More robust matrix decomposition

ui/gfx/transform_unittest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // MSVC++ requires this to be set before any other includes to get M_PI.
 #define _USE_MATH_DEFINES
 
 #include "ui/gfx/transform.h"
 
 #include <cmath>
@@ skipping 1343 matching lines @@
     while (rotation > 360.0)
       rotation -= 360.0;
 
     const float epsilon = 0.00015f;
     EXPECT_NEAR(rotation, degrees, epsilon);
     EXPECT_NEAR(decomp.scale[0], degrees + 1, epsilon);
     EXPECT_NEAR(decomp.scale[1], 2 * degrees + 1, epsilon);
   }
 }
 
+TEST(XFormTest, DecomposeTransform) {
+  for (float scale = 0.001f; scale < 2.0f; scale += 0.001f) {
+    gfx::Transform transform;
+    transform.Scale(scale, scale);
+    EXPECT_TRUE(transform.Preserves2dAxisAlignment());
+
+    DecomposedTransform decomp;
+    bool success = DecomposeTransform(&decomp, transform);
+    EXPECT_TRUE(success);
+
+    gfx::Transform compose_transform = ComposeTransform(decomp);
+    EXPECT_TRUE(compose_transform.Preserves2dAxisAlignment());
+  }
+}
+
 TEST(XFormTest, IntegerTranslation) {
   gfx::Transform transform;
   EXPECT_TRUE(transform.IsIdentityOrIntegerTranslation());
 
   transform.Translate3d(1, 2, 3);
   EXPECT_TRUE(transform.IsIdentityOrIntegerTranslation());
 
   transform.MakeIdentity();
   transform.Translate3d(-1, -2, -3);
   EXPECT_TRUE(transform.IsIdentityOrIntegerTranslation());
@@ skipping 1311 matching lines @@
   EXPECT_EQ(expected.ToString(), box.ToString());
 
   Transform singular;
   singular.Scale3d(0.f, 0.f, 0.f);
   EXPECT_FALSE(singular.TransformBoxReverse(&box));
 }
 
 }  // namespace
 
 }  // namespace gfx