This option should be removed and gzdoom's behavior should be 'quality' at least for ATI to avoid such questions. Otherwise you will be compelled to answer similar questions permanently. I don't know any games except for doom ports with this precision problem on ATI. If we cannot force to work some things correctly everywhere for any reasons, we should not make it as option (like fog in slade). It is bad style and demonstration of disrespect. John Carmack would not do so. ATI has a big part of market nevertheless and maybe it more than NVidia has. We should not forget it.Do you have rendering quality set to quality, or to speed? If the latter, try switching to the former.