Bug 885621. Fix gfxPattern::GetMatrix() with azure and add GetInverseMatrix(). r=bas

Currently SetMatrix will take the Inverse of the passed in matrix but GetMatrix
doesn't not invert it on the way out. This fixes that and adds a
GetInverseMatrix() so that we don't double invert it when we need the inverse.

--HG--
extra : rebase_source : 6bb2049ccee22c62b1825687ecd09ddd1aad8b2e

gfx/thebes/gfxContext.cpp

@@ -1431,8 +1431,7 @@ gfxContext::Mask(gfxPattern *pattern)
       }
 
       if (needsClip) {
-        Matrix mat = ToMatrix(pattern->GetMatrix());
-        mat.Invert();
+        Matrix mat = ToMatrix(pattern->GetInverseMatrix());
         mat = mat * GetDTTransform();
 
         mDT->SetTransform(mat);

gfx/thebes/gfxPattern.cpp

@@ -122,6 +122,23 @@ gfxPattern::GetMatrix() const
     cairo_matrix_t mat;
     cairo_pattern_get_matrix(mPattern, &mat);
     return gfxMatrix(*reinterpret_cast<gfxMatrix*>(&mat));
+  } else {
+    // invert at the higher precision of gfxMatrix
+    // cause we need to convert at some point anyways
+    gfxMatrix mat = ThebesMatrix(mTransform);
+    mat.Invert();
+    return mat;
+  }
+}
+
+gfxMatrix
+gfxPattern::GetInverseMatrix() const
+{
+  if (mPattern) {
+    cairo_matrix_t mat;
+    cairo_pattern_get_matrix(mPattern, &mat);
+    cairo_matrix_invert(&mat);
+    return gfxMatrix(*reinterpret_cast<gfxMatrix*>(&mat));
   } else {
     return ThebesMatrix(mTransform);
   }

gfx/thebes/gfxPattern.h

@@ -41,6 +41,7 @@ public:
 
     void SetMatrix(const gfxMatrix& matrix);
     gfxMatrix GetMatrix() const;
+    gfxMatrix GetInverseMatrix() const;
 
     /* Get an Azure Pattern for the current Cairo pattern. aPattern transform
      * specifies the transform that was set on the DrawTarget when the pattern