Migrate more functions from MathUtil to gfx::Transform

ui/gfx/transform_util.h

Index: ui/gfx/transform_util.h
diff --git a/ui/gfx/transform_util.h b/ui/gfx/transform_util.h
index b6da7b0782d3b63d461fa685912bff11b0c8cfda..b1e59efcc7c7344febdda6811b88a4d3756394f2 100644
--- a/ui/gfx/transform_util.h
+++ b/ui/gfx/transform_util.h
@@ -46,11 +46,45 @@ UI_EXPORT bool BlendDecomposedTransforms(DecomposedTransform* out,
 UI_EXPORT bool DecomposeTransform(DecomposedTransform* out,
                                   const Transform& transform);
 
+// Set 3rd row and 3rd colum to (0, 0, 1, 0). Note that this flattening
+// operation is not quite the same as an orthographic projection and is
+// technically not a linear operation.
+//
+// One useful interpretation of doing this operation:
+//  - For x and y values, the new transform behaves effectively like an
+//    orthographic projection was added to the matrix sequence.
+//  - For z values, the new transform overrides any effect that the transform
+//    had on z, and instead it preserves the z value for any points that are
+//    transformed.
+//  - Because of linearity of transforms, this flattened transform also
+//    preserves the effect that any subsequent (multiplied from the right)
+//    transforms would have on z values.
+//
+UI_EXPORT void FlattenTransformTo2d(gfx::Transform& transform);

[danakj, 2013/01/07 23:22:35]

Why not a member of Transform?

[shawnsingh, 2013/01/07 23:59:53]

No strong reason;  I'll move it into class.

+
 // Composes a transform from the given translation, scale, skew, prespective,
 // and rotation components following the routines detailed in this spec:
 // http://www.w3.org/TR/css3-3d-transforms/.
 UI_EXPORT Transform ComposeTransform(const DecomposedTransform& decomp);
 
+// Constructs a transform from explicit 16 matrix elements. Elements should be
+// given in column-major order. Recommended to use this only for unit tests.

[danakj, 2013/01/07 23:22:35]

Let's stick test-only things into test/

+UI_EXPORT Transform CreateGfxTransform(

[danakj, 2013/01/07 23:22:35]

The Gfx part is a bit redundant with the namespace this lives in, can we drop
it?

[Ian Vollick, 2013/01/08 00:41:21]

How would you feel about adding some gfx::Transform ctors that takes 16 and 6
doubles?

+    double col1row1, double col1row2, double col1row3, double col1row4,
+    double col2row1, double col2row2, double col2row3, double col2row4,
+    double col3row1, double col3row2, double col3row3, double col3row4,
+    double col4row1, double col4row2, double col4row3, double col4row4);
+
+// Constructs a transform from explicit 2d elements.  All other matrix elements
+// remain the same as the corresponding elements of an identity matrix.
+// Recommended to use this only for unit tests.
+UI_EXPORT Transform CreateGfxTransform(
+    double col1row1, double col1row2, double col2row1,
+    double col2row2, double x_translation, double y_translation);
+
+// Constructs a flattened version of the given transform.
+UI_EXPORT Transform CreateFlattenedTransform(const Transform& transform);

[danakj, 2013/01/07 23:22:35]

Why are we breaking the pattern of always modifying existing matrices and not
creating new ones here? Should we just provide one way to flatten - ie
FlattenTransformTo2d?

[shawnsingh, 2013/01/07 23:59:53]

not "breaking" so much as keeping status quo.... but, no problem, I'll see if I
can change it in this patch, too.

+
 }  // namespace gfx
 
 #endif  // UI_GFX_TRANSFORM_UTIL_H_