Category: hou-effects

Archived post by WhileRomeBurns

the other thing houdini does is accumulate air resistance and target velocity if you have 2 or more wind forces. the function to do that yourself: “`void addWindForce(vector targetv2; float airresist2; vector _targetv; float _airresist) {
float airresist_sum = _airresist + airresist2; _targetv = (_targetv * _airresist + targetv2 * airresist2) / airresist_sum; _airresist = airresist_sum; }“`

Archived post by WhileRomeBurns

if you want to use `targetv`, `airresist`, `drag` you could do the math yourself and store them in custom attributes like `@c_targetv` so bullet doesn’t pick um up and make nans

it’ll be something like this:

“`float imass = 1.0 / @mass;
@c_airresist = @c_airresist * @c_drag; if (@c_airresist > 0) {
    // the relative ang vel     v@v -= v@c_targetv;
    // quadratic drag     v@v *= 1.0 / ( (@c_airresist * imass * @TimeInc * length(v@v)) + 1.0 );
    // restore frame     v@v += v@c_targetv; }“`

i don’t see how that could produce a nan unless c_airresist was negative or mass was zero

which you can add checks for if you like

just skip zero-mass dudes

Archived post by CiaranM

It’s a SOP Solver, so just do your group masking the SOP way 🙂 Specifically, set the group mask on your wrangle nodes to @name=boxes* or @name=spheres*. You really only need a single SOP solver (with Data Name and Group back to default) with as much wrangling per-group as you like inside of it. I really like to keep it simple and keep all of my packed geometry coming from a single SOP source into a single RBD Packed Object. Do as much as you can with SOP-type workflows, avoiding DOP anachronisms at all costs.

Archived post by TOADSTORM

fluids are a shitload easier to solve when you can assume that they’re incompressible. with that assumption in mind, what you don’t want is fluid velocities that are pushing into each other or away from each other, because this would result in fluid densities increasing in some areas and decreasing in others… i.e. compression.
the non-divergent projection iteratively goes over your velocity field and finds ways to redirect those velocities so that they’re not going to result in an increase in pressure. this redirection manifests itself as swirly behavior, which is typically what you want with fluids.

you could see this pretty quickly in action with a 2D pyro sim… make a little ball of gas and apply a uniform outward force from the center. without the non-divergent projection step, the gas would simply expand. with it, it instead starts to swirl around itself in an effort to not increase or decrease pressure.

i’m probably leaving out details that one of you actual smart people can fill in, but that’s my understanding of the process

Archived post by trzanko

lil bit of triangle stretch and skin sliding + bend plasticity

was kind of all about finding the right balance of attach stiffness and slide

if you stiffen the slide and loosen the constraint you get bigger folds

and if both stiff you get really fine wrinkles, could be really cool to run on a face or hands

Attachments in this post:
http://fx-td.com/houdiniandchill/wp-content/uploads/discord/20195512/06/19/skinSlide_v001.hip

Archived post by trzanko

there’s a pretty neat trick to getting noisey edges without the rbdmaterial fracture sop

the stuff they do in rbd material fracture to compute the intersection planes is pretty intense

so there’s this as an alternative

doesn’t pass every test

but with some love it can get pretty nice results

excited for the guiding stuff, rolling my own on a job rn and would be interested to see their approach ( it’s for sure better haha )

i imagine their guiding method point deforms a tet mesh to the anim geo, and then perhaps they extract a rigid anim xform off the derivatives of the rest / anim tet deformation, and activate pieces by the difs in the rest / anim xforms; shear, scale, rot difs, etc

Attachments in this post:
http://fx-td.com/houdiniandchill/wp-content/uploads/discord/20195411/07/19/edgeFrac_trzanko_v001.hip