• Create Account

# sobeit

Member Since 16 Jul 2009
Offline Last Active Feb 06 2016 03:35 PM

### In Topic: Help with box stacking instability

09 July 2014 - 02:29 PM

Dirk and Randy, thank you for the information, I think that's enough to get me started.

### In Topic: Help with box stacking instability

07 July 2014 - 04:28 PM

do you know where I can find more information on this topic, especially discussion about stability? books or websites?

### In Topic: Help with box stacking instability

07 July 2014 - 02:23 AM

You should try using 2 contact points, not just one.

I work in 3d, I'm not sure how to generate more than one contact point, maybe using some convex shape clipping algorithm? But as far as what I searched on the internet, it seems finding the deepest penetrating point is enough. maybe I miss something.

You'll also want to have some penetration tolerance instead of trying to achieve exactly zero penetration.

You should also verify your own code against Box2D Lite (not recent Box2D, but the Lite version)

Thanks for the suggestion. I actually followed Erin's 09 GDC talk, I will download that and try to find out what I did wrong.

one more question. If I do contact caching, how would I use the cached contact points? find the average of them?

03 July 2014 - 11:34 AM

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.

01 July 2014 - 01:10 PM

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)?

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.

PARTNERS