chromium/third_party/blink/renderer/core/editing/granularity_strategy.h

// Copyright 2015 The Chromium Authors
// 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_EDITING_GRANULARITY_STRATEGY_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_EDITING_GRANULARITY_STRATEGY_H_

#include "third_party/blink/renderer/core/editing/forward.h"
#include "third_party/blink/renderer/core/editing/selection_strategy.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "ui/gfx/geometry/vector2d.h"

namespace gfx {
class Point;
}

namespace blink {

class LocalFrame;

enum class TextGranularity;

class GranularityStrategy { … };

// Always uses character granularity.
class CharacterGranularityStrategy final : public GranularityStrategy { … };

// "Expand by word, shrink by character" selection strategy.
// Uses character granularity when selection is shrinking. If the selection is
// expanding, granularity doesn't change until a word boundary is passed, after
// which the granularity switches to "word".
// In word granularity, the word is not selected until the extent point passes
// the middle of the word.
//
// The "offset" feature:
// The offset is the horizontal distance between the extent point (passed in
// updateExtent) and the end of the selection. In character granularity the
// offset is typically zero or near zero, however in word granularity it can be
// significant. When the offset is positive and the extent point moved to the
// left, the offset is preserved, i.e. the selection tracks the extent point
// with the constant offset. When the offset is positive and the extent point
// is moved to the right, the offset gets reduced. Selection will not grow
// until the offset is reduced all the way to zero.
//
// This behavior is best illustrated by an example:
//
// ^ marks base, | marks extent point, > marks selection end:
// Lorem ip^sum|> dolor sit amet, consectetur
//
// Move extent over the middle of "dolor". Granularity should change to word
// granularity and the selection end should jump to the end of the word.
// Lorem ip^sum dolo|r> sit amet, consectetur
//
// Move extent back one character. Granularity changes to "character". The
// selection end should move back one character as well. Note an offset between
// the extent and the selection end.
// Lorem ip^sum dol|o>r sit amet, consectetur
//
// Move extent forward one character. The offset is reduced to 0. Selection end
// doesn't change.
// Lorem ip^sum dolo|>r sit amet, consectetur
//
// Move forward one character. End moves with extent in character granularity.
// Lorem ip^sum dolor|> sit amet, consectetur
class DirectionGranularityStrategy final : public GranularityStrategy { … };

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_EDITING_GRANULARITY_STRATEGY_H_