stamping a changing value.

General TouchDesigner Discussion
1

Hello. I wonder if anyone could help point me in the right direction?

I’m trying to use the copy sop’s stamping ability to stamp values from a chop that changes over time onto copies. However, I want the value of the channel, when it is stamped to remain constant (as if i was stamping a rand function) for that object for it’s life (the copies are copied onto a particle system) but what’s happening is that each copy instead animates along with the channel. Help?

I have attached an example .toe file and an image to better explain the problem I am having and the result I am trying to achieve.
[url]http://www.jackbutnotjill.com/extra/touchme.gif[/url]
stampingissue.toe (5.46 KB)

2

Hi.

If you turn on ‘Add Particle ID’ (and restart or reset the particle SOP) then each point
will have a unique ID attribute with it.
You can access this value with the point() expression, or more simply in this case by
the $ID local variable in the Copy SOP.

You can then use this ID in a formula (such as rand) or to look up non-animating channels
(example chopi function)

As a quick test, turn on ‘Add Particle ID’, reset the particle SOP, and change the value
expression to rand($ID)

Cheers
Rob.

3

I should add, alternatives to stamping may include preparing translate, scale, rotate, color channels in a CHOP then feeding these channels either to a limit SOP (which converts them to geometry) or the Instance tab of a Geometry component (which draws multiple instances efficiently).

Cheers
Rob

4

Thanks Rob! very helpful

Any ideas how I might go about stamping a value from an animating chop but not have that value animate on the object it’s stamped onto?

For example:
At fame 30 particle 1 is generated and the animated chop’s value is 0.5. I’d like to stamp this onto the particle1/copy1’s size attribute but for it to remain at 0.5 even though the chop’s value continues to change.

For example:
At frame 67 particle 2 is generated and the animated chop’s value is 1.2. I’d like to stamp this onto the particle2/copy2’s size attribute but for it to remain at 1.2 even though the chop’s value continues to change. (at frame 67 particle1/copy1’s size should still be at 0.5).

[my animated chop could be any value at any time].

The solution feels like it should be simple, but i don’t seem to be able to crack it.

5

The way I see it you have to hold/store those values over the length of your animation. You should do that in chops; sampling your animation and generating separate, static channels that can then be assigned where you wish.