how to vary activation time

[rohandalvi]

hi,

This is a simple question, but I cant figure out the expression.

How can I vary the activation time for an effect or a force?

Lets say I want it to start between frame 20 and 50 based on rand($ID) what would be the expression?

Or even if I can bring particles into a group over a period of time, I guess even that would work. Still what would be the expression?

with regards

Rohan Dalvi

Edited January 27, 2009 by rohandalvi

[rdg]

How can I vary the activation time for an effect or a force?

Lets say I want it to start between frame 20 and 50 based on rand($ID) what would be the expression?

something like:

if($F > int(fit01(rand($ID), 20, 50)), 1, 0)

* rand returns a 0..1 value

* fit01 rescales this value to the new min max

* int makes an integer - maybe unnecessary if you are dealing with floating frame numbers

* if(cond, then, else) sets the activation to 1 if condition is true.

untested.

Edited January 27, 2009 by rdg

[rdg]

thinking about it:

Activation might not be controllable on a per particle basis.

In this case keep the force activated and animate the strength based on the expression ...

[rdg]

Or even if I can bring particles into a group over a period of time, I guess even that would work. Still what would be the expression?

Indeed for WindPOP this is the most reliable approach.

setup_activate_force_at_random_frame.hipnc

eof

[rohandalvi]

thanks a lot RDG,

thats exactly what I wanted. I am just not very good with expressions, so even though i can understand the logic of what I need to do, I can"t always get the expressions right.

so thanks again.

Edited January 27, 2009 by rohandalvi