1 // Copyright 2014 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 COMPONENTS_HISTORY_CORE_COMMON_THUMBNAIL_SCORE_H_ 6 #define COMPONENTS_HISTORY_CORE_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, const base::Time& time); 24 ~ThumbnailScore(); 25 26 // Tests for equivalence between two ThumbnailScore objects. 27 bool Equals(const ThumbnailScore& rhs) const; 28 29 // Returns string representation of this object. 30 std::string ToString() const; 31 32 // How "boring" a thumbnail is. The boring score is the 0,1 ranged 33 // percentage of pixels that are the most common luma. Higher boring 34 // scores indicate that a higher percentage of a bitmap are all the 35 // same brightness (most likely the same color). 36 // 37 // The score should only be used for comparing two thumbnails taken from 38 // the same page to see which one is more boring/interesting. The 39 // absolute score is not suitable for judging whether the thumbnail is 40 // actually boring or not. For instance, www.google.com is very 41 // succinct, so the boring score can be as high as 0.9, depending on the 42 // browser window size. 43 double boring_score; 44 45 // Whether the thumbnail was taken with height greater than 46 // width or width greater than height and the aspect ratio less than 47 // kTooWideAspectRatio. In cases where we don't have |good_clipping|, 48 // the thumbnails are either clipped from the horizontal center of the 49 // window, or are otherwise weirdly stretched. 50 bool good_clipping; 51 52 // Whether this thumbnail was taken while the renderer was 53 // displaying the top of the page. Most pages are more recognizable 54 // by their headers then by a set of random text half way down the 55 // page; i.e. most MediaWiki sites would be indistinguishable by 56 // thumbnails with |at_top| set to false. 57 bool at_top; 58 59 // Whether this thumbnail was taken after load was completed. 60 // Thumbnails taken while page loading may only contain partial 61 // contents. 62 bool load_completed; 63 64 // Record the time when a thumbnail was taken. This is used to make 65 // sure thumbnails are kept fresh. 66 base::Time time_at_snapshot; 67 68 // The number of hops from the final destination page that this thumbnail was 69 // taken at. When a thumbnail is taken, this will always be the redirect 70 // destination (value of 0). 71 // 72 // For the most visited view, we'll sometimes get thumbnails for URLs in the 73 // middle of a redirect chain. In this case, the top sites component will set 74 // this value so the distance from the destination can be taken into account 75 // by the comparison function. 76 // 77 // If "http://google.com/" redirected to "http://www.google.com/", then 78 // a thumbnail for the first would have a redirect hop of 1, and the second 79 // would have a redirect hop of 0. 80 int redirect_hops_from_dest; 81 82 // How bad a thumbnail needs to be before we completely ignore it. 83 static const double kThumbnailMaximumBoringness; 84 85 // We consider a thumbnail interesting enough if the boring score is 86 // lower than this. 87 static const double kThumbnailInterestingEnoughBoringness; 88 89 // Time before we take a worse thumbnail (subject to 90 // kThumbnailMaximumBoringness) over what's currently in the database 91 // for freshness. 92 static const int64 kUpdateThumbnailTimeDays; 93 94 // Penalty of how much more boring a thumbnail should be per hour. 95 static const double kThumbnailDegradePerHour; 96 97 // If a thumbnail is taken with the aspect ratio greater than or equal to 98 // this value, |good_clipping| is to false. 99 static const double kTooWideAspectRatio; 100 101 // Checks whether we should consider updating a new thumbnail based on 102 // this score. For instance, we don't have to update a new thumbnail 103 // if the current thumbnail is new and interesting enough. 104 bool ShouldConsiderUpdating(); 105 }; 106 107 // Checks whether we should replace one thumbnail with another. 108 bool ShouldReplaceThumbnailWith(const ThumbnailScore& current, 109 const ThumbnailScore& replacement); 110 111 #endif // COMPONENTS_HISTORY_CORE_COMMON_THUMBNAIL_SCORE_H_ 112