eetu's lab

[eetu 526]

Hello, all

While learning this beast of a software, I bet everyone has accumulated a bunch of more or less interesting tests and stupid tricks on their hard drives.

Here's some of what has been accumulating on mine, before bit rot takes them, hopefully some might inspire others on this same road..

First, one from the mailing list a couple of days ago

>>Tom Nixon wrote:

>> Is there a quick and dirty way to calculate the center of mass of geometry?

>>

> Louis Dunlevy wrote:

> A super duper cheapo way would be to use the attribute promote sop.

> Stick position in the colour and then promote the colour to a detail

> attribute using the avarage method..

>

The average of point positions is not necessarily very close to center

of mass. think of a large cube connected to a small geosphere, average P

would be a lot closer to the sphere.

Here's a quickly knitted vop sop doing it via a volume;

http://eetu.iki.fi/hou/center_of_gravity.hip

The idea is to take a volume representation of the object, and

take the average of the voxel positions, weighted with voxel opacity.

Of course there are probably 5 more elegant ways to do it, but anyway..

eetu.

center_of_gravity.hip

[eetu 526]

Playing with SDF's.

A font object is converted to sdf, and some particles spawned inside.

After that, the inverse of the sdf gradient at the point location is copied to the velocity of the point, every frame.

animation

[eetu 526]

More volumes.

This time stacking a bunch of fractal images to make up an i3d volume.

anim1

anim2

- and one from real confocal microscope data, from an ear of a mouse, iirc

anim3

[eetu 526]

This was supposed to become foam

I was wondering how to make those bubbles that stick to each other, and conform to each other's shape..

The end result is probably something a bit closer to bark or something - but i kinda like the look anyway

[eetu 526]

This was a small shader vopnet to help Karma build some npr shader.

All it really does is turn all reflections black

(well, ok, it only does ray casting which means the hit point need not be shaded, and it doesn't recurse..)

karma_ref_occ.hip

Edited February 3, 2009 by eetu

[eetu 526]

Something a bit older, as with much of these things I was supposed to do something good looking with it,

but as that hasn't happened yet I'll just post these

This ugly thing is a texture map creator test really. The object is hit by particles, and the texture map gets damaged

at the hit location.

anim, and the texture map after getting hit by the particles.

[aracid 5]

hey man

I really like the volume rendering man:)

keep it coming !

[eetu 526]

After talking with the lads at Anima Vitae, who were making snow for their Niko movie, I got to thinking about

how to make foot prints in Houdini.

This is a combination of ray sop doing the penetration testing, and chops keeping the mesh distorted.

Add two spoonfuls of smooth sop to get the bulging sides.

anim

[eetu 526]

This is a small technique test on how to drive a morph by proximity to another object.

It's really just a bunch of expressions on two point sops. (Although I guess many effects are just that, too

..more tomorrow

proximity_morph_01.hip

Edited February 3, 2009 by eetu

[Andz 9]

This is a combination of ray sop doing the penetration testing, and chops keeping the mesh distorted.

anim

... and I thoght we needed ICE for that?!?!?

Congratulations eetu, great experiments!

[GallenWolf 27]

Good stuff mate! Keep 'em coming!

[rdg 16]

Good stuff mate! Keep 'em coming!

yeah! don't stop!

thanks for sharing.

[CeeGee 78]

Good work.

Thanks for the sceen files...

[cdrom 0]

Hi eetu! very interesting effect of i3d volume with fractal images. can you post hip file or explain how to do this.

[eetu 526]

Hi eetu! very interesting effect of i3d volume with fractal images. can you post hip file or explain how to do this.

I had a sequence of, say, 512 images from a fractal animation. Then there was a vop vex i3d shop that references the sequence, used

by the 3d texture (i3d) generator rop. The shader used the volume x and z coordinate to index into a single image, and the y coordinate

to determine the index of the needed image file. To get the color into the i3d volume, the shader exports the sampled rgb value, plus

uses the largest component value as the density.

The grid effect in the first animation was a rounding error in the "which image file to use" -logic..

A couple of earlier tests; anim anim

eetu.

[eetu 526]

Aggregation.

A friend of mine made a fast dla in xsi's ice, so I naturally had to give it a try.



aggrow_01.mov
aggrow_02.mov

dla in wikipedia and in pictures.

From the start I decided to fake it. I started thinking about the probability of any point in any timestep receiving a randomly walking new aggregate particle.
I thought it would be close to occlusion at that point, so I made an occlusion scatter component.


Each frame I occlusion-scatter a couple of points on last frame's geometry, and then copy new geometry to those. Iterate to taste.

A nice thing about this approach is that one can have invisible geometry constraining the aggregation process.
(The first anim is constrained inside a sphere, the second a torus.)

The particle counts here are really quite low, perhaps I'll leave it running the next time I go for a vacation

eetu.

ee_aodla_05.hip

Edited November 29, 2020 by eetu

[Mario Marengo 32]

Great stuff, Eetu!

Thank you for sharing!

[eetu 526]

Something a bit different this time - a sin scroller.

This is a companion to the peeling spheres topic from before.

anim

I've been using a lot of this technique of rendering something temporary with another camera, and then using the result to create something final for

another camera. It can be done via cops, but here it's done by prerendering the intermediary frames to disk.

hip and a zip with the rendered intermediary lores frames (you can render these from the .hip, too)

Next I have a long tale of woe and joy. Concerning particles. But not tonight.

eetu.

[Netvudu 114]

Great stuff eetu.

I

[eetu 526]

I