How to use only one color channel from texture?

Unity Engine
1

Hi guys!

This is probably a total noob question but I have to ask it anyway since I was not able to find anything about this, whether in the docs nor the forum.

What I need to know is if and how I can get only one channel out of a texture without using a custom Cg shader but by using only standard ShaderLab functionality.

I need to get the Red, Green, Blue and Alpha channels seperately instead of all of them combined.

Is something like this possible?

An (probably not working) example of what I try to accomplish:

SetTexture [_MainTex] {
    constantColor [_Color]
    combine texture.r * constant
}

I know how to do this by using a custom Cg shader, but I would rather like to do this with standard ShaderLab functionality…

2

“Standard Shaderlab functionality” is basically equivalent to that of the fixed function pipeline. If you can’t do it without Cg, it’s usually a hardware limitation rather than simply a missing Shaderlab feature.

The closest thing I can think of to what you’re asking is the Colormask keyword. This allows you to make a pass only write to a specific combination of channels. However, you can’t change the mask in-between texture operations, so you might need four passes to treat all of your channels separately.

3

This Colormask sounds pretty much like what I’m looking for. Thank you for this hint, I’ll look into that. Thanks :smile:

Edit: Ok, my happyness was a bit premature, I guess. But thank you anyway, since I didn’t know the ColorMask keyword anyway. So at least I learned something new :wink:

Well then, I guess it has to be a Cg shader then. :slight_smile: