Bug 445081. Refactor code to use ComputeNormalizedHypotenuse ... relanding with a fix so that we don't lose precision and break SVG text mochitests. r=longsonr,sr=mats

content/svg/content/src/nsSVGSVGElement.cpp

@@ -1401,7 +1401,7 @@ nsSVGSVGElement::GetLength(PRUint8 aCtxType)
   case nsSVGUtils::Y:
     return h;
   case nsSVGUtils::XY:
-    return (float)sqrt((w*w+h*h)/2.0);
+    return float(nsSVGUtils::ComputeNormalizedHypotenuse(w, h));
   }
   return 0;
 }

layout/svg/base/src/nsSVGGlyphFrame.cpp

@@ -1230,7 +1230,7 @@ nsSVGGlyphFrame::EnsureTextRun(float *aDrawScale, float *aMetricsScale,
     // diagonal vector (1,1) to the length of the untransformed diagonal
     // (which is sqrt(2)).
     gfxPoint p = m.Transform(gfxPoint(1, 1)) - m.Transform(gfxPoint(0, 0));
-    double contextScale = sqrt((p.x*p.x + p.y*p.y)/2);
+    double contextScale = nsSVGUtils::ComputeNormalizedHypotenuse(p.x, p.y);
 
     nsCAutoString langGroup;
     nsIAtom *langGroupAtom = presContext->GetLangGroup();

layout/svg/base/src/nsSVGUtils.cpp

@@ -944,6 +944,12 @@ nsSVGUtils::NotifyAncestorsOfFilterRegionChange(nsIFrame *aFrame)
   }
 }
 
+double
+nsSVGUtils::ComputeNormalizedHypotenuse(double aWidth, double aHeight)
+{
+  return sqrt((aWidth*aWidth + aHeight*aHeight)/2);
+}
+
 float
 nsSVGUtils::ObjectSpace(nsIDOMSVGRect *aRect, nsSVGLength2 *aLength)
 {
@@ -961,7 +967,7 @@ nsSVGUtils::ObjectSpace(nsIDOMSVGRect *aRect, nsSVGLength2 *aLength)
     float width, height;
     aRect->GetWidth(&width);
     aRect->GetHeight(&height);
-    axis = sqrt(width * width + height * height)/sqrt(2.0f);
+    axis = float(ComputeNormalizedHypotenuse(width, height));
   }
   }
 

layout/svg/base/src/nsSVGUtils.h

@@ -283,6 +283,11 @@ public:
   /* enum for specifying coordinate direction for ObjectSpace/UserSpace */
   enum ctxDirection { X, Y, XY };
 
+  /**
+   * Computes sqrt((aWidth^2 + aHeight^2)/2);
+   */
+  static double ComputeNormalizedHypotenuse(double aWidth, double aHeight);
+
   /* Computes the input length in terms of object space coordinates.
      Input: rect - bounding box
             length - length to be converted