Bug 441780. Fix radial gradient clamping to be more aggressive. r=jwatt,sr=roc

--HG--
extra : rebase_source : 477e5305530e86348a3526a8157f5f93340c644b

layout/reftests/svg/radialGradient-basic-03-ref.svg

@@ -0,0 +1,34 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/licenses/publicdomain/
+-->
+<svg xmlns="http://www.w3.org/2000/svg" >
+
+    <title>Reference for gradient</title>
+
+    <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=441780 -->
+
+    <defs>
+        <radialGradient id="gradient1" fx="0.002">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+        <radialGradient id="gradient2" r="0.4" fx="0.104">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+        <radialGradient id="gradient3" fx="0.998">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+        <radialGradient id="gradient4" r="0.7" fx="1.197">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+    </defs>
+
+    <circle cx="100" cy="100" r="50" fill="url(#gradient1)"/>
+    <circle cx="100" cy="200" r="50" fill="url(#gradient2)"/>
+    <circle cx="200" cy="100" r="50" fill="url(#gradient3)"/>
+    <circle cx="200" cy="200" r="50" fill="url(#gradient4)"/>
+</svg>

layout/reftests/svg/radialGradient-basic-03.svg

@@ -0,0 +1,34 @@
+<!--
+     Any copyright is dedicated to the Public Domain.
+     http://creativecommons.org/licenses/publicdomain/
+-->
+<svg xmlns="http://www.w3.org/2000/svg" >
+
+    <title>Testcase for gradient</title>
+
+    <!-- From https://bugzilla.mozilla.org/show_bug.cgi?id=441780 -->
+
+    <defs>
+        <radialGradient id="gradient1" fx="0">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+        <radialGradient id="gradient2" r="0.4" fx="0.1">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+        <radialGradient id="gradient3" fx="1">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+        <radialGradient id="gradient4" r="0.7" fx="1.3">
+            <stop offset="0" stop-color="lime" />
+            <stop offset="1" stop-color="red"/>
+        </radialGradient>
+    </defs>
+
+    <circle cx="100" cy="100" r="50" fill="url(#gradient1)"/>
+    <circle cx="100" cy="200" r="50" fill="url(#gradient2)"/>
+    <circle cx="200" cy="100" r="50" fill="url(#gradient3)"/>
+    <circle cx="200" cy="200" r="50" fill="url(#gradient4)"/>
+</svg>

layout/reftests/svg/reftest.list

@@ -81,6 +81,7 @@ random-if(MOZ_WIDGET_TOOLKIT=="cocoa") == opacity-and-gradient-01.svg pass.svg
 == pseudo-classes-02.svg pseudo-classes-02-ref.svg
 == radialGradient-basic-01.svg pass.svg
 == radialGradient-basic-02.svg pass.svg
+== radialGradient-basic-03.svg radialGradient-basic-03-ref.svg
 == rect-01.svg pass.svg
 == rect-with-rx-and-ry-01.svg pass.svg
 == rect-with-rx-or-ry-01.svg rect-with-rx-or-ry-01-ref.svg

layout/svg/base/src/nsSVGGradientFrame.cpp

@@ -563,11 +563,14 @@ nsSVGRadialGradientFrame::CreateGradient()
     // The focal point (fFx and fFy) must be clamped to be *inside* - not on -
     // the circumference of the gradient or we'll get rendering anomalies. We
     // calculate the distance from the focal point to the gradient center and
-    // make sure it is *less* than the gradient radius. 0.999 is used as the
+    // make sure it is *less* than the gradient radius. 0.99 is used as the
     // factor of the radius because it's close enough to 1 that we won't get a
     // fringe at the edge of the gradient if we clamp, but not so close to 1
     // that rounding error will give us the same results as using fR itself.
-    double dMax = 0.999 * r;
+    // Also note that .99 < 255/256/2 which is the limit of the fractional part
+    // of cairo's 24.8 fixed point representation divided by 2 to ensure that
+    // we get different cairo fractions
+    double dMax = 0.99 * r;
     float dx = fx - cx;
     float dy = fy - cy;
     double d = sqrt((dx * dx) + (dy * dy));