[SVGDom] Don't truncate opacity scalars

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 "SkSVGRenderContext.h"
@@ skipping 95 matching lines @@
     case SkSVGPaint::Type::kCurrentColor:
         SkDebugf("unimplemented 'currentColor' paint type");
         // Fall through.
     case SkSVGPaint::Type::kNone:
         // Fall through.
     case SkSVGPaint::Type::kInherit:
         break;
     }
 }
 
+inline uint8_t opacity_to_alpha(SkScalar o) {
+    return SkTo<uint8_t>(SkScalarRoundToInt(o * 255));
+}
+
 // Commit the selected attribute to the paint cache.
 template <SkSVGAttribute>
 void commitToPaint(const SkSVGPresentationAttributes&,
                    const SkSVGLengthContext&,
                    SkSVGPresentationContext*);
 
 template <>
 void commitToPaint<SkSVGAttribute::kFill>(const SkSVGPresentationAttributes& attrs,
                                           const SkSVGLengthContext&,
                                           SkSVGPresentationContext* pctx) {
     applySvgPaint(*attrs.fFill.get(), &pctx->fFillPaint);
 }
 
 template <>
 void commitToPaint<SkSVGAttribute::kStroke>(const SkSVGPresentationAttributes& attrs,
                                             const SkSVGLengthContext&,
                                             SkSVGPresentationContext* pctx) {
     applySvgPaint(*attrs.fStroke.get(), &pctx->fStrokePaint);
 }
 
 template <>
 void commitToPaint<SkSVGAttribute::kFillOpacity>(const SkSVGPresentationAttributes& attrs,
                                                  const SkSVGLengthContext&,
                                                  SkSVGPresentationContext* pctx) {
-    pctx->fFillPaint.setAlpha(static_cast<uint8_t>(*attrs.fFillOpacity.get() * 255));
+    pctx->fFillPaint.setAlpha(opacity_to_alpha(*attrs.fFillOpacity.get()));
 }
 
 template <>
 void commitToPaint<SkSVGAttribute::kStrokeLineCap>(const SkSVGPresentationAttributes& attrs,
                                                    const SkSVGLengthContext&,
                                                    SkSVGPresentationContext* pctx) {
     const auto& cap = *attrs.fStrokeLineCap.get();
     if (cap.type() != SkSVGLineCap::Type::kInherit) {
         pctx->fStrokePaint.setStrokeCap(toSkCap(cap));
     }
 }
 
 template <>
 void commitToPaint<SkSVGAttribute::kStrokeLineJoin>(const SkSVGPresentationAttributes& attrs,
                                                     const SkSVGLengthContext&,
                                                     SkSVGPresentationContext* pctx) {
     const auto& join = *attrs.fStrokeLineJoin.get();
     if (join.type() != SkSVGLineJoin::Type::kInherit) {
         pctx->fStrokePaint.setStrokeJoin(toSkJoin(join));
     }
 }
 
 template <>
 void commitToPaint<SkSVGAttribute::kStrokeOpacity>(const SkSVGPresentationAttributes& attrs,
                                                    const SkSVGLengthContext&,
                                                    SkSVGPresentationContext* pctx) {
-    pctx->fStrokePaint.setAlpha(static_cast<uint8_t>(*attrs.fStrokeOpacity.get() * 255));
+    pctx->fStrokePaint.setAlpha(opacity_to_alpha(*attrs.fStrokeOpacity.get()));
 }
 
 template <>
 void commitToPaint<SkSVGAttribute::kStrokeWidth>(const SkSVGPresentationAttributes& attrs,
                                                  const SkSVGLengthContext& lctx,
                                                  SkSVGPresentationContext* pctx) {
     auto strokeWidth = lctx.resolve(*attrs.fStrokeWidth.get(),
                                     SkSVGLengthContext::LengthType::kOther);
     pctx->fStrokePaint.setStrokeWidth(strokeWidth);
 }
@@ skipping 61 matching lines @@
     ApplyLazyInheritedAttribute(StrokeLineJoin);
     ApplyLazyInheritedAttribute(StrokeOpacity);
     ApplyLazyInheritedAttribute(StrokeWidth);
 
 #undef ApplyLazyInheritedAttribute
 
     // Uninherited attributes.  Only apply to the current context.
 
     if (auto* opacity = attrs.fOpacity.getMaybeNull()) {
         SkPaint opacityPaint;
-        opacityPaint.setAlpha(static_cast<uint8_t>(opacity->value() * 255));
+        opacityPaint.setAlpha(opacity_to_alpha(opacity->value()));
         // 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;
 }