[SVGDom] Opacity optimization

Apply opacity as fill/stroke paint alpha instead of saveLayer, when
possible.

R=robertphillips@google.com,stephana@google.com,reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2353503005

Committed: https://skia.googlesource.com/skia/+/3dbb7b9f196d793fbd16243157ee67638891f5dc
Review-Url: https://codereview.chromium.org/2353503005

6 files changed, 47 insertions, 6 deletions

diff --git a/experimental/svg/model/SkSVGContainer.cpp b/experimental/svg/model/SkSVGContainer.cpp
index 4f91b30bab..af19608d25 100644
--- a/experimental/svg/model/SkSVGContainer.cpp
+++ b/experimental/svg/model/SkSVGContainer.cpp
@@ -14,6 +14,10 @@ void SkSVGContainer::appendChild(sk_sp<SkSVGNode> node) {
     fChildren.push_back(std::move(node));
 }
 
+bool SkSVGContainer::hasChildren() const {
+    return !fChildren.empty();
+}
+
 void SkSVGContainer::onRender(const SkSVGRenderContext& ctx) const {
     for (int i = 0; i < fChildren.count(); ++i) {
         fChildren[i]->render(ctx);
diff --git a/experimental/svg/model/SkSVGContainer.h b/experimental/svg/model/SkSVGContainer.h
index 73c7c1803b..25296fcddb 100644
--- a/experimental/svg/model/SkSVGContainer.h
+++ b/experimental/svg/model/SkSVGContainer.h
@@ -22,6 +22,8 @@ protected:
 
     void onRender(const SkSVGRenderContext&) const override;
 
+    bool hasChildren() const final;
+
     // TODO: add some sort of child iterator, and hide the container.
     SkSTArray<1, sk_sp<SkSVGNode>, true> fChildren;
 
diff --git a/experimental/svg/model/SkSVGNode.cpp b/experimental/svg/model/SkSVGNode.cpp
index 012c7d2277..f40ee5dadb 100644
--- a/experimental/svg/model/SkSVGNode.cpp
+++ b/experimental/svg/model/SkSVGNode.cpp
@@ -31,7 +31,8 @@ bool SkSVGNode::asPaint(const SkSVGRenderContext& ctx, SkPaint* paint) const {
 }
 
 bool SkSVGNode::onPrepareToRender(SkSVGRenderContext* ctx) const {
-    ctx->applyPresentationAttributes(fPresentationAttributes);
+    ctx->applyPresentationAttributes(fPresentationAttributes,
+                                     this->hasChildren() ? 0 : SkSVGRenderContext::kLeaf);
     return true;
 }
 
diff --git a/experimental/svg/model/SkSVGNode.h b/experimental/svg/model/SkSVGNode.h
index dcdb58958a..2a7c836413 100644
--- a/experimental/svg/model/SkSVGNode.h
+++ b/experimental/svg/model/SkSVGNode.h
@@ -69,6 +69,8 @@ protected:
 
     virtual void onSetAttribute(SkSVGAttribute, const SkSVGValue&);
 
+    virtual bool hasChildren() const { return false; }
+
 private:
     SkSVGTag                    fTag;
 
diff --git a/experimental/svg/model/SkSVGRenderContext.cpp b/experimental/svg/model/SkSVGRenderContext.cpp
index 7e2e90e22c..147d64edb3 100644
--- a/experimental/svg/model/SkSVGRenderContext.cpp
+++ b/experimental/svg/model/SkSVGRenderContext.cpp
@@ -239,7 +239,8 @@ const SkSVGNode* SkSVGRenderContext::findNodeById(const SkString& id) const {
     return v ? v->get() : nullptr;
 }
 
-void SkSVGRenderContext::applyPresentationAttributes(const SkSVGPresentationAttributes& attrs) {
+void SkSVGRenderContext::applyPresentationAttributes(const SkSVGPresentationAttributes& attrs,
+                                                     uint32_t flags) {
 
 #define ApplyLazyInheritedAttribute(ATTR)                                               \
     do {                                                                                \
@@ -267,10 +268,36 @@ void SkSVGRenderContext::applyPresentationAttributes(const SkSVGPresentationAttr
 
     // Uninherited attributes.  Only apply to the current context.
 
-    auto* opacity = attrs.fOpacity.getMaybeNull();
-    if (opacity && opacity->value() < 1) {
+    if (auto* opacity = attrs.fOpacity.getMaybeNull()) {
+        this->applyOpacity(opacity->value(), flags);
+    }
+}
+
+void SkSVGRenderContext::applyOpacity(SkScalar opacity, uint32_t flags) {
+    if (opacity >= 1) {
+        return;
+    }
+
+    const bool hasFill   = SkToBool(this->fillPaint());
+    const bool hasStroke = SkToBool(this->strokePaint());
+
+    // We can apply the opacity as paint alpha iif it only affects one atomic draw.
+    // For now, this means a) the target node doesn't have any descendants, and
+    // b) it only has a stroke or a fill (but not both).  Going forward, we may need
+    // to refine this heuristic (e.g. to accommodate markers).
+    if ((flags & kLeaf) && (hasFill ^ hasStroke)) {
+        auto* pctx = fPresentationContext.writable();
+        if (hasFill) {
+            pctx->fFillPaint.setAlpha(
+                SkScalarRoundToInt(opacity * pctx->fFillPaint.getAlpha()));
+        } else {
+            pctx->fStrokePaint.setAlpha(
+                SkScalarRoundToInt(opacity * pctx->fStrokePaint.getAlpha()));
+        }
+    } else {
+        // Expensive, layer-based fall back.
         SkPaint opacityPaint;
-        opacityPaint.setAlpha(opacity_to_alpha(opacity->value()));
+        opacityPaint.setAlpha(opacity_to_alpha(opacity));
         // Balanced in the destructor, via restoreToCount().
         fCanvas->saveLayer(nullptr, &opacityPaint);
     }
diff --git a/experimental/svg/model/SkSVGRenderContext.h b/experimental/svg/model/SkSVGRenderContext.h
index 68209a73cc..393c2849eb 100644
--- a/experimental/svg/model/SkSVGRenderContext.h
+++ b/experimental/svg/model/SkSVGRenderContext.h
@@ -67,7 +67,10 @@ public:
 
     SkCanvas* canvas() const { return fCanvas; }
 
-    void applyPresentationAttributes(const SkSVGPresentationAttributes&);
+    enum ApplyFlags {
+        kLeaf = 1 << 0, // the target node doesn't have descendants
+    };
+    void applyPresentationAttributes(const SkSVGPresentationAttributes&, uint32_t flags);
 
     const SkSVGNode* findNodeById(const SkString&) const;
 
@@ -80,6 +83,8 @@ private:
     void* operator new(size_t, void*)                        = delete;
     SkSVGRenderContext& operator=(const SkSVGRenderContext&) = delete;
 
+    void applyOpacity(SkScalar opacity, uint32_t flags);
+
     const SkSVGIDMapper&                          fIDMapper;
     SkTCopyOnFirstWrite<SkSVGLengthContext>       fLengthContext;
     SkTCopyOnFirstWrite<SkSVGPresentationContext> fPresentationContext;