[Webkit-unassigned] [Bug 82956] [chromium] TransformationMatrix::to2dTransform seems unnecessary in LayerRendererChromium

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=82956


Adrienne Walker <enne at google.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[chromium]                  |[chromium]
                   |TransformationMatrix::to2dT |TransformationMatrix::to2dT
                   |ransform seems unnecessary. |ransform seems unnecessary
                   |                            |in LayerRendererChromium




--- Comment #1 from Adrienne Walker <enne at google.com>  2012-04-02 15:41:34 PST ---
(In reply to comment #0)
> Pasting from comment 9 on https://bugs.webkit.org/show_bug.cgi?id=80806
> > The "3d part" of the transform doesn't affect the final x and y components of the quad in device space, only the z component.  In other words, for all values of quad:
> > 
> > transform.to2dTransform().mapQuad(quad) == transform.mapQuad(quad)
> 
> At first I believed that removing the 3d stuff in the transform will remove any intrinsic perspective that was also in it.  It turns out the 3d perspective properties are still retained on the bottom row of the matrix.  So even though the function is called to2dTransform(), it is actually still a 3d transform.  So I feel the function name is severely misleading.

Can you clarify what you mean by "perspective"?

> As it stands, the function seems to be a gigantic no-op then, isn't it?  why do we need to do this operation?  It doesn't make anything faster; using 2d quads and points will already bypass the 3rd row and 3rd column, and everything else (inversion in particular) still operates on a 4x4 matrix.

The function is not a no-op.  For some values of transform,

transform.to2dtransform().inverse().mapQuad(quad) != transform.inverse().mapQuad(quad)

> We can mark this as WontFix, I'd like to be convinced first about why its actually necessary before doing that.  Otherwise, I think we should remove it entirely.

This is WontFix.

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