Bug 1247218 - Should consider CSS transform when using non-scaling-stroke r=longsonr

We remove initial x/y offset for nsSVGUtils::GetTransformMatrixInUserSpace
so that it can be used in not-nondisplay context. Previously it was only
used in nondisplay context, where x/y offset is always 0.

Then we use this utility to get the transform matrix to judge whether we need
special care for non-scaling-stroke. The old matrix doesn't account for CSS
transform.

Differential Revision: https://phabricator.services.mozilla.com/D28193

--HG--
extra : moz-landing-system : lando

layout/reftests/svg/reftest.list

@@ -162,6 +162,7 @@ fuzzy-if(d2d&&layersGPUAccelerated,0-3,0-1200) == dynamic-rect-02.svg dynamic-re
 == dynamic-stroke-01.svg pass.svg
 == dynamic-stroke-opacity-01.svg pass.svg
 == dynamic-stroke-width-01.svg pass.svg
+== test_bug1247218.html test_bug1247218-ref.html
 == dynamic-switch-01.svg pass.svg
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == dynamic-text-01.svg dynamic-text-01-ref.svg # bug 1392106
 fuzzy-if(d2d&&layersGPUAccelerated,0-3,0-12739) == dynamic-text-02.svg dynamic-text-02-ref.svg # bug 776038 for Win7, Win8

layout/reftests/svg/test_bug1247218-ref.html

@@ -0,0 +1,3 @@
+<svg style="width: 500px; height: 500px; border: 1px solid green;">
+  <rect id="square" transform="translate(100,200) scale(1,2.5)" stroke="blue" vector-effect="non-scaling-stroke" stroke-width="6" x="50px" y="50px" width="50px" height="50px" fill="pink" />
+</svg>

layout/reftests/svg/test_bug1247218.html

@@ -0,0 +1,8 @@
+<style>
+  #square{
+    transform: translate(100px,200px) scale(1,2.5);
+  }
+</style>
+<svg style="width: 500px; height: 500px; border: 1px solid green;">
+  <rect id="square" stroke="blue" vector-effect="non-scaling-stroke" stroke-width="6" x="50px" y="50px" width="50px" height="50px" fill="pink" />
+</svg>

layout/svg/nsSVGUtils.cpp

@@ -1248,13 +1248,12 @@ bool nsSVGUtils::GetNonScalingStrokeTransform(nsIFrame* aFrame,
     return false;
   }
 
-  nsIContent* content = aFrame->GetContent();
-  MOZ_ASSERT(content->IsSVGElement(), "bad cast");
+  MOZ_ASSERT(aFrame->GetContent()->IsSVGElement(), "should be an SVG element");
 
-  *aUserToOuterSVG = ThebesMatrix(
-      SVGContentUtils::GetCTM(static_cast<SVGElement*>(content), true));
+  nsSVGOuterSVGFrame* outer = nsSVGUtils::GetOuterSVGFrame(aFrame);
+  *aUserToOuterSVG = nsSVGUtils::GetTransformMatrixInUserSpace(aFrame, outer);
 
-  return !aUserToOuterSVG->IsIdentity();
+  return aUserToOuterSVG->HasNonTranslation();
 }
 
 // The logic here comes from _cairo_stroke_style_max_distance_from_path
@@ -1705,19 +1704,21 @@ gfxMatrix nsSVGUtils::GetTransformMatrixInUserSpace(const nsIFrame* aFrame,
              "Only use this wrapper for SVG elements");
 
   Matrix mm;
-  auto trans = nsLayoutUtils::GetTransformToAncestor(aFrame, aAncestor);
+  auto trans = nsLayoutUtils::GetTransformToAncestor(aFrame, aAncestor,
+                                                     nsIFrame::IN_CSS_UNITS);
+
   trans.ProjectTo2D();
   trans.CanDraw2D(&mm);
   gfxMatrix ret = ThebesMatrix(mm);
 
-  float devPixelPerCSSPixel = float(AppUnitsPerCSSPixel()) /
-                              aFrame->PresContext()->AppUnitsPerDevPixel();
+  float initPositionX = NSAppUnitsToFloatPixels(aFrame->GetPosition().x,
+                                                AppUnitsPerCSSPixel()),
+        initPositionY = NSAppUnitsToFloatPixels(aFrame->GetPosition().y,
+                                                AppUnitsPerCSSPixel());
 
-  // The matrix obtained by nsIFrame::GetTransformMatrix is "from
-  // device space to device space", we need to change it to be "from
-  // user space to user space".
-  ret.PreScale(devPixelPerCSSPixel, devPixelPerCSSPixel);
-  ret.PostScale(1.f / devPixelPerCSSPixel, 1.f / devPixelPerCSSPixel);
+  // Remove the initial displacement to mimic the behavior
+  // of SVGElement::PrependLocalTransformsTo().
+  ret = ret.PreTranslate(-initPositionX, -initPositionY);
 
   return ret;
 }