Q3: How do I make a transparent object?

A3: This is a simple sample that makes a 50% transparent mesh pyramid that uses the rock texture:

material  
name alpha_rock  
texture wall  
notexalpha  
color 1 1 1 0.5  
end  
 
meshpyr  
name Pyramid  
matref alpha_rock  
position 0 0 0  
rotation 0  
size 10 10 10  
end  

A fully transparent object can be made by:

material   
name transparent 
color 0 0 0 0   
end 
 
meshbox 
name box 
matref transparent 
position 0 0 0 
rotation 0 
size 10 10 10 
end 

Q4: How do I make a translucent object?

A4: There are 3 ways to make an object translucent:

1. use a translucent texture (without using notexalpha)
2. use a translucent color
3. use a translucent dynamic color

Translucent faces take more time to draw because they require sorting to draw them from back to front (note that bzflag currently does a poor job on this aspect). As well, you never get the depth buffer clipping that you'll get from opaque objects. This means that each pixel will have to have all of its rendering information processed even if it is behind a plane.

I would advise keeping the number of translucent faces in any given map to a bare minimum. As well, try to keep the translucent faces small, so as to avoid the ugliness that is caused by bzflag's poor sorting algorithm.