First pass at Rect Effect

src/core/SkMatrix.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMatrix.h"
 #include "Sk64.h"
 #include "SkFloatBits.h"
@@ skipping 171 matching lines @@
 
     SkScalar mx = fMat[kMScaleX];
     SkScalar my = fMat[kMScaleY];
     // if no skew, can just compare scale factors
     if (!(mask & kAffine_Mask)) {
         return !SkScalarNearlyZero(mx) && SkScalarNearlyEqual(SkScalarAbs(mx), SkScalarAbs(my));
     }
     SkScalar sx = fMat[kMSkewX];
     SkScalar sy = fMat[kMSkewY];
 
+    // TODO: I (rphillips) think there should be an || in here (see preservesRightAngles)
     // degenerate matrix, non-similarity
     if (SkScalarNearlyZero(mx) && SkScalarNearlyZero(my)
         && SkScalarNearlyZero(sx) && SkScalarNearlyZero(sy)) {
         return false;
     }
 
     // it has scales and skews, but it could also be rotation, check it out.
     SkVector vec[2];
     vec[0].set(mx, sx);
     vec[1].set(sy, my);
 
     return SkScalarNearlyZero(vec[0].dot(vec[1]), SkScalarSquare(tol)) &&
            SkScalarNearlyEqual(vec[0].lengthSqd(), vec[1].lengthSqd(),
-                SkScalarSquare(tol));
+                               SkScalarSquare(tol));
+}
+
+bool SkMatrix::preservesRightAngles(SkScalar tol) const {
+    TypeMask mask = this->getType();
+    
+    if (mask <= (SkMatrix::kTranslate_Mask | SkMatrix::kScale_Mask)) {
+        // identity, translate and/or scale
+        return true;
+    }
+    if (mask & kPerspective_Mask) {
+        return false;
+    }
+
+    SkASSERT(mask & kAffine_Mask);
+
+    SkScalar mx = fMat[kMScaleX];
+    SkScalar my = fMat[kMScaleY];
+    SkScalar sx = fMat[kMSkewX];
+    SkScalar sy = fMat[kMSkewY];
+
+    if ((SkScalarNearlyZero(mx) && SkScalarNearlyZero(sx)) ||
+        (SkScalarNearlyZero(my) && SkScalarNearlyZero(sy))) {
+        // degenerate matrix
+        return false;
+    }
+
+    // it has scales and skews, but it could also be rotation, check it out.
+    SkVector vec[2];
+    vec[0].set(mx, sx);
+    vec[1].set(sy, my);
+
+    return SkScalarNearlyZero(vec[0].dot(vec[1]), SkScalarSquare(tol)) &&
+           SkScalarNearlyEqual(vec[0].lengthSqd(), vec[1].lengthSqd(),
+                               SkScalarSquare(tol));
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkMatrix::setTranslate(SkScalar dx, SkScalar dy) {
     if (SkScalarToCompareType(dx) || SkScalarToCompareType(dy)) {
         fMat[kMTransX] = dx;
         fMat[kMTransY] = dy;
 
         fMat[kMScaleX] = fMat[kMScaleY] = SK_Scalar1;
@@ skipping 1708 matching lines @@
         dst.fLeft *= scale;
         dst.fTop *= scale;
         dst.fRight *= scale;
         dst.fBottom *= scale;
     }
 
     SkIRect idst;
     dst.round(&idst);
     return isrc == idst;
 }