REG: QPainter renders horizontal lines incorrectly to QGLFramebufferObjects (ATI cards)

The attached example can be used to reproduce the issue. This seems to be regression to bug fix of QTBUG-16043. The commit 67b24ac50637ecda00990b239fc5ed0b73e54d75 "Fixed stroke / fill inconsistencies in GL 2 paint engine" (14.12.2010, 4.8) is causing this behavior with systems that use ATI graphics drivers. The attached images shows the issue also.

The attached patch reverts the commit made to QTBUG-16043.

As a workaround the issue one can add some tiny fractional amount (like 0.001) to either the line start or end point y-coordinate. There reason might be that there is a difference in how ATI and NVIDIA handle floating point rounding and that on ATI cards a round-down occurs when it doesn't on NVIDIA cards. Since the ogl2 paint engine renders lines with triangle strips this round down will result in either no line - where the y-coordinates of each triangle vertex is the same, resulting in degenerate triangles - or a 1px too thick line.