# How do I convert light into an alpha value in Strumpy?

Discussion in 'Shaders' started by TomBrien, Apr 29, 2012.

1. ### TomBrien

Joined:
Apr 28, 2012
Posts:
107
Hey! I'm completely new to manipulating shaders.
I've used 3DSMax for a long time, so I have a knowledge of how diffuse and bumps maps work, and what Fresnel and Self-illumination is and so on, but I'm not GREAT at it.

Anyway- How can I get an Emission map to have an alpha based on how much light is hitting an object? Here's me in 3DStudio:

(I'm finding out this software deserves a lot of credit for how easy to use it is)

And here's me in the Strumpy Shader Editor:

(Strumpy is also fairly intuitive, considering I've not had to learn any coding)

I think it's using the Luminance Constant, but I don't know how to covert that into a 0 to 1 value.
...And then I THINK I can bend the gradient from light to dark using Clamp- but hey one step at a time right.

2. ### Jesus

Joined:
Jul 12, 2010
Posts:
319
In the strumpy examples you should find one called 'Ramp Lighting' or similar.

This grabs the luminosity at a pixel, and maps it to the U channel of the Ramp Texture.

Take some time to understand the buts of that shader, how and why everything works, and it shouldn't be hard to rebuild a similar one that uses luminosity to affect the Alpha channel.

3. ### TomBrien

Joined:
Apr 28, 2012
Posts:
107

I couldn't figure out how to do it in Strumpy, but LUCKILY I found an old thread where someone literally pasted a graph.

It's still not great though: because the colour is a mix of the diffuse map and the light ramp, it always comes out as really desaturated on either the red or the blue:

I can't really even tell if the ramp is recognising the RGB of the colours, or just measuring how bright they are.

Here's what I had in 3DS, applied to the Self-Illuminating (Emission) map:

But I can't apply any light-based nodes to Emission here.

Last edited: May 3, 2012
4. ### TomBrien

Joined:
Apr 28, 2012
Posts:
107
Alright well... I got the shadows to go from being white-to-black to being a warm hue to a cool hue (red to blue in this case)

Which was really the MAIN THING I wanted... I guess this is the closest I'm gonna get. I tried applying a ramp texture to the lighting, but the light seems to cut off at like 80% darkness. I don't know what's up with it:

No matter what kind of ramp texture I put in, it always switches to pure red where it should be dark blue. It even does it with the Strumpy example. Someone else had this problem but I don't get how he fixed it.

WELL whatever, I'll just do it without the toon shader step-down.

Last edited: Apr 30, 2012