From 3b61eb914aef80dc27ea1eabce3c53918edbd0d0 Mon Sep 17 00:00:00 2001
From: Zack Weinberg <zweinberg@mozilla.com>
Date: Mon, 2 Nov 2009 21:00:46 -0800
Subject: [PATCH] Bug 526075: Clamp tiny sines to zero when computing
 transformation matrices.

---
 layout/base/tests/test_bug435293-skew.html | 14 ++------------
 layout/reftests/transform/reftest.list     |  6 +++---
 layout/style/nsStyleTransformMatrix.cpp    | 17 ++++++++++++++---
 3 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/layout/base/tests/test_bug435293-skew.html b/layout/base/tests/test_bug435293-skew.html
index 5ac7744c9aa4..b6e6e5066cb0 100644
--- a/layout/base/tests/test_bug435293-skew.html
+++ b/layout/base/tests/test_bug435293-skew.html
@@ -121,19 +121,9 @@ function runtests() {
   is(style.getPropertyValue("-moz-transform"), "matrix(1, 1, 1, 1, 0px, 0px)",
      "Test3: Skew proper matrix is applied");
 
-  // Argument reduction here may give us a value that is close to but not
-  // exactly zero.
   style = window.getComputedStyle(document.getElementById("test4"), "");
-  tformStyle = style.getPropertyValue("-moz-transform");
-  tformValues = tformStyle.substring(tformStyle.indexOf('(') + 1,
-                                     tformStyle.indexOf(')')).split(',');
-  is((+tformValues[0]), 1, "Test4: skew angle wrap: param 0 is 1");
-  is((+tformValues[1]), 1, "Test4: skew angle wrap: param 1 is 1");
-  ok(verifyRounded(tformValues[2], 0),
-     "Test4: skew angle wrap: rounded param 2 is 0");
-  is((+tformValues[3]), 1, "Test4: skew angle wrap: param 3 is 1");
-  is(tformValues[4].trim(), "0px", "Test4: skew angle wrap: param 4 is 0px");
-  is(tformValues[5].trim(), "0px", "Test4: skew angle wrap: param 5 is 0px");
+  is(style.getPropertyValue("-moz-transform"), "matrix(1, 1, 0, 1, 0px, 0px)",
+     "Test4: Skew angle wrap: proper matrix is applied");
 
   style = window.getComputedStyle(document.getElementById("test5"), "");
   is(style.getPropertyValue("-moz-transform"), "matrix(1, -1, 1, 1, 0px, 0px)",
diff --git a/layout/reftests/transform/reftest.list b/layout/reftests/transform/reftest.list
index 923a8a8217b3..1995d16c06c4 100644
--- a/layout/reftests/transform/reftest.list
+++ b/layout/reftests/transform/reftest.list
@@ -7,14 +7,14 @@
 != compound-1a.html compound-1-fail.html
 # translatex should act like position: relative
 == translatex-1a.html translatex-1-ref.html
-random-if(MOZ_WIDGET_TOOLKIT=="cocoa") == translatex-1b.html translatex-1-ref.html
+== translatex-1b.html translatex-1-ref.html
 == translatex-1c.html translatex-1-ref.html
 == translatex-1d.html translatex-1-ref.html
 == translatex-1e.html translatex-1-ref.html
 == translatex-1a.html translatex-1-ref-2.html
 # translatey should act like position: relative
 == translatey-1a.html translatey-1-ref.html
-random-if(MOZ_WIDGET_TOOLKIT=="cocoa") == translatey-1b.html translatey-1-ref.html
+== translatey-1b.html translatey-1-ref.html
 == translatey-1c.html translatey-1-ref.html
 == translatey-1d.html translatey-1-ref.html
 == translatey-1e.html translatey-1-ref.html
@@ -23,7 +23,7 @@ random-if(MOZ_WIDGET_TOOLKIT=="cocoa") == translatey-1b.html translatey-1-ref.ht
 == translatey-2.html translatey-1-ref.html
 # translate should act like position: relative
 != translate-1a.html translate-1-ref.html
-random-if(MOZ_WIDGET_TOOLKIT=="cocoa") == translate-1b.html translate-1-ref.html
+== translate-1b.html translate-1-ref.html
 == translate-1c.html translate-1-ref.html
 == translate-1d.html translate-1-ref.html
 == translate-1e.html translate-1-ref.html
diff --git a/layout/style/nsStyleTransformMatrix.cpp b/layout/style/nsStyleTransformMatrix.cpp
index 13d0ecbf0ceb..fd3bd842a295 100644
--- a/layout/style/nsStyleTransformMatrix.cpp
+++ b/layout/style/nsStyleTransformMatrix.cpp
@@ -53,6 +53,17 @@
  * involving angles need to be done in 'double'.
  */
 
+/* Force small values to zero.  We do this to avoid having sin(360deg)
+ * evaluate to a tiny but nonzero value.
+ */
+static double FlushToZero(double aVal)
+{
+  if (-FLT_EPSILON < aVal && aVal < FLT_EPSILON)
+    return 0.0f;
+  else
+    return aVal;
+}
+
 /* Computes tan(aTheta).  For values of aTheta such that tan(aTheta) is
  * undefined or very large, SafeTangent returns a manageably large value
  * of the correct sign.
@@ -73,7 +84,7 @@ static double SafeTangent(double aTheta)
   else if (cosTheta < 0 && cosTheta >= -kEpsilon)
     cosTheta = -kEpsilon;
 
-  return sinTheta / cosTheta;
+  return FlushToZero(sinTheta / cosTheta);
 }
 
 /* Constructor sets the data to the identity matrix. */
@@ -425,8 +436,8 @@ static void ProcessRotate(float aMain[4], const nsCSSValue::Array* aData)
    * (see http://www.w3.org/TR/SVG/coords.html#RotationDefined)
    */
   double theta = aData->Item(1).GetAngleValueInRadians();
-  float cosTheta = cos(theta);
-  float sinTheta = sin(theta);
+  float cosTheta = FlushToZero(cos(theta));
+  float sinTheta = FlushToZero(sin(theta));
 
   aMain[0] = cosTheta;
   aMain[1] = sinTheta;