Rigid Bodies Masterclass with Thibault Gauriau

Thibault is from the effects department at ILM and has an impressive portfolio of simulation work for both feature film and games. Here are some notes I took down from the class:

1) To fake a lightning shot, just turn on a light that casts strong rims on your character and objects for one frame.

2) A lot of faking work involved. We are not trying to achieve real world physics. We just need to make the picture nice.

3) For pure CG films, only use rigid body simulation when that is the only method to achieve the shot. Example is the fight scene at the rope-bridge in KungFu Panda.

4) 2 types of systems: Simple and Advanced. The simple one is in the dynamics tab while the advanced one is in nDynamics. The simple one works for non-keyframe simulations only.

5) Checklist for a simulation would be to check for
– Passive objects first (Not moving like walls)
– Active objects next (Moving)
– Fields influencing the objects (Gravity etc.)
– Make sure ‘play every frame’ is selected in the animation playback options
– Apply constraints where required

6) The nail constraint ‘nails’ an active rigid body to a point in space, causing a pendulum effect.

7) You will need to use nDynamics if you want to deal with keyframe-animated object. Passive colliders are passive objects while nCloth are active objects. We could be using the ‘concrete’ preset on the ncloth node to prevent deformations (but it requires further tweaking such as setting rigidity to 1).

8) Use ‘input mesh attract’ attribute in the ncloth to switch between keyframe and simulation by giving it a value of 1 when not using simulation and 0 when using.

9) Rigidity allows an ncloth to get back to its original shape. Animate that value to allow an object to quickly get back to its shape after collision. Example: Soft Toy against piece of glass. Keep that value high if you want to maintain volume on an object.

10) Stickiness controls how much an object can stick to a surface at collision. Friction controls how much the surface slows down the ncloth object.

11) For something like cables, use either the transform constraint (one object’s vertices) or component to component constrain (between objects) to attach ncloth objects to a point in space or to poles.

12) Use cache/ncache to record a simulation so that you are able to preview it using the timeline.

13) The constraint method attribute defines what method an nconstraint is using. If we use max distance, we can define how many vertices gets constrained between two objects calculated by their distance apart.

14) To simulate exploding debris, just place your objects in one area and have a radial field underneath to push them out of their rest position.


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