Check for identity before doing matrix math in more places in gfx::Transform

ui/gfx/transform.cc

Index: ui/gfx/transform.cc
diff --git a/ui/gfx/transform.cc b/ui/gfx/transform.cc
index b75bb7fb419113197228c69c6e699521fb904188..3dc339cd7bb67da6c1a20a873b11383fb5d6b296 100644
--- a/ui/gfx/transform.cc
+++ b/ui/gfx/transform.cc
@@ -207,13 +207,17 @@ void Transform::ApplyPerspectiveDepth(double depth) {
 }
 
 void Transform::PreconcatTransform(const Transform& transform) {
-  if (!transform.matrix_.isIdentity()) {
+  if (matrix_.isIdentity()) {
+    *this = transform;

[danakj, 2012/11/30 01:29:26]

matrix_ = transform.matrix_; like below?

+  } else if (!transform.matrix_.isIdentity()) {
     matrix_.preConcat(transform.matrix_);
   }
 }
 
 void Transform::ConcatTransform(const Transform& transform) {
-  if (!transform.matrix_.isIdentity()) {
+  if (matrix_.isIdentity()) {
+    matrix_ = transform.matrix_;
+  } else if (!transform.matrix_.isIdentity()) {
     matrix_.postConcat(transform.matrix_);
   }
 }
@@ -223,6 +227,9 @@ bool Transform::IsIdentity() const {
 }
 
 bool Transform::IsIdentityOrTranslation() const {
+  if (matrix_.isIdentity())
+    return true;
+
   bool has_no_perspective = !matrix_.getDouble(3, 0) &&
                             !matrix_.getDouble(3, 1) &&
                             !matrix_.getDouble(3, 2) &&
@@ -243,6 +250,9 @@ bool Transform::IsIdentityOrTranslation() const {
 }
 
 bool Transform::IsScaleOrTranslation() const {
+  if (matrix_.isIdentity())
+    return true;
+
   bool has_no_perspective = !matrix_.getDouble(3, 0) &&
                             !matrix_.getDouble(3, 1) &&
                             !matrix_.getDouble(3, 2) &&
@@ -270,6 +280,9 @@ bool Transform::IsInvertible() const {
 }
 
 bool Transform::IsBackFaceVisible() const {
+  if (matrix_.isIdentity())
+    return false;
+
   // Compute whether a layer with a forward-facing normal of (0, 0, 1) would
   // have its back face visible after applying the transform.
   //
@@ -368,13 +381,17 @@ bool Transform::Blend(const Transform& from, double progress) {
 }
 
 Transform Transform::operator*(const Transform& other) const {
+  if (matrix_.isIdentity())
+    return other;
+  if (other.matrix_.isIdentity())
+    return *this;
   Transform to_return;
   to_return.matrix_.setConcat(matrix_, other.matrix_);
   return to_return;
 }
 
 Transform& Transform::operator*=(const Transform& other) {
-  matrix_.preConcat(other.matrix_);
+  PreconcatTransform(other);
   return *this;
 }