TouchDesigner | Email | Shrink Instance

Original Email – Mon, Jul 13, 2015 at 9:43 PM

Hey Matt!
So I’ve tried banging my brain around 10 different ways to where I’m sure it now resembles a sphereSOP – noiseSOP but I’m still coming up a little short. Naturally, I thought about your THP 494 Shape lesson but I was not able to figure out what I’m missing so I’m coming straight to teacher for some guidance.

I’m trying to recreate the attached image. I’m using a GridSOP, MetaballSOP – MagnetSOP which sort of works but I’m missing some very important part of the process. Can you have a look at this and give me a hint as to what I’m missing?

You certainly do not have to correct the work unless you want to but a point in the right direction (haha) would really help me sleep tonight!


Reply – Tue, Jul 14, 2015 at 12:23 AM,

That was a good brain teaser.

I’m including two different approaches to solve this problem. The first looks at using your magnet approach, and the second is more GPU focused.

Screenshot_072115_120220_AM

Following your model with magnet, you had just about nailed it – all of the information you needed was in that SOP to CHOP, it was just a matter of reformatting it. In the magnet base, I grabbed the tz channel of the SOP to CHOP, scaled it, and renamed it scale, merged it in your instance CHOP, then applied it to the scale parameter of your instances. Pretty right on with your existing approach. The draw back here is that the magnet SOP is very expensive – nearly 7 milliseconds by itself – bottle-necking your performance at about 30 fps. This also keeps you pretty limited in terms of the number of points you can work with – CPU bottlenecks can be tricky to work around.

MetaBall

So, I started to think about how I would solve this problem on the GPU, and remembered that an array of pixels is just a different kind of grid. The second approach translates a circle TOP, and then converts that to CHOP information, merges this with a SOP to CHOP (using the xyz data from a gird), and then instances from there. I was looking at over 1400 instances without a problem. The challenge you’ll encounter, however, is when you try to replicate that many source textures. I did a quick test, and things slowed down when I had that many texture instances drawn using the newer texture instance approach. I was, however, able to get performance back up to 60 FPS if I loaded a 3D Texture Array TOP, and then turned off it’s active parameter. Markus uses this trick often.

circleTOP

Anyway, that’s as far as a I got in the little bit of time that I carved out. The next steps (in terms of mimicking your source image) would be to get the displacement right pushing instances up and down to make an opening in the center of the array.

circleTOPdisplacement

Alright, well I put another hour into this because I got really interested in the idea of displacement. I think this still needs a little more work to really dial it in, but it’s a solid starting point for sure.

Screenshot_072115_120617_AM

Hope this helps.

Best,
Matthew

scaleDisplacementExample

Look at the example file on GitHub – shrinkInstance_locked