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Jan
06-10-2003, 05:34 AM
Hi there

I was thinking of using the GL_EXT_clip_volume_hint extension. However in the spec it says, that implementations are free to ignore this hint.
So does anyone know, if it is worth using this extension, at all? AFAIK clipping is done quite fast. Therefore iŽd like to know, if current cards do still support this extension, and if there is a noticable speed-increase.
Also is it bad to frequently set/unset this hint?

Thanks,
Jan.

markfcsl
06-10-2003, 05:54 AM
I looked into this a few months ago but found it didn't do anything for performance. I've also had other colleagues say the same.

I queried with ATI and their response was that the extension spec says it's ok to ignore the hint, so they do after their driver team experimented with it.

As for NVIDIA, I didn't get a response to my query.

I didn't look into whether it caused any performance hits to set/unset it.

I'm not sure how OpenGL's clipping compares with Direct3D's, but I've heard that the D3D clipping renderstate can be quite good for performance if you're able to disable it.

Mark

ehart
06-10-2003, 11:42 AM
Just a follow-up to the mail you got from ATI. Present drivers on recent HW ignore it. There was a time when the clip volume hint could provide meaningful performance gains, so it isn't just there for the sake of being ignored.

-Evan