Re: Mesa bug?

["Eric G. Miller" <egm2@jps.net>]

On Sun, Sep 22, 2002 at 04:11:44PM +0930, Tom Cook wrote:
> Hi all,
> 
> This may be a mesa bug or it may be a manifestation of my ignorance of
> opengl.  If the latter then I apologise for OT posting.
> 
> I am playing with clipping planes in an effort to do some fancy stuff
> in 3D graphics.  My problem is that mesa appears to only let me define
> a client clipping plane once.  That is, the first call of:
> 
> glClipPlane( GL_CLIP_PLANE0, vector );
> 
> correctly defines a clipping plane.  But all subsequent calls to it
> have no effect on the clipping planes.
> 
> This seems something of a major restriction to me, since mesa only has
> 6 client defined clipping planes to play with, and these are soon
> exhausted.
> 
> So have I misunderstood something, or is this a mesa bug?  I wanted to
> ask before I filed a bug.

In grunting around some code that does clipping planes, seems you
need to call glEnable/glDisable after glClipPlane.  At least,
that's what the code I looked at does. Calls glEnable if the
plane was turned on, and glDisable if it was off.  It queries
glIsEnabled(GL_CLIP_PLANE0 + (num)) prior to calling glClipPlane().
I guess glClipPlane() possibly toggles the state (or just turns it
off).  I'm no OpenGL guru ...

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