Delete primitives with death of particles

[Ezz]

Hi Houdini-folks :-)

Im working hard to learn Houdini.

And I have been working trough some of the examples found on this page.

So I have a setup containing a logo-geometry that I want to disolve. To do so

I have conected my primitives to a POP-net. I have set the lifespan of the

particles to 5.

My problem is that when the particles die, my primitives are replaces again wich is

kind logical when I think about it.

So I guess I have to put in a delete-SOP to delete the primitives as the particles die.

I need some help to figur out how to get the information from my particles ( $DEAD ??)

so that I can put them in to a group that delete the primtives acordingly.

I hope it makes sense, but I have attached my hip-file so that you can have a look.

Thank you so much

Erik

disolve.hipnc

[GallenWolf]

Check out this REALLY cheesy way doing it. Basically I just move the incoming primitive's original location off screen I'm sure someone will figure out the "right" way to do it but gotta be fast while my render cranks

GW

disolve2.hipnc

[Ezz]

Hey GW.

Thank you very much for your solution :-)

But if you look closer on the primitives when the particles die, there order is changes and

gives it a rather funky look.

So it brings me back to the idea of transferring the particle ID from the POP-network

to drive a group that controls a delete-node. But I dont know if thats the rigth approach

Erik

[GallenWolf]

What you could try, is to do an ordered sourcing of the points via the prim centers, and then back in SOPs, use a copy sop to stamp that particular primitive onto the particle. You'll need to do the connectivity sop -> partition sop trick as well as to shift the individual primitives to the origin, but I think i should be do-able. Hope you figure it out! I'll try if I get a moment.

[GallenWolf]

You will observe that some of the primitives are off; this is because when the particles are emitted, the center of the primitive is calculated differently. If you can figure that out you are gold

GW

disolve3.hipnc

[Ezz]

Hey thanks for your effort GW :-)

Still its not exactly what I was planning. There must be a way to

transfer the information from the POP-network to a group-SOP which then controls a delete-SOP.

The $PT from the POP-network could give me what I want. I have created an attribute based on that called $KILLPRIM

But I can not understand how to put the information into a group. I have tried all the attribute_nodes there is, to try and combine

the datas..No luck :-(

AAhh my mind is starting to blow

Erik

[old school]

The Primitive SOP is not as flexible as the Copy SOP in that it can't transfer attributes from the second point input.

You can easily work around this in several ways. The most straight forward way is to use your existing Primitive SOP and the point() expression to index in to the particle geometry. It's straightforward as you have a 1:1 relationship between primitives and points.

See your modified example file attached.

I used a more graceful blending out the alpha instead of cutting them right off before deleting them. I also changed the lifetime of the particles back to 100 as you don't need to kill them off. I replicated the same falloff to the alpha as you had in the death variance. See the "point__dissovle_alpha" Point SOP for that expression in the Alpha field.

disolve_sesi_v01.hipnc

[Ezz]

Hi Old School.

Thank you very much.

It a beautyfull solution with the alpha I must say.

I just need to digest trough the expression that controls the alpha.

Thanks again

Erik