Re: OpenGL changes

Bram Biesbrouck wrote:

>The thing is this: I render OpenGL-commentboxes (textballoons, etc), that are 
>defined in a Wavefront .obj file. The renderings in Ubuntu Breezy were very 
>good (using Nvidia's proprietary driver), but in Dapper, they are all messed 
>up. It looks like the vertices are rendered at random (or sometimes not at 
>all). The strange thing is that, for example, Blender doesn't seem to have 
>any problems, so I must be doing something wrong.
>
>Does anyone know of any important OpenGL-changes in this release? I know it's 
>all a bit vague, but I have no clue where to begin my debugging quest. All 
>help/suggestions are welcome.
>
>  
>
It's been my experience that incompatibilities across drivers are 
occasionally (unfortunately not rarely) the fault of the driver, but 
more often the fault of the developer assuming something about OpenGL 
state that cannot, in fact, be safely assumed.

Your description of the problem doesn't leave a lot to go on. If you 
have a web page you can post both good and bad screenshots on (for 
comparison) someone might be able to look at it and give you some hints.

OpenGL debugging is often a case of forcing certain things in your 
rendering loop. Make it so you can flat-shade everything, for example -- 
then you can more easily see vertex bugs. Try testing every coordinate 
you're rendering to make sure it's in the expected range, and log 
anything that isn't. Calculate a face normal and dot it with your camera 
vector, and log it if it's wildly out of range. Basically, give yourself 
some switches to turn on and off various parts of the rendering pipeline 
so you can debug it.

    Kent

----- 
FAQ and OpenGL Resources at:
  http://www.geocities.com/SiliconValley/Hills/9956/OpenGL

-- 
Author: Kent Quirk
  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).