well basically it's just a 32 bit .tga file and a shader.
Create your texture... now switch to the channels tab and create a new Chanel called
"Alpha 1"
Now this works like this:
everything that is white in the alpha Shader will be opaque ingame.
Whereas black ares will be translucent.
So if this is your texture:
http://www.level-designer.de/images/stories/texturentuts/tex-zaubermark.jpg)
Your Alpha Shader should look like this:
http://www.level-designer.de/images/stories/texturentuts/tex-alphafertig.jpg)
And the shader should look something like this then:
textures/fiesling/baum_gruen
{
surfaceparm trans
surfaceparm alphashadow
cull none
nopicmip
{
map textures/fiesling/baum_gruen.tga
blendFunc GL_ONE GL_ZERO
alphaFunc GE128
depthWrite
rgbGen identity
}
{
map $lightmap
rgbGen identity
blendFunc GL_DST_COLOR GL_ZERO
depthFunc equal
}
}
Ignore the weird pathnames ... everything was stolen from a Tutorial on
www.Level-Designer.de)
:p