path: root/vcl/source/gdi/CommonSalLayout.cxx

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This file incorporates work covered by the following license notice:
 *
 *   Licensed to the Apache Software Foundation (ASF) under one or more
 *   contributor license agreements. See the NOTICE file distributed
 *   with this work for additional information regarding copyright
 *   ownership. The ASF licenses this file to you under the Apache
 *   License, Version 2.0 (the "License"); you may not use this file
 *   except in compliance with the License. You may obtain a copy of
 *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
 */

#include <sal/config.h>

#include <sal/log.hxx>
#include <comphelper/configuration.hxx>
#include <o3tl/temporary.hxx>

#include <vcl/unohelp.hxx>
#include <vcl/font/Feature.hxx>
#include <vcl/font/FeatureParser.hxx>
#include <vcl/svapp.hxx>

#include <ImplLayoutArgs.hxx>
#include <TextLayoutCache.hxx>
#include <font/FontSelectPattern.hxx>
#include <salgdi.hxx>
#include <sallayout.hxx>

#include <com/sun/star/i18n/CharacterIteratorMode.hpp>

#include <unicode/uchar.h>
#include <hb-ot.h>
#include <hb-graphite2.h>
#include <hb-icu.h>
#include <hb-aat.h>

#include <map>
#include <memory>
#include <set>

GenericSalLayout::GenericSalLayout(LogicalFontInstance &rFont)
    : m_GlyphItems(rFont)
    , mpVertGlyphs(nullptr)
    , mbFuzzing(comphelper::IsFuzzing())
{
}

GenericSalLayout::~GenericSalLayout()
{
    if (mpVertGlyphs)
        hb_set_destroy(mpVertGlyphs);
}

void GenericSalLayout::ParseFeatures(std::u16string_view aName)
{
    vcl::font::FeatureParser aParser(aName);
    const OUString& sLanguage = aParser.getLanguage();
    if (!sLanguage.isEmpty())
        msLanguage = OUStringToOString(sLanguage, RTL_TEXTENCODING_ASCII_US);

    for (auto const &rFeat : aParser.getFeatures())
    {
        hb_feature_t aFeature { rFeat.m_nTag, rFeat.m_nValue, rFeat.m_nStart, rFeat.m_nEnd };
        maFeatures.push_back(aFeature);
    }
}

namespace {

struct SubRun
{
    int32_t mnMin;
    int32_t mnEnd;
    hb_script_t maScript;
    hb_direction_t maDirection;
};

struct UnclusteredGlyphData
{
    sal_Int32 m_nGlyphId;
    bool m_bUsed = false;

    explicit UnclusteredGlyphData(sal_Int32 nGlyphId)
        : m_nGlyphId(nGlyphId)
    {
    }
};

// This is a helper class to enable correct styling and glyph placement when a grapheme cluster is
// split across multiple adjoining layouts.
//
// In order to justify text, we need glyphs grouped into grapheme clusters so diacritics will stay
// attached to characters under adjustment. However, in order to correctly position and style
// grapheme clusters that span multiple layouts, we need best-effort character-level position data.
//
// At time of writing, HarfBuzz cannot provide both types of information simultaneously. As a work-
// around, this helper class runs HarfBuzz a second time to get the missing information. Should a
// future version of HarfBuzz support this use case directly, this helper code should be deleted.
//
// See tdf#61444, tdf#71956, tdf#124116
class UnclusteredGlyphMapper
{
private:
    hb_buffer_t* m_pHbBuffer = nullptr;
    std::multimap<sal_Int32, UnclusteredGlyphData> m_aGlyphs;
    bool m_bEnable = false;

public:
    UnclusteredGlyphMapper(bool bEnable, int nGlyphCapacity)
        : m_bEnable(bEnable)
    {
        if (!m_bEnable)
        {
            return;
        }

        m_pHbBuffer = hb_buffer_create();
        hb_buffer_pre_allocate(m_pHbBuffer, nGlyphCapacity);
    }

    ~UnclusteredGlyphMapper()
    {
        if (m_bEnable)
        {
            hb_buffer_destroy(m_pHbBuffer);
        }
    }

    [[nodiscard]] sal_Int32 RemapGlyph(sal_Int32 nClusterId, sal_Int32 nGlyphId)
    {
        if (auto it = m_aGlyphs.lower_bound(nClusterId); it != m_aGlyphs.end())
        {
            for (; it != m_aGlyphs.end(); ++it)
            {
                if (it->second.m_nGlyphId == nGlyphId && !it->second.m_bUsed)
                {
                    it->second.m_bUsed = true;
                    return it->first;
                }
            }
        }

        return nClusterId;
    }

    void Reset()
    {
        for (auto& rElement : m_aGlyphs)
        {
            rElement.second.m_bUsed = false;
        }
    }

    void ShapeSubRun(const sal_Unicode* pStr, const int nLength, const SubRun& aSubRun,
                     hb_font_t* pHbFont, const std::vector<hb_feature_t>& maFeatures,
                     hb_language_t oHbLanguage)
    {
        if (!m_bEnable)
        {
            return;
        }

        m_aGlyphs.clear();

        hb_buffer_clear_contents(m_pHbBuffer);

        const int nMinRunPos = aSubRun.mnMin;
        const int nEndRunPos = aSubRun.mnEnd;
        const int nRunLen = nEndRunPos - nMinRunPos;

        int nHbFlags = HB_BUFFER_FLAGS_DEFAULT;
        nHbFlags |= HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL;

        if (nMinRunPos == 0)
        {
            nHbFlags |= HB_BUFFER_FLAG_BOT; /* Beginning-of-text */
        }

        if (nEndRunPos == nLength)
        {
            nHbFlags |= HB_BUFFER_FLAG_EOT; /* End-of-text */
        }

        hb_buffer_set_flags(m_pHbBuffer, static_cast<hb_buffer_flags_t>(nHbFlags));

        hb_buffer_set_cluster_level(m_pHbBuffer, HB_BUFFER_CLUSTER_LEVEL_CHARACTERS);

        hb_buffer_set_direction(m_pHbBuffer, aSubRun.maDirection);
        hb_buffer_set_script(m_pHbBuffer, aSubRun.maScript);
        hb_buffer_set_language(m_pHbBuffer, oHbLanguage);

        hb_buffer_add_utf16(m_pHbBuffer, reinterpret_cast<uint16_t const*>(pStr), nLength,
                            nMinRunPos, nRunLen);

        // The shapers that we want HarfBuzz to use, in the order of
        // preference.
        const char* const pHbShapers[] = { "graphite2", "ot", "fallback", nullptr };
        bool ok
            = hb_shape_full(pHbFont, m_pHbBuffer, maFeatures.data(), maFeatures.size(), pHbShapers);
        assert(ok);
        (void)ok;

        int nRunGlyphCount = hb_buffer_get_length(m_pHbBuffer);
        hb_glyph_info_t* pHbGlyphInfos = hb_buffer_get_glyph_infos(m_pHbBuffer, nullptr);

        for (int i = 0; i < nRunGlyphCount; ++i)
        {
            int32_t nGlyphIndex = pHbGlyphInfos[i].codepoint;
            int32_t nCharPos = pHbGlyphInfos[i].cluster;

            m_aGlyphs.emplace(nCharPos, UnclusteredGlyphData{ nGlyphIndex });
        }
    }
};
}

namespace {
    int32_t GetVerticalOrientation(sal_UCS4 cCh, const LanguageTag& rTag)
    {
        // Override orientation of fullwidth colon , semi-colon,
        // and Bopomofo tonal marks.
        if ((cCh == 0xff1a || cCh == 0xff1b
           || cCh == 0x2ca || cCh == 0x2cb || cCh == 0x2c7 || cCh == 0x2d9)
                && rTag.getLanguage() == "zh")
            return U_VO_TRANSFORMED_UPRIGHT;

        return u_getIntPropertyValue(cCh, UCHAR_VERTICAL_ORIENTATION);
    }
} // namespace

SalLayoutGlyphs GenericSalLayout::GetGlyphs() const
{
    SalLayoutGlyphs glyphs;
    glyphs.AppendImpl(m_GlyphItems.clone());
    return glyphs;
}

void GenericSalLayout::SetNeedFallback(vcl::text::ImplLayoutArgs& rArgs, sal_Int32 nCharPos,
                                       sal_Int32 nCharEnd, bool bRightToLeft)
{
    if (nCharPos < 0 || nCharPos == nCharEnd || mbFuzzing)
        return;

    if (!mxBreak.is())
        mxBreak = vcl::unohelper::CreateBreakIterator();

    const css::lang::Locale& rLocale(rArgs.maLanguageTag.getLocale());

    //if position nCharPos is missing in the font, grab the entire grapheme and
    //mark all glyphs as missing so the whole thing is rendered with the same
    //font
    sal_Int32 nDone;
    int nGraphemeEndPos = mxBreak->nextCharacters(rArgs.mrStr, nCharEnd - 1, rLocale,
                                                  css::i18n::CharacterIteratorMode::SKIPCELL, 1, nDone);
    // Safely advance nCharPos in case it is a non-BMP character.
    rArgs.mrStr.iterateCodePoints(&nCharPos);
    int nGraphemeStartPos =
        mxBreak->previousCharacters(rArgs.mrStr, nCharPos, rLocale,
            css::i18n::CharacterIteratorMode::SKIPCELL, 1, nDone);

    // tdf#107612
    // If the start of the fallback run is Mongolian character and the previous
    // character is NNBSP, we want to include the NNBSP in the fallback since
    // it has special uses in Mongolian and have to be in the same text run to
    // work.
    sal_Int32 nTempPos = nGraphemeStartPos;
    if (nGraphemeStartPos > 0)
    {
        auto nCurrChar = rArgs.mrStr.iterateCodePoints(&nTempPos, 0);
        auto nPrevChar = rArgs.mrStr.iterateCodePoints(&nTempPos, -1);
        if (nPrevChar == 0x202F
            && u_getIntPropertyValue(nCurrChar, UCHAR_SCRIPT) == USCRIPT_MONGOLIAN)
            nGraphemeStartPos = nTempPos;
    }

    //stay inside the Layout range (e.g. with tdf124116-1.odt)
    nGraphemeStartPos = std::max(rArgs.mnMinCharPos, nGraphemeStartPos);
    nGraphemeEndPos = std::min(rArgs.mnEndCharPos, nGraphemeEndPos);

    rArgs.AddFallbackRun(nGraphemeStartPos, nGraphemeEndPos, bRightToLeft);
}

void GenericSalLayout::AdjustLayout(vcl::text::ImplLayoutArgs& rArgs)
{
    SalLayout::AdjustLayout(rArgs);

    if (!rArgs.mstJustification.empty())
    {
        ApplyJustificationData(rArgs.mstJustification);
    }
    else if (rArgs.mnLayoutWidth)
    {
        Justify(rArgs.mnLayoutWidth);
    }
    else if ((rArgs.mnFlags & SalLayoutFlags::KerningAsian)
         && !(rArgs.mnFlags & SalLayoutFlags::Vertical))
    {
        // apply asian kerning if the glyphs are not already formatted
        ApplyAsianKerning(rArgs.mrStr);
    }
}

void GenericSalLayout::DrawText(SalGraphics& rSalGraphics) const
{
    //call platform dependent DrawText functions
    rSalGraphics.DrawTextLayout( *this );
}

// Find if the nominal glyph of the character is an input to “vert” feature.
// We don’t check for a specific script or language as it shouldn’t matter
// here; if the glyph would be the result from applying “vert” for any
// script/language then we want to always treat it as upright glyph.
bool GenericSalLayout::HasVerticalAlternate(sal_UCS4 aChar, sal_UCS4 aVariationSelector)
{
    sal_GlyphId nGlyphIndex = GetFont().GetGlyphIndex(aChar, aVariationSelector);
    if (!nGlyphIndex)
        return false;

    if (!mpVertGlyphs)
    {
        hb_face_t* pHbFace = hb_font_get_face(GetFont().GetHbFont());
        mpVertGlyphs = hb_set_create();

        // Find all GSUB lookups for “vert” feature.
        hb_set_t* pLookups = hb_set_create();
        hb_tag_t const pFeatures[] = { HB_TAG('v','e','r','t'), HB_TAG_NONE };
        hb_ot_layout_collect_lookups(pHbFace, HB_OT_TAG_GSUB, nullptr, nullptr, pFeatures, pLookups);
        if (!hb_set_is_empty(pLookups))
        {
            // Find the input glyphs in each lookup (i.e. the glyphs that
            // this lookup applies to).
            hb_codepoint_t nIdx = HB_SET_VALUE_INVALID;
            while (hb_set_next(pLookups, &nIdx))
            {
                hb_set_t* pGlyphs = hb_set_create();
                hb_ot_layout_lookup_collect_glyphs(pHbFace, HB_OT_TAG_GSUB, nIdx,
                        nullptr,  // glyphs before
                        pGlyphs,  // glyphs input
                        nullptr,  // glyphs after
                        nullptr); // glyphs out
                hb_set_union(mpVertGlyphs, pGlyphs);
            }
        }
        hb_set_destroy(pLookups);
    }

    return hb_set_has(mpVertGlyphs, nGlyphIndex) != 0;
}

bool GenericSalLayout::LayoutText(vcl::text::ImplLayoutArgs& rArgs, const SalLayoutGlyphsImpl* pGlyphs)
{
    // No need to touch m_GlyphItems at all for an empty string.
    if (rArgs.mnEndCharPos - rArgs.mnMinCharPos <= 0)
        return true;

    ImplLayoutRuns aFallbackRuns;

    if (pGlyphs)
    {
        // Work with pre-computed glyph items.
        m_GlyphItems = *pGlyphs;

        for(const GlyphItem& item : m_GlyphItems)
            if(!item.glyphId())
                aFallbackRuns.AddPos(item.charPos(), item.IsRTLGlyph());

        for (const auto& rRun : aFallbackRuns)
        {
            SetNeedFallback(rArgs, rRun.m_nMinRunPos, rRun.m_nEndRunPos, rRun.m_bRTL);
        }

        // Some flags are set as a side effect of text layout, restore them here.
        rArgs.mnFlags |= pGlyphs->GetFlags();
        return true;
    }

    hb_font_t *pHbFont = GetFont().GetHbFont();
    bool isGraphite = GetFont().IsGraphiteFont();

    // tdf#163215: Identify layouts that don't have strict kashida position validation.
    m_bHasFontKashidaPositions = false;
    if (!(rArgs.mnFlags & SalLayoutFlags::DisableKashidaValidation))
    {
        hb_face_t* pHbFace = hb_font_get_face(pHbFont);
        m_bHasFontKashidaPositions = !hb_aat_layout_has_substitution(pHbFace);
    }

    int nGlyphCapacity = 2 * (rArgs.mnEndCharPos - rArgs.mnMinCharPos);
    m_GlyphItems.reserve(nGlyphCapacity);

    const int nLength = rArgs.mrStr.getLength();
    const sal_Unicode *pStr = rArgs.mrStr.getStr();

    std::shared_ptr<const vcl::text::TextLayoutCache> pNewScriptRun;
    vcl::text::TextLayoutCache const* pTextLayout;
    if (rArgs.m_pTextLayoutCache)
    {
        pTextLayout = rArgs.m_pTextLayoutCache; // use cache!
    }
    else
    {
        // tdf#92064, tdf#162663:
        // Also use the global LRU cache for full string script runs.
        // This obviates O(n^2) calls to vcl::ScriptRun::next() when laying out large paragraphs.
        pNewScriptRun = vcl::text::TextLayoutCache::Create(rArgs.mrStr);
        pTextLayout = pNewScriptRun.get();
    }

    // nBaseOffset is used to align vertical text to the center of rotated
    // horizontal text. That is the offset from original baseline to
    // the center of EM box. Maybe we can use OpenType base table to improve this
    // in the future.
    double nBaseOffset = 0;
    if (rArgs.mnFlags & SalLayoutFlags::Vertical)
    {
        hb_font_extents_t extents;
        if (hb_font_get_h_extents(pHbFont, &extents))
            nBaseOffset = ( extents.ascender + extents.descender ) / 2.0;
    }

    UnclusteredGlyphMapper stClusterMapper{
        bool{ rArgs.mnFlags & SalLayoutFlags::UnclusteredGlyphs }, nGlyphCapacity
    };

    hb_buffer_t* pHbBuffer = hb_buffer_create();
    hb_buffer_pre_allocate(pHbBuffer, nGlyphCapacity);

    const vcl::font::FontSelectPattern& rFontSelData = GetFont().GetFontSelectPattern();
    if (rArgs.mnFlags & SalLayoutFlags::DisableKerning)
    {
        SAL_INFO("vcl.harfbuzz", "Disabling kerning for font: " << rFontSelData.maTargetName);
        maFeatures.push_back({ HB_TAG('k','e','r','n'), 0, 0, static_cast<unsigned int>(-1) });
    }

    if (rArgs.mnFlags & SalLayoutFlags::DisableLigatures)
    {
        SAL_INFO("vcl.harfbuzz", "Disabling ligatures for font: " << rFontSelData.maTargetName);

        // Both of these are optional ligatures, enabled by default but not for
        // orthographically-required ligatures.
        maFeatures.push_back({ HB_TAG('l','i','g','a'), 0, 0, static_cast<unsigned int>(-1) });
        maFeatures.push_back({ HB_TAG('c','l','i','g'), 0, 0, static_cast<unsigned int>(-1) });
    }

    ParseFeatures(rFontSelData.maTargetName);

    double nXScale = 0;
    double nYScale = 0;
    GetFont().GetScale(&nXScale, &nYScale);

    double nCurrX = 0.0;
    while (true)
    {
        int nBidiMinRunPos, nBidiEndRunPos;
        bool bRightToLeft;
        if (!rArgs.GetNextRun(&nBidiMinRunPos, &nBidiEndRunPos, &bRightToLeft))
            break;

        // Find script subruns.
        std::vector<SubRun> aSubRuns;
        int nCurrentPos = nBidiMinRunPos;
        size_t k = 0;
        for (; k < pTextLayout->runs.size(); ++k)
        {
            vcl::text::Run const& rRun(pTextLayout->runs[k]);
            if (rRun.nStart <= nCurrentPos && nCurrentPos < rRun.nEnd)
            {
                break;
            }
        }

        if (isGraphite)
        {
            hb_script_t aScript = hb_icu_script_to_script(pTextLayout->runs[k].nCode);
            aSubRuns.push_back({ nBidiMinRunPos, nBidiEndRunPos, aScript, bRightToLeft ? HB_DIRECTION_RTL : HB_DIRECTION_LTR });
        }
        else
        {
            while (nCurrentPos < nBidiEndRunPos && k < pTextLayout->runs.size())
            {
                int32_t nMinRunPos = nCurrentPos;
                int32_t nEndRunPos = std::min(pTextLayout->runs[k].nEnd, nBidiEndRunPos);
                hb_direction_t aDirection = bRightToLeft ? HB_DIRECTION_RTL : HB_DIRECTION_LTR;
                hb_script_t aScript = hb_icu_script_to_script(pTextLayout->runs[k].nCode);
                // For vertical text, further divide the runs based on character
                // orientation.
                if (rArgs.mnFlags & SalLayoutFlags::Vertical)
                {
                    sal_Int32 nIdx = nMinRunPos;
                    while (nIdx < nEndRunPos)
                    {
                        sal_Int32 nPrevIdx = nIdx;
                        sal_UCS4 aChar = rArgs.mrStr.iterateCodePoints(&nIdx);
                        int32_t aVo = GetVerticalOrientation(aChar, rArgs.maLanguageTag);

                        sal_UCS4 aVariationSelector = 0;
                        if (nIdx < nEndRunPos)
                        {
                            sal_Int32 nNextIdx = nIdx;
                            sal_UCS4 aNextChar = rArgs.mrStr.iterateCodePoints(&nNextIdx);
                            if (u_hasBinaryProperty(aNextChar, UCHAR_VARIATION_SELECTOR))
                            {
                                nIdx = nNextIdx;
                                aVariationSelector = aNextChar;
                            }
                        }

                        // Characters with U and Tu vertical orientation should
                        // be shaped in vertical direction. But characters
                        // with Tr should be shaped in vertical direction
                        // only if they have vertical alternates, otherwise
                        // they should be shaped in horizontal direction
                        // and then rotated.
                        // See http://unicode.org/reports/tr50/#vo
                        if (aVo == U_VO_UPRIGHT || aVo == U_VO_TRANSFORMED_UPRIGHT ||
                            (aVo == U_VO_TRANSFORMED_ROTATED &&
                             HasVerticalAlternate(aChar, aVariationSelector)))
                        {
                            aDirection = HB_DIRECTION_TTB;
                        }
                        else
                        {
                            aDirection = bRightToLeft ? HB_DIRECTION_RTL : HB_DIRECTION_LTR;
                        }

                        if (aSubRuns.empty() || aSubRuns.back().maDirection != aDirection || aSubRuns.back().maScript != aScript)
                            aSubRuns.push_back({ nPrevIdx, nIdx, aScript, aDirection });
                        else
                            aSubRuns.back().mnEnd = nIdx;
                    }
                }
                else
                {
                    aSubRuns.push_back({ nMinRunPos, nEndRunPos, aScript, aDirection });
                }

                nCurrentPos = nEndRunPos;
                ++k;
            }
        }

        // RTL subruns should be reversed to ensure that final glyph order is
        // correct.
        if (bRightToLeft)
            std::reverse(aSubRuns.begin(), aSubRuns.end());

        for (const auto& aSubRun : aSubRuns)
        {
            hb_buffer_clear_contents(pHbBuffer);

            const int nMinRunPos = aSubRun.mnMin;
            const int nEndRunPos = aSubRun.mnEnd;
            const int nRunLen = nEndRunPos - nMinRunPos;

            int nHbFlags = HB_BUFFER_FLAGS_DEFAULT;

            // Produce HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL that we use below.
            nHbFlags |= HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL;

            if (nMinRunPos == 0)
                nHbFlags |= HB_BUFFER_FLAG_BOT; /* Beginning-of-text */
            if (nEndRunPos == nLength)
                nHbFlags |= HB_BUFFER_FLAG_EOT; /* End-of-text */

            hb_buffer_set_direction(pHbBuffer, aSubRun.maDirection);
            hb_buffer_set_script(pHbBuffer, aSubRun.maScript);

            hb_language_t oHbLanguage = nullptr;
            if (!msLanguage.isEmpty())
            {
                oHbLanguage = hb_language_from_string(msLanguage.getStr(), msLanguage.getLength());
            }
            else
            {
                OString sLanguage
                    = OUStringToOString(rArgs.maLanguageTag.getBcp47(), RTL_TEXTENCODING_ASCII_US);
                oHbLanguage = hb_language_from_string(sLanguage.getStr(), sLanguage.getLength());
            }

            hb_buffer_set_language(pHbBuffer, oHbLanguage);

            hb_buffer_set_flags(pHbBuffer, static_cast<hb_buffer_flags_t>(nHbFlags));
            hb_buffer_add_utf16(
                pHbBuffer, reinterpret_cast<uint16_t const *>(pStr), nLength,
                nMinRunPos, nRunLen);

            // The shapers that we want HarfBuzz to use, in the order of
            // preference.
            const char*const pHbShapers[] = { "graphite2", "ot", "fallback", nullptr };
            bool ok = hb_shape_full(pHbFont, pHbBuffer, maFeatures.data(), maFeatures.size(), pHbShapers);
            assert(ok);
            (void) ok;

            // Populate glyph cluster remapping data
            stClusterMapper.ShapeSubRun(pStr, nLength, aSubRun, pHbFont, maFeatures, oHbLanguage);

            int nRunGlyphCount = hb_buffer_get_length(pHbBuffer);
            hb_glyph_info_t *pHbGlyphInfos = hb_buffer_get_glyph_infos(pHbBuffer, nullptr);
            hb_glyph_position_t *pHbPositions = hb_buffer_get_glyph_positions(pHbBuffer, nullptr);

            // tdf#164106: Grapheme clusters can be split across multiple layouts. To do this,
            // the complete string is laid out, and only the necessary glyphs are extracted.
            // These sub-layouts are positioned side-by-side to form the complete text.
            // This approach is good enough for most diacritic cases, but it cannot handle cases
            // where a glyph with an advance is reordered into a different sub-layout.
            bool bStartClusterOutOfOrder = false;
            bool bEndClusterOutOfOrder = false;
            {
                double nNormalAdvance = 0.0;
                double nStartAdvance = 0.0;
                double nEndAdvance = 0.0;

                auto fnHandleGlyph = [&](int i)
                {
                    int32_t nGlyphIndex = pHbGlyphInfos[i].codepoint;
                    int32_t nCluster = pHbGlyphInfos[i].cluster;
                    auto nOrigCharPos = stClusterMapper.RemapGlyph(nCluster, nGlyphIndex);

                    double nAdvance = 0.0;
                    if (aSubRun.maDirection == HB_DIRECTION_TTB)
                    {
                        nAdvance = -pHbPositions[i].y_advance;
                    }
                    else
                    {
                        nAdvance = pHbPositions[i].x_advance;
                    }

                    nNormalAdvance += nAdvance;

                    if (nOrigCharPos < rArgs.mnDrawMinCharPos)
                    {
                        nStartAdvance += nAdvance;
                        if (nStartAdvance != nNormalAdvance)
                        {
                            bStartClusterOutOfOrder = true;
                        }
                    }

                    if (nOrigCharPos < rArgs.mnDrawEndCharPos)
                    {
                        nEndAdvance += nAdvance;
                        if (nEndAdvance != nNormalAdvance)
                        {
                            bEndClusterOutOfOrder = true;
                        }
                    }
                };

                if (bRightToLeft)
                {
                    for (int i = nRunGlyphCount - 1; i >= 0; --i)
                    {
                        fnHandleGlyph(i);
                    }
                }
                else
                {
                    for (int i = 0; i < nRunGlyphCount; ++i)
                    {
                        fnHandleGlyph(i);
                    }
                }

                stClusterMapper.Reset();
            }

            for (int i = 0; i < nRunGlyphCount; ++i) {
                int32_t nGlyphIndex = pHbGlyphInfos[i].codepoint;
                int32_t nCharPos = pHbGlyphInfos[i].cluster;
                int32_t nCharCount = 0;
                bool bInCluster = false;
                bool bClusterStart = false;

                // Find the number of characters that make up this glyph.
                if (!bRightToLeft)
                {
                    // If the cluster is the same as previous glyph, then this
                    // already consumed, skip.
                    if (i > 0 && pHbGlyphInfos[i].cluster == pHbGlyphInfos[i - 1].cluster)
                    {
                        nCharCount = 0;
                        bInCluster = true;
                    }
                    else
                    {
                        // Find the next glyph with a different cluster, or the
                        // end of text.
                        int j = i;
                        int32_t nNextCharPos = nCharPos;
                        while (nNextCharPos == nCharPos && j < nRunGlyphCount)
                            nNextCharPos = pHbGlyphInfos[j++].cluster;

                        if (nNextCharPos == nCharPos)
                            nNextCharPos = nEndRunPos;
                        nCharCount = nNextCharPos - nCharPos;
                        if ((i == 0 || pHbGlyphInfos[i].cluster != pHbGlyphInfos[i - 1].cluster) &&
                            (i < nRunGlyphCount - 1 && pHbGlyphInfos[i].cluster == pHbGlyphInfos[i + 1].cluster))
                            bClusterStart = true;
                    }
                }
                else
                {
                    // If the cluster is the same as previous glyph, then this
                    // will be consumed later, skip.
                    if (i < nRunGlyphCount - 1 && pHbGlyphInfos[i].cluster == pHbGlyphInfos[i + 1].cluster)
                    {
                        nCharCount = 0;
                        bInCluster = true;
                    }
                    else
                    {
                        // Find the previous glyph with a different cluster, or
                        // the end of text.
                        int j = i;
                        int32_t nNextCharPos = nCharPos;
                        while (nNextCharPos == nCharPos && j >= 0)
                            nNextCharPos = pHbGlyphInfos[j--].cluster;

                        if (nNextCharPos == nCharPos)
                            nNextCharPos = nEndRunPos;
                        nCharCount = nNextCharPos - nCharPos;
                        if ((i == nRunGlyphCount - 1 || pHbGlyphInfos[i].cluster != pHbGlyphInfos[i + 1].cluster) &&
                            (i > 0 && pHbGlyphInfos[i].cluster == pHbGlyphInfos[i - 1].cluster))
                            bClusterStart = true;
                    }
                }

                // if needed request glyph fallback by updating LayoutArgs
                auto nOrigCharPos = stClusterMapper.RemapGlyph(nCharPos, nGlyphIndex);
                if (!nGlyphIndex)
                {
                    // Only request fallback for grapheme clusters that are drawn
                    if (nOrigCharPos >= rArgs.mnDrawMinCharPos
                        && nOrigCharPos < rArgs.mnDrawEndCharPos)
                    {
                        aFallbackRuns.AddPos(nOrigCharPos, bRightToLeft);
                        if (SalLayoutFlags::ForFallback & rArgs.mnFlags)
                            continue;
                    }
                }

                GlyphItemFlags nGlyphFlags = GlyphItemFlags::NONE;
                if (bRightToLeft)
                    nGlyphFlags |= GlyphItemFlags::IS_RTL_GLYPH;

                if (bClusterStart)
                    nGlyphFlags |= GlyphItemFlags::IS_CLUSTER_START;

                if (bInCluster)
                    nGlyphFlags |= GlyphItemFlags::IS_IN_CLUSTER;

                sal_UCS4 aChar
                    = rArgs.mrStr.iterateCodePoints(&o3tl::temporary(sal_Int32(nCharPos)), 0);

                if (u_isUWhiteSpace(aChar))
                    nGlyphFlags |= GlyphItemFlags::IS_SPACING;

                if (hb_glyph_info_get_glyph_flags(&pHbGlyphInfos[i]) & HB_GLYPH_FLAG_UNSAFE_TO_BREAK)
                    nGlyphFlags |= GlyphItemFlags::IS_UNSAFE_TO_BREAK;

                if (!m_bHasFontKashidaPositions
                    || (hb_glyph_info_get_glyph_flags(&pHbGlyphInfos[i])
                        & HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL))
                    nGlyphFlags |= GlyphItemFlags::IS_SAFE_TO_INSERT_KASHIDA;

                double nAdvance, nXOffset, nYOffset;
                if (aSubRun.maDirection == HB_DIRECTION_TTB)
                {
                    nGlyphFlags |= GlyphItemFlags::IS_VERTICAL;

                    nAdvance = -pHbPositions[i].y_advance;
                    nXOffset = -pHbPositions[i].y_offset;
                    nYOffset = -pHbPositions[i].x_offset - nBaseOffset;

                    if (GetFont().NeedOffsetCorrection(pHbPositions[i].y_offset))
                    {
                        // We need glyph's advance, top bearing, and height to
                        // correct y offset.
                        basegfx::B2DRectangle aRect;
                        // Get cached bound rect value for the font,
                        GetFont().GetGlyphBoundRect(nGlyphIndex, aRect, true);

                        nXOffset = -(aRect.getMinX() / nXScale  + ( pHbPositions[i].y_advance
                                    + ( aRect.getHeight() / nXScale ) ) / 2.0 );
                    }

                }
                else
                {
                    nAdvance =  pHbPositions[i].x_advance;
                    nXOffset =  pHbPositions[i].x_offset;
                    nYOffset = -pHbPositions[i].y_offset;
                }

                nAdvance = nAdvance * nXScale;
                nXOffset = nXOffset * nXScale;
                nYOffset = nYOffset * nYScale;
                if (!GetSubpixelPositioning())
                {
                    nAdvance = std::round(nAdvance);
                    nXOffset = std::round(nXOffset);
                    nYOffset = std::round(nYOffset);
                }

                basegfx::B2DPoint aNewPos(nCurrX + nXOffset, nYOffset);
                const GlyphItem aGI(nCharPos, nCharCount, nGlyphIndex, aNewPos, nGlyphFlags,
                                    nAdvance, nXOffset, nYOffset, nOrigCharPos);

                auto nLowerBound = (bStartClusterOutOfOrder ? aGI.charPos() : aGI.origCharPos());
                auto nUpperBound = (bEndClusterOutOfOrder ? aGI.charPos() : aGI.origCharPos());
                if (nLowerBound >= rArgs.mnDrawMinCharPos && nUpperBound < rArgs.mnDrawEndCharPos)
                {
                    m_GlyphItems.push_back(aGI);
                }

                if (nLowerBound >= rArgs.mnDrawOriginCluster
                    && nUpperBound < rArgs.mnDrawEndCharPos)
                {
                    nCurrX += nAdvance;
                }
            }
        }
    }

    hb_buffer_destroy(pHbBuffer);

    for (const auto& rRun : aFallbackRuns)
    {
        SetNeedFallback(rArgs, rRun.m_nMinRunPos, rRun.m_nEndRunPos, rRun.m_bRTL);
    }

    // Some flags are set as a side effect of text layout, save them here.
    if (rArgs.mnFlags & SalLayoutFlags::GlyphItemsOnly)
        m_GlyphItems.SetFlags(rArgs.mnFlags);

    return true;
}

void GenericSalLayout::GetCharWidths(std::vector<double>& rCharWidths, const OUString& rStr) const
{
    const int nCharCount = mnEndCharPos - mnMinCharPos;

    rCharWidths.clear();
    rCharWidths.resize(nCharCount, 0);

    css::uno::Reference<css::i18n::XBreakIterator> xBreak;
    const css::lang::Locale& rLocale(maLanguageTag.getLocale());

    for (auto const& aGlyphItem : m_GlyphItems)
    {
        if (aGlyphItem.charPos() >= mnEndCharPos)
            continue;

        unsigned int nGraphemeCount = 0;
        if (aGlyphItem.charCount() > 1 && aGlyphItem.newWidth() != 0 && !rStr.isEmpty())
        {
            // We are calculating DX array for cursor positions and this is a
            // ligature, find out how many grapheme clusters are in it.
            if (!xBreak.is())
                xBreak = mxBreak.is() ? mxBreak : vcl::unohelper::CreateBreakIterator();

            // Count grapheme clusters in the ligature.
            sal_Int32 nDone;
            sal_Int32 nPos = aGlyphItem.charPos();
            while (nPos < aGlyphItem.charPos() + aGlyphItem.charCount())
            {
                nPos = xBreak->nextCharacters(rStr, nPos, rLocale,
                    css::i18n::CharacterIteratorMode::SKIPCELL, 1, nDone);
                nGraphemeCount++;
            }
        }

        if (nGraphemeCount > 1)
        {
            // More than one grapheme cluster, we want to distribute the glyph
            // width over them.
            std::vector<double> aWidths(nGraphemeCount);

            // Check if the glyph has ligature caret positions.
            unsigned int nCarets = nGraphemeCount;
            std::vector<hb_position_t> aCarets(nGraphemeCount);
            hb_ot_layout_get_ligature_carets(GetFont().GetHbFont(),
                aGlyphItem.IsRTLGlyph() ? HB_DIRECTION_RTL : HB_DIRECTION_LTR,
                aGlyphItem.glyphId(), 0, &nCarets, aCarets.data());

            // Carets are 1-less than the grapheme count (since the last
            // position is defined by glyph width), if the count does not
            // match, ignore it.
            if (nCarets == nGraphemeCount - 1)
            {
                // Scale the carets and apply glyph offset to them since they
                // are based on the default glyph metrics.
                double fScale = 0;
                GetFont().GetScale(&fScale, nullptr);
                for (size_t i = 0; i < nCarets; i++)
                    aCarets[i] = (aCarets[i] * fScale) + aGlyphItem.xOffset();

                // Use the glyph width for the last caret.
                aCarets[nCarets] = aGlyphItem.newWidth();

                // Carets are absolute from the X origin of the glyph, turn
                // them to relative widths that we need below.
                for (size_t i = 0; i < nGraphemeCount; i++)
                    aWidths[i] = aCarets[i] - (i == 0 ? 0 : aCarets[i - 1]);

                // Carets are in visual order, but we want widths in logical
                // order.
                if (aGlyphItem.IsRTLGlyph())
                    std::reverse(aWidths.begin(), aWidths.end());
            }
            else
            {
                // The glyph has no carets, distribute the width evenly.
                auto nWidth = aGlyphItem.newWidth() / nGraphemeCount;
                std::fill(aWidths.begin(), aWidths.end(), nWidth);

                // Add rounding difference to the last component to maintain
                // ligature width.
                aWidths[nGraphemeCount - 1] += aGlyphItem.newWidth() - (nWidth * nGraphemeCount);
            }

            // Set the width of each grapheme cluster.
            sal_Int32 nDone;
            sal_Int32 nPos = aGlyphItem.charPos();
            for (auto nWidth : aWidths)
            {
                rCharWidths[nPos - mnMinCharPos] += nWidth;
                nPos = xBreak->nextCharacters(rStr, nPos, rLocale,
                    css::i18n::CharacterIteratorMode::SKIPCELL, 1, nDone);
            }
        }
        else
            rCharWidths[aGlyphItem.charPos() - mnMinCharPos] += aGlyphItem.newWidth();
    }
}

// - stJustification:
//   - contains adjustments to glyph advances (usually due to justification).
//   - contains kashida insertion positions, for Arabic script justification.
//     - The number of kashidas is calculated from the adjusted advances.
void GenericSalLayout::ApplyJustificationData(const JustificationData& rstJustification)
{
    int nCharCount = mnEndCharPos - mnMinCharPos;
    std::vector<double> aOldCharWidths;
    std::unique_ptr<double[]> const pNewCharWidths(new double[nCharCount]);

    // Get the natural character widths (i.e. before applying DX adjustments).
    GetCharWidths(aOldCharWidths, {});

    // Calculate the character widths after DX adjustments.
    for (int i = 0; i < nCharCount; ++i)
    {
        if (i == 0)
        {
            pNewCharWidths[i] = rstJustification.GetTotalAdvance(mnMinCharPos + i);
        }
        else
        {
            pNewCharWidths[i] = rstJustification.GetTotalAdvance(mnMinCharPos + i)
                                - rstJustification.GetTotalAdvance(mnMinCharPos + i - 1);
        }
    }

    // Map of Kashida insertion points (in the glyph items vector) and the
    // requested width.
    std::map<size_t, std::pair<double, double>> pKashidas;

    // The accumulated difference in X position.
    double nDelta = 0;

    // Apply the DX adjustments to glyph positions and widths.
    size_t i = 0;
    while (i < m_GlyphItems.size())
    {
        // Accumulate the width difference for all characters corresponding to
        // this glyph.
        int nCharPos = m_GlyphItems[i].charPos() - mnMinCharPos;
        double nDiff = 0;
        for (int j = 0; j < m_GlyphItems[i].charCount(); j++)
            nDiff += pNewCharWidths[nCharPos + j] - aOldCharWidths[nCharPos + j];

        if (!m_GlyphItems[i].IsRTLGlyph())
        {
            // Adjust the width and position of the first (leftmost) glyph in
            // the cluster.
            m_GlyphItems[i].addNewWidth(nDiff);
            m_GlyphItems[i].adjustLinearPosX(nDelta);

            // Adjust the position of the rest of the glyphs in the cluster.
            while (++i < m_GlyphItems.size())
            {
                if (!m_GlyphItems[i].IsInCluster())
                    break;
                m_GlyphItems[i].adjustLinearPosX(nDelta);
            }
        }
        else if (m_GlyphItems[i].IsInCluster())
        {
            // RTL glyph in the middle of the cluster, will be handled in the
            // loop below.
            i++;
        }
        else // RTL
        {
            // Adjust the width and position of the first (rightmost) glyph in
            // the cluster. This is RTL, so we put all the adjustment to the
            // left of the glyph.
            m_GlyphItems[i].addNewWidth(nDiff);
            m_GlyphItems[i].adjustLinearPosX(nDelta + nDiff);

            // Adjust the X position of the rest of the glyphs in the cluster.
            // We iterate backwards since this is an RTL glyph.
            for (size_t j = i; j >= 1 && m_GlyphItems[j - 1].IsInCluster(); --j)
                m_GlyphItems[j - 1].adjustLinearPosX(nDelta + nDiff);

            // This is a Kashida insertion position, mark it. Kashida glyphs
            // will be inserted below.
            if (rstJustification.GetPositionHasKashida(mnMinCharPos + nCharPos).value_or(false))
            {
                pKashidas[i] = { nDiff, pNewCharWidths[nCharPos] };
            }

            i++;
        }

        // Increment the delta, the loop above makes sure we do so only once
        // for every character (cluster) not for every glyph (otherwise we
        // would apply it multiple times for each glyph belonging to the same
        // character which is wrong as DX adjustments are character based).
        nDelta += nDiff;
    }

    // Insert Kashida glyphs.
    if (pKashidas.empty())
        return;

    // Find Kashida glyph width and index.
    sal_GlyphId nKashidaIndex = GetFont().GetGlyphIndex(0x0640);
    double nKashidaWidth = GetFont().GetKashidaWidth();
    if (!GetSubpixelPositioning())
        nKashidaWidth = std::ceil(nKashidaWidth);

    if (nKashidaWidth <= 0)
    {
        SAL_WARN("vcl.gdi", "Asked to insert Kashidas in a font with bogus Kashida width");
        return;
    }

    size_t nInserted = 0;
    for (auto const& pKashida : pKashidas)
    {
        auto pGlyphIter = m_GlyphItems.begin() + nInserted + pKashida.first;

        // The total Kashida width.
        auto const& [nTotalWidth, nClusterWidth] = pKashida.second;

        // Number of times to repeat each Kashida.
        int nCopies = 1;
        if (nTotalWidth > nKashidaWidth)
            nCopies = nTotalWidth / nKashidaWidth;

        // See if we can improve the fit by adding an extra Kashidas and
        // squeezing them together a bit.
        double nOverlap = 0;
        double nShortfall = nTotalWidth - nKashidaWidth * nCopies;
        if (nShortfall > 0)
        {
            ++nCopies;
            double nExcess = nCopies * nKashidaWidth - nTotalWidth;
            if (nExcess > 0)
                nOverlap = nExcess / (nCopies - 1);
        }

        basegfx::B2DPoint aPos = pGlyphIter->linearPos();
        int nCharPos = pGlyphIter->charPos();
        GlyphItemFlags const nFlags = GlyphItemFlags::IS_IN_CLUSTER | GlyphItemFlags::IS_RTL_GLYPH;
        // Move to the left side of the adjusted width and start inserting
        // glyphs there.
        aPos.adjustX(-nClusterWidth + pGlyphIter->origWidth());
        while (nCopies--)
        {
            GlyphItem aKashida(nCharPos, 0, nKashidaIndex, aPos, nFlags, 0, 0, 0, nCharPos);
            pGlyphIter = m_GlyphItems.insert(pGlyphIter, aKashida);
            aPos.adjustX(nKashidaWidth - nOverlap);
            ++pGlyphIter;
            ++nInserted;
        }
    }
}

bool GenericSalLayout::HasFontKashidaPositions() const { return m_bHasFontKashidaPositions; }

// Kashida will be inserted between nCharPos and nNextCharPos.
bool GenericSalLayout::IsKashidaPosValid(int nCharPos, int nNextCharPos) const
{
    // Search for glyph items corresponding to nCharPos and nNextCharPos.
    auto const aGlyph = std::find_if(m_GlyphItems.begin(), m_GlyphItems.end(),
                                      [&](const GlyphItem& g) { return g.charPos() == nCharPos; });
    auto const aNextGlyph = std::find_if(m_GlyphItems.begin(), m_GlyphItems.end(),
                                          [&](const GlyphItem& g) { return g.charPos() == nNextCharPos; });

    // If either is not found then a ligature is created at this position, we
    // can’t insert Kashida here.
    if (aGlyph == m_GlyphItems.end() || aNextGlyph == m_GlyphItems.end())
        return false;

    // If the either character is not supported by this layout, return false so
    // that fallback layouts would be checked for it.
    if (aGlyph->glyphId() == 0 || aNextGlyph->glyphId() == 0)
        return false;

    // Lastly check if this position is kashida-safe.
    return aNextGlyph->IsSafeToInsertKashida();
}

void GenericSalLayout::drawSalLayout(void* pSurface, const basegfx::BColor& rTextColor, bool bAntiAliased) const
{
    Application::GetDefaultDevice()->GetGraphics()->DrawSalLayout(*this, pSurface, rTextColor, bAntiAliased);
}

/* vim:set shiftwidth=4 softtabstop=4 expandtab: */