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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;


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.. :)



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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 ;)


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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..)


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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.

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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.


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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


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



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 smile.gif



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Something a bit different this time - a sin scroller.

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



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.


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