Implement transform snapping for gfx::Transforms.

ui/gfx/transform_util_unittest.cc

 // Copyright (c) 2012 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.
 
 #include "ui/gfx/transform_util.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/point.h"
+#include "ui/gfx/point3_f.h"
+#include "ui/gfx/rect_f.h"
 
 namespace gfx {
 namespace {
 
 TEST(TransformUtilTest, GetScaleTransform) {
   const Point kAnchor(20, 40);
   const float kScale = 0.5f;
 
   Transform scale = GetScaleTransform(kAnchor, kScale);
 
   const int kOffset = 10;
   for (int sign_x = -1; sign_x <= 1; ++sign_x) {
     for (int sign_y = -1; sign_y <= 1; ++sign_y) {
       Point test(kAnchor.x() + sign_x * kOffset,
                  kAnchor.y() + sign_y * kOffset);
       scale.TransformPoint(&test);
 
       EXPECT_EQ(Point(kAnchor.x() + sign_x * kOffset * kScale,
                       kAnchor.y() + sign_y * kOffset * kScale),
                 test);
     }
   }
 }
 
+TEST(TransformUtilTest, SnapRotation) {
+  gfx::Transform transform;
+
+  // Translation must be a multiple of scale or else the back mapping will not
+  // be an integer.
+  transform.Translate(20.0, -30.0);
+  transform.Scale(2.0, 2.0);
+  transform.RotateAboutZAxis(89.99);
+
+  DecomposedTransform decomposed, result;
+
+  DecomposeTransform(&decomposed, transform);
+
+  RectF viewport(1920.0, 1200.0);
+  bool snapped = SnapRotation(&result, decomposed, viewport);
+
+  EXPECT_TRUE(snapped) << "Viewport should snap for this rotation.";
+}
+
+TEST(TransformUtilTest, NoSnapRotation) {
+  gfx::Transform transform;
+
+  // Translation must be a multiple of scale or else the back mapping will not
+  // be an integer.
+  transform.Translate(102.0, -96.0);
+  transform.Scale(2.0, 2.0);
+  transform.RotateAboutZAxis(89.9);
+
+  DecomposedTransform decomposed, result;
+
+  DecomposeTransform(&decomposed, transform);
+
+  RectF viewport(1920.0, 1200.0);
+  bool snapped = SnapRotation(&result, decomposed, viewport);
+
+  EXPECT_FALSE(snapped) << "Viewport should not snap for this rotation.";
+}

[Ian Vollick, 2013/09/11 12:19:48]

Please add tests for a viewport that's far away from the center of rotation. I'm
hoping you can find a case where snapping succeeds when the viewport is close to
the center of rotation, but fails when it's far away, even though the matrix is
the same.

[avallee, 2013/09/14 01:32:25]

Done.

+
 }  // namespace
 }  // namespace gfx