chrome/common/thumbnail_score.h

   1 // Copyright (c) 2012 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 #ifndef CHROME_COMMON_THUMBNAIL_SCORE_H_
   6 #define CHROME_COMMON_THUMBNAIL_SCORE_H_
   7
   8 #include <string>
   9 #include "base/time/time.h"
  10
  11 // A set of metadata about a Thumbnail.
  12 struct ThumbnailScore {
  13   // Initializes the ThumbnailScore to the absolute worst possible values
  14   // except for time, which is set to Now(), and redirect_hops_from_dest which
  15   // is set to 0.
  16   ThumbnailScore();
  17
  18   // Builds a ThumbnailScore with the passed in values, and sets the
  19   // thumbnail generation time to Now().
  20   ThumbnailScore(double score, bool clipping, bool top);
  21
  22   // Builds a ThumbnailScore with the passed in values.
  23   ThumbnailScore(double score, bool clipping, bool top,
  24                  const base::Time& time);
  25   ~ThumbnailScore();
  26
  27   // Tests for equivalence between two ThumbnailScore objects.
  28   bool Equals(const ThumbnailScore& rhs) const;
  29
  30   // Returns string representation of this object.
  31   std::string ToString() const;
  32
  33   // How "boring" a thumbnail is. The boring score is the 0,1 ranged
  34   // percentage of pixels that are the most common luma. Higher boring
  35   // scores indicate that a higher percentage of a bitmap are all the
  36   // same brightness (most likely the same color).
  37   //
  38   // The score should only be used for comparing two thumbnails taken from
  39   // the same page to see which one is more boring/interesting. The
  40   // absolute score is not suitable for judging whether the thumbnail is
  41   // actually boring or not. For instance, www.google.com is very
  42   // succinct, so the boring score can be as high as 0.9, depending on the
  43   // browser window size.
  44   double boring_score;
  45
  46   // Whether the thumbnail was taken with height greater than
  47   // width or width greater than height and the aspect ratio less than
  48   // kTooWideAspectRatio. In cases where we don't have |good_clipping|,
  49   // the thumbnails are either clipped from the horizontal center of the
  50   // window, or are otherwise weirdly stretched.
  51   bool good_clipping;
  52
  53   // Whether this thumbnail was taken while the renderer was
  54   // displaying the top of the page. Most pages are more recognizable
  55   // by their headers then by a set of random text half way down the
  56   // page; i.e. most MediaWiki sites would be indistinguishable by
  57   // thumbnails with |at_top| set to false.
  58   bool at_top;
  59
  60   // Whether this thumbnail was taken after load was completed.
  61   // Thumbnails taken while page loading may only contain partial
  62   // contents.
  63   bool load_completed;
  64
  65   // Record the time when a thumbnail was taken. This is used to make
  66   // sure thumbnails are kept fresh.
  67   base::Time time_at_snapshot;
  68
  69   // The number of hops from the final destination page that this thumbnail was
  70   // taken at. When a thumbnail is taken, this will always be the redirect
  71   // destination (value of 0).
  72   //
  73   // For the most visited view, we'll sometimes get thumbnails for URLs in the
  74   // middle of a redirect chain. In this case, the top sites component will set
  75   // this value so the distance from the destination can be taken into account
  76   // by the comparison function.
  77   //
  78   // If "http://google.com/" redirected to "http://www.google.com/", then
  79   // a thumbnail for the first would have a redirect hop of 1, and the second
  80   // would have a redirect hop of 0.
  81   int redirect_hops_from_dest;
  82
  83   // How bad a thumbnail needs to be before we completely ignore it.
  84   static const double kThumbnailMaximumBoringness;
  85
  86   // We consider a thumbnail interesting enough if the boring score is
  87   // lower than this.
  88   static const double kThumbnailInterestingEnoughBoringness;
  89
  90   // Time before we take a worse thumbnail (subject to
  91   // kThumbnailMaximumBoringness) over what's currently in the database
  92   // for freshness.
  93   static const int64 kUpdateThumbnailTimeDays;
  94
  95   // Penalty of how much more boring a thumbnail should be per hour.
  96   static const double kThumbnailDegradePerHour;
  97
  98   // If a thumbnail is taken with the aspect ratio greater than or equal to
  99   // this value, |good_clipping| is to false.
 100   static const double kTooWideAspectRatio;
 101
 102   // Checks whether we should consider updating a new thumbnail based on
 103   // this score. For instance, we don't have to update a new thumbnail
 104   // if the current thumbnail is new and interesting enough.
 105   bool ShouldConsiderUpdating();
 106 };
 107
 108 // Checks whether we should replace one thumbnail with another.
 109 bool ShouldReplaceThumbnailWith(const ThumbnailScore& current,
 110                                 const ThumbnailScore& replacement);
 111
 112 #endif  // CHROME_COMMON_THUMBNAIL_SCORE_H_