rendercheck triangles test is regressed with pixman >= 0.27.4. Regression is due to pixman_composite_trapezoids() has been changed to composite across the entire destination. This changes the color that triangles test is expecting outside of the triangles.
Appears to be fixed by this commit: http://cgit.freedesktop.org/xorg/app/rendercheck/commit/?id=b015a64ba19fb832af22e79f54b492ae85f6590e
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