Exponential shadow maps
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In another ShaderX6 article, Macro Salvi presents "Exponential Shadow Maps". Like variance shadow maps, they can be hardware filtered, but they only require storing a single moment. They're also faster, with a simpler depth comparison equation.
...but... to avoid overflow issues when storing the exponential depth, the paper stores linear depth instead, deferring the exponential until the depth comparison and using ln to recover the proper value for filtering. This means emulating (separable) filtering in a shader. :(
Nevertheless, my current implementation uses regular hardware filtering with linear depth, which is likely the cause of the massive light bleeding when the occluder is near the receiver, and poor filtering when they're far apart.
In the depth comparison, ek(o-r), where k is the slope coefficient, which can be raised to reduce light bleeding at the expense of poorer filtering, k=32 for the above screenshot. [wow]
I saved 8ms per frame by using this algorithm, so it shouldn't be a big deal to sacrifice a few of those ms to emulate filtering for better quality.
...but... to avoid overflow issues when storing the exponential depth, the paper stores linear depth instead, deferring the exponential until the depth comparison and using ln to recover the proper value for filtering. This means emulating (separable) filtering in a shader. :(
Nevertheless, my current implementation uses regular hardware filtering with linear depth, which is likely the cause of the massive light bleeding when the occluder is near the receiver, and poor filtering when they're far apart.
In the depth comparison, ek(o-r), where k is the slope coefficient, which can be raised to reduce light bleeding at the expense of poorer filtering, k=32 for the above screenshot. [wow]
uniform sampler2D shadowSampler;varying vec4 shadowCoord;const float k = 32;float GetInvShadowImpl(){ float moment = texture2D(shadowSampler, shadowCoord.xy).r; return clamp(exp(k * (moment - shadowCoord.z)), 0, 1);}I saved 8ms per frame by using this algorithm, so it shouldn't be a big deal to sacrifice a few of those ms to emulate filtering for better quality.
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