Category: hou-effects

Archived post by JeffLMnT

Oh… A cool way to mask disturbance based on velocity is to set the control field to vel… And Crack open the disturbance microsolver>disturb field gas vop and the adding a length vop after the control field parm.

Another fx artist at work pointed this out to me

Saved the 5 mins to takes me to build a speed field

Archived post by TOADSTORM

i don’t. i mean literally that’s all there is to it… make a bunch of crumped up planes, texture them with a transparent cracked texture (literally just photograph some ice cracks and use it like a mask), wedge the planes inside your ice object, then turn off primary visibility. enable glossy refractions on your ice material and you’re good to go

it wasn’t fast but it was simpler than a volumetric shader, especially in vray 6 years ago

Archived post by matte

I had an RBD sim that I wanted to cache, only very small like 20 packed prims, but wanted it to play back realtime

but even though the bgeos were small, reading them off the network was slow.. .even reading them off a local disk was not realtime (and wouldn’t work on the farm)

so I made a stupid setup to ‘cache’ it in memory inside the hipfile

chopnet -> geometry chop in animated mode -> (lock the geometry chop) -> then channel sop to read it back to sops

was super fast, and didn’t make the hipfile too big cause it was a small sim

Archived post by Solitude

Pyro Cd Field Setup

@mestela

that gif is crunchy… meh

looks nicer in the vp

there might be a way with the gas calculate… but I used a really simple wrangle.

Attachments in this post:
http://fx-td.com/houdiniandchill/wp-content/uploads/discord/20185306/01/18/pyro_CdField.gif
http://fx-td.com/houdiniandchill/wp-content/uploads/discord/20185306/01/18/Pyro_Cd.hipnc
http://fx-td.com/houdiniandchill/wp-content/uploads/discord/20185306/01/18/pyro_cd.jpg

Archived post by TOADSTORM

so what you’re trying to avoid when you’re dealing with mushrooms is a smooth pressure front. the project non-divergent step of the smoke solver computes the pressure field, and when you have areas of high density right next to areas of low density, like at the beginning of a smoke emission, the velocity field is going to be more or less “combed” straight out along the gradient of that pressure. short answer, you get mushrooms.
so what you want to do is mess up that velocity field a little bit in order to encourage smoke to swirl around a bit, along that pressure front. the way i like to do it is in a sop solver. use the sop solver to import the `vel` data from your smoke object. when you jump inside, you’ll see the `dop_geometry` node is importing that field. copy this node and change the geometry data path to `pressure`. we’ll use this pressure field as a mask, so we can only mess with the velocity field exactly along the “edge” of the pressure field. use a volume wrangle on this field to isolate just the edge like so: `@density = fit(@density, 0, 0.1, 0, 1);`. make sure “bind each volume to density” is enabled. now we can scatter points along the “edge” of the pressure field in a scatter sop.
next, use a vdb from particles to create a fog vdb around these points. the goal is to use this field to “punch holes” in the velocity field, like swiss cheese. convert the vdb into a standard volume, then use a volume mix sop to invert the volume (set the mix method to “user”, then value to `1-$V`). then post-add a small amount, like 0.3 or so. what this does is make it so that most of your volume has a value of 1, but the holes will have a value of 0.3. then just multiply this against your `vel` field in another volume mix.
the end result should be that the velocity field has holes punched in it, but only around areas on the edges of the pressure field, which should help break up mushrooms without disturbing the rest of the simulation.