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d1g1t@lm0nk

tutorial: alpha maps

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Due to lack of documentation(or in depth documentation)of alpha maps/channels and how they work in doom III, i have decided to make a short tutorial for them in case any of you doomers out there have been running into the same problems as me. Most of you probably know that making a material file(.mtr) for doom 3 custom textures isnt that hard when it comes to diffuse maps,radiant editor maps, and even specular or bump/normal maps. For some reason, they dont really talk that much about alpha channels, and how you can make transparency/opacity maps with the material editor to create things like grate textures.

this site has some good information:
http://www.iddevnet.com/doom3/

and now for the alpha map information,from what im understanding so far ;)

in your material file(.mtr)a regular texture should have code similar to this:

textures/custom/test
{
twosided

qer_editorimage textures/custom/test_ed.tga
{
blend diffusemap
map textures/custom/test_d.tga
alphaTest 0.5
}
}
*********

-two sided is there so that the texture/material will be drawn from both sides(front side of the normal and the backside).
-blend diffusemap is there to mix the diffusemap with the alpha channel that is inside of that same texture.
-keep in mind that since you are blending the rgb channels of the diffusemap with the alpha channel of the same texture, the "diffusemap" parameter is not at the top, it is used during the blend command instead.
-map is used to tell the engine where the diffusemap is(and it assumes the alpha is inside of that texture).
-alphaTest is used to tell the engine to write if the alpha value is greater than the exponential you give it(0.5 seems to work fine, and id software uses that number in most of the alpha channel textures).

i hope this helps anyone having trouble with alpha channels working in doom 3. if there is more that you need to know, please tell me and i will see what i can do.

m0nk

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