modules/svg/src/SkSVGText.cpp

/*
 * Copyright 2019 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "modules/svg/include/SkSVGText.h"

#include <limits>

#include "include/core/SkCanvas.h"
#include "include/core/SkFont.h"
#include "include/core/SkFontMgr.h"
#include "include/core/SkFontStyle.h"
#include "include/core/SkString.h"
#include "modules/skshaper/include/SkShaper.h"
#include "modules/svg/include/SkSVGRenderContext.h"
#include "modules/svg/include/SkSVGValue.h"
#include "modules/svg/src/SkSVGTextPriv.h"
#include "src/utils/SkUTF.h"

namespace {

static SkFont ResolveFont(const SkSVGRenderContext& ctx) {
    auto weight = [](const SkSVGFontWeight& w) {
        switch (w.type()) {
            case SkSVGFontWeight::Type::k100:     return SkFontStyle::kThin_Weight;
            case SkSVGFontWeight::Type::k200:     return SkFontStyle::kExtraLight_Weight;
            case SkSVGFontWeight::Type::k300:     return SkFontStyle::kLight_Weight;
            case SkSVGFontWeight::Type::k400:     return SkFontStyle::kNormal_Weight;
            case SkSVGFontWeight::Type::k500:     return SkFontStyle::kMedium_Weight;
            case SkSVGFontWeight::Type::k600:     return SkFontStyle::kSemiBold_Weight;
            case SkSVGFontWeight::Type::k700:     return SkFontStyle::kBold_Weight;
            case SkSVGFontWeight::Type::k800:     return SkFontStyle::kExtraBold_Weight;
            case SkSVGFontWeight::Type::k900:     return SkFontStyle::kBlack_Weight;
            case SkSVGFontWeight::Type::kNormal:  return SkFontStyle::kNormal_Weight;
            case SkSVGFontWeight::Type::kBold:    return SkFontStyle::kBold_Weight;
            case SkSVGFontWeight::Type::kBolder:  return SkFontStyle::kExtraBold_Weight;
            case SkSVGFontWeight::Type::kLighter: return SkFontStyle::kLight_Weight;
            case SkSVGFontWeight::Type::kInherit: {
                SkASSERT(false);
                return SkFontStyle::kNormal_Weight;
            }
        }
        SkUNREACHABLE;
    };

    auto slant = [](const SkSVGFontStyle& s) {
        switch (s.type()) {
            case SkSVGFontStyle::Type::kNormal:  return SkFontStyle::kUpright_Slant;
            case SkSVGFontStyle::Type::kItalic:  return SkFontStyle::kItalic_Slant;
            case SkSVGFontStyle::Type::kOblique: return SkFontStyle::kOblique_Slant;
            case SkSVGFontStyle::Type::kInherit: {
                SkASSERT(false);
                return SkFontStyle::kUpright_Slant;
            }
        }
        SkUNREACHABLE;
    };

    const auto& family = ctx.presentationContext().fInherited.fFontFamily->family();
    const SkFontStyle style(weight(*ctx.presentationContext().fInherited.fFontWeight),
                            SkFontStyle::kNormal_Width,
                            slant(*ctx.presentationContext().fInherited.fFontStyle));

    const auto size =
            ctx.lengthContext().resolve(ctx.presentationContext().fInherited.fFontSize->size(),
                                        SkSVGLengthContext::LengthType::kVertical);

    // TODO: we likely want matchFamilyStyle here, but switching away from legacyMakeTypeface
    // changes all the results when using the default fontmgr.
    auto tf = ctx.fontMgr()->legacyMakeTypeface(family.c_str(), style);

    SkFont font(std::move(tf), size);
    font.setHinting(SkFontHinting::kNone);
    font.setSubpixel(true);
    font.setLinearMetrics(true);
    font.setBaselineSnap(false);
    font.setEdging(SkFont::Edging::kAntiAlias);

    return font;
}

static std::vector<float> ResolveLengths(const SkSVGLengthContext& lctx,
                                         const std::vector<SkSVGLength>& lengths,
                                         SkSVGLengthContext::LengthType lt) {
    std::vector<float> resolved;
    resolved.reserve(lengths.size());

    for (const auto& l : lengths) {
        resolved.push_back(lctx.resolve(l, lt));
    }

    return resolved;
}

static float ComputeAlignmentFactor(const SkSVGPresentationContext& pctx) {
    switch (pctx.fInherited.fTextAnchor->type()) {
    case SkSVGTextAnchor::Type::kStart : return  0.0f;
    case SkSVGTextAnchor::Type::kMiddle: return -0.5f;
    case SkSVGTextAnchor::Type::kEnd   : return -1.0f;
    case SkSVGTextAnchor::Type::kInherit:
        SkASSERT(false);
        return 0.0f;
    }
    SkUNREACHABLE;
}

} // namespace

SkSVGTextContext::ScopedPosResolver::ScopedPosResolver(const SkSVGTextContainer& txt,
                                                       const SkSVGLengthContext& lctx,
                                                       SkSVGTextContext* tctx,
                                                       size_t charIndexOffset)
    : fTextContext(tctx)
    , fParent(tctx->fPosResolver)
    , fCharIndexOffset(charIndexOffset)
    , fX(ResolveLengths(lctx, txt.getX(), SkSVGLengthContext::LengthType::kHorizontal))
    , fY(ResolveLengths(lctx, txt.getY(), SkSVGLengthContext::LengthType::kVertical))
{
    fTextContext->fPosResolver = this;
}

SkSVGTextContext::ScopedPosResolver::ScopedPosResolver(const SkSVGTextContainer& txt,
                                                       const SkSVGLengthContext& lctx,
                                                       SkSVGTextContext* tctx)
    : ScopedPosResolver(txt, lctx, tctx, tctx->fCurrentCharIndex) {}

SkSVGTextContext::ScopedPosResolver::~ScopedPosResolver() {
    fTextContext->fPosResolver = fParent;
}

SkSVGTextContext::PosAttrs SkSVGTextContext::ScopedPosResolver::resolve(size_t charIndex) const {
    PosAttrs attrs;

    if (charIndex < fLastPosIndex) {
        SkASSERT(charIndex >= fCharIndexOffset);
        const auto localCharIndex = charIndex - fCharIndexOffset;

        const auto hasAllLocal = localCharIndex < fX.size() &&
                                 localCharIndex < fY.size();
        if (!hasAllLocal && fParent) {
            attrs = fParent->resolve(charIndex);
        }

        if (localCharIndex < fX.size()) {
            attrs[PosAttrs::kX] = fX[localCharIndex];
        }
        if (localCharIndex < fY.size()) {
            attrs[PosAttrs::kY] = fY[localCharIndex];
        }

        if (!attrs.hasAny()) {
            // Once we stop producing explicit position data, there is no reason to
            // continue trying for higher indices.  We can suppress future lookups.
            fLastPosIndex = charIndex;
        }
    }

    return attrs;
}

SkSVGTextContext::SkSVGTextContext(const SkSVGPresentationContext& pctx, sk_sp<SkFontMgr> fmgr)
    : fShaper(SkShaper::Make(std::move(fmgr)))
    , fChunkPos{ 0, 0 }
    , fChunkAlignmentFactor(ComputeAlignmentFactor(pctx))
{}

void SkSVGTextContext::appendFragment(const SkString& txt, const SkSVGRenderContext& ctx,
                                      SkSVGXmlSpace xs) {
    // https://www.w3.org/TR/SVG11/text.html#WhiteSpace
    // https://www.w3.org/TR/2008/REC-xml-20081126/#NT-S
    auto filterWSDefault = [this](SkUnichar ch) -> SkUnichar {
        // Remove all newline chars.
        if (ch == '\n') {
            return -1;
        }

        // Convert tab chars to space.
        if (ch == '\t') {
            ch = ' ';
        }

        // Consolidate contiguous space chars and strip leading spaces (fPrevCharSpace
        // starts off as true).
        if (fPrevCharSpace && ch == ' ') {
            return -1;
        }

        // TODO: Strip trailing WS?  Doing this across chunks would require another buffering
        //   layer.  In general, trailing WS should have no rendering side effects. Skipping
        //   for now.
        return ch;
    };
    auto filterWSPreserve = [](SkUnichar ch) -> SkUnichar {
        // Convert newline and tab chars to space.
        if (ch == '\n' || ch == '\t') {
            ch = ' ';
        }
        return ch;
    };

    // Stash paints for access from SkShaper callbacks.
    fCurrentFill   = ctx.fillPaint();
    fCurrentStroke = ctx.strokePaint();

    const auto font = ResolveFont(ctx);

    SkSTArray<128, char, true> filtered;
    filtered.reserve_back(SkToInt(txt.size()));

    auto shapePending = [&filtered, &font, this]() {
        // TODO: directionality hints?
        const auto LTR  = true;
        // Initiate shaping: this will generate a series of runs via callbacks.
        fShaper->shape(filtered.data(), filtered.size(), font, LTR, SK_ScalarMax, this);
        filtered.reset();
    };

    const char* ch_ptr = txt.c_str();
    const char* ch_end = ch_ptr + txt.size();

    while (ch_ptr < ch_end) {
        auto ch = SkUTF::NextUTF8(&ch_ptr, ch_end);
        ch = (xs == SkSVGXmlSpace::kDefault)
                ? filterWSDefault(ch)
                : filterWSPreserve(ch);

        if (ch < 0) {
            // invalid utf or char filtered out
            continue;
        }

        SkASSERT(fPosResolver);
        const auto pos = fPosResolver->resolve(fCurrentCharIndex++);

        // Absolute position adjustments define a new chunk.
        // (https://www.w3.org/TR/SVG11/text.html#TextLayoutIntroduction)
        if (pos.has(PosAttrs::kX) || pos.has(PosAttrs::kY)) {
            shapePending();
            this->flushChunk(ctx);

            // New chunk position.
            if (pos.has(PosAttrs::kX)) {
                fChunkPos.fX = pos[PosAttrs::kX];
            }
            if (pos.has(PosAttrs::kY)) {
                fChunkPos.fY = pos[PosAttrs::kY];
            }
        }

        char utf8_buf[SkUTF::kMaxBytesInUTF8Sequence];
        filtered.push_back_n(SkToInt(SkUTF::ToUTF8(ch, utf8_buf)), utf8_buf);

        fPrevCharSpace = (ch == ' ');
    }

    // Note: at this point we have shaped and buffered the current fragment  The active
    // text chunk continues until an explicit or implicit flush.
    shapePending();
}

void SkSVGTextContext::flushChunk(const SkSVGRenderContext& ctx) {
    // The final rendering offset is determined by cumulative chunk advances and alignment.
    const auto pos = fChunkPos + fChunkAdvance * fChunkAlignmentFactor;

    SkTextBlobBuilder blobBuilder;

    for (const auto& run : fRuns) {
        const auto& buf = blobBuilder.allocRunPos(run.font, SkToInt(run.glyphCount));
        std::copy(run.glyphs  .get(), run.glyphs  .get() + run.glyphCount, buf.glyphs);
        std::copy(run.glyphPos.get(), run.glyphPos.get() + run.glyphCount, buf.points());

        // Technically, blobs with compatible paints could be merged --
        // but likely not worth the effort.
        const auto blob = blobBuilder.make();
        if (run.fillPaint) {
            ctx.canvas()->drawTextBlob(blob, pos.fX, pos.fY, *run.fillPaint);
        }
        if (run.strokePaint) {
            ctx.canvas()->drawTextBlob(blob, pos.fX, pos.fY, *run.strokePaint);
        }
    }

    fChunkPos += fChunkAdvance;
    fChunkAdvance = {0,0};
    fChunkAlignmentFactor = ComputeAlignmentFactor(ctx.presentationContext());

    fRuns.clear();
}

SkShaper::RunHandler::Buffer SkSVGTextContext::runBuffer(const RunInfo& ri) {
    SkASSERT(ri.glyphCount);

    fRuns.push_back({
        ri.fFont,
        fCurrentFill   ? std::make_unique<SkPaint>(*fCurrentFill)   : nullptr,
        fCurrentStroke ? std::make_unique<SkPaint>(*fCurrentStroke) : nullptr,
        std::make_unique<SkGlyphID[]>(ri.glyphCount),
        std::make_unique<SkPoint[]  >(ri.glyphCount),
        ri.glyphCount,
        ri.fAdvance,
    });

    return {
        fRuns.back().glyphs.get(),
        fRuns.back().glyphPos.get(),
        nullptr,
        nullptr,
        fChunkAdvance,
    };
}

void SkSVGTextContext::commitRunBuffer(const RunInfo& ri) {
    fChunkAdvance += ri.fAdvance;
}

void SkSVGTextFragment::renderText(const SkSVGRenderContext& ctx, SkSVGTextContext* tctx,
                                   SkSVGXmlSpace xs) const {
    SkSVGRenderContext localContext(ctx, this);

    if (this->onPrepareToRender(&localContext)) {
        this->onRenderText(localContext, tctx, xs);
    }
}

SkPath SkSVGTextFragment::onAsPath(const SkSVGRenderContext&) const {
    // TODO
    return SkPath();
}

void SkSVGTextContainer::appendChild(sk_sp<SkSVGNode> child) {
    // Only allow text nodes.
    switch (child->tag()) {
    case SkSVGTag::kText:
    case SkSVGTag::kTextLiteral:
    case SkSVGTag::kTSpan:
        fChildren.push_back(
            sk_sp<SkSVGTextFragment>(static_cast<SkSVGTextFragment*>(child.release())));
        break;
    default:
        break;
    }
}

void SkSVGTextContainer::onRenderText(const SkSVGRenderContext& ctx, SkSVGTextContext* tctx,
                                      SkSVGXmlSpace) const {
    const SkSVGTextContext::ScopedPosResolver resolver(*this, ctx.lengthContext(), tctx);

    for (const auto& frag : fChildren) {
        // Containers always override xml:space with the local value.
        frag->renderText(ctx, tctx, this->getXmlSpace());
    }
}

// https://www.w3.org/TR/SVG11/text.html#WhiteSpace
template <>
bool SkSVGAttributeParser::parse(SkSVGXmlSpace* xs) {
    static constexpr std::tuple<const char*, SkSVGXmlSpace> gXmlSpaceMap[] = {
            {"default" , SkSVGXmlSpace::kDefault },
            {"preserve", SkSVGXmlSpace::kPreserve},
    };

    return this->parseEnumMap(gXmlSpaceMap, xs) && this->parseEOSToken();
}

bool SkSVGTextContainer::parseAndSetAttribute(const char* name, const char* value) {
    return INHERITED::parseAndSetAttribute(name, value) ||
           this->setX(SkSVGAttributeParser::parse<std::vector<SkSVGLength>>("x", name, value)) ||
           this->setY(SkSVGAttributeParser::parse<std::vector<SkSVGLength>>("y", name, value)) ||
           this->setXmlSpace(SkSVGAttributeParser::parse<SkSVGXmlSpace>("xml:space", name, value));
}

void SkSVGTextContainer::onRender(const SkSVGRenderContext& ctx) const {
    // Root text nodes establish a new text layout context.
    SkSVGTextContext tctx(ctx.presentationContext(), ctx.fontMgr());

    this->onRenderText(ctx, &tctx, this->getXmlSpace());

    tctx.flushChunk(ctx);
}

void SkSVGTextLiteral::onRenderText(const SkSVGRenderContext& ctx, SkSVGTextContext* tctx,
                                    SkSVGXmlSpace xs) const {
    SkASSERT(tctx);

    tctx->appendFragment(this->getText(), ctx, xs);
}