Handle special angles with care in SkMatrix44

src/utils/SkMatrix44.cpp

Index: src/utils/SkMatrix44.cpp 
=================================================================== 
--- src/utils/SkMatrix44.cpp	(revision 1698) 
+++ src/utils/SkMatrix44.cpp	(working copy) 
@@ -17,6 +17,41 @@ 
 
 #include "SkMatrix44.h" 
 
+#include <algorithm> 
+ 
+namespace { 
+ 
+#ifdef SK_MSCALAR_IS_DOUBLE 
+const static SkMScalar SK_SkMTolerance = 1e-12; 
+#else 
+const static SkMScalar SK_SkMTolerance = 1e-6; 
+#endif 
+ 
+bool ApproximatelyZero(SkMScalar value) { 
+ return fabs(value) <= SK_SkMTolerance; 
+} 
+ 
+// On inputs near multiples of M_PI_2, cos and sin return values that are 
+// close to, but not quite zero. Since this is the common case in rotation, 
+// and because these small errors can lead to future rounding errors, we 
+// clamp to zero where appropriate. 
+ 
+double clamped_cos(SkMScalar radians) { 
+ SkMScalar result = SkDoubleToScalar(cos(radians)); 
+ if (ApproximatelyZero(result)) 
+ result = 0; 
+ return result; 
+} 
+ 
+double clamped_sin(SkMScalar radians) { 
+ SkMScalar result = SkDoubleToScalar(sin(radians)); 
+ if (ApproximatelyZero(result)) 
+ result = 0; 
+ return result; 
+} 
+ 
+} // anonymous namespace 
+ 
 SkMatrix44::SkMatrix44() { 
 this->setIdentity(); 
 } 
@@ -180,8 +215,8 @@ 
 
 void SkMatrix44::setRotateAboutUnit(SkMScalar x, SkMScalar y, SkMScalar z, 
 SkMScalar radians) { 
- double c = cos(radians); 
- double s = sin(radians); 
+ double c = clamped_cos(radians); 
+ double s = clamped_sin(radians); 
 double C = 1 - c; 
 double xs = x * s; 
 double ys = y * s; 
@@ -383,6 +418,3 @@ 
 
 return dst; 
 } 
- 
- 
-