Bug 1807479 - fill fallback should always be black and stroke fallback should always be invisible r=emilio

If we encounter fill: context-stroke, which neither Chrome nor Firefox currently support for markers Chrome falls back to the initial fill colour (black), whereas Firefox falls back to the initial stroke color (none). The reverse happens for stroke: context-fill. This patch aligns us with Chrome till we support context-fill and context-stroke properly.

https://www.w3.org/TR/SVG2/painting.html#SpecifyingFillPaint and https://www.w3.org/TR/SVG2/painting.html#SpecifyingStrokePaint define the initial fill and stroke colours.

Differential Revision: https://phabricator.services.mozilla.com/D165495

layout/reftests/svg/fallback-color-02-ref.svg

@@ -4,7 +4,7 @@
 -->
 <svg xmlns="http://www.w3.org/2000/svg" >
 
-<title>Reference for fallback colours</title>
+<title>Reference for stroke fallback colours</title>
 
 <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=368840 -->
 

layout/reftests/svg/fallback-color-05b.svg

@@ -0,0 +1,12 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<svg xmlns="http://www.w3.org/2000/svg">
+
+  <title>Testcase for context-stroke fallback colour</title>
+
+  <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=1807479 -->
+
+  <rect width="100%" height="100%" fill="context-stroke"/>
+</svg>

layout/reftests/svg/fallback-color-06-ref.svg

@@ -0,0 +1,12 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<svg xmlns="http://www.w3.org/2000/svg" >
+
+<title>Reference for fill fallback colours</title>
+
+<!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=1807479 -->
+
+	<rect x="0%" y="0%" width="100%" height="100%" fill="black"/>
+</svg>

layout/reftests/svg/reftest.list

@@ -204,11 +204,12 @@ random == dynamic-use-nested-01b.svg dynamic-use-nested-01-ref.svg
 
 == fallback-color-01a.svg pass.svg
 == fallback-color-01b.svg pass.svg
-== fallback-color-02a.svg fallback-color-02-ref.svg
-== fallback-color-02b.svg fallback-color-02-ref.svg
+== fallback-color-02.svg fallback-color-02-ref.svg
 == fallback-color-03.svg pass.svg
 fuzzy(0-1,0-2) == fallback-color-04.svg pass.svg
-== fallback-color-05.svg fallback-color-05-ref.svg
+== fallback-color-05a.svg fallback-color-05-ref.svg
+== fallback-color-05b.svg fallback-color-05-ref.svg
+== fallback-color-06.svg fallback-color-06-ref.svg
 
 == filter-and-clip.svg filter-and-clip-ref.svg
 == filter-basic-01.svg pass.svg

layout/svg/SVGContextPaint.cpp

@@ -100,6 +100,7 @@ static void SetupInheritablePaint(const DrawTarget* aDrawTarget,
                                   SVGContextPaint* aOuterContextPaint,
                                   SVGContextPaintImpl::Paint& aTargetPaint,
                                   StyleSVGPaint nsStyleSVG::*aFillOrStroke,
+                                  nscolor aDefaultFallbackColor,
                                   imgDrawingParams& aImgParams) {
   const nsStyleSVG* style = aFrame->StyleSVG();
   SVGPaintServerFrame* ps =
@@ -138,8 +139,8 @@ static void SetupInheritablePaint(const DrawTarget* aDrawTarget,
     }
   }
 
-  nscolor color =
-      SVGUtils::GetFallbackOrPaintColor(*aFrame->Style(), aFillOrStroke);
+  nscolor color = SVGUtils::GetFallbackOrPaintColor(
+      *aFrame->Style(), aFillOrStroke, aDefaultFallbackColor);
   aTargetPaint.SetColor(color);
 }
 
@@ -161,7 +162,7 @@ DrawMode SVGContextPaintImpl::Init(const DrawTarget* aDrawTarget,
 
     SetupInheritablePaint(aDrawTarget, aContextMatrix, aFrame, opacity,
                           aOuterContextPaint, mFillPaint, &nsStyleSVG::mFill,
-                          aImgParams);
+                          NS_RGB(0, 0, 0), aImgParams);
 
     SetFillOpacity(opacity);
 
@@ -175,9 +176,9 @@ DrawMode SVGContextPaintImpl::Init(const DrawTarget* aDrawTarget,
     float opacity =
         SVGUtils::GetOpacity(style->mStrokeOpacity, aOuterContextPaint);
 
-    SetupInheritablePaint(aDrawTarget, aContextMatrix, aFrame, opacity,
-                          aOuterContextPaint, mStrokePaint,
-                          &nsStyleSVG::mStroke, aImgParams);
+    SetupInheritablePaint(
+        aDrawTarget, aContextMatrix, aFrame, opacity, aOuterContextPaint,
+        mStrokePaint, &nsStyleSVG::mStroke, NS_RGBA(0, 0, 0, 0), aImgParams);
 
     SetStrokeOpacity(opacity);
 

layout/svg/SVGUtils.cpp

@@ -1308,20 +1308,17 @@ gfxRect SVGUtils::PathExtentsToMaxStrokeExtents(const gfxRect& aPathExtents,
 
 /* static */
 nscolor SVGUtils::GetFallbackOrPaintColor(
-    const ComputedStyle& aStyle, StyleSVGPaint nsStyleSVG::*aFillOrStroke) {
+    const ComputedStyle& aStyle, StyleSVGPaint nsStyleSVG::*aFillOrStroke,
+    nscolor aDefaultFallbackColor) {
   const auto& paint = aStyle.StyleSVG()->*aFillOrStroke;
   nscolor color;
   switch (paint.kind.tag) {
     case StyleSVGPaintKind::Tag::PaintServer:
     case StyleSVGPaintKind::Tag::ContextStroke:
-      color = paint.fallback.IsColor()
-                  ? paint.fallback.AsColor().CalcColor(aStyle)
-                  : NS_RGBA(0, 0, 0, 0);
-      break;
     case StyleSVGPaintKind::Tag::ContextFill:
       color = paint.fallback.IsColor()
                   ? paint.fallback.AsColor().CalcColor(aStyle)
-                  : NS_RGB(0, 0, 0);
+                  : aDefaultFallbackColor;
       break;
     default:
       color = paint.kind.AsColor().CalcColor(aStyle);
@@ -1407,8 +1404,8 @@ void SVGUtils::MakeFillPatternFor(nsIFrame* aFrame, gfxContext* aContext,
   // On failure, use the fallback colour in case we have an
   // objectBoundingBox where the width or height of the object is zero.
   // See http://www.w3.org/TR/SVG11/coords.html#ObjectBoundingBox
-  sRGBColor color(sRGBColor::FromABGR(
-      GetFallbackOrPaintColor(*aFrame->Style(), &nsStyleSVG::mFill)));
+  sRGBColor color(sRGBColor::FromABGR(GetFallbackOrPaintColor(
+      *aFrame->Style(), &nsStyleSVG::mFill, NS_RGB(0, 0, 0))));
   color.a *= fillOpacity;
   aOutPattern->InitColorPattern(ToDeviceColor(color));
 }
@@ -1474,8 +1471,8 @@ void SVGUtils::MakeStrokePatternFor(nsIFrame* aFrame, gfxContext* aContext,
   // On failure, use the fallback colour in case we have an
   // objectBoundingBox where the width or height of the object is zero.
   // See http://www.w3.org/TR/SVG11/coords.html#ObjectBoundingBox
-  sRGBColor color(sRGBColor::FromABGR(
-      GetFallbackOrPaintColor(*aFrame->Style(), &nsStyleSVG::mStroke)));
+  sRGBColor color(sRGBColor::FromABGR(GetFallbackOrPaintColor(
+      *aFrame->Style(), &nsStyleSVG::mStroke, NS_RGBA(0, 0, 0, 0))));
   color.a *= strokeOpacity;
   aOutPattern->InitColorPattern(ToDeviceColor(color));
 }

layout/svg/SVGUtils.h

@@ -477,7 +477,8 @@ class SVGUtils final {
   }
 
   static nscolor GetFallbackOrPaintColor(
-      const ComputedStyle&, StyleSVGPaint nsStyleSVG::*aFillOrStroke);
+      const ComputedStyle&, StyleSVGPaint nsStyleSVG::*aFillOrStroke,
+      nscolor aDefaultFallbackColor);
 
   static void MakeFillPatternFor(nsIFrame* aFrame, gfxContext* aContext,
                                  GeneralPattern* aOutPattern,