Unity 5 Surface Shader - Passes

You would need to write a vertex & pixel shader, because that's actually the whole purpose of the surface shader : it will generate base pass, lighting pass, shadow caster pass etc... for you.

So you can't use a Surface Shader for just one of those pass, as it's a "meta" shader used to generate those in turn.

In an broad sense/approximation, Unity Standard Shader is the hand written version of what a surface shader generate for you

But if you know shader code well enough, you can bypass surface shader and rewrite all those pass yourself indeed, allowing to do some "ultra custom" lighting process. There is a lot of dependency though, so would have to be careful to not miss a thing! (best way is probably starting from a Standard Shader and replacing function one by one...)

 

I may be mistaken, I'm not fully accustomed to new rendering pipeline yet, but I think the function :

"Lighting<CustomLightingName>_GI" is "called" to fill the data (indirect & direct lighting) And it's input UnityGIInput have an atten value.

Usually that function call UnityGlobalIllumination, who initialize the gi varfor the "Unity lighting". But you don't have to, you can fill the gi data as you what.

So if your Lighting Model is called AwesomeLighting, you can define a function :

Code (CSharp):

1. inline void LightingAwesomeLighting_GI (
2.     SurfaceOutput s, //replace by your input struct if you have one
3.     UnityGIInput data,
4.     inout UnityGI gi)
5. {
6.     gi = UnityGlobalIllumination (data, s.Occlusion, s.Smoothness, s.Normal); // this is default lighting
7.  
8.     //either override some data
9.    gi.light.color = float3(0,1,0);
10.  
11.     ///or never call UnityGlobalIllumination  and do whatever your like. Check UnityGlobalIllumination function to see what unity does and copy past it to modify it at your will
12. }

 

Damn tested more in depth and you're right : GI is only for...well the GI =D So it cover only the "main light" of the scene.

If you open the generated code for a shader in Unity (button "Show Generated code" when a shader is selected), you have what unity have generated from your surface shader (and can indeed see that it generate all the pass you saw in the Standard Shader).

And you will see that, for the additive forward pass (so for all other light than the main light) :

Code (CSharp):

1.  UnityGI gi;
2.   UNITY_INITIALIZE_OUTPUT(UnityGI, gi);
3.   gi.indirect.diffuse = 0;
4.   gi.indirect.specular = 0;
5.   #if !defined(LIGHTMAP_ON)
6.       gi.light.color = _LightColor0.rgb;
7.       gi.light.dir = lightDir;
8.       gi.light.ndotl = LambertTerm (o.Normal, gi.light.dir);
9.   #endif
10. gi.light.color *= atten;// HERE
11. //call the lighting function defined in your SurfaceShader
12.   c += LightingFunction (o, worldViewDir, gi);

it multiply by atten before passing the gi data = /


For deferred path...well light are rendered after that and composited, so you can't access their informations...(but that's a deferred rendering limitation, you would need to write custom light rendering shaders, vert+pixels, and not possible in Unity so far I think...Apart using CommandBuffer to render into the light buffer directly with custom light types)


I don't know why atten is not a parameter anymore, there may be a deeper reason regarding on how Unity 5 rendering work, but no idea sorry : / (Maybe @Aras or @robert know)