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// Copyright 2018 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 THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_JANK_REGION_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_JANK_REGION_H_
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/platform/geometry/int_rect.h"
#include "third_party/blink/renderer/platform/wtf/allocator.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"
namespace blink {
// Represents a per-frame jank region for JankTracker. Only used when the
// JankTrackingSweepLine feature is enabled.
//
// This class uses a sweep line algorithm to compute the area in O(n log n) time
// where n is the number of rects recorded by AddRect. For complex jank regions,
// this is more efficient than using blink::Region, which is worst-case O(n^2)
// from the repeated calls to Region::Unite.
//
// The high-level approach is described here:
// http://jeffe.cs.illinois.edu/open/klee.html
//
// The sweep line moves from left to right. (TODO: compare performance against a
// top-to-bottom sweep.)
//
// The sweep line's current intersection with the jank region ("active length")
// is tracked by a segment tree, similar to what is described at:
// https://en.wikipedia.org/wiki/Segment_tree
//
// There are some subtleties to the segment tree, which are described by the
// comments in the implementation.
class CORE_EXPORT JankRegion {
DISALLOW_NEW();
public:
void AddRect(const IntRect& rect) {
if (!rect.IsEmpty())
rects_.push_back(rect);
}
const Vector<IntRect>& GetRects() const { return rects_; }
bool IsEmpty() const { return rects_.IsEmpty(); }
void Reset() { rects_.clear(); }
uint64_t Area() const;
private:
Vector<IntRect> rects_;
};
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_JANK_REGION_H_
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