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// Copyright 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "chrome/common/thumbnail_score.h"
#include "base/logging.h"
const TimeDelta ThumbnailScore::kUpdateThumbnailTime = TimeDelta::FromDays(1);
const double ThumbnailScore::kThumbnailMaximumBoringness = 0.94;
const double ThumbnailScore::kThumbnailDegradePerHour = 0.01;
// Calculates a numeric score from traits about where a snapshot was
// taken. We store the raw components in the database because I'm sure
// this will evolve and I don't want to break databases.
static int GetThumbnailType(bool good_clipping, bool at_top) {
if (good_clipping && at_top) {
return 0;
} else if (good_clipping && !at_top) {
return 1;
} else if (!good_clipping && at_top) {
return 2;
} else if (!good_clipping && !at_top) {
return 3;
} else {
NOTREACHED();
return -1;
}
}
ThumbnailScore::ThumbnailScore()
: boring_score(1.0),
good_clipping(false),
at_top(false),
time_at_snapshot(Time::Now()) {
}
ThumbnailScore::ThumbnailScore(double score, bool clipping, bool top)
: boring_score(score),
good_clipping(clipping),
at_top(top),
time_at_snapshot(Time::Now()) {
}
ThumbnailScore::ThumbnailScore(double score, bool clipping, bool top,
const Time& time)
: boring_score(score),
good_clipping(clipping),
at_top(top),
time_at_snapshot(time) {
}
ThumbnailScore::~ThumbnailScore() {
}
bool ThumbnailScore::Equals(const ThumbnailScore& rhs) const {
// When testing equality we use ToTimeT() because that's the value
// stuck in the SQL database, so we need to test equivalence with
// that lower resolution.
return boring_score == rhs.boring_score &&
good_clipping == rhs.good_clipping &&
at_top == rhs.at_top &&
time_at_snapshot.ToTimeT() == rhs.time_at_snapshot.ToTimeT();
}
bool ShouldReplaceThumbnailWith(const ThumbnailScore& current,
const ThumbnailScore& replacement) {
int current_type = GetThumbnailType(current.good_clipping, current.at_top);
int replacement_type = GetThumbnailType(replacement.good_clipping,
replacement.at_top);
if (replacement_type < current_type) {
// If we have a better class of thumbnail, add it if it meets
// certain minimum boringness.
return replacement.boring_score <
ThumbnailScore::kThumbnailMaximumBoringness;
} else if (replacement_type == current_type) {
if (replacement.boring_score < current.boring_score) {
// If we have a thumbnail that's straight up less boring, use it.
return true;
}
// Slowly degrade the boring score of the current thumbnail
// so we take thumbnails which are slightly less good:
TimeDelta since_last_thumbnail =
replacement.time_at_snapshot - current.time_at_snapshot;
double degraded_boring_score = current.boring_score +
(since_last_thumbnail.InHours() *
ThumbnailScore::kThumbnailDegradePerHour);
if (degraded_boring_score > ThumbnailScore::kThumbnailMaximumBoringness)
degraded_boring_score = ThumbnailScore::kThumbnailMaximumBoringness;
if (replacement.boring_score < degraded_boring_score)
return true;
}
// If the current thumbnail doesn't meet basic boringness
// requirements, but the replacement does, always replace the
// current one even if we're using a worse thumbnail type.
return current.boring_score >= ThumbnailScore::kThumbnailMaximumBoringness &&
replacement.boring_score < ThumbnailScore::kThumbnailMaximumBoringness;
}
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