View Full Version : Linking motion of a primitive to hi-poly object

11-15-2004, 04:20 PM
Hi all,

I was wondering if somone could tell me how to link a hard fx motion of one object to another... basically i have a high poly object which is dropped. Due to the high poly i dont want to wait for LW to calculate especially if i have lots of them, and just in general id like to know how to link the motion of a primitive object in a similar but much lower poly shell to a high poly one.

For this example lets use a high poly and a low poly box. What i did was added hard_fx to the low poly model, and tweaked the settings till i got it to drop and bounce off a collision object (plane). Now id like to link that motion to a high poly box. I tried useing hardLink but the motions don't transfer over so im guessing its for softbody like in the monkey chain tutorial. Note i did parent the high poly box to the low poly one. Ive been a long time LW user but never managed to need the physics engine that much, other then sparks and what not.

Anyway, if anyone can help id very much apprechiate it.

Sub question: Also one more thing. Is there a way to get LW to accurately stop. What i mean is, currently the box will continue to shake as you keep calculating even though the floor has friction and the box has resistance/weight. Any ideas? My only workaround so far is to try and stop the calculation process when it gets to a certain point.

Thanks in advance!

11-17-2004, 10:10 AM
hum, so should i assume its not possible?, seems like a easy thing to do especially when there is a way to do complicated 2 point poly chain to complex model transfer of motion. Maybe there is a way to export the path of the object to a null to which i can then parent the high poly box? Im pretty sure that is possible but not off the pivot point of the original. Thanks again.

11-17-2004, 02:06 PM
fxhardlink (or fxmetalink for soft). if i recall correctly you set the PARENT as your
Low Poly object, and the child is the High Poly object. dynamics are run on the Parent object, the FXHardLink/MetaLink plugin is aplied to the Child, now the child object will inherit the dynamics and movement of the parent object. thenyou can bake the frames to the high poly object and delete the low, or use mdscan, or just make it unseen by camera etc etc...

there are tutorials on this in the tutorial bank, the chain of monkeys i think it was. lemme find the direct link. Its hardlink002.avi but i dont know where they stuck it now....
I'll poke around for it more indepth when i get a chance, but its one of the videos proton did way backbefore they actually released 8 i think - or just after it.

- Will.

11-17-2004, 04:30 PM
Basically it's as cameron said. You can Hardlink/Metalink any object to any other that's had a Dynamic effect on it. You parent the 'Hi poly' object to the 'Low poly' one (though it could be the other way round if you like pain!) and apply one of those two deformation plugins to your child object. For it to work, the parent has to have had it's point data calculated by one of the DynamicFX, cloth, soft or hard. If you don't want your parent object to wobble or whatever (for example, you just want a boned motion), you can set cloth FX> File>scan motion to just get the object's deformation and the child will work with that.

11-18-2004, 01:46 AM
Hum, i must be doing something wrong because my child object just doesnt react.

I have a low poly (6 side) cube, that has hard_fx applied to it. I have a collision plane. The box is raised to a few meters, and twisted slightly so as to land on a corner. I apply gravity and the settings and what not to get the box to drop down and bounce as is expected.

Now, i get a high poly box, basically a jittered more subdivision version of the first... just to tell them appart. Main diff being lots more points. I parent this object to my low poly one, making it the child.

I then apply hardlink fx from the deform tab to the child / high poly object. I play the animation and nothing, i recalculate the animation and nothing. The low poly behaves as it should and the high stays put. I have tried both metalink even though thats for soft_fx, and i have tried boy polygone mode, 1 piece, or parts in the hardlink properties and nothing seems to work.

However i have found an alternative for anyone who is looking for the same thing i am, which is to use the editFX tool and select the pivot point of the box (low poly) and choose create motion which exports it to a null from the commands list, bakes it as you guys put it. I then parent my high poly object to that null and it tumbles and jumps exactly like the low poly one did. I tried this in the scene i was building this for in the first place where i have a car crash and roll and it worked great. I think LW's physics engine has indeed come a long way. Im pretty sure a full fledged pinball table could be built within layout :)

Thanks for all your help guys.

11-18-2004, 09:36 AM
Hmmm, I can get it to work a bit if I Use clothFX after hard FX but this seems like a bit of a cock up to me :P

11-18-2004, 12:52 PM
Yeah i stopped messing with it also because i have to load the saved motion every time since recalculating twice may result in completely different outcomes and i mean completely different. Baking it to a null seems to be the quickest as well. I do save the motion however in case i want to speed up / slow down the whole thing... this is a really sweet feature by the way. All in all its much better to have it crash like this then to try and animate the rotation / movement of it by hand. :)