add SkMatrix::decomposeScale

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 "SkString.h"
@@ skipping 1585 matching lines @@
     SK_COMPILE_ASSERT(offsetof(SkMatrix, fTypeMask) == offsetof(PODMatrix, typemask), BadfTypeMask);
 
     static const PODMatrix invalid =
         { {SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
            SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
            SK_ScalarMax, SK_ScalarMax, SK_ScalarMax },
          kTranslate_Mask | kScale_Mask | kAffine_Mask | kPerspective_Mask };
     return invalid.asSkMatrix();
 }
 
+bool SkMatrix::decomposeScale(SkSize* scale, SkMatrix* remaining) const {
+    if (this->hasPerspective()) {
+        return false;
+    }
+
+    const SkScalar sx = SkVector::Length(this->getScaleX(), this->getSkewY());
+    const SkScalar sy = SkVector::Length(this->getSkewX(), this->getScaleY());
+    if (!SkScalarIsFinite(sx) || !SkScalarIsFinite(sy) ||
+        SkScalarNearlyZero(sx) || SkScalarNearlyZero(sy)) {
+        return false;
+    }
+
+    if (scale) {
+        scale->set(sx, sy);
+    }
+    if (remaining) {
+        *remaining = *this;
+        remaining->postScale(SkScalarInvert(sx), SkScalarInvert(sy));
+    }
+    return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 size_t SkMatrix::writeToMemory(void* buffer) const {
     // TODO write less for simple matrices
     static const size_t sizeInMemory = 9 * sizeof(SkScalar);
     if (buffer) {
         memcpy(buffer, fMat, sizeInMemory);
     }
     return sizeInMemory;
 }
@@ skipping 168 matching lines @@
         rotation1->fX = cos1;
         rotation1->fY = sin1;
     }
     if (rotation2) {
         rotation2->fX = cos2;
         rotation2->fY = sin2;
     }
 
     return true;
 }