Copy Stamping question

[thanaras]

Hello,

The solution to my problem might be easy but I can't get my head finding a solution at the moment. So lets say we have some points and we want to copy some spheres on them. And let's say we want to start scaling the spheres randomly based on a point attribute (let's say random_seed) that assigns to each point a number which is a frame between $RFSTART and $RFEND. I then want to start scaling the sphere once $F >= $RANDOM_SEED and have the size to be between 0.05 and 2.0 for example. I attached a simple file where I start scaling the spheres when $F >= $RANDOM_SEED but because of the wrong expression I am using, each sphere starts growing from a certain scale and on, and not from 0.05. If you could take a look guys I would be very thankful. Cheers.

[hopbin9]

No attachment.

[Matt_K]

Hey thanaras,

Without seeing your scene file, it's difficult to judge just what you are after.

If you have the spheres copied at the right random sizes - [ try using this as a random size stamping function in your copy SOP: fit01(rand($PT),0.05,2) ], then you could try this expression in a Scale param (on the Particle tab) of a point SOP, before the copy node:

if($F >= $RANDOM_SEED, 1 + ($F * 0.1), 1)

This will only work if the $RANDOM_SEED value is available to the template points coming in to the copy SOP.

I have used $F*0.1 as a value that will change each frame and scale the objects by that value.

You can of course substitute any value that works for you.

Hope this helps,

Matt.

[thanaras]

Hello Matt_K,

Thanks for the reply. Sorry that i forgot to attach the file. I will attach it later on in the day.

Using your expression i still have the same problem. For example in frame 40, I have 5 spheres "enabled" because their random seed exceeded $F, and they start growing, but they have the same size. So a couple of frames later that another one is enabled, its going to be the same size as the others which they keep growing. The question is how can each one grown in random frames and to start from (lets say) 0.1 and end to 2.0 all the way. Hope this is more clear. Thanks

[anim]

just subtract the starting frame so every scale starts at 0

so expression like if($F>$RANDOM_SEED, $F-$RANDOM_SEED, 0) will be 0 until the frame specified by $RANDOM_SPEED then it will start growing by 1 each frame

so you can easily do this

fit(if($FF>$RANDOM_SEED, $FF-$RANDOM_SEED, 0), 0, 10, 0.05, 0.2)

and you spheres will start at 0.05 and grow from 0.05 to 0.2 over 10 frames from frame defined by $RANDOM_SEED