Make SkMatrix44::invert() check for finite 1/det instead of magic value

src/utils/SkMatrix44.cpp

Index: src/utils/SkMatrix44.cpp
diff --git a/src/utils/SkMatrix44.cpp b/src/utils/SkMatrix44.cpp
index 92c8715faaec94972770f8db05b372c1245366a8..a33b2ed8ae9dc3a5f0d75139ecf3e0b6c1fd2090 100644
--- a/src/utils/SkMatrix44.cpp
+++ b/src/utils/SkMatrix44.cpp
@@ -529,13 +529,13 @@ bool SkMatrix44::invert(SkMatrix44* inverse) const {
     // Calculate the determinant
     double det = b00 * b11 - b01 * b10 + b02 * b09 + b03 * b08 - b04 * b07 + b05 * b06;
 
-    if (dabs(det) < TOO_SMALL_FOR_DETERMINANT) {
+    double invdet = 1.0 / det;

[reed1, 2013/08/15 19:40:46]

// If det is zero, we want to return false. However, we also want to return
false
// if 1/det overflows to infinity (i.e. det is denomralized). Both of these are 
// handled by checking that 1/det is finite.

+    if (!isfinite(invdet)) {
         return false;
     }
     if (NULL == inverse) {
         return true;
     }
-    double invdet = 1.0 / det;
 
     b00 *= invdet;
     b01 *= invdet;
@@ -568,7 +568,6 @@ bool SkMatrix44::invert(SkMatrix44* inverse) const {
     inverse->fMat[3][3] = SkDoubleToMScalar(a20 * b03 - a21 * b01 + a22 * b00);
     inverse->dirtyTypeMask();
 
-    inverse->dirtyTypeMask();
     return true;
 }