Rigidbody2D and ForceMode.AddVelocity?

Questions & Answers
1

The new 2D update (Unity v4.3, released 2013-11-12) have come with the new Rigidbody2D component.

My previous code uses the 3D-based rigidbody, moving it using Rigidbody.AddForce(). I specified that the AddForce() uses ForceMode.VelocityChange, which conveniently ignores mass and just makes it better for a playable character.

Rigidbody2D.AddForce() on the other hand does not support ForceMode at all, it has only one way of dealing with velocity and that is ‘force = mass * acceleration’.

Here’s the part of my code that applies the target velocity to the rigidbody:

			/* Apply motion */
	        Vector3 _velocity = myRigidbody.velocity;
			Vector3 _velocityChange = (TargetVelocity - _velocity);

			/* Move rigidbody */
			myRigidbody.AddForce(_velocityChange,ForceMode.VelocityChange);

How to convert this movement to the Rigidbody2D? Preferably I am looking for an identical conversion, as I am quite keen on how the character feels right now when moving.

3

Here are some extension methods for Physics2D to add this missing functionality to AddForce, strongly based on the solution by gfoot at this thread.

public static class Physics2DExtensions {
	public static void AddForce (this Rigidbody2D rigidbody2D, Vector2 force, ForceMode mode = ForceMode.Force) {
		switch (mode) {
		case ForceMode.Force:
			rigidbody2D.AddForce (force);
			break;
		case ForceMode.Impulse:
			rigidbody2D.AddForce (force / Time.fixedDeltaTime);
			break;
		case ForceMode.Acceleration:
			rigidbody2D.AddForce (force * rigidbody2D.mass);
			break;
		case ForceMode.VelocityChange:
			rigidbody2D.AddForce (force * rigidbody2D.mass / Time.fixedDeltaTime);
			break;
		}
	}
	
	public static void AddForce (this Rigidbody2D rigidbody2D, float x, float y, ForceMode mode = ForceMode.Force) {
		rigidbody2D.AddForce (new Vector2 (x, y), mode);
	}
}
2

Yeah, no forcemodes (yet?) on Rigidbody2D. However, you should be able to the same result as ForceMode.VelocityChange by just adding your new velocity to the rigidbody2D.velocity.

4

Force mode has been added 2d rigidbodies