Source/WebCore/platform/graphics/harfbuzz/ComplexTextControllerHarfBuzz.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2017 Apple Inc. All rights reserved.
  * Copyright (C) 2017 Igalia S.L.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. 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.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS 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 APPLE INC. OR ITS 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 "config.h"
 #include "ComplexTextController.h"

 #include "CairoUtilities.h"
 #include "FontCascade.h"
 #include "HbUniquePtr.h"
 #include "SurrogatePairAwareTextIterator.h"
 #include <hb-ft.h>
 #include <hb-icu.h>
 #include <hb-ot.h>

 #if ENABLE(VARIATION_FONTS)
 #include FT_MULTIPLE_MASTERS_H
 #endif

 namespace WebCore {

 static inline float harfBuzzPositionToFloat(hb_position_t value)
 {
     return static_cast<float>(value) / (1 << 16);
 }

 static inline hb_position_t floatToHarfBuzzPosition(float value)
 {
     return static_cast<hb_position_t>(value * (1 << 16));
 }

 static inline hb_position_t doubleToHarfBuzzPosition(double value)
 {
     return static_cast<hb_position_t>(value * (1 << 16));
 }

 static hb_font_funcs_t* harfBuzzFontFunctions()
 {
     static hb_font_funcs_t* fontFunctions = nullptr;

     // We don't set callback functions which we can't support.
     // Harfbuzz will use the fallback implementation if they aren't set.
     if (!fontFunctions) {
         fontFunctions = hb_font_funcs_create();
 #if HB_VERSION_ATLEAST(1, 2, 3)
         hb_font_funcs_set_nominal_glyph_func(fontFunctions, [](hb_font_t*, void* context, hb_codepoint_t unicode, hb_codepoint_t* glyph, void*) -> hb_bool_t {
             auto& font = *static_cast<Font*>(context);
             *glyph = font.glyphForCharacter(unicode);
             return !!*glyph;
         }, nullptr, nullptr);

         hb_font_funcs_set_variation_glyph_func(fontFunctions, [](hb_font_t*, void* context, hb_codepoint_t unicode, hb_codepoint_t variation, hb_codepoint_t* glyph, void*) -> hb_bool_t {
             auto& font = *static_cast<Font*>(context);
             auto* scaledFont = font.platformData().scaledFont();
             ASSERT(scaledFont);

             CairoFtFaceLocker cairoFtFaceLocker(scaledFont);
             if (FT_Face ftFace = cairoFtFaceLocker.ftFace()) {
                 *glyph = FT_Face_GetCharVariantIndex(ftFace, unicode, variation);
                 return true;
             }
             return false;
             }, nullptr, nullptr);
 #else
         hb_font_funcs_set_glyph_func(fontFunctions, [](hb_font_t*, void* context, hb_codepoint_t unicode, hb_codepoint_t, hb_codepoint_t* glyph, void*) -> hb_bool_t {
             auto& font = *static_cast<Font*>(context);
             *glyph = font.glyphForCharacter(unicode);
             return !!*glyph;
         }, nullptr, nullptr);
 #endif
         hb_font_funcs_set_glyph_h_advance_func(fontFunctions, [](hb_font_t*, void* context, hb_codepoint_t point, void*) -> hb_bool_t {
             auto& font = *static_cast<Font*>(context);
             auto* scaledFont = font.platformData().scaledFont();
             ASSERT(scaledFont);

             cairo_text_extents_t glyphExtents;
             cairo_glyph_t glyph = { point, 0, 0 };
             cairo_scaled_font_glyph_extents(scaledFont, &glyph, 1, &glyphExtents);

             bool hasVerticalGlyphs = glyphExtents.y_advance;
             return doubleToHarfBuzzPosition(hasVerticalGlyphs ? -glyphExtents.y_advance : glyphExtents.x_advance);
         }, nullptr, nullptr);

         hb_font_funcs_set_glyph_h_origin_func(fontFunctions, [](hb_font_t*, void*, hb_codepoint_t, hb_position_t*, hb_position_t*, void*) -> hb_bool_t {
             // Just return true, following the way that Harfbuzz-FreeType implementation does.
             return true;
         }, nullptr, nullptr);

         hb_font_funcs_set_glyph_extents_func(fontFunctions, [](hb_font_t*, void* context, hb_codepoint_t point, hb_glyph_extents_t* extents, void*) -> hb_bool_t {
             auto& font = *static_cast<Font*>(context);
             auto* scaledFont = font.platformData().scaledFont();
             ASSERT(scaledFont);

             cairo_text_extents_t glyphExtents;
             cairo_glyph_t glyph = { point, 0, 0 };
             cairo_scaled_font_glyph_extents(scaledFont, &glyph, 1, &glyphExtents);

             bool hasVerticalGlyphs = glyphExtents.y_advance;
             extents->x_bearing = doubleToHarfBuzzPosition(glyphExtents.x_bearing);
             extents->y_bearing = doubleToHarfBuzzPosition(hasVerticalGlyphs ? -glyphExtents.y_bearing : glyphExtents.y_bearing);
             extents->width = doubleToHarfBuzzPosition(hasVerticalGlyphs ? -glyphExtents.height : glyphExtents.width);
             extents->height = doubleToHarfBuzzPosition(hasVerticalGlyphs ? glyphExtents.width : glyphExtents.height);
             return true;
         }, nullptr, nullptr);

         hb_font_funcs_make_immutable(fontFunctions);
     }
     return fontFunctions;
 }

 ComplexTextController::ComplexTextRun::ComplexTextRun(hb_buffer_t* buffer, const Font& font, const UChar* characters, unsigned stringLocation, unsigned stringLength, unsigned indexBegin, unsigned indexEnd)
     : m_initialAdvance(0, 0)
     , m_font(font)
     , m_characters(characters)
     , m_stringLength(stringLength)
     , m_indexBegin(indexBegin)
     , m_indexEnd(indexEnd)
     , m_glyphCount(hb_buffer_get_length(buffer))
     , m_stringLocation(stringLocation)
     , m_isLTR(HB_DIRECTION_IS_FORWARD(hb_buffer_get_direction(buffer)))
 {
     if (!m_glyphCount)
         return;

     m_glyphs.grow(m_glyphCount);
     m_baseAdvances.grow(m_glyphCount);
     m_glyphOrigins.grow(m_glyphCount);
     m_coreTextIndices.grow(m_glyphCount);

     hb_glyph_info_t* glyphInfos = hb_buffer_get_glyph_infos(buffer, nullptr);
     hb_glyph_position_t* glyphPositions = hb_buffer_get_glyph_positions(buffer, nullptr);

     // HarfBuzz returns the shaping result in visual order. We don't need to flip for RTL.
     for (unsigned i = 0; i < m_glyphCount; ++i) {
         m_coreTextIndices[i] = glyphInfos[i].cluster;

         uint16_t glyph = glyphInfos[i].codepoint;
         if (m_font.isZeroWidthSpaceGlyph(glyph)) {
             m_glyphs[i] = glyph;
             m_baseAdvances[i] = { };
             m_glyphOrigins[i] = { };
             continue;
         }

         float offsetX = harfBuzzPositionToFloat(glyphPositions[i].x_offset);
         float offsetY = -harfBuzzPositionToFloat(glyphPositions[i].y_offset);
         float advanceX = harfBuzzPositionToFloat(glyphPositions[i].x_advance);
         float advanceY = harfBuzzPositionToFloat(glyphPositions[i].y_advance);

         m_glyphs[i] = glyph;
         m_baseAdvances[i] = { advanceX, advanceY };
         m_glyphOrigins[i] = { offsetX, offsetY };
     }
 }

 static const hb_tag_t s_vertTag = HB_TAG('v', 'e', 'r', 't');
 static const hb_tag_t s_vrt2Tag = HB_TAG('v', 'r', 't', '2');
 static const hb_tag_t s_kernTag = HB_TAG('k', 'e', 'r', 'n');
 static const unsigned s_hbEnd = static_cast<unsigned>(-1);

 static Vector<hb_feature_t, 4> fontFeatures(const FontCascade& font, FontOrientation orientation)
 {
     Vector<hb_feature_t, 4> features;

     if (orientation == FontOrientation::Vertical) {
         features.append({ s_vertTag, 1, 0, s_hbEnd });
         features.append({ s_vrt2Tag, 1, 0, s_hbEnd });
     }

     hb_feature_t kerning = { s_kernTag, 0, 0, s_hbEnd };
     if (font.enableKerning())
         kerning.value = 1;
     features.append(WTFMove(kerning));

     for (auto& feature : font.fontDescription().featureSettings()) {
         auto& tag = feature.tag();
         features.append({ HB_TAG(tag[0], tag[1], tag[2], tag[3]), static_cast<uint32_t>(feature.value()), 0, s_hbEnd });
     }

     return features;
 }

 static Optional<UScriptCode> characterScript(UChar32 character)
 {
     UErrorCode errorCode = U_ZERO_ERROR;
     UScriptCode script = uscript_getScript(character, &errorCode);
     if (U_FAILURE(errorCode))
         return WTF::nullopt;
     return script;
 }

 struct HBRun {
     unsigned startIndex;
     unsigned endIndex;
     UScriptCode script;
 };

 static Optional<HBRun> findNextRun(const UChar* characters, unsigned length, unsigned offset)
 {
     SurrogatePairAwareTextIterator textIterator(characters + offset, offset, length, length);
     UChar32 character;
     unsigned clusterLength = 0;
     if (!textIterator.consume(character, clusterLength))
         return WTF::nullopt;

     auto currentScript = characterScript(character);
     if (!currentScript)
         return WTF::nullopt;

     unsigned startIndex = offset;
     for (textIterator.advance(clusterLength); textIterator.consume(character, clusterLength); textIterator.advance(clusterLength)) {
         if (FontCascade::treatAsZeroWidthSpace(character))
             continue;

         auto nextScript = characterScript(character);
         if (!nextScript)
             return WTF::nullopt;

         // §5.1 Handling Characters with the Common Script Property.
         // Programs must resolve any of the special Script property values, such as Common,
         // based on the context of the surrounding characters. A simple heuristic uses the
         // script of the preceding character, which works well in many cases.
         // http://www.unicode.org/reports/tr24/#Common.
         //
         // FIXME: cover all other cases mentioned in the spec (ie. brackets or quotation marks).
         // https://bugs.webkit.org/show_bug.cgi?id=177003.
         //
         // If next script is inherited or common, keep using the current script.
         if (nextScript == USCRIPT_INHERITED || nextScript == USCRIPT_COMMON)
             continue;
         // If current script is inherited or common, set the next script as current.
         if (currentScript == USCRIPT_INHERITED || currentScript == USCRIPT_COMMON) {
             currentScript = nextScript;
             continue;
         }

         if (currentScript != nextScript && !uscript_hasScript(character, currentScript.value()))
             return Optional<HBRun>({ startIndex, textIterator.currentIndex(), currentScript.value() });
     }

     return Optional<HBRun>({ startIndex, textIterator.currentIndex(), currentScript.value() });
 }

 static hb_script_t findScriptForVerticalGlyphSubstitution(hb_face_t* face)
 {
     static const unsigned maxCount = 32;

     unsigned scriptCount = maxCount;
     hb_tag_t scriptTags[maxCount];
     hb_ot_layout_table_get_script_tags(face, HB_OT_TAG_GSUB, 0, &scriptCount, scriptTags);
     for (unsigned scriptIndex = 0; scriptIndex < scriptCount; ++scriptIndex) {
         unsigned languageCount = maxCount;
         hb_tag_t languageTags[maxCount];
         hb_ot_layout_script_get_language_tags(face, HB_OT_TAG_GSUB, scriptIndex, 0, &languageCount, languageTags);
         for (unsigned languageIndex = 0; languageIndex < languageCount; ++languageIndex) {
             unsigned featureIndex;
             if (hb_ot_layout_language_find_feature(face, HB_OT_TAG_GSUB, scriptIndex, languageIndex, s_vertTag, &featureIndex)
                 || hb_ot_layout_language_find_feature(face, HB_OT_TAG_GSUB, scriptIndex, languageIndex, s_vrt2Tag, &featureIndex))
                 return hb_ot_tag_to_script(scriptTags[scriptIndex]);
         }
     }
     return HB_SCRIPT_INVALID;
 }

 void ComplexTextController::collectComplexTextRunsForCharacters(const UChar* characters, unsigned length, unsigned stringLocation, const Font* font)
 {
     if (!font) {
         // Create a run of missing glyphs from the primary font.
         m_complexTextRuns.append(ComplexTextRun::create(m_font.primaryFont(), characters, stringLocation, length, 0, length, m_run.ltr()));
         return;
     }

     Vector<HBRun> runList;
     unsigned offset = 0;
     while (offset < length) {
         auto run = findNextRun(characters, length, offset);
         if (!run)
             break;
         runList.append(run.value());
         offset = run->endIndex;
     }

     size_t runCount = runList.size();
     if (!runCount)
         return;

     const auto& fontPlatformData = font->platformData();
     auto* scaledFont = fontPlatformData.scaledFont();
     CairoFtFaceLocker cairoFtFaceLocker(scaledFont);
     FT_Face ftFace = cairoFtFaceLocker.ftFace();
     if (!ftFace)
         return;

     HbUniquePtr<hb_face_t> face(hb_ft_face_create_cached(ftFace));
     HbUniquePtr<hb_font_t> harfBuzzFont(hb_font_create(face.get()));
     hb_font_set_funcs(harfBuzzFont.get(), harfBuzzFontFunctions(), const_cast<Font*>(font), nullptr);
     const float size = fontPlatformData.size();
     if (floorf(size) == size)
         hb_font_set_ppem(harfBuzzFont.get(), size, size);
     int scale = floatToHarfBuzzPosition(size);
     hb_font_set_scale(harfBuzzFont.get(), scale, scale);

 #if ENABLE(VARIATION_FONTS)
     FT_MM_Var* ftMMVar;
     if (!FT_Get_MM_Var(ftFace, &ftMMVar)) {
         Vector<FT_Fixed, 4> coords;
         coords.resize(ftMMVar->num_axis);
         if (!FT_Get_Var_Design_Coordinates(ftFace, coords.size(), coords.data())) {
             Vector<hb_variation_t, 4> variations(coords.size());
             for (FT_UInt i = 0; i < ftMMVar->num_axis; ++i) {
                 variations[i].tag = ftMMVar->axis[i].tag;
                 variations[i].value = coords[i] / 65536.0;
             }
             hb_font_set_variations(harfBuzzFont.get(), variations.data(), variations.size());
         }
         FT_Done_MM_Var(ftFace->glyph->library, ftMMVar);
     }
 #endif

     hb_font_make_immutable(harfBuzzFont.get());

     auto features = fontFeatures(m_font, fontPlatformData.orientation());
     HbUniquePtr<hb_buffer_t> buffer(hb_buffer_create());
     if (fontPlatformData.orientation() == FontOrientation::Vertical)
         hb_buffer_set_script(buffer.get(), findScriptForVerticalGlyphSubstitution(face.get()));

     for (unsigned i = 0; i < runCount; ++i) {
         auto& run = runList[m_run.rtl() ? runCount - i - 1 : i];

         if (fontPlatformData.orientation() != FontOrientation::Vertical)
             hb_buffer_set_script(buffer.get(), hb_icu_script_to_script(run.script));
         if (!m_mayUseNaturalWritingDirection || m_run.directionalOverride())
             hb_buffer_set_direction(buffer.get(), m_run.rtl() ? HB_DIRECTION_RTL : HB_DIRECTION_LTR);
         else {
             // Leaving direction to HarfBuzz to guess is *really* bad, but will do for now.
             hb_buffer_guess_segment_properties(buffer.get());
         }
         hb_buffer_add_utf16(buffer.get(), reinterpret_cast<const uint16_t*>(characters), length, run.startIndex, run.endIndex - run.startIndex);

         hb_shape(harfBuzzFont.get(), buffer.get(), features.isEmpty() ? nullptr : features.data(), features.size());
         m_complexTextRuns.append(ComplexTextRun::create(buffer.get(), *font, characters, stringLocation, length, run.startIndex, run.endIndex));
         hb_buffer_reset(buffer.get());
     }
 }

 } // namespace WebCore
	/*
	* Copyright (C) 2017 Apple Inc. All rights reserved.
	* Copyright (C) 2017 Igalia S.L.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. 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.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS 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 APPLE INC. OR ITS 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 "config.h"
	#include "ComplexTextController.h"

	#include "CairoUtilities.h"
	#include "FontCascade.h"
	#include "HbUniquePtr.h"
	#include "SurrogatePairAwareTextIterator.h"
	#include <hb-ft.h>
	#include <hb-icu.h>
	#include <hb-ot.h>

	#if ENABLE(VARIATION_FONTS)
	#include FT_MULTIPLE_MASTERS_H
	#endif

	namespace WebCore {

	static inline float harfBuzzPositionToFloat(hb_position_t value)
	{
	return static_cast<float>(value) / (1 << 16);
	}

	static inline hb_position_t floatToHarfBuzzPosition(float value)
	{
	return static_cast<hb_position_t>(value * (1 << 16));
	}

	static inline hb_position_t doubleToHarfBuzzPosition(double value)
	{
	return static_cast<hb_position_t>(value * (1 << 16));
	}

	static hb_font_funcs_t* harfBuzzFontFunctions()
	{
	static hb_font_funcs_t* fontFunctions = nullptr;

	// We don't set callback functions which we can't support.
	// Harfbuzz will use the fallback implementation if they aren't set.
	if (!fontFunctions) {
	fontFunctions = hb_font_funcs_create();
	#if HB_VERSION_ATLEAST(1, 2, 3)
	hb_font_funcs_set_nominal_glyph_func(fontFunctions, [](hb_font_t, void context, hb_codepoint_t unicode, hb_codepoint_t* glyph, void*) -> hb_bool_t {
	auto& font = static_cast<Font>(context);
	*glyph = font.glyphForCharacter(unicode);
	return !!*glyph;
	}, nullptr, nullptr);

	hb_font_funcs_set_variation_glyph_func(fontFunctions, [](hb_font_t, void context, hb_codepoint_t unicode, hb_codepoint_t variation, hb_codepoint_t* glyph, void*) -> hb_bool_t {
	auto& font = static_cast<Font>(context);
	auto* scaledFont = font.platformData().scaledFont();
	ASSERT(scaledFont);

	CairoFtFaceLocker cairoFtFaceLocker(scaledFont);
	if (FT_Face ftFace = cairoFtFaceLocker.ftFace()) {
	*glyph = FT_Face_GetCharVariantIndex(ftFace, unicode, variation);
	return true;
	}
	return false;
	}, nullptr, nullptr);
	#else
	hb_font_funcs_set_glyph_func(fontFunctions, [](hb_font_t, void context, hb_codepoint_t unicode, hb_codepoint_t, hb_codepoint_t* glyph, void*) -> hb_bool_t {
	auto& font = static_cast<Font>(context);
	*glyph = font.glyphForCharacter(unicode);
	return !!*glyph;
	}, nullptr, nullptr);
	#endif
	hb_font_funcs_set_glyph_h_advance_func(fontFunctions, [](hb_font_t, void context, hb_codepoint_t point, void*) -> hb_bool_t {
	auto& font = static_cast<Font>(context);
	auto* scaledFont = font.platformData().scaledFont();
	ASSERT(scaledFont);

	cairo_text_extents_t glyphExtents;
	cairo_glyph_t glyph = { point, 0, 0 };
	cairo_scaled_font_glyph_extents(scaledFont, &glyph, 1, &glyphExtents);

	bool hasVerticalGlyphs = glyphExtents.y_advance;
	return doubleToHarfBuzzPosition(hasVerticalGlyphs ? -glyphExtents.y_advance : glyphExtents.x_advance);
	}, nullptr, nullptr);

	hb_font_funcs_set_glyph_h_origin_func(fontFunctions, [](hb_font_t, void, hb_codepoint_t, hb_position_t, hb_position_t, void*) -> hb_bool_t {
	// Just return true, following the way that Harfbuzz-FreeType implementation does.
	return true;
	}, nullptr, nullptr);

	hb_font_funcs_set_glyph_extents_func(fontFunctions, [](hb_font_t, void context, hb_codepoint_t point, hb_glyph_extents_t* extents, void*) -> hb_bool_t {
	auto& font = static_cast<Font>(context);
	auto* scaledFont = font.platformData().scaledFont();
	ASSERT(scaledFont);

	cairo_text_extents_t glyphExtents;
	cairo_glyph_t glyph = { point, 0, 0 };
	cairo_scaled_font_glyph_extents(scaledFont, &glyph, 1, &glyphExtents);

	bool hasVerticalGlyphs = glyphExtents.y_advance;
	extents->x_bearing = doubleToHarfBuzzPosition(glyphExtents.x_bearing);
	extents->y_bearing = doubleToHarfBuzzPosition(hasVerticalGlyphs ? -glyphExtents.y_bearing : glyphExtents.y_bearing);
	extents->width = doubleToHarfBuzzPosition(hasVerticalGlyphs ? -glyphExtents.height : glyphExtents.width);
	extents->height = doubleToHarfBuzzPosition(hasVerticalGlyphs ? glyphExtents.width : glyphExtents.height);
	return true;
	}, nullptr, nullptr);

	hb_font_funcs_make_immutable(fontFunctions);
	}
	return fontFunctions;
	}

	ComplexTextController::ComplexTextRun::ComplexTextRun(hb_buffer_t* buffer, const Font& font, const UChar* characters, unsigned stringLocation, unsigned stringLength, unsigned indexBegin, unsigned indexEnd)
	: m_initialAdvance(0, 0)
	, m_font(font)
	, m_characters(characters)
	, m_stringLength(stringLength)
	, m_indexBegin(indexBegin)
	, m_indexEnd(indexEnd)
	, m_glyphCount(hb_buffer_get_length(buffer))
	, m_stringLocation(stringLocation)
	, m_isLTR(HB_DIRECTION_IS_FORWARD(hb_buffer_get_direction(buffer)))
	{
	if (!m_glyphCount)
	return;

	m_glyphs.grow(m_glyphCount);
	m_baseAdvances.grow(m_glyphCount);
	m_glyphOrigins.grow(m_glyphCount);
	m_coreTextIndices.grow(m_glyphCount);

	hb_glyph_info_t* glyphInfos = hb_buffer_get_glyph_infos(buffer, nullptr);
	hb_glyph_position_t* glyphPositions = hb_buffer_get_glyph_positions(buffer, nullptr);

	// HarfBuzz returns the shaping result in visual order. We don't need to flip for RTL.
	for (unsigned i = 0; i < m_glyphCount; ++i) {
	m_coreTextIndices[i] = glyphInfos[i].cluster;

	uint16_t glyph = glyphInfos[i].codepoint;
	if (m_font.isZeroWidthSpaceGlyph(glyph)) {
	m_glyphs[i] = glyph;
	m_baseAdvances[i] = { };
	m_glyphOrigins[i] = { };
	continue;
	}

	float offsetX = harfBuzzPositionToFloat(glyphPositions[i].x_offset);
	float offsetY = -harfBuzzPositionToFloat(glyphPositions[i].y_offset);
	float advanceX = harfBuzzPositionToFloat(glyphPositions[i].x_advance);
	float advanceY = harfBuzzPositionToFloat(glyphPositions[i].y_advance);

	m_glyphs[i] = glyph;
	m_baseAdvances[i] = { advanceX, advanceY };
	m_glyphOrigins[i] = { offsetX, offsetY };
	}
	}

	static const hb_tag_t s_vertTag = HB_TAG('v', 'e', 'r', 't');
	static const hb_tag_t s_vrt2Tag = HB_TAG('v', 'r', 't', '2');
	static const hb_tag_t s_kernTag = HB_TAG('k', 'e', 'r', 'n');
	static const unsigned s_hbEnd = static_cast<unsigned>(-1);

	static Vector<hb_feature_t, 4> fontFeatures(const FontCascade& font, FontOrientation orientation)
	{
	Vector<hb_feature_t, 4> features;

	if (orientation == FontOrientation::Vertical) {
	features.append({ s_vertTag, 1, 0, s_hbEnd });
	features.append({ s_vrt2Tag, 1, 0, s_hbEnd });
	}

	hb_feature_t kerning = { s_kernTag, 0, 0, s_hbEnd };
	if (font.enableKerning())
	kerning.value = 1;
	features.append(WTFMove(kerning));

	for (auto& feature : font.fontDescription().featureSettings()) {
	auto& tag = feature.tag();
	features.append({ HB_TAG(tag[0], tag[1], tag[2], tag[3]), static_cast<uint32_t>(feature.value()), 0, s_hbEnd });
	}

	return features;
	}

	static Optional<UScriptCode> characterScript(UChar32 character)
	{
	UErrorCode errorCode = U_ZERO_ERROR;
	UScriptCode script = uscript_getScript(character, &errorCode);
	if (U_FAILURE(errorCode))
	return WTF::nullopt;
	return script;
	}

	struct HBRun {
	unsigned startIndex;
	unsigned endIndex;
	UScriptCode script;
	};

	static Optional<HBRun> findNextRun(const UChar* characters, unsigned length, unsigned offset)
	{
	SurrogatePairAwareTextIterator textIterator(characters + offset, offset, length, length);
	UChar32 character;
	unsigned clusterLength = 0;
	if (!textIterator.consume(character, clusterLength))
	return WTF::nullopt;

	auto currentScript = characterScript(character);
	if (!currentScript)
	return WTF::nullopt;

	unsigned startIndex = offset;
	for (textIterator.advance(clusterLength); textIterator.consume(character, clusterLength); textIterator.advance(clusterLength)) {
	if (FontCascade::treatAsZeroWidthSpace(character))
	continue;

	auto nextScript = characterScript(character);
	if (!nextScript)
	return WTF::nullopt;

	// §5.1 Handling Characters with the Common Script Property.
	// Programs must resolve any of the special Script property values, such as Common,
	// based on the context of the surrounding characters. A simple heuristic uses the
	// script of the preceding character, which works well in many cases.
	// http://www.unicode.org/reports/tr24/#Common.
	//
	// FIXME: cover all other cases mentioned in the spec (ie. brackets or quotation marks).
	// https://bugs.webkit.org/show_bug.cgi?id=177003.
	//
	// If next script is inherited or common, keep using the current script.
	if (nextScript == USCRIPT_INHERITED \|\| nextScript == USCRIPT_COMMON)
	continue;
	// If current script is inherited or common, set the next script as current.
	if (currentScript == USCRIPT_INHERITED \|\| currentScript == USCRIPT_COMMON) {
	currentScript = nextScript;
	continue;
	}

	if (currentScript != nextScript && !uscript_hasScript(character, currentScript.value()))
	return Optional<HBRun>({ startIndex, textIterator.currentIndex(), currentScript.value() });
	}

	return Optional<HBRun>({ startIndex, textIterator.currentIndex(), currentScript.value() });
	}

	static hb_script_t findScriptForVerticalGlyphSubstitution(hb_face_t* face)
	{
	static const unsigned maxCount = 32;

	unsigned scriptCount = maxCount;
	hb_tag_t scriptTags[maxCount];
	hb_ot_layout_table_get_script_tags(face, HB_OT_TAG_GSUB, 0, &scriptCount, scriptTags);
	for (unsigned scriptIndex = 0; scriptIndex < scriptCount; ++scriptIndex) {
	unsigned languageCount = maxCount;
	hb_tag_t languageTags[maxCount];
	hb_ot_layout_script_get_language_tags(face, HB_OT_TAG_GSUB, scriptIndex, 0, &languageCount, languageTags);
	for (unsigned languageIndex = 0; languageIndex < languageCount; ++languageIndex) {
	unsigned featureIndex;
	if (hb_ot_layout_language_find_feature(face, HB_OT_TAG_GSUB, scriptIndex, languageIndex, s_vertTag, &featureIndex)
	\|\| hb_ot_layout_language_find_feature(face, HB_OT_TAG_GSUB, scriptIndex, languageIndex, s_vrt2Tag, &featureIndex))
	return hb_ot_tag_to_script(scriptTags[scriptIndex]);
	}
	}
	return HB_SCRIPT_INVALID;
	}

	void ComplexTextController::collectComplexTextRunsForCharacters(const UChar* characters, unsigned length, unsigned stringLocation, const Font* font)
	{
	if (!font) {
	// Create a run of missing glyphs from the primary font.
	m_complexTextRuns.append(ComplexTextRun::create(m_font.primaryFont(), characters, stringLocation, length, 0, length, m_run.ltr()));
	return;
	}

	Vector<HBRun> runList;
	unsigned offset = 0;
	while (offset < length) {
	auto run = findNextRun(characters, length, offset);
	if (!run)
	break;
	runList.append(run.value());
	offset = run->endIndex;
	}

	size_t runCount = runList.size();
	if (!runCount)
	return;

	const auto& fontPlatformData = font->platformData();
	auto* scaledFont = fontPlatformData.scaledFont();
	CairoFtFaceLocker cairoFtFaceLocker(scaledFont);
	FT_Face ftFace = cairoFtFaceLocker.ftFace();
	if (!ftFace)
	return;

	HbUniquePtr<hb_face_t> face(hb_ft_face_create_cached(ftFace));
	HbUniquePtr<hb_font_t> harfBuzzFont(hb_font_create(face.get()));
	hb_font_set_funcs(harfBuzzFont.get(), harfBuzzFontFunctions(), const_cast<Font*>(font), nullptr);
	const float size = fontPlatformData.size();
	if (floorf(size) == size)
	hb_font_set_ppem(harfBuzzFont.get(), size, size);
	int scale = floatToHarfBuzzPosition(size);
	hb_font_set_scale(harfBuzzFont.get(), scale, scale);

	#if ENABLE(VARIATION_FONTS)
	FT_MM_Var* ftMMVar;
	if (!FT_Get_MM_Var(ftFace, &ftMMVar)) {
	Vector<FT_Fixed, 4> coords;
	coords.resize(ftMMVar->num_axis);
	if (!FT_Get_Var_Design_Coordinates(ftFace, coords.size(), coords.data())) {
	Vector<hb_variation_t, 4> variations(coords.size());
	for (FT_UInt i = 0; i < ftMMVar->num_axis; ++i) {
	variations[i].tag = ftMMVar->axis[i].tag;
	variations[i].value = coords[i] / 65536.0;
	}
	hb_font_set_variations(harfBuzzFont.get(), variations.data(), variations.size());
	}
	FT_Done_MM_Var(ftFace->glyph->library, ftMMVar);
	}
	#endif

	hb_font_make_immutable(harfBuzzFont.get());

	auto features = fontFeatures(m_font, fontPlatformData.orientation());
	HbUniquePtr<hb_buffer_t> buffer(hb_buffer_create());
	if (fontPlatformData.orientation() == FontOrientation::Vertical)
	hb_buffer_set_script(buffer.get(), findScriptForVerticalGlyphSubstitution(face.get()));

	for (unsigned i = 0; i < runCount; ++i) {
	auto& run = runList[m_run.rtl() ? runCount - i - 1 : i];

	if (fontPlatformData.orientation() != FontOrientation::Vertical)
	hb_buffer_set_script(buffer.get(), hb_icu_script_to_script(run.script));
	if (!m_mayUseNaturalWritingDirection \|\| m_run.directionalOverride())
	hb_buffer_set_direction(buffer.get(), m_run.rtl() ? HB_DIRECTION_RTL : HB_DIRECTION_LTR);
	else {
	// Leaving direction to HarfBuzz to guess is really bad, but will do for now.
	hb_buffer_guess_segment_properties(buffer.get());
	}
	hb_buffer_add_utf16(buffer.get(), reinterpret_cast<const uint16_t*>(characters), length, run.startIndex, run.endIndex - run.startIndex);

	hb_shape(harfBuzzFont.get(), buffer.get(), features.isEmpty() ? nullptr : features.data(), features.size());
	m_complexTextRuns.append(ComplexTextRun::create(buffer.get(), *font, characters, stringLocation, length, run.startIndex, run.endIndex));
	hb_buffer_reset(buffer.get());
	}
	}

	} // namespace WebCore