[Bf-committers] Softbody revisited :)
Ton Roosendaal
ton at blender.org
Thu Mar 31 11:22:03 CEST 2005
Hi BM,
Maybe it's easier to move the discussion to this list then.
Below I've put your text in ">" quotes. (For those who didn't read the
wiki page, it's about conventions for how a user can control simulation
steps, or actually control "time").
* Proposed: On frame advance, lesser than 10 steps, softbody simulates
time steps
> Is fine, but see : origT is interpolated linear from previous calling
> object_softbody_step(...) to calling it this time .. so it is
completely unaware of
> the nonlinear movements the goal targets made within the (up to 10
frames time line ).
> What I want to say is : it's on the callers side to care for
correctness of the goal's
> evolution in time. Otherways we'd need to carry all that IPO stuff in
here.
It will depend on speed of course, but my idea was that steps of 10
frames should still give a softbody simulation "as close as possible"
to what should have been achieved with doing (in Blender UI) 10 single
frame steps. How this will be achieved needs to be experimented... I
still don't really grasp your wiki text about what "time" means for the
simulator...
The simplest solution I first like to check on is just putting the
Blender animation system in (time+10), and do 10 simulation steps for
softbody.
> So i'd propose to make it a task of the caller to split the "up to 10
frame step" to
> nice "user desired accuracy in time evolution (means how precise
should the goal
> target be moved in time; eg 1/10 .. 10 frames)"
I don't understand this... guaranteeing accuracy on large time steps
doesn't have be done for me, it should just be possible - for the
animator - to quickly walk through an animation with larger steps to
'get the picture', or to 'advance to a new frame for editing'.
Accuracy on simulation we can restrict (per definition) to single frame
steps.
* proposed: On frame advance, larger than 10 steps, softbody doesn't
refresh
> having a reasonable algo for hop forward as stated above, this
restricion could be
> weakend by user option
Maybe larger time steps should also fully reset the softbody system...
needs to be checked on if a "not refresh" is useful. For me the "not
refresh" means just don't call the simulator, and signal the softbody
to be "OK" for that new time.
*proposed:
- On frame steps back, Softbody resets completely.
- On exit editmode, reset completely
- While transform Softbody in object mode, do simulation steps, but
reset at end
- And of course a button in the Panel causing a reset
> ... hum on resetting .. there's still the question : what's the
correct state
> ( position and velocity vector ) to be reset to ? ( to say it the
math way: a dynamic
> system is defined by the differential equations ruling time evolution
AND the state to
> start from [called initial conditions] .. which (in most cases) needs
all time
> dependant variables to have a predefined value at time == t0 )
> May be that was not that clear until now, but having keys in the past
> (frame_numbers < 0 )when defining actions was doing that .. so reset
to the first
> available key and run time from there ?
A "Reset" is just setting all speed vectors to zero, and put the
body-point locations on desired "goal" for the current frame. Isn't
that sufficient?
-Ton-
On 31 Mar, 2005, at 1:00, bjornmose wrote:
> Ton Roosendaal wrote:
>> Hi,
>> I've appended my last mail about the topic, with 3 strategies, and a
>> proposal to the wiki page here;
>> http://wiki.blender.org/bin/view.pl/Blenderdev/Softbodies
>> -Ton-
>> ----------------------------------------------------------------------
>> -- --
>> Ton Roosendaal Blender Foundation ton at blender.org
>> http://www.blender.org
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> some more thinking about it
> http://wiki.blender.org/bin/view.pl/Blenderdev/Softbodies
> cheese == :)
> BM
>
>
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Ton Roosendaal Blender Foundation ton at blender.org
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