[Mesa3d-users] Alpha blending

[Gian P. L. <gi...@cs...>]

Hi all,

I'm trying to draw a scene containing an arbitrary number of
semi-transparent polygons, as well as several solid objects. The
solid objects I have placed in a display list, and if all the
trasparent polygons have the same alpha value, things work OK (although
there is a noticable change in the brightness of solid objects when the
transparent objects are added to the scene - this may be somethign I'm
doing wrong with the lighting/material properties, I really don't know).

My real problem comes when I change one of the transparent objects to
solid (or near solid) - this causes ALL the transparent objects to become 
solid. If the solid object is removed from the scene the transparent
objects are once again displayed correctly.

I'm using glMaterial* to set the colour and alpha values, and using a
blend func of 

glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

I've checked the red book, and I _think_ these paramters are what I'm
after.

Any help would be greatly appreciated. I haven't included source for
brevity, but if it would be helpful I can send it to you (it's basically
glutskel.c from the Mesa 3.4 utils dir, with some additions :). 

Thanks in advance,
Gian

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"I wish there was a knob on the TV to turn up the intelligence. 
 There's a knob called `brightness', but it doesn't work." 
                                                   -- Gallagher
Gian Paolo Lorenzetto 
Dept of Computer Science and Software Engineering  
The University of Western Australia  
Nedlands, W.A., 6907
                                        >- gi...@cs... -<
                                  http://www.cs.uwa.edu.au/~gian
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