Copying different objects to points

Sometimes you need to copy a bunch of different objects to points. Eg. You have 5 variations of wood splinters and you're emitting them from a snapping plank.
Instead of using the slower copy stamp with random point values, you can use a ForEach loop and a Switch node..and of course a point wrangle.

Connect the objects to the Switch node. In a point wrangle, give each point an (random) integer value (eg "instanceID") ranging from 0 to the number of objects you have.
Make a ForEach network and connect the Point wrangle into the top. Create a null node directly after the start of the Foreach Begin. This will be a "temporary holder" node. It will carry the instanceID value to the Switch node. I've called it PT
The clever bit happens in the Switch node. In the parameter window, click on the cog wheel and add a Spare Input. This will create a new dialog box called Spare Input 0. Type in:

../PT

This will point the spare input to our temporary null & its instanceID value.
In the Select Input dialog box, type

point(-1, 0, "instanceID", 0)

here we are telling the Switch node to get a point attribute from input -1 (which is the spare dialog....which is pointing to the PT temporary null..). The attribute in question is instanceID.. NICE.
A purple arrow going from PT to Switch should have appeared now. This represents that link we've just made.

All that is left to do is to create a Copy To Points node & put the Switch output into the objects input & plug PT into the points input. Finally plug the output of all of that into the Foreach End.

Check names for duplicates

point wrangle snippet from Mike

int find = findattribval(0,"point","name",s@name);
int count = findattribvalcount(0,"point","name",s@name);
i@find = find;
i@count = count;

solver sop and moving geometry

So, the Solver SOP doesn't behave as "I" expected with animated (ie. moving) points/geo.

You need to manually update the position if you want your geo to still move!
SOOOOOOOOOO. Inside the solver, copy the P (for position) attribute from Input 1 to Prev Frame...

Weird stuff. But hey.

removing RBD from a sim

Sometimes you need to remove an RBD from a sim completely. Eg, you're using a block to push something and then need it to get out of the way...

Make sure you have a group for it on SOP level. It will probably be a point group, as you're most likely using packed geo.

Now use a SOP solver in your DOP network. Attach it to a multisolver, alongside your Bullet/RBD solver..
Inside the SOP solver, blast the group that you created earlier. Use a switch node or some other timing device (you could use a point wrangle with removepoint I think)  to trigger the group's deletion.
Eg. Switch node  could use $F>1000. Here it will switch from "all the geo" to "all the geo minus the group" input.

Select a random point from a group each frame

Some code snippets from Walter to use points from a group randomly, for emission (or other things)

In a Detail Attribute Wrangle-

int npts = npoints(0);
float keep = rand(@Time + 235.624) * npts;
i@keep = int(keep);

Every time step, a random point id is chosen as the "keep" point.

Then in a blast, we kill everything but the kept point

`detail(0, "keep", 0)`

Don't forget to invert the blast selection

Bullets solver, setting or changing attributes

Bullet solver is a bit strange in Houdini. It might not update values as you expect. Eg, you're trying to change the @active value using a sop-solver.
One solution is to use the Bullet mode in the RBD Solver. This usually works..But it might be slower? I think it has a multi solver built into it..

Another way to make it work is by utilising a multi solver and the Geometry Wrangle. This will let you access the SOP level stuff (there is an input tab you can mess around with)

So, your input RBD goes into the first input of the multi solver, then your Bullet Solver and any Geo Wrangles go into the purple input of the multi solver..

V IS FOR..............

"v" is for RBD and pops.. "vel" is for volumes...