[SVGDom] Opacity optimization

experimental/svg/model/SkSVGRenderContext.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkSVGAttribute.h"
 #include "SkSVGNode.h"
@@ skipping 221 matching lines @@
 
 SkSVGRenderContext::~SkSVGRenderContext() {
     fCanvas->restoreToCount(fCanvasSaveCount);
 }
 
 const SkSVGNode* SkSVGRenderContext::findNodeById(const SkString& id) const {
     const auto* v = fIDMapper.find(id);
     return v ? v->get() : nullptr;
 }
 
-void SkSVGRenderContext::applyPresentationAttributes(const SkSVGPresentationAttributes& attrs) {
+void SkSVGRenderContext::applyPresentationAttributes(const SkSVGPresentationAttributes& attrs,
+                                                     uint32_t flags) {
 
 #define ApplyLazyInheritedAttribute(ATTR)                                               \
     do {                                                                                \
         /* All attributes should be defined on the inherited context. */                \
         SkASSERT(fPresentationContext->fInherited.f ## ATTR.isValid());                 \
         const auto* value = attrs.f ## ATTR.getMaybeNull();                             \
         if (value && *value != *fPresentationContext->fInherited.f ## ATTR.get()) {     \
             /* Update the local attribute value */                                      \
             fPresentationContext.writable()->fInherited.f ## ATTR.set(*value);          \
             /* Update the cached paints */                                              \
             commitToPaint<SkSVGAttribute::k ## ATTR>(attrs, *this,    \
                                                      fPresentationContext.writable());  \
         }                                                                               \
     } while (false)
 
     ApplyLazyInheritedAttribute(Fill);
     ApplyLazyInheritedAttribute(FillOpacity);
     ApplyLazyInheritedAttribute(Stroke);
     ApplyLazyInheritedAttribute(StrokeLineCap);
     ApplyLazyInheritedAttribute(StrokeLineJoin);
     ApplyLazyInheritedAttribute(StrokeOpacity);
     ApplyLazyInheritedAttribute(StrokeWidth);
 
 #undef ApplyLazyInheritedAttribute
 
     // 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);
     }
 }
 
 const SkPaint* SkSVGRenderContext::fillPaint() const {
     const SkSVGPaint::Type paintType = fPresentationContext->fInherited.fFill.get()->type();
     return paintType != SkSVGPaint::Type::kNone ? &fPresentationContext->fFillPaint : nullptr;
 }
 
 const SkPaint* SkSVGRenderContext::strokePaint() const {
     const SkSVGPaint::Type paintType = fPresentationContext->fInherited.fStroke.get()->type();
     return paintType != SkSVGPaint::Type::kNone ? &fPresentationContext->fStrokePaint : nullptr;
 }