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// Copyright 2023 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_PLATFORM_FONTS_SHAPING_HAN_KERNING_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_SHAPING_HAN_KERNING_H_
#include "base/gtest_prod_util.h"
#include "third_party/blink/renderer/platform/fonts/shaping/font_features.h"
#include "third_party/blink/renderer/platform/platform_export.h"
#include "third_party/blink/renderer/platform/text/han_kerning_char_type.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "third_party/blink/renderer/platform/wtf/forward.h"
#include "third_party/blink/renderer/platform/wtf/text/wtf_string.h"
namespace blink {
class FontDescription;
class LayoutLocale;
class SimpleFontData;
//
// This class implements the behavior necessary for the CSS `text-spacing-trim`
// property[1].
//
// In short, it's similar to kerning to be applied to Han-derived scripts such
// as Chinese or Japanese. In OpenType, this behavior is defined as the
// `chws`[2] feature.
//
// It's different from the regular kerning that the kerning pairs and amounts
// are computable. There are tools to add the features to existing fonts[3][4].
//
// This class complements the OpenType feature in that:
// 1. Handles the desired beahvior at the font boundaries. OpenType features
// can't handle kerning at font boundaries by design.
// 2. Emulates the behavior when the font doesn't have the `chws` feature.
//
// [1]: https://drafts.csswg.org/css-text-4/#text-spacing-trim-property
// [2]:
// https://learn.microsoft.com/en-us/typography/opentype/spec/features_ae#tag-chws
// [3]: https://github.com/googlefonts/chws_tool
// [4]: https://github.com/kojiishi/east_asian_spacing
//
class PLATFORM_EXPORT HanKerning {
STACK_ALLOCATED();
public:
struct Options {
bool is_horizontal = true;
bool is_line_start = false;
bool apply_start = false;
bool apply_end = false;
};
HanKerning(const String& text,
wtf_size_t start,
wtf_size_t end,
const SimpleFontData& font_data,
const FontDescription& font_description,
Options options,
FontFeatures* features) {
if (text.Is8Bit()) {
return;
}
Compute(text, start, end, font_data, font_description, options, features);
}
~HanKerning() {
if (features_) [[unlikely]] {
ResetFeatures();
}
}
const Vector<unsigned, 32>& UnsafeToBreakBefore() const {
return unsafe_to_break_before_;
}
using CharType = HanKerningCharType;
// Data retrieved from fonts for `HanKerning`.
struct PLATFORM_EXPORT FontData {
FontData() = default;
FontData(const SimpleFontData& font,
const LayoutLocale& locale,
bool is_horizontal);
// True if this font has `halt` (or `vhal` in vertical.)
// https://learn.microsoft.com/en-us/typography/opentype/spec/features_fj#tag-halt
bool has_alternate_spacing = false;
// True if this font has `chws` (or `vchw` in vertical.)
// https://learn.microsoft.com/en-us/typography/opentype/spec/features_ae#tag-chws
bool has_contextual_spacing = false;
// True if quote characters are fullwdith. In a common convention, they are
// proportional (Latin) in Japanese, but fullwidth in Chinese.
bool is_quote_fullwidth = false;
// `CharType` for "fullwidth dot punctuation."
// https://drafts.csswg.org/css-text-4/#text-spacing-classes
CharType type_for_dot = CharType::kOther;
// `CharType` for "fullwidth colon punctuation."
// Type for colon and semicolon are separated, to support the Adobe's
// convention for vertical flow, which rotates Japanese colon, but doesn't
// rotate semicolon.
CharType type_for_colon = CharType::kOther;
CharType type_for_semicolon = CharType::kOther;
};
private:
FRIEND_TEST_ALL_PREFIXES(HanKerningTest, MayApply);
static CharType GetCharType(UChar ch, const FontData& font_data);
static bool MayApply(StringView text);
static bool ShouldKern(CharType type, CharType last_type);
static bool ShouldKernLast(CharType type, CharType last_type);
void Compute(const String& text,
wtf_size_t start,
wtf_size_t end,
const SimpleFontData& font_data,
const FontDescription& font_description,
Options options,
FontFeatures* features);
void ResetFeatures();
FontFeatures* features_ = nullptr;
wtf_size_t num_features_before_;
Vector<unsigned, 32> unsafe_to_break_before_;
};
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_SHAPING_HAN_KERNING_H_
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