1 // Copyright (c) 2009 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 #pragma once 8 9 #include <string> 10 #include "base/time.h" 11 12 // A set of metadata about a Thumbnail. 13 struct ThumbnailScore { 14 // Initializes the ThumbnailScore to the absolute worst possible values 15 // except for time, which is set to Now(), and redirect_hops_from_dest which 16 // is set to 0. 17 ThumbnailScore(); 18 19 // Builds a ThumbnailScore with the passed in values, and sets the 20 // thumbnail generation time to Now(). 21 ThumbnailScore(double score, bool clipping, bool top); 22 23 // Builds a ThumbnailScore with the passed in values. 24 ThumbnailScore(double score, bool clipping, bool top, 25 const base::Time& time); 26 ~ThumbnailScore(); 27 28 // Tests for equivalence between two ThumbnailScore objects. 29 bool Equals(const ThumbnailScore& rhs) const; 30 31 // Returns string representation of this object. 32 std::string ToString() const; 33 34 // How "boring" a thumbnail is. The boring score is the 0,1 ranged 35 // percentage of pixels that are the most common luma. Higher boring 36 // scores indicate that a higher percentage of a bitmap are all the 37 // same brightness (most likely the same color). 38 double boring_score; 39 40 // Whether the thumbnail was taken with height greater then 41 // width. In cases where we don't have |good_clipping|, the 42 // thumbnails are either clipped from the horizontal center of the 43 // window, or are otherwise weirdly stretched. 44 bool good_clipping; 45 46 // Whether this thumbnail was taken while the renderer was 47 // displaying the top of the page. Most pages are more recognizable 48 // by their headers then by a set of random text half way down the 49 // page; i.e. most MediaWiki sites would be indistinguishable by 50 // thumbnails with |at_top| set to false. 51 bool at_top; 52 53 // Record the time when a thumbnail was taken. This is used to make 54 // sure thumbnails are kept fresh. 55 base::Time time_at_snapshot; 56 57 // The number of hops from the final destination page that this thumbnail was 58 // taken at. When a thumbnail is taken, this will always be the redirect 59 // destination (value of 0). 60 // 61 // For the most visited view, we'll sometimes get thumbnails for URLs in the 62 // middle of a redirect chain. In this case, the top sites component will set 63 // this value so the distance from the destination can be taken into account 64 // by the comparison function. 65 // 66 // If "http://google.com/" redirected to "http://www.google.com/", then 67 // a thumbnail for the first would have a redirect hop of 1, and the second 68 // would have a redirect hop of 0. 69 int redirect_hops_from_dest; 70 71 // How bad a thumbnail needs to be before we completely ignore it. 72 static const double kThumbnailMaximumBoringness; 73 74 // We consider a thumbnail interesting enough if the boring score is 75 // lower than this. 76 static const double kThumbnailInterestingEnoughBoringness; 77 78 // Time before we take a worse thumbnail (subject to 79 // kThumbnailMaximumBoringness) over what's currently in the database 80 // for freshness. 81 static const base::TimeDelta kUpdateThumbnailTime; 82 83 // Penalty of how much more boring a thumbnail should be per hour. 84 static const double kThumbnailDegradePerHour; 85 86 // Checks whether we should consider updating a new thumbnail based on 87 // this score. For instance, we don't have to update a new thumbnail 88 // if the current thumbnail is new and interesting enough. 89 bool ShouldConsiderUpdating(); 90 }; 91 92 // Checks whether we should replace one thumbnail with another. 93 bool ShouldReplaceThumbnailWith(const ThumbnailScore& current, 94 const ThumbnailScore& replacement); 95 96 #endif // CHROME_COMMON_THUMBNAIL_SCORE_H_ 97