Managed to get cube shadow mapping working today. I'm not completely happy with the result but it was certainly easy enough to set up in the end, once I figured my way around the inevitable issues and artifacts. I'm using a 1024x1024 cube map in the screenshot above, but it looks kind of acceptable with a 512x512, even without PCF, although I do intend to tackle that eventually.

But now I want to have multiple lights supported. I can't imagine being able to hold a coherent level together if only one light at a time can cast shadows.

I've been reading around the various approaches to this. The result I'm looking for is for a shadowed pixel to not be blended multiple times. I'd rather all the shadowed pixels are a constant darkness.

So what I think I'm going to try is first render the scene to the backbuffer with only ambient lighting as if every pixel was shadowed, then for each light source:

• Generate the cube map with the distances from the light source to pixel
  
• Do an additive lighting pass over the backbuffer, but skip pixels that are in shadow
  

My hope is that I'll then get nice, constant darkness shadows. Seems legit in theory anyway.

Seems to be bewilderingly fast to generate the six faces of the cube map, so I think I can manage to render a few of these per frame. Three light sources should be sufficient to be able to link different rooms with different main lights together, then decorative, non-shadowing lights can be added in a single pass.

That's the theory anyway. Will see how it works out.

[EDIT Slightly later...]

Just wanted to update here as I've just added PCF to this, and the results are remarkably good for a simple effort.



Even right up close, the quality is far better than I expected:



I'm just doing a 3x3 sample around the original vector, using an arbitrary offset in the pixel shader:

#define am 0.1ffloat3 filter[] = { { -am, am, 0 }, { 0, am, 0 }, { am, am, 0 }, { -am, 0, 0 }, { 0, 0, 0 }, { am, 0, 0 }, { -am, -am, 0 }, { 0, -am, 0 }, { am, -am, 0 } };float shadowFac(float3 tolight, float3 normal){ float shadow = 0.0f; if(dot(tolight, normal) < 0) { for(int i = 0; i < 9; ++i) { float sampled = texCUBE(ds, tolight + filter).r; float actual = (length(tolight) - 0.5f) / 200; if(sampled < actual) shadow += 1.0f / 9.0f; } } return shadow;}I guess the value of am would have to be changed depending on the resolution of the cube map, but I'm pretty pleased with the effect there.

Just hanging out around a camp-fire



Thanks for stopping by.

[EDIT]

In response to IYP's comment below, I thought I should post another image showing how the PCF looks when the shadows are parallel to the world axes, as I think the lucky diagonal screenshot is giving a misleading impression of how good the PCF is here:



I think this can be improved by using a random sampling kernel, but this can wait until I have multiple light sources working.