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View Full Version : drops make new drops when hit displaced water: how?



4dartist
08-17-2007, 12:49 PM
I have an ocean plane that is using a few displacement maps for waves and we have an object crashing into the water that makes a big splash. I want these splash particles to make new little splashes when they hit the water. Is that possible?
I have been able to create collision objects with the event turned on, and an emitter as a child to the main splash emitter called resplash, and it will make new particles when the original ones hit the collision object. So i can get the secondary splash to work just fine, my only problem I am having is getting the collision object to be displaced so the splashes happen on the waves. I've tried setting the collision object to object-subdiv and object-adv but it still just shows a grid where the object isn't displaced at all.

Any ideas? I though about figured out how to create an .mdd file for the water and see if that works. not sure how do save the .mdd or even load it yet. We have pointoven on another computer but might have to buy another license to get it on this one.

Ben

4dartist
08-17-2007, 01:53 PM
Well I looked up how to save a .mdd file and exported the water object motion and applied it via the .mdd and used that as the collision object. No luck, they still generate when colliding with the water in it's un-deformed state. ;(

Ben

Bytehawk
08-17-2007, 05:16 PM
weird...
would an object sequence work as collision object ?

SplineGod
08-17-2007, 05:59 PM
You can make the water surface a collision object. Any object thats set to be an emitter can emit particles everytime it collisions with the water surface.
Those can be set to parent emitter so that each particle emitted in turn become particle emitters.
You can also fxlink very small droplet objects to the particle emitters and make the droplets themselves particle emitters etc etc.

This example was done that way.
http://www.3dtrainingonline.com/examples/splash.mov

Bytehawk
08-17-2007, 06:42 PM
yep but does it work on a deformed object? That 's what he's having problems with...

Mr Rid
08-17-2007, 06:53 PM
Well I looked up how to save a .mdd file and exported the water object motion and applied it via the .mdd and used that as the collision object. No luck, they still generate when colliding with the water in it's un-deformed state. ;(

Ben


Did you click the 'calculate' button first? This gets all the deformations and dynamics talking to each other. The effect it sounds like you are describing should work.

Mr Rid
08-17-2007, 07:09 PM
P.S.

There can be a problem with parent particle event or erase used to emit secondary child-particles because there is no sub- or fractional- frame calculation in LW for the particles (which there desperately needs to be NT). Depending on their speed, the parent particle event or erase may occur at a distance before they actually make contact with the collision object- the faster the particle speed, the greater the distance can become. So in this case, your secondary splash will birth inches or feet (depending) above the water surface they are meant to appear to be colliding with.

Depending on your sim, and speed of your parent particles, it may or may not be apparent. I found a ridiculous workaround where you scale and calculate your whole scene at a lower speed in order to minimize the gap, bake the PFX, then load that into your original scene but increase the playback speed of the PFX appropriate to however much you slowed down during calculation.

4dartist
08-18-2007, 12:35 PM
Bytehawk - what is an object sequence? Do you mean a .mdd file or do you have to have a new object per frame with the displacement baked into the model?

Splinegod - sorry I worded my post weird. I know that making particles impacting a collision object can birth new particles. I have that working fine, and it looks great. My problem is getting the particles to collide with the deformed waves. When you set the water object to be collision object, it undeforms it and makes a grid where the undeformed object would be.

I have 2 shots that need this effect, so for the 1st one which i had to finish, I just baked the waves at a frame where a majority of the splash impacts the water and used that as my collision object. It looks decent.

Mr Rid - I haven't actually tried calculating it. Everything looks like it's working real time i didn't even think about it. I'll give it a go.
As for the subframe calculation problem, I have seen what you are describing, but in this case it's pretty spot on. The splash drops aren't traveling too fast so the collisions are detected with pretty decent accuracy.

Thanks guys for your posts i appreciate your time. I have one scene left that i'm working on this weekend. It's been a water filled week for me! hehe.

Ben

Mr Rid
08-18-2007, 09:22 PM
Mr Rid - I haven't actually tried calculating it. Everything looks like it's working real time i didn't even think about it. I'll give it a go.


PFX may appear to work but will behave accurately when you click Calculate, but particularly with deformed collisions.


And no, PFX do not really collide with object sequences since the collision mesh changes on every frame.

ndrangesh
08-22-2007, 07:07 AM
G'day mate
4dartist i have tried this several time
the particles does not interact with displaced object surface. i tried to do a water fall as if the particles flowing on the surface it did not work.
but you can export the object as transformed object then the particles interact.
but in your case try exporting 2 sets of transformed and try to get the same poly count and morph them .

Mr Rid
08-22-2007, 09:58 AM
G'day mate
4dartist i have tried this several time
the particles does not interact with displaced object surface. i tried to do a water fall as if the particles flowing on the surface it did not work...

Something like this?
http://www.box.net/shared/static/fsct1fze3f.mov
Particles do collide with deformed objects. Are you clicking on 'Calculate?'

ndrangesh
08-24-2007, 04:10 AM
yes Mr.Rid of course it works
i hit calculate it works great
but should save motion immediately because lw kills the calc if any othe changes are done
thanks for clearing the darkness Mr.Rid