chromium/cc/base/reverse_spiral_iterator.h

// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CC_BASE_REVERSE_SPIRAL_ITERATOR_H_
#define CC_BASE_REVERSE_SPIRAL_ITERATOR_H_

#include "cc/base/base_export.h"
#include "cc/base/index_rect.h"

namespace cc {

// The spiral iterator which iterates in reverse direction based on directions
// around the center rect in the given region. If the center rect is at index
// (2, 2), reverse spiral iterator gives following sequence on iterating.
//
//    x 0   1   2   3   4
//  y ┌───┬───┬───┬───┬───┐
//  0 │  9│ 10│ 11│ 12│ 13│
//    ├───┼───┼───┼───┼───┤
//  1 │  8│ 21│ 22│ 23│ 14│
//    ├───┼───┼───┼───┼───┤
//  2 │  7│ 20│  *│ 24│ 15│
//    ├───┼───┼───┼───┼───┤
//  3 │  6│ 19│ 18│ 17│ 16│
//    ├───┼───┼───┼───┼───┤
//  4 │  5│  4│  3│  2│  1│
//    └───┴───┴───┴───┴───┘
class CC_BASE_EXPORT ReverseSpiralIterator { … };

}  // namespace cc

#endif  // CC_BASE_REVERSE_SPIRAL_ITERATOR_H_