Get Main Light Position

Could someone please tell me how I'd be able to access the _MainLightPosition constant using shader graph?

I've tried to get it via a custom function node but it tells me the variable isn't defined.

I reviewed the source for URP and in the ForwardLights.cs (https://github.com/Unity-Technologi...-pipelines.universal/Runtime/ForwardLights.cs) it does indeed seem to be setting a global variable...

Code (CSharp):

1. void SetupMainLightConstants(CommandBuffer cmd, ref LightData lightData)
2.         {
3.             Vector4 lightPos, lightColor, lightAttenuation, lightSpotDir, lightOcclusionChannel;
4.             InitializeLightConstants(lightData.visibleLights, lightData.mainLightIndex, out lightPos, out lightColor, out lightAttenuation, out lightSpotDir, out lightOcclusionChannel);
5.  
6.             cmd.SetGlobalVector(LightConstantBuffer._MainLightPosition, lightPos);
7.             cmd.SetGlobalVector(LightConstantBuffer._MainLightColor, lightColor);
8.         }

And in the Lighting.hlsl library I can see it being used...

Code (CSharp):

1. Light GetMainLight()
2. {
3.     Light light;
4.     light.direction = _MainLightPosition.xyz;
5.     // unity_LightData.z is 1 when not culled by the culling mask, otherwise 0.
6.     light.distanceAttenuation = unity_LightData.z;
7. #if defined(LIGHTMAP_ON) || defined(_MIXED_LIGHTING_SUBTRACTIVE)
8.     // unity_ProbesOcclusion.x is the mixed light probe occlusion data
9.     light.distanceAttenuation *= unity_ProbesOcclusion.x;
10. #endif
11.     light.shadowAttenuation = 1.0;
12.     light.color = _MainLightColor.rgb;
13.  
14.     return light;
15. }

Any help would be GREATLY appreciated!

 

*UPDATE*
It 'seems' as though I can now get it by wrapping it around an if SHADERGRAPH_PREVIEW statement, but it is set to 0,0,0

Code (CSharp):

1. #if SHADERGRAPH_PREVIEW
2.     Color = 1;
3.     DistanceAtten = 1;
4.     ShadowAtten = 1;
5.     LightPos = half3(10,10,0);
6. #else
7.     LightPos = _MainLightPosition;
8. //..........//
9. #endif

Do I need to trigger the SRP to update the light constants manually? I would have assumed this would be done per frame based on the rendering diagram on the documentation -> https://docs.unity3d.com/Packages/c...rsal@7.1/manual/rendering-in-universalrp.html

 

Ohhhh - yes you're totally right - I was so focused on finding the position I didn't really click that it is indeed the direction.

In my project I'm basically wanting an omnidirecitonal light (a point light with no falloff I suppose) which will be a sun in a small solar system.

This works perfectly if I hard code the light position, but this position will change at times.

I'm aware of the issues with shadows and I will not be using realtime shadows.
I suppose I could do this with a point-light and manually tune the light attenuation in my shader.

After looking at the light struct I'd love to put the world position in there!

 

I got some help with what I needed from evangelist Adam Single. This solution is exactly what I was after!

Thanks Adam
https://github.com/adamsingle/OmnidirectionalShaderGraph