Created attachment 16215 [details] testcase Here's a magic matrix that makes the Xlib backend screw up. The image backend and the X fallback code renders it fine. I shortly tried some obvious rotations, but couldn't make it fail, so I pasted the matrix verbatim into the test. But I did enough of a job already, the initial test was 300 lines long. ;) I also shortly checked various other clipping and extend-none related bugs, but they never where xlib specific, so I filed a new bug.
Owen mentioned that this is related (likely the same as) bug 15369, but I wasn't sure how they affect each other, so I'm not amrking this a duplicate.
The problem cannot be reproduced with current Cairo/Pixman/X (and Xlib, XCB and image now share the matrix computation code). The specific commit which actually fixed this has probably been pushed long ago, but I cannot bisect it easily because the current autotools suite does not work smoothly on cairo 1.6 (./configure dies with an error).
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