Migrate from MathUtil::inverse() to gfx::Transform::GetInverse()

BUG=159972, 163769

Review URL: https://codereview.chromium.org/11644008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175363 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 75 insertions, 1 deletions

diff --git a/ui/gfx/transform.cc b/ui/gfx/transform.cc
index a4a4e64..c2b6ba2 100644
--- a/ui/gfx/transform.cc
+++ b/ui/gfx/transform.cc
@@ -245,7 +245,14 @@ bool Transform::IsBackFaceVisible() const {
 }
 
 bool Transform::GetInverse(Transform* transform) const {
-  return matrix_.invert(&transform->matrix_);
+  if (!matrix_.invert(&transform->matrix_)) {
+    // Initialize the return value to identity if this matrix turned
+    // out to be un-invertible.
+    transform->MakeIdentity();
+    return false;
+  }
+
+  return true;
 }
 
 void Transform::Transpose() {
diff --git a/ui/gfx/transform.h b/ui/gfx/transform.h
index 6cd10b1..95de30f 100644
--- a/ui/gfx/transform.h
+++ b/ui/gfx/transform.h
@@ -22,7 +22,17 @@ class Vector3dF;
 // copy/assign.
 class UI_EXPORT Transform {
  public:
+
+  enum SkipInitialization {
+    kSkipInitialization
+  };
+
   Transform() : matrix_(SkMatrix44::kIdentity_Constructor) {}
+
+  // Skips initializing this matrix to avoid overhead, when we know it will be
+  // initialized before use.
+  Transform(SkipInitialization)
+      : matrix_(SkMatrix44::kUninitialized_Constructor) {}
   Transform(const Transform& rhs) : matrix_(rhs.matrix_) {}
   // Initialize with the concatenation of lhs * rhs.
   Transform(const Transform& lhs, const Transform& rhs)
diff --git a/ui/gfx/transform_unittest.cc b/ui/gfx/transform_unittest.cc
index 31892c3..1984fea 100644
--- a/ui/gfx/transform_unittest.cc
+++ b/ui/gfx/transform_unittest.cc
@@ -1182,6 +1182,63 @@ TEST(XFormTest, IntegerTranslation) {
   EXPECT_FALSE(transform.IsIdentityOrIntegerTranslation());
 }
 
+TEST(XFormTest, verifyMatrixInversion)
+{
+  {
+    // Invert a translation
+    gfx::Transform translation;
+    translation.Translate3d(2, 3, 4);
+    EXPECT_TRUE(translation.IsInvertible());
+
+    gfx::Transform inverse_translation;
+    bool is_invertible = translation.GetInverse(&inverse_translation);
+    EXPECT_TRUE(is_invertible);
+    EXPECT_ROW1_EQ(1, 0, 0, -2, inverse_translation);
+    EXPECT_ROW2_EQ(0, 1, 0, -3, inverse_translation);
+    EXPECT_ROW3_EQ(0, 0, 1, -4, inverse_translation);
+    EXPECT_ROW4_EQ(0, 0, 0,  1, inverse_translation);
+  }
+
+  {
+    // Invert a non-uniform scale
+    gfx::Transform scale;
+    scale.Scale3d(4, 10, 100);
+    EXPECT_TRUE(scale.IsInvertible());
+
+    gfx::Transform inverse_scale;
+    bool is_invertible = scale.GetInverse(&inverse_scale);
+    EXPECT_TRUE(is_invertible);
+    EXPECT_ROW1_EQ(0.25,   0,    0, 0, inverse_scale);
+    EXPECT_ROW2_EQ(0,    .1f,    0, 0, inverse_scale);
+    EXPECT_ROW3_EQ(0,      0, .01f, 0, inverse_scale);
+    EXPECT_ROW4_EQ(0,      0,    0, 1, inverse_scale);
+  }
+
+  {
+    // Try to invert a matrix that is not invertible.
+    // The inverse() function should reset the output matrix to identity.
+    gfx::Transform uninvertible;
+    uninvertible.matrix().setDouble(0, 0, 0);
+    uninvertible.matrix().setDouble(1, 1, 0);
+    uninvertible.matrix().setDouble(2, 2, 0);
+    uninvertible.matrix().setDouble(3, 3, 0);
+    EXPECT_FALSE(uninvertible.IsInvertible());
+
+    gfx::Transform inverse_of_uninvertible;
+
+    // Add a scale just to more easily ensure that inverse_of_uninvertible is
+    // reset to identity.
+    inverse_of_uninvertible.Scale3d(4, 10, 100);
+
+    bool is_invertible = uninvertible.GetInverse(&inverse_of_uninvertible);
+    EXPECT_FALSE(is_invertible);
+    EXPECT_TRUE(inverse_of_uninvertible.IsIdentity());
+    EXPECT_ROW1_EQ(1, 0, 0, 0, inverse_of_uninvertible);
+    EXPECT_ROW2_EQ(0, 1, 0, 0, inverse_of_uninvertible);
+    EXPECT_ROW3_EQ(0, 0, 1, 0, inverse_of_uninvertible);
+    EXPECT_ROW4_EQ(0, 0, 0, 1, inverse_of_uninvertible);
+  }
+}
 
 }  // namespace