Additive Animation

[rdg]

Hi,

I try to redo some of my recent 3dsmax discoveries in houdini.

Yes, I have to admit I still have a relapse every now and then.

This time is is about:

additive animation

I know I can set a variable/spare channel to hold $speed and set the x transform of a object:

$F * $speed

This works well, as long as the the object is moving all the time.

but what if there is boolean switch like:

$moving

$F * $speed should only be added to the current position if $moving is true.

How would one do this the houdini way?

I tried 'set/setenv' in a custom function and probably missed the right syntax as it just threw an error.

Georg

[digitallysane]

CHOPs maybe? Something like the Logic CHOP might help.

[sibarrick]

How about using the warp chop? (using index method I find easiest)

or just replace $F with a linear channel that is either increasing or held?

[antoinedurr]

If it's a one-time stop, then you could do something like min($F,40)*$speed, which would stop your animation at frame 40. If the scenario is more complicated, i.e. multiple stops and starts, then I'd figure out how to create a square wave where it's 0 when there's no motion and 1 when there is, and slurp it into an area CHOP.

-- Antoine

[rdg]

lurp it into an area CHOP.

Thanks Antoine,

the area CHOP was my last thought last evening and my first thought this morning.

It is good to know I haven't been wrong - but it is an disturbing situation, nevertheless.

As the area CHOP outputs the integrals of a given function and way is a function/derivative of speed - this is the way to go.

Georg

[rdg]

The areaSOP approach worked very well for my first experiment:

a rotor that is controlled by a on/off switch and a RPM-parameter.

But on ran aground on my next experiment:

I have an animated cube: it just travels from -3 to +3 in tx.

How do I calculate the way traveled?

If I just use the area for tx - this isn't the way traveled.

I tried a spare parameter with

ch("./tx") - chf("./tx", $F -1)

but this is neither speed nor acceleration?

I want to add this "distance" every frame to a channel.

chf(".", $F - 1) + ch("./tx") - chf("./tx", $F -1)

didn't work either.

Maybe you can shed some light on this issue

Kind regards,

Georg

[rdg]

I had another idea:

a spare channel with this expression:

{

float sum = 0;

for (i = 0; i<$F; i++){

sum += chf("./tx", i) - chf("./tx", i - 1);

}

return sum;

}

This does what I was looking for ... I guess.

Georg

[rdg]

to keep this complete:

{
	 float sum = 0;
	 for (i = 0; i<$F; i++){
		sum += length(chf("./tx", i) - chf("./tx", i - 1), chf("./ty", i) - chf("./ty", i - 1), chf("./tz", i) - chf("./tz", i - 1));
	 }
	 return sum;
 }

this is the *real* way traveled - not just in x.