[ODE] ODE-GIMPACT performance and advices
f.brebion at vrcontext.com
Thu Oct 26 15:42:47 MST 2006
Francisco Leon wrote:
>triangles for saving work on successive queries. It is
>specially good with static meshes that don't move very
>frequent. So that is my personal interpretation of
>temporal coherence. OPCODE claims to have it, but it
>isn't applicable when you have to find all contacts
>between two trimeshes, and OPCODE forces the app to
>calculate transformed vertices (and planes) on each
>query every time.
Static meshes that don't move very frequently. Is that really useful ? I
mean, i can understand static meshes vs simple primitives, or dynamic
trimesh vs static trimesh, or dynamic trimesh vs dynamic tri mesh ( in
this context, a "dynamic" trimesh would be a trimesh whose
transformation matrix is updated by ODE every step ). I can imagine a
dynamic trimesh, like a vehicle, that moves continuously every step,
then is parked and becomes static. But i can't imagine a dynamic trimesh
that you'd only update every N steps.
>Transformating vertices A PRIORY isn't reasonable when
>you have large trimeshes moving, but I think that it
>is a quite rare: Do you imagine a Building moving
>every time? Do you imagine a Mountain moving every
>time? it sounds impossible.
As i explained in my e-mail, i'm working on a sci-fi game that features
spaceships of all forms and dimensions, some of them being definately
building / mountain sized.
I understand that my game is more the exception than the rule, but i
have to wonder if it's a good idea to replace opcode ( which is quite
generic ) with GImpact, which from the sound of it, is more geared
towards specific types of scenes.
Don't forget that ODE is not only used for games.
>system, and each particle corresponds to a vertex on
>the trimesh. In that case vertices are transformed
>every time without any worry about. GIMPACT has an
>advantage in this case.
>Currently GIMPACT precision is for 32 bit only. But if
>we want 64 bits we'll have to change some #defines and
>constants, and compile it on a 64bit platform. We can
>leave that task for later.
Just wanted to be sure.
>GIMPACT has to limit the scene bounding to
>[-1638.0f,+1638.0f] because it does spatial sorting in
>two dimentions : X and Z. It reaches more speed but
>limits the scene dimentions.
In my scene, i have a terrain that is planetary size ( spherical terrain
). Your portal / section idea wouldn't work in my system. The size of
the scene is absolutely gigantic, i have human-sized features (
vehicles, buildings ) on a perfect 10,000 Km planet. But again, i'm an
>So Flavien, thanks a lot. Every critice is welcome.
>You have to understand that GIMPACT is a quite
>inmadure, and it is currently on Alpha stage. I'm
>working hard for complete the whole documentation, and
>your questions helps to complement information about
>the library. Documentation is often harder than
>programming, you know that.
I know, and i'm not criticizing your work. I believe it's definately a
step in the good direction, even though i'm starting to believe it's not
the "magical solution" to replace opcode as i initially thought.
I just wanted to speak of those issues since i saw many people on this
mailing list proposing to replace Opcode by GImpact. I'm not saying it's
a bad idea, but i just want to make sure it's an educated decision and
that everybody is well aware of the new "restrictions" that GImpact
would add to ODE in comparison to Opcode.
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