Re: clipping planes bypassed in CG vertex shaders
Rhadamés Carmona <[email protected]>
| Newsgroups | gmane.games.devel.opengl |
|---|---|
| Organization | Fat City Network Services, San Diego, California |
| Message-ID | <[email protected]> |
Guys, thanks for all comments. Well, clipping must be applied per primitive (i.e. triangle)... so, it could be done before shading... Primitives can be removed, or clipped (it could add new verteces). So, in vertex shader, we can receive unclipped or new verteces, and we can play with them as we need (modify: move, translate, whatever). I think, it is good. After vertex shader, clipping even works, but it could not be good enough, because we do not want to waste gpu time shading verteces of objects which are going to be removed by clipping. Well, anyway, the point is that user clipping planes are disable in programmable pipeline (at least in my fx5200 and fx6800). I think, it is a little damn for some programmers. Regards Rhadamés Rhadamés Carmona wrote: > I agree. It must not be implemented in vertex shader. But, it can be > implemented after or before vertex shader. No - it can't be implemented before the vertex shader because the vertex shader can move the vertex around. Since any pre-shader clipper would have no idea where the vertex would ultimately end up - there is no way it could possibly clip it correctly. I have vertex shaders that totally ignore the incoming vertex coordinate and instead read the coordinate out of texture memory. There is no possible way that a pre-shader clipper could figure that out. It has to go AFTER the vertex shader. However, it could be implemented either before or after the fragment shader. The frag shader can't move the positions of vertices - so clipping either before or after that stage would be OK. (Although you'd hope it would be before frag shader because it's more efficient there). > I found in internet that user clipping planes are disable for programmable > pipeline. Only frustum clipping planes work after vertex shader... Where did you see that? -- Author: Stephen J Baker INET: sjbaker@... ----- FAQ and OpenGL Resources at: http://www.geocities.com/SiliconValley/Hills/9956/OpenGL -- Author: =?iso-8859-1?Q?Rhadam=E9s_Carmona?= INET: [email protected] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [email protected] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB OPENGL-GAMEDEV-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).