To clarify, the shadows aren’t deep shadows as you might expect them, they are implemented from this paper: cemyuksel.com/research/deepopacity/ so are kind of like very limited deep shadow maps.
1.) The filtering is currently forced to bilinear, mostly out of spite. I can change this fairly easily.
2.) What do you propose for the naming? It doesn’t really matter to me. The only part suggested by OpenEXR was to use AR, AG, AB since the stored values are alphas. I can easily pad the number to 4 digits or so.
3.) The depth is stored to the first particle along a pixel/ray. After that the layers are sampled at a regular Z-distance (which can be read of the EXR via a float property called “PFDeepAttenuation:SampleSpacing”). Check out my sweet diagram below.
4.) The samples are stored only after the Z-distance specified in the Z image in the EXR.
I plan to get around to deep shadow maps eventually, but I needed to pound out an implementation pretty quickly so this is what we ended up going with.
Deep Opacity Maps:
z0 z0+d z0+2d z0+3d z0+4d z0+5d
Camera ----------|--------------|--------------|--------------|--------------|--------------|-----------------------Infinity
sample0 sample1 sample2 sample3 sample4The Z pass marks the first particle along a ray(ie. pixel) and attenuation values are stored at regular spacings (of ‘d’) along the ray after this depth. At z0 (the value read from the Z image) there is no attenuation. The attenuation is linearly interpolated between samples. Any evaluation beyond the final layer (z0+5d in this case) will return the attenuation value stored at sample4.