Change body shape and(or) it's properties

[wrenge]

Hello! Couldn't find anywhere on the Internet how to change properties of existing shape. I think I'm figured it out, but I'm not sure is it the right approach.

TypedIndex originalShape = Sim.Bodies.GetDescription(colRef.BodyHandle).Collidable.Shape;
var shape = Sim.Shapes.GetShape<Box>(originalShape.Index);
shape.Width = opts.Size.X;
shape.Height = opts.Size.Y;
shape.Length = opts.Size.Z;
inertia = shape.ComputeInertia(opts.Mass);

var desc = Sim.Bodies.GetDescription(colRef.BodyHandle);
desc.LocalInertia = inertia;

However I don't know how change shape type (for example box to capsule) without completely recreating body. Is it even intended?

[RossNordby]

Almost! GetShape returns a reference to the shape. Since the shape itself is a value type, assigning to a non-ref variable just copies it, so it's no longer a reference to the original memory.

If you changed it to:

ref var shape = ref Sim.Shapes.GetShape<Box>(originalShape.Index);

then it would be a memory reference.

GetDescription works differently; it builds a BodyDescription for you, but modifying it will not modify the original because it's just a copy of the data again. Because there is no place in the library where a BodyDescription actually sits around, it can't return a ref to it. You can use ApplyDescription to set all of a body's properties to match the description.

You can also grab a BodyReference by doing Simulation.Bodies[bodyHandle]. BodyReference has a bunch of handy stuff on it, including a LocalInertia property which does grab a direct reference to the local inertia data for the body. There are some subtleties to using direct memory references, though; if the body is asleep, changing the memory directly doesn't wake it up (you'd have to use BodyReference.Awake = true). Also, directly changing the inertia tensor memory won't handle transitions between dynamic and kinematic by itself.

BodyReference.SetLocalInertia lets you specify a new local inertia and it'll handle the transitions for you.

If you want to change the shape referenced by a body, you can use BodyReference.SetShape. Like SetLocalInertia, it'll handle transitions and awakening. Note that you don't have to use that if you've just modified the shape memory directly; the body is still pointing at the same memory either way. You just might have to call Awake= true if you want it to wake up to respond to new collisions or something.

[wrenge]

Thanks for the reply!
Do I need to destroy old shape when I'm creating new for existing object?