Comment # 31
on bug 57875
from Henri Verbeet
You're mixing things up a bit, the functionality this bug is about is mostly controlled by D3DRS_ZENABLE in d3d9. Considering only pre-transformed (D3DFVF_XYZRHW) vertices, the behaviour is like this: - When D3DRS_ZENABLE is D3DZB_TRUE, Z values are clipped when D3DPMISCCAPS_CLIPTLVERTS is set, clamped when it isn't. Depth testing works pretty much as expected. In practice that means the default GL behaviour is fine as long as we set D3DPMISCCAPS_CLIPTLVERTS. - When D3DRS_ZENABLE is D3DZB_FALSE, depth value processing is technically just completely disabled. We get equivalent behaviour by disabling the depth test, and clamping depth values. This does mean that always clamping Z for pre-transformed vertices through an output modifier could be a valid implementation, as long as we don't set D3DPMISCCAPS_CLIPTLVERTS in wined3d. However, it also means that you can't then require the depth test to be always disabled when that output modifier is used. If I'm still understanding the bug correctly, the whole point was that enabling both depth clamping and the depth test at the same time is problematic on r300. You could of course specify an appropriate interaction with GL_DEPTH_TEST in the extension spec instead of just "always clamp Z / disable clipping and viewport transform". That would probably work for us, but would also probably make for a more complicated extension. It would also make it impossible to ever implement this on things like r200 that can't properly do GLSL, although that may not be enough of a concern to avoid doing it this way. What would be the main advantage from r300g's point of view of making this an output modifier?
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