koobas.hobune.stream
How could I access light direction in a surface shader?
Hi, everyone! I'm trying to write a shader that adds a second Diffuse texture depending on where the lights hit the mesh. Something like this: 
However, I can't for the life of me figure out how to access the "Light Direction" in the "surf" function of the shader. Is it possible?
Best Answer
You don't access light direction in surf(), but you can access it in a lighting model. Define a custom struct that contains both your diffuse textures:
struct CustomSurfaceOutput {
half3 Albedo;
half3 Normal;
half3 Emission;
half3 Gloss;
half Specular;
half Alpha;
half3 Diff1;
half3 Diff2;
};
Pass this struct to a custom lighting model, e.g.:
#pragma surface surf CustomLighting
half4 LightingCustomLighting (SurfaceOutput s, half3 lightDir, half3 viewDir, half atten) { ... }
and, in the model itself, set the RGB components of the return value based on NdotL as desired. Something like:
if(NDotL > 0) {
c.rgb = s.Diff1;
}
else {
c.rgb = s.Diff2;
}
More info and examples at http://docs.unity3d.com/Documentation/Components/SL-SurfaceShaderLightingExamples.html
