I've implemented the variance shadow map, but still got a problem that is the shadow fades when it approaches the occluder. The same issue was posted here
It seems like it's the weakness of the algorithm because p_max ( = variance / [variance + d * d]) would inevitably go to 1 when d becomes smaller. But I don't see the same problem in the authors' paper or demo, neither did they mention it. I guess I probably did something wrong. Do you have the same issue? how do you address it? Thanks.
guessing that might be light bleeding or small map size?
http://http.developer.nvidia.com/GPUGems3/gpugems3_ch08.html
Ignore that comment
This is a natural and obnoxious part of VSM that can be addressed with the light bleeding fix, to some extent. It's soured me on VSM considerably in recent years. You might find this presentation helpful: http://developer.download.nvidia.com/presentations/2008/GDC/GDC08_SoftShadowMapping.pdf
ESM, or VSM+ESM, may be a useful approach.
Are you rendering the ground plane into the shadow map too?
And are you clamping variance so that it never goes below some small value (and have tweaked that small value)?
thanks for the reply.
Yes, I rendered the ground plane into the shadow map. I tried not, but the artifact I mentioned became worse.
Yes, I clamped the variance to 0.002. But I think it doesn't matter, because p_max = variance / (variance + d * d).
This is a natural and obnoxious part of VSM that can be addressed with the light bleeding fix, to some extent. It's soured me on VSM considerably in recent years. You might find this presentation helpful: http://developer.download.nvidia.com/presentations/2008/GDC/GDC08_SoftShadowMapping.pdf
ESM, or VSM+ESM, may be a useful approach.
But the reason for the light bleeding is different, right? and it was mentioned in the paper. That's why I think I probably did something wrong.
thank you for the resource mentioned, I will try to implement that and compare the results.
Depending on the units you're using, that may be a large value.Yes, I clamped the variance to 0.002. But I think it doesn't matter, because p_max = variance / (variance + d * d)
With v=0.002, and d=sqrt(v)~=0.045, then we end up with p=1/2.
So if your units are in meters, then at 4.5cm behind the caster, the shadow will be at 50% intensity. It will reach 99% intensity at 4.43m behind the caster.
Reducing your minimum variance value will reduce these distances.
sorry, I'm not sure if I get what you mean?
so you are suggesting using normalized distance? divide d by (light_far - light_near), like this?
thanks.
I used smaller minimum variance value (something like 0.0000001 instead of 0.002) and changed texture format from 16bit float to 32bit float or 16bit unsigned int (better accuracy because there is no exponent, but your values are not allowed to overflow), that solved it for me.
