[Webkit-unassigned] [Bug 88587] New: Z coordinate corrupt in -webkit-transform-origin Safari

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=88587

           Summary: Z coordinate corrupt in -webkit-transform-origin
                    Safari
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Macintosh Intel
        OS/Version: Mac OS X 10.7
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: New Bugs
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: ccameron at chromium.org
                CC: simon.fraser at apple.com


Created an attachment (id=146404)
 --> (https://bugs.webkit.org/attachment.cgi?id=146404&action=review)
Sample image rendered in Chrome

It appears that the Z coordinate of -webkit-transform-origin does not behave correctly on Safari.

If the point <x,y,z> is specified by -webkit-transform-origin, and the transformation matrix T is specified by -webkit-transform, then the overall transformation should be:
  [1 0 0 x]       [1 0 0 -x]
  [0 1 0 y] * T * [0 1 0 -y]
  [0 0 1 z]       [0 0 0 -z]
  [0 0 0 1]       [0 0 0  1]
It appears that in Safari, the transformation is actually:
  [1 0 0 x]       [1 0 0 -x]
  [0 1 0 y] * T * [0 1 0 -y]
  [0 0 1 0]       [0 0 0 -z]
  [0 0 0 1]       [0 0 0  1]
Note the zero in row 3 column 4 of the leftmost matrix.  Consequently, the resulting Z position is incorrect.

I've attached a stripped-down test (from the Chromium bug) which shows this behavior, along with pictures of its rendering.  In the example, the top image shows text that should have no transformation applied to it, but it has a translation in the Z dimension as a consequence of this bug.  The middle image shows an ordinary rotateY(180deg), which renders correctly on Safari.  The bottom image does a rotateY(180deg) around non-zero Z-origin, which is also impacted by this bug on Safari.

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