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<DIV><FONT size=2>Hi,</FONT></DIV>
<DIV><FONT size=2> Justin, before thicking about reducing the
size of the array passed to ode collide function to receive the colision
contacts information, </FONT><FONT size=2>maybe you should remember what i told
you about managed versus unmanaged memory use in the ode plugin.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2> Maybe you should think about what is being
done by framework to convert the array from managed memory space to unmanaged
and then back again on each call.</FONT></DIV>
<DIV><FONT size=2> If you do that (or just remember the
details i told you) maybe you will see how to save some cpu without
reducing the stability of the simulation to a useless state.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2> Also before doing hard testing with
diferent ode supporting libs, maybe you should also review
managed/unmanaged issues on other parts of the plugin. JointCreateContact
? GeomHeightfieldDataBuildSingle ? ....</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2> Best Regards,</FONT></DIV>
<DIV><FONT size=2>Ubit Umarov</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2></FONT> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=teravus@gmail.com href="mailto:teravus@gmail.com">Teravus Ovares</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=opensim-dev@lists.berlios.de
href="mailto:opensim-dev@lists.berlios.de">opensim-dev@lists.berlios.de</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, January 04, 2012 7:53
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Opensim-dev] Prospective
ODE physics changes</DIV>
<DIV><BR></DIV>
<DIV>ODE Documentation and examples :)</DIV>
<DIV> </DIV>
<DIV>Regards</DIV>
<DIV><BR>Dan<BR><BR></DIV>
<DIV class=gmail_quote>On Wed, Jan 4, 2012 at 2:46 PM, Justin Clark-Casey
<SPAN dir=ltr><<A
href="mailto:jjustincc@googlemail.com">jjustincc@googlemail.com</A>></SPAN>
wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>Hi Teravus, nice to hear from you again!<BR><BR>Yes, more
testing is needed, hopefully on OSGrid. But it seems there may be a
tradeoff between having super smooth physics objects and being able to get
more avatars in a scene without encountering cpu limits. My perception
is having more avatars is a more common use case then lots of physics
objects, particularly as OpenSim's current ODE use does not seem to provide
a good physics simulation). Anybody who does want to try for better
physics could always turn the collision number back up.<BR><BR>In any case,
what was the rationale for choosing 80 as the default?
<DIV class=im><BR><BR>On 03/01/12 22:30, Teravus Ovares wrote:<BR></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>
<DIV class=im>With ODE, it depends on the physics situation.<BR>With
Tri-Mesh and the heightfield collider specifically, ODE generates lots of
small effect contacts and then the<BR>stepper integrates them all into a
contact resolution force. With tri-mesh and the heightfield,
depending on how an<BR>object collides with another, there could be 20 or
30 contacts that all factor into getting the object to react<BR>normally.
So, to test, you're going to want to use a stack of
'active'(physical in the client) tri-mesh objects. You<BR>may also
want two or more trimesh LINKSETS to see how they react.<BR>My guess, is
the first thing that you're going to notice is that a tri-mesh object
sitting on another object will become<BR>more unstable (vibrate more).
Each mini-contact represents a part of the force to keep the object
from rotating from<BR>the other parts of the contact resolution force.
As the effect gets worse, you're going to notice 'rotation
anomolies'<BR>that occur when objects collide.<BR>Think of it like...
you have a cube shaped trimesh... and the cube's
corners are touching a flat ground. In<BR>theory, that would
generate 4 contact points for each of the vertices touching the flat
ground. If you cut one off,<BR>then only three of the corners are
being held above ground. On a larger scale, If you do that
enough, then the<BR>object will partially fall through the ground and then
bounce back up from an excessive contact resolution force<BR>creating
instability and vibrating.<BR>Those are the indicators that I would use to
determine if it's OK to make that change. Are 8 contacts enough for
ODE<BR>to react properly in our usage? That remains to be seen
:).<BR>Regards<BR>Teravus<BR><BR></DIV>
<DIV class=im>On Tue, Jan 3, 2012 at 4:58 PM, Adams, Robert <<A
href="mailto:robert.adams@intel.com"
target=_blank>robert.adams@intel.com</A> <mailto:<A
href="mailto:robert.adams@intel.com"
target=_blank>robert.adams@intel.com</A><U></U>>>
wrote:<BR><BR> > ...<BR> > According to
[2], the maximum reported scripting collision contacts is 8.<BR>
><BR> > Testing with 8 on Wright Plaza today in
the Tuesday meeting seemed to greatly reduce physics scene time compared
to<BR> > previously without any apparent loss of required
fidelity (50ms with 18 avatars, albeit mostly sitting down -<BR>
> unfortunately I didn't record previous week's numbers but they
were higher. Nebadon tested one of his vehicles).<BR><BR>
Looking at the code, contacts_per_collision is the number of
collision points reported by ODE for each collision --<BR>
like a prim sitting on rough terrain and touching multiple places on
the ground. Reducing the count to 8 means that<BR> no more
than 8 contact points will be reported by ODE and, if there are more, you
can't be sure you get the 'best' ones.<BR><BR> I suspect that
most of the time there are only a few contact points so it doesn't make
sense that reducing the<BR> number from 80 to 8 would
significantly reduce the compute time. If it is the number of contact
points causing the<BR> computation overhead then ODE must be
normally returning more than 8 contact points. Is this really the case? Or
is<BR> something else going on?<BR><BR> --
ra<BR>
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<DIV class=im><BR>-- <BR>Justin Clark-Casey (justincc)<BR><A
href="http://justincc.org/blog"
target=_blank>http://justincc.org/blog</A><BR><A
href="http://twitter.com/justincc"
target=_blank>http://twitter.com/justincc</A><BR></DIV>
<DIV>
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