How to modify shadow maps?

Graphics Lighting & Global Illumination
1

Does anybody know how I can take Unity’s shadow maps before they’re rendered on the screen, apply some custom processing to them on a per light basis and then send them back on their way?

2

Hello,
I’m not a professional, but I have some ideas which might interest you.

If you want to replace the shadows for every objects:
You can replace a Built in shader by your own in Edit → Project settings → graphics. Just copy their original shadow caster add a pass and then replace.

For only one shader you can add the subshader with “LightMode” = “ShadowCaster”.

3

Thanks for the info :smile:

For the built-in shader, isn’t that only for the directional light?

4

The shadowcaster pass is used for shadows from all lights, as well as the camera depth texture in forward rendering. Depending on what you want to do you could use a custom one for your shaders. Alternatively you could use command buffers to render stuff into / copy the shadow maps, but I don’t know of any good way to modify the shadow maps like via a shader and have the game still use them.

1 Like
5

Unity seems to use the RHalf format for the shadow caster pass, do you know if there is a way of getting the current format as I think this might vary with platforms?

  shadow.GetTemporaryRT(idd, 4096, 4096, 32, FilterMode.Point, RenderTextureFormat.RHalf);
            shadow.CopyTexture(BuiltinRenderTextureType.CurrentActive, idd);
            shadow.Blit(idd, BuiltinRenderTextureType.CurrentActive, shadowMat);
            shadow.SetGlobalTexture(idd, BuiltinRenderTextureType.CurrentActive);
            shadow.ReleaseTemporaryRT(idd);
6

There is RenderTextureFormat.ShadowMap but not sure if that works. I think what you are actually creating in your sample is a RHalf color buffer with a 32 bit depth buffer. AFAIK, you have to pass RenderTextureFormat.Depth or .ShadowMap to avoid creating an unnecessary color buffer.

The difference between .Depth and .ShadowMap is the sampler. .ShadowMap creates a comparison sampler which can be used for percentage closer filtering (PCF).