_; }
+
+  // Returns the next candidate to be processed, or an empty value if no
+  // further work is demanded, although clients are allowed to feed in new
+  // downloads via ProcessDownloadedImage().
+  base::Optional<Candidate> DequeueCandidate();
+
+  // Returns the current candidate without dequeueing it.
+  const Candidate* CurrentCandidate() const;
+
+  // Feeds in the bitmaps of a downloaded image, which will be compared against
+  // the best one processed so far. |bitmaps| and |original_sizes| must have the
+  // same size. Returns true if |icon_url| was chosen as the best one so far.
+  bool ProcessDownloadedImage(const GURL& icon_url,
+                              favicon_base::IconType icon_type,
+                              const std::vector<SkBitmap>& bitmaps,
+                              const std::vector<gfx::Size>& original_sizes);
+
+  // Returns the best-matching bitmap downloaded/processed so far, if any.
+  const base::Optional<BestCandidate>& BestBitmap() const {
+    return best_candidate_;
+  }
+
+ private:
+  // Returns whether a good enough bitmap was found (i.e. no further work
+  // demanded by this selector, although callers are allowed to process and feed
+  // in more processed downloads)
+  bool IsSatisfied() const;
+
+  // Desired icon size.
+  class TargetSizeSpec target_size_spec_;
+
+  // The prioritized favicon candidates from the page. There cannot be
+  // multiple candidates for the same icon URL.
+  std::list<Candidate> pending_candidates_;
+
+  // Best bitmap we've seen so far, if any.
+  base::Optional<BestCandidate> best_candidate_;
+
+  DISALLOW_COPY_AND_ASSIGN(FaviconSelector);
+};
+
+}  // namespace favicon
+
+#endif  // COMPONENTS_FAVICON_CORE_FAVICON_SELECTOR_H_