RE: [PyOpenGL-Users] Lighting and texturing

[Mike C. F. <mcf...@ho...>]

21.030 Why doesn't lighting work when I turn on texture mapping?

There are many well-meaning texture map demos available on the Web that set
the texture environment to GL_DECAL or GL_REPLACE. These environment modes
effectively replace the primitive color with the texture color. Because
lighting values are calculated before texture mapping (lighting is a per
vertex operation, while texture mapping is a per fragment operation), the
texture color replaces the colors calculated by lighting. The result is that
lighting appears to stop working when texture mapping is enabled.

The default texture environment is GL_MODULATE, which multiplies the texture
color by the primitive (or lighting) color. Most applications that use both
OpenGL lighting and texture mapping use the GL_MODULATE texture environment.

Look for the following line in your code:

glTexEnv (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); /* or GL_REPLACE
*/
You should change GL_DECAL to GL_MODULATE, or simply delete the line
entirely (since GL_MODULATE is the default).



Might that be the problem in your code?  I'll take a look at your code
tomorrow if I can get some time and see if I can see anything.  Also need to
make sure none of my code is well meaning :o) , pretty sure I have a few of
those hanging around...
Mike

-----Original Message-----
From: pyo...@li...
[mailto:pyo...@li...]On Behalf Of Richard
Jones
Sent: September 22, 2001 07:33
To: pyo...@li...
Subject: Re: [PyOpenGL-Users] Lighting and texturing


On Sat, 22 Sep 2001 20:15, Richard Jones wrote:
> I can't seem to figure how to have a surface lit and textured. The demo
> that comes with pyopengl (NeHe/lesson18.py) doesn't work, and my code
looks
> very similar to it...
>
> Ideas?
...
        glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL)
...