skia2/experimental/svg/model/SkSVGGradient.cpp

/*
 * Copyright 2017 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "experimental/svg/model/SkSVGGradient.h"
#include "experimental/svg/model/SkSVGRenderContext.h"
#include "experimental/svg/model/SkSVGStop.h"
#include "experimental/svg/model/SkSVGValue.h"

void SkSVGGradient::setHref(const SkSVGStringType& href) {
    fHref = std::move(href);
}

void SkSVGGradient::setGradientTransform(const SkSVGTransformType& t) {
    fGradientTransform = t;
}

void SkSVGGradient::setSpreadMethod(const SkSVGSpreadMethod& spread) {
    fSpreadMethod = spread;
}

void SkSVGGradient::onSetAttribute(SkSVGAttribute attr, const SkSVGValue& v) {
    switch (attr) {
    case SkSVGAttribute::kGradientTransform:
        if (const auto* t = v.as<SkSVGTransformValue>()) {
            this->setGradientTransform(*t);
        }
        break;
    case SkSVGAttribute::kHref:
        if (const auto* href = v.as<SkSVGStringValue>()) {
            this->setHref(*href);
        }
        break;
    case SkSVGAttribute::kSpreadMethod:
        if (const auto* spread = v.as<SkSVGSpreadMethodValue>()) {
            this->setSpreadMethod(*spread);
        }
        break;
    default:
        this->INHERITED::onSetAttribute(attr, v);
    }
}

// https://www.w3.org/TR/SVG11/pservers.html#LinearGradientElementHrefAttribute
void SkSVGGradient::collectColorStops(const SkSVGRenderContext& ctx,
                                      StopPositionArray* pos,
                                      StopColorArray* colors) const {
    // Used to resolve percentage offsets.
    const SkSVGLengthContext ltx(SkSize::Make(1, 1));

    for (const auto& child : fChildren) {
        if (child->tag() != SkSVGTag::kStop) {
            continue;
        }

        const auto& stop = static_cast<const SkSVGStop&>(*child);
        colors->push_back(this->resolveStopColor(ctx, stop));
        pos->push_back(SkTPin(ltx.resolve(stop.offset(), SkSVGLengthContext::LengthType::kOther),
                              0.f, 1.f));
    }

    SkASSERT(colors->count() == pos->count());

    if (pos->empty() && !fHref.isEmpty()) {
        const auto ref = ctx.findNodeById(fHref);
        if (ref && (ref->tag() == SkSVGTag::kLinearGradient ||
                    ref->tag() == SkSVGTag::kRadialGradient)) {
            static_cast<const SkSVGGradient*>(ref.get())->collectColorStops(ctx, pos, colors);
        }
    }
}

SkColor SkSVGGradient::resolveStopColor(const SkSVGRenderContext& ctx,
                                        const SkSVGStop& stop) const {
    const SkSVGStopColor& stopColor = stop.stopColor();
    SkColor color;
    switch (stopColor.type()) {
        case SkSVGStopColor::Type::kColor:
            color = stopColor.color();
            break;
        case SkSVGStopColor::Type::kCurrentColor:
            color = *ctx.presentationContext().fInherited.fColor;
            break;
        case SkSVGStopColor::Type::kICCColor:
            SkDebugf("unimplemented 'icccolor' stop-color type\n");
            color = SK_ColorBLACK;
            break;
        case SkSVGStopColor::Type::kInherit:
            SkDebugf("unimplemented 'inherit' stop-color type\n");
            color = SK_ColorBLACK;
            break;
    }
    return SkColorSetA(color, SkScalarRoundToInt(stop.stopOpacity() * 255));
}

bool SkSVGGradient::onAsPaint(const SkSVGRenderContext& ctx, SkPaint* paint) const {
    StopColorArray colors;
    StopPositionArray pos;

    this->collectColorStops(ctx, &pos, &colors);

    // TODO:
    //       * stop (lazy?) sorting
    //       * href loop detection
    //       * href attribute inheritance (not just color stops)
    //       * objectBoundingBox units support

    static_assert(static_cast<SkTileMode>(SkSVGSpreadMethod::Type::kPad) ==
                  SkTileMode::kClamp, "SkSVGSpreadMethod::Type is out of sync");
    static_assert(static_cast<SkTileMode>(SkSVGSpreadMethod::Type::kRepeat) ==
                  SkTileMode::kRepeat, "SkSVGSpreadMethod::Type is out of sync");
    static_assert(static_cast<SkTileMode>(SkSVGSpreadMethod::Type::kReflect) ==
                  SkTileMode::kMirror, "SkSVGSpreadMethod::Type is out of sync");
    const auto tileMode = static_cast<SkTileMode>(fSpreadMethod.type());

    paint->setShader(this->onMakeShader(ctx, colors.begin(), pos.begin(), colors.count(), tileMode,
                                        fGradientTransform));
    return true;
}