set_lin_acc is useless outside of nphysics.

[sebcrozet]

The acceleration of each object is reset to the world's gravity at the beginning of each update. This mean that any call to set_lin_acc (or set_ang_acc) is just a no-op from the user point of view.

Here are some possible fixes:

1. Let the user define his own force generator (which would replace the default BodyForceGenerator).
2. Implement something like box2d's setGravityScale.
3. Let each rigid body have a user-defined resultant force that would later be added to the gravity.

[tomaka]

set_lin_acc_scale has an effect on gravity, but set_lin_acc still doesn't seem to have any effect.

If I call lin_acc I obtain the value that I have previously set, but no matter which value this has the object won't move.

[sebcrozet]

That's right, my previous patch did not intend to make set_lin_acc effectful, but to add set_lin_acc_scale as a workaround. A better solution that would make set_lin_acc really effectful is more complicated.

In the mean time, I reopen this issue because I realize that it is worked around but not fixed.
Do you have a use-case where something like set_lin_acc would do something that set_lin_acc_scale cannot?

[tomaka]

The idea is to do set_gravity(1.0, 1.0) and then manage all the accelerations manually using set_lin_acc_scale?
I didn't think of this, but it should work!

[sebcrozet]

Exactly! Though I know that this looks like a hack.

[sebcrozet]

Starting with v0.8.0, nphysics, set_lin_acc no longer exists. Force generators are not the way to go to customize, e.g., gravity (using force_generator::ConstrantAcceleration) in a per-object basis.