Box2D rotate an object, how?

Question

How I can rotate an object in Box2D? Tried..

private static final double DEGREES_TO_RADIANS = (double)(Math.PI/180);
float angle = (float) (45*DEGREES_TO_RADIANS);
object.body.setTransform(object.body.getPosition(), angle);

..but not working.

Answer 1

If you want to rotate the object to an angle then you use setTransform method like

b2body->SetTransform( playerBody_->GetPosition(), angleInRadian );

And if you want to rotate the body continuously then use SetAngularVelocity method like

b2body->SetAngularVelocity(<float32>)

Remember b2body object must be a dynamic or kinematic to be able to be rotated.

Answer 2

Firstly the object must be a dynamic or kinematic to be able to be rotated, in addition use SetAngularVelocity() to achieve the rotation.

Answer 3

I think you can use force or impulses,not use setTransform methord directly. example:

body->ApplyForce( b2Vec2(force,0), body->GetWorldPoint( b2Vec2(1,1) ) );

this code let body rote.

Answer 4

use the world center instead position, like this

private static final double DEGREES_TO_RADIANS = (double)(Math.PI/180);
float angle = (float) (45*DEGREES_TO_RADIANS);
object.body.setTransform(object.body.getWorldCenter(), angle);

Answer 5

The idea is to rotate to an angle, the easiest method I found by myself is to use:

float rotation = MathUtils.PI; // target rotation

float c = 1; //speed of rotation
float q = rotation-groundBody.getAngle();
groundBody.setAngularVelocity(c*q);

the body will rotate quicker at the beginning and slower at the end but you can use Interpolation function to achieve desired speed of rotation.