Bug 1090211 - Calculate the bounds of circles and ellipses using Math when we have a rectilinear transform. r=longsonr

dom/svg/SVGCircleElement.cpp

@@ -81,6 +81,34 @@ SVGCircleElement::GetLengthInfo()
 //----------------------------------------------------------------------
 // nsSVGPathGeometryElement methods
 
+bool
+SVGCircleElement::GetGeometryBounds(Rect* aBounds, Float aStrokeWidth,
+                                    const Matrix& aTransform)
+{
+  float x, y, r;
+  GetAnimatedLengthValues(&x, &y, &r, nullptr);
+
+  if (r <= 0.f) {
+    // Rendering of the element is disabled
+    aBounds->MoveTo(x, y);
+    aBounds->SetEmpty();
+    return true;
+  }
+
+  if (aTransform.IsRectilinear()) {
+    // Optimize the case where we can treat the circle as a rectangle and
+    // still get tight bounds.
+    if (aStrokeWidth > 0.f) {
+      r += aStrokeWidth / 2.f;
+    }
+    Rect rect(x - r, y - r, 2 * r, 2 * r);
+    *aBounds = aTransform.TransformBounds(rect);
+    return true;
+  }
+
+  return false;
+}
+
 TemporaryRef<Path>
 SVGCircleElement::BuildPath(PathBuilder* aBuilder)
 {

dom/svg/SVGCircleElement.h

@@ -30,6 +30,8 @@ public:
   virtual bool HasValidDimensions() const MOZ_OVERRIDE;
 
   // nsSVGPathGeometryElement methods:
+  virtual bool GetGeometryBounds(Rect* aBounds, Float aStrokeWidth,
+                                 const Matrix& aTransform) MOZ_OVERRIDE;
   virtual TemporaryRef<Path> BuildPath(PathBuilder* aBuilder) MOZ_OVERRIDE;
 
   virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const MOZ_OVERRIDE;

dom/svg/SVGEllipseElement.cpp

@@ -92,6 +92,35 @@ SVGEllipseElement::GetLengthInfo()
 //----------------------------------------------------------------------
 // nsSVGPathGeometryElement methods
 
+bool
+SVGEllipseElement::GetGeometryBounds(Rect* aBounds, Float aStrokeWidth,
+                                     const Matrix& aTransform)
+{
+  float x, y, rx, ry;
+  GetAnimatedLengthValues(&x, &y, &rx, &ry, nullptr);
+
+  if (rx <= 0.f || ry <= 0.f) {
+    // Rendering of the element is disabled
+    aBounds->MoveTo(x, y);
+    aBounds->SetEmpty();
+    return true;
+  }
+
+  if (aTransform.IsRectilinear()) {
+    // Optimize the case where we can treat the ellipse as a rectangle and
+    // still get tight bounds.
+    if (aStrokeWidth > 0.f) {
+      rx += aStrokeWidth / 2.f;
+      ry += aStrokeWidth / 2.f;
+    }
+    Rect rect(x - rx, y - ry, 2 * rx, 2 * ry);
+    *aBounds = aTransform.TransformBounds(rect);
+    return true;
+  }
+
+  return false;
+}
+
 TemporaryRef<Path>
 SVGEllipseElement::BuildPath(PathBuilder* aBuilder)
 {

dom/svg/SVGEllipseElement.h

@@ -30,6 +30,8 @@ public:
   virtual bool HasValidDimensions() const MOZ_OVERRIDE;
 
   // nsSVGPathGeometryElement methods:
+  virtual bool GetGeometryBounds(Rect* aBounds, Float aStrokeWidth,
+                                 const Matrix& aTransform) MOZ_OVERRIDE;
   virtual TemporaryRef<Path> BuildPath(PathBuilder* aBuilder) MOZ_OVERRIDE;
 
   virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const MOZ_OVERRIDE;

dom/svg/nsSVGPathGeometryElement.h

@@ -70,6 +70,12 @@ public:
   virtual bool IsMarkable();
   virtual void GetMarkPoints(nsTArray<nsSVGMark> *aMarks);
 
+  /**
+   * A method that can be faster than using a Moz2D Path and calling GetBounds/
+   * GetStrokedBounds on it.  It also helps us avoid rounding error for simple
+   * shapes and simple transforms where the Moz2D Path backends can fail to
+   * produce the clean integer bounds that content authors expect in some cases.
+   */
   virtual bool GetGeometryBounds(Rect* aBounds, Float aStrokeWidth,
                                  const Matrix& aTransform) {
     return false;