Re: clipping planes bypassed in CG vertex shaders
"Stephen J Baker" <[email protected]>
| Newsgroups | gmane.games.devel.opengl |
|---|---|
| Organization | Fat City Network Services, San Diego, California |
| Message-ID | <[email protected]> |
Rhadamés Carmona wrote: > I tested the plane [1,0,0,0] and it clips in the middle (non vertex shader > version), but still it does not work in CG vertex shader. I think user > clipping planes are removed in programmable pipeline. Might this only be on particular hardware? Some of the older nVidia chips use a 1D alpha texture to implement user clip planes without custom clipping hardware. I could easily believe that this would be hard for them to implement correctly with the standard pipeline being subsumed by shaders. Newer nVidia chips do user-clipping in hardware and ought not to have this problem. However, it makes no sense for the OpenGL specification to remove this ability. Clipping happens after the vertex shader - and there is no way to implement user clip planes using the shader itself because the shader only sees one vertex at a time. User clip planes are a widely-used feature that would be exceedingly painful to do at the application level and impossible to implement efficiently in shader-land. ----------------------------------------------------------------------- The second law of Frisbee throwing states: "Never precede any maneuver by a comment more predictive than "Watch this!"...it turns out that this also applies to writing Fragment Shaders. ----------------------------------------------------------------------- Steve Baker (817)619-2657 (Vox/Vox-Mail) L3Com/Link Simulation & Training (817)619-2466 (Fax) Work: [email protected] http://www.link.com Home: [email protected] http://www.sjbaker.org ----- FAQ and OpenGL Resources at: http://www.geocities.com/SiliconValley/Hills/9956/OpenGL -- Author: Stephen J Baker 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).