modules/sksg/src/SkSGRenderNode.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 "SkSGRenderNode.h"

#include "SkCanvas.h"
#include "SkImageFilter.h"
#include "SkPaint.h"

namespace sksg {

RenderNode::RenderNode(uint32_t inval_traits) : INHERITED(inval_traits) {}

void RenderNode::render(SkCanvas* canvas, const RenderContext* ctx) const {
    SkASSERT(!this->hasInval());
    if (!this->bounds().isEmpty()) {
        this->onRender(canvas, ctx);
    }
}

const RenderNode* RenderNode::nodeAt(const SkPoint& p) const {
    return this->bounds().contains(p.x(), p.y()) ? this->onNodeAt(p) : nullptr;
}

static SkAlpha ScaleAlpha(SkAlpha alpha, float opacity) {
   return SkToU8(sk_float_round2int(alpha * opacity));
}

bool RenderNode::RenderContext::requiresIsolation() const {
    // Note: fShader is never applied on isolation layers.
    return ScaleAlpha(SK_AlphaOPAQUE, fOpacity) != SK_AlphaOPAQUE
        || fColorFilter
        || fBlendMode != SkBlendMode::kSrcOver;
}

void RenderNode::RenderContext::modulatePaint(const SkMatrix& ctm, SkPaint* paint) const {
    paint->setAlpha(ScaleAlpha(paint->getAlpha(), fOpacity));
    paint->setColorFilter(SkColorFilters::Compose(fColorFilter, paint->refColorFilter()));
    if (fShader) {
        if (fShaderCTM != ctm) {
            // The shader is declared to operate under a specific transform, but due to the
            // deferral mechanism, other transformations might have been pushed to the state.
            // We want to undo these transforms:
            //
            //   shaderCTM x T = ctm
            //
            //   =>  T = Inv(shaderCTM) x ctm
            //
            //   =>  Inv(T) = Inv(Inv(shaderCTM) x ctm)
            //
            //   =>  Inv(T) = Inv(ctm) x shaderCTM

            SkMatrix inv_ctm;
            if (ctm.invert(&inv_ctm)) {
                paint->setShader(
                            fShader->makeWithLocalMatrix(SkMatrix::Concat(inv_ctm, fShaderCTM)));
            }
        } else {
            // No intervening transforms.
            paint->setShader(fShader);
        }
    }
    paint->setBlendMode(fBlendMode);
}

RenderNode::ScopedRenderContext::ScopedRenderContext(SkCanvas* canvas, const RenderContext* ctx)
    : fCanvas(canvas)
    , fCtx(ctx ? *ctx : RenderContext())
    , fRestoreCount(canvas->getSaveCount()) {}

RenderNode::ScopedRenderContext::~ScopedRenderContext() {
    if (fRestoreCount >= 0) {
        fCanvas->restoreToCount(fRestoreCount);
    }
}

RenderNode::ScopedRenderContext&&
RenderNode::ScopedRenderContext::modulateOpacity(float opacity) {
    SkASSERT(opacity >= 0 && opacity <= 1);
    fCtx.fOpacity *= opacity;
    return std::move(*this);
}

RenderNode::ScopedRenderContext&&
RenderNode::ScopedRenderContext::modulateColorFilter(sk_sp<SkColorFilter> cf) {
    fCtx.fColorFilter = SkColorFilters::Compose(std::move(fCtx.fColorFilter), std::move(cf));
    return std::move(*this);
}

RenderNode::ScopedRenderContext&&
RenderNode::ScopedRenderContext::modulateShader(sk_sp<SkShader> sh, const SkMatrix& shader_ctm) {
    // Topmost shader takes precedence.
    if (!fCtx.fShader) {
        fCtx.fShader = std::move(sh);
        fCtx.fShaderCTM = shader_ctm;
    }

    return std::move(*this);
}

RenderNode::ScopedRenderContext&&
RenderNode::ScopedRenderContext::modulateBlendMode(SkBlendMode mode) {
    fCtx.fBlendMode = mode;
    return std::move(*this);
}

RenderNode::ScopedRenderContext&&
RenderNode::ScopedRenderContext::setIsolation(const SkRect& bounds, const SkMatrix& ctm,
                                              bool isolation) {
    if (isolation && fCtx.requiresIsolation()) {
        SkPaint layer_paint;
        fCtx.modulatePaint(ctm, &layer_paint);
        fCanvas->saveLayer(bounds, &layer_paint);

        // Reset only the props applied via isolation layers.
        fCtx.fColorFilter = nullptr;
        fCtx.fOpacity     = 1;
        fCtx.fBlendMode   = SkBlendMode::kSrcOver;
    }

    return std::move(*this);
}

RenderNode::ScopedRenderContext&&
RenderNode::ScopedRenderContext::setFilterIsolation(const SkRect& bounds, const SkMatrix& ctm,
                                                    sk_sp<SkImageFilter> filter) {
    SkPaint layer_paint;
    fCtx.modulatePaint(ctm, &layer_paint);

    SkASSERT(!layer_paint.getImageFilter());
    layer_paint.setImageFilter(std::move(filter));
    fCanvas->saveLayer(bounds, &layer_paint);
    fCtx = RenderContext();

    return std::move(*this);
}

} // namespace sksg