Re: [Algorithms] Speculative Contacts

[Jamie F. <ja...@qu...>]

On 01/04/2011 04:00, Jon Watte wrote:
> This is pretty cool! Thanks for sharing.
> What I've found when doing the "remove velocity" thing in the past
> (sweeping spheres against trimeshes, mostly), is that the amount of
> bounce you get (if you have >0 restitution) varies randomly. The reason
> being that "almost all" versus "almost none" of the velocity will be
> removed for any given timestep, depending on how soon within the
> timestep the object will intersect the target.
> It's possible to hack with things like "assumed velocity" being
> remembered at the beginning of the time step -- do you have any thoughts
> on possibly better solutions?
> (There's also the discontinuity in motion from removing a random amount
> of time, but as you say -- you gotta stop somewhere ;-)

I did stuff that looked a lot like this some years ago, off the back of 
the Jakobsen Hitman physics paper. It's pretty easy to eliminate the 
discontinuity and get the bounce right for this sort of simple collision...

I spent a lot more time generalizing the solution to 3D bodies (with 
constraints?), and I can't honestly remember if I got all the way 
there... have some notes somewhere....

But it all worked really surprisingly well in a number of tests. Lots of 
nasty situations Just Worked with no special cases (Newton's cradle was 
a favourite).

But if I read Paul's article correctly, the whole point of his 
Speculative Contacts approach is to make sure the objects are perfectly 
in contact at the start of the next frame. And, like you say, there'll 
be artefacts from that....

The way we did it way back when, it stabilized pretty decently in the 
first place without that... so what am I missing? :)

May be rambling, not nearly enough sleep!

Jamie

> Sincerely,
> jw
>
>
> --
> Americans might object: there is no way we would sacrifice our living
> standards for the benefit of people in the rest of the world.
> Nevertheless, whether we get there willingly or not, we shall soon have
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>
>
>
> On Mon, Mar 28, 2011 at 12:27 PM, Paul Firth <pa...@wi...
> <mailto:pa...@wi...>> wrote:
>
>     Hi guys,
>
>     Just thought i'd post this here in case you've not already seen the
>     article in the thread on gamdev.net <http://gamdev.net/>:
>
>     http://www.wildbunny.co.uk/blog/2011/03/25/speculative-contacts-an-continuous-collision-engine-approach-part-1/
>
>     Its my blog post on a new collision detection technique as seen in
>     games such as Little Big Planet...
>
>     Hope you enjoy it :)
>
>     Cheers, Paul.
>
>     --
>     Paul Firth
>     http://www.wildbunny.co.uk <http://www.wildbunny.co.uk/>
>     http://www.facebook.com/WildbunnyLtd
>     email: pa...@wi... <mailto:pa...@wi...>