Added check for ill-conditioned invert

include/core/SkMatrix.h

Index: include/core/SkMatrix.h
diff --git a/include/core/SkMatrix.h b/include/core/SkMatrix.h
index 0252bc7101c423217093f1a7f281af71b792dfb5..9a75b3db1f2e62d9f93a5c96681ffdd3a032d0b8 100644
--- a/include/core/SkMatrix.h
+++ b/include/core/SkMatrix.h
@@ -719,6 +719,12 @@ private:
     SkScalar         fMat[9];
     mutable uint32_t fTypeMask;
 
+    /** Are all elements of the matrix finite?
+     */
+    bool isFinite() const;
+
+    static void ComputeInv(const SkScalar* src, SkScalar* dst, SkScalar scale, bool isPersp);

[reed1, 2015/06/17 19:27:56]

nit:
- skia tries to use [] for parameters that are many...
- document scale as 1/determinant ?
- 1 dst and lots of src params --> (dst, src0, src1, src2)

... ComputeInv(SkScaar dst[], const SkScalar src[], SkScalar invDet, bool
isPersp);

[robertphillips, 2015/06/17 19:44:46]

Done.

+
     void setScaleTranslate(SkScalar sx, SkScalar sy, SkScalar tx, SkScalar ty) {
         fMat[kMScaleX] = sx;
         fMat[kMSkewX]  = 0;