SkMatrix::preScale() is too conservative

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 "SkFloatBits.h"
 #include "SkRSXform.h"
@@ skipping 362 matching lines @@
     // so we can get away with these blind multiplies.
 
     fMat[kMScaleX] *= sx;
     fMat[kMSkewY]  *= sx;
     fMat[kMPersp0] *= sx;
 
     fMat[kMSkewX]  *= sy;
     fMat[kMScaleY] *= sy;
     fMat[kMPersp1] *= sy;
 
+#ifndef SK_SUPPORT_LEGACY_PRESCALE_SEMANTICS
+    // Attempt to simplify our type when applying an inverse scale.
+    // TODO: The persp/affine preconditions are in place to keep the mask consistent with
+    //       what computeTypeMask() would produce (persp/skew always implies kScale).
+    //       We should investigate whether these flag dependencies are truly needed.
+    if (fMat[kMScaleX] == 1 && fMat[kMScaleY] == 1
+        && !(fTypeMask & (kPerspective_Mask | kAffine_Mask))) {
+        this->clearTypeMask(kScale_Mask);
+    } else {
+        this->orTypeMask(kScale_Mask);
+    }
+#else
     this->orTypeMask(kScale_Mask);
+#endif
 }
 
 void SkMatrix::postScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
     if (1 == sx && 1 == sy) {
         return;
     }
     SkMatrix    m;
     m.setScale(sx, sy, px, py);
     this->postConcat(m);
 }
@@ skipping 1379 matching lines @@
     const SkScalar m11 = m00;
     const SkScalar m12 = fTy;
 
     quad[0].set(m02, m12);
     quad[1].set(m00 * width + m02, m10 * width + m12);
     quad[2].set(m00 * width + m01 * height + m02, m10 * width + m11 * height + m12);
     quad[3].set(m01 * height + m02, m11 * height + m12);
 #endif
 }