[Webkit-unassigned] [Bug 82956] New: [chromium] TransformationMatrix::to2dTransform seems unnecessary.

[bugzilla-daemon at webkit.org]

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

           Summary: [chromium] TransformationMatrix::to2dTransform seems
                    unnecessary.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: shawnsingh at chromium.org
                CC: enne at google.com, reveman at chromium.org


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.

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.

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.

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