Celestia Forums

I'm working on nebulae using CMOD models with sprites. Now I thought that you could just define a bunch of materials at the top, and the nth mesh would use the nth material defined. But that doesn't seem to be the case.

Attached below is a sprite model of Abell 6. In it, I have two materials defined, the first with an opacity of 0.10, the second with an opacity of 0.03. The first mesh (with 882 vertices) is the outer shell, and the second mesh (with 176 vertices) is for the inner gas.

When I change the second material's opacity from 0.03 to say, 0.15, then nothing changes. Moreover, when I change the first material's opacity from 0.10 to 0.0 (i.e. totally transparent), then all the sprites become fully transparent—the model becomes invisible.

What's going on here? How can I have meshes made from materials other than the first material? I'd like to be able to use different opacities for different point sprites.

Thanks in advance,
LukeCEL

It looks to me like there's a bug in whatever program you're using to create the CMOD model. Apparently that program is not trying to use the 2nd material (material 1) at all.

In a CMOD model, the first value after the word "sprites" is supposed to be the index value of the material which is be used for the listed vertices. The first material definition is material 0, the second one is material 1.

A grep of the CMOD found two sprite declarations and both of them specify material #0.

A workaround would be to manually edit abell6.cmod to change the second sprites declaration
from
sprites 0 176
to
sprites 1 176

selden wrote:In a CMOD model, the first value after the word "sprites" is supposed to be the index value of the material which is be used for the listed vertices. The first material definition is material 0, the second one is material 1.

Ohhh! Thank you for the explanation! I had no idea that the "0" after the sprites refers to the index of the material. (I thought it was just to specify the start of the point sprites, i.e. from 0 to 176. What a goof.)

I'm actually making CMOD models using a combination of programs to automate tasks (such as Microsoft Excel to calculate XYZ coordinates, etc.), and my own editing. So I'll just manually edit the sprite declarations, that'll be quick work.

Once again, thank you selden very much for potentially expanding what I can do with sprites.

Luke

Good luck!

I did a quick test after posting my response, and it didn't do what I expected. I probably made a typo of my own somewhere. *sigh*