add SkMatrix::decomposeScale

tests/MatrixTest.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMath.h"
 #include "SkMatrix.h"
 #include "SkMatrixUtils.h"
@@ skipping 753 matching lines @@
         for (int j = 0; j < kTripleCount; ++j) {
             SkScalar dst[3];
             mats[i].mapHomogeneousPoints(dst, &randTriples[j*3], 1);
             REPORTER_ASSERT(reporter, naive_homogeneous_mapping(mats[i], &randTriples[j*3], dst));
         }
     }
     }
 
 }
 
+static bool check_decompScale(const SkMatrix& matrix) {
+    SkSize scale;
+    SkMatrix remaining;
+
+    if (!matrix.decomposeScale(&scale, &remaining)) {
+        return false;
+    }
+    if (scale.width() <= 0 || scale.height() <= 0) {
+        return false;
+    }
+    remaining.preScale(scale.width(), scale.height());
+    return nearly_equal(matrix, remaining);
+}
+
+static void test_decompScale(skiatest::Reporter* reporter) {
+    SkMatrix m;
+
+    m.reset();
+    REPORTER_ASSERT(reporter, check_decompScale(m));
+    m.setScale(2, 3);
+    REPORTER_ASSERT(reporter, check_decompScale(m));
+    m.setRotate(35, 0, 0);
+    REPORTER_ASSERT(reporter, check_decompScale(m));
+
+    m.setScale(1, 0);
+    REPORTER_ASSERT(reporter, !check_decompScale(m));
+}
+
 DEF_TEST(Matrix, reporter) {
     SkMatrix    mat, inverse, iden1, iden2;
 
     mat.reset();
     mat.setTranslate(SK_Scalar1, SK_Scalar1);
     REPORTER_ASSERT(reporter, mat.invert(&inverse));
     iden1.setConcat(mat, inverse);
     REPORTER_ASSERT(reporter, is_identity(iden1));
 
     mat.setScale(SkIntToScalar(2), SkIntToScalar(4));
@@ skipping 98 matching lines @@
     mat.set(SkMatrix::kMSkewX, SK_ScalarNaN);
     mat2.set(SkMatrix::kMSkewX, SK_ScalarNaN);
     REPORTER_ASSERT(reporter, !are_equal(reporter, mat, mat2));
 
     test_matrix_min_max_scale(reporter);
     test_matrix_preserve_shape(reporter);
     test_matrix_recttorect(reporter);
     test_matrix_decomposition(reporter);
     test_matrix_homogeneous(reporter);
     test_set9(reporter);
+
+    test_decompScale(reporter);
 }
 
 DEF_TEST(Matrix_Concat, r) {
     SkMatrix a;
     a.setTranslate(10, 20);
 
     SkMatrix b;
     b.setScale(3, 5);
 
     SkMatrix expected;
     expected.setConcat(a,b);
 
     REPORTER_ASSERT(r, expected == SkMatrix::Concat(a, b));
 }