is there a way to set the angle of a box2d body?

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is there a way to set the angle of a box2d body?

(14 posts) (7 voices)

Started 1 year ago by finder39
Latest reply from EviluS

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finder39
Member
something like this?
```
b->SetAngle(-45);
```
Posted 1 year ago #
mobilebros
Moderator
a bodydef can just do:
```
b.angle = CC_DEGREES_TO_RADIANS(-45);
```
if you're an actual body, I think you need to use:
```
b.SetTransform(b.GetPosition(), CC_DEGREES_TO_RADIANS(-45));
```
Posted 1 year ago #

steg90
Member

Or if using rectangles :

b2PolygonShape staticBox;
	staticBox.SetAsBox(width.x/32, width.y/32, b2Vec2(width.x /32,-width.y/32), angle);

Posted 1 year ago #

finder39
Member

thanks, this worked

b->SetTransform(b->GetPosition(), CC_DEGREES_TO_RADIANS(25));

Posted 1 year ago #

steg90
Member

Try not to use SetTransform, it can 'mess' the physics up.

Regards,
Steve

Posted 1 year ago #
robodude666
Member

The "proper" way to change a body's rotation is to apply just enough torque to rotate the body. However, this requires some messy math and is cumbersome to do. Most people on the Box2D community recommend you set the transform of the body, like mentioned in post #2. Though, use a -> as you have a pointer to a b2Body.

Posted 1 year ago #
gaurav
Member

Hi , when we use the settransform the body keeps on rotating without stopping... how can i rotate a body to a particular angle and stop?
Thanks

Posted 8 months ago #
EviluS
Member
If you want to forbid rotation for a body just use this:
```
body->SetFixedRotation(true);
```
when you need it or set it directly to the body definition when you create your box2d body like this:
```
b2BodyDef bodyDef;
....
bodyDef.fixedRotation = true;
```
Hope this helped :)
Posted 8 months ago #
gaurav
Member

@EviluS Thanks for the reply . The fixed rotation is fine but my body keeps on rotating if i set the cc_degree_to_radian(Some_angle)

what i want to implement is that i want to move the body in the direction of motion .. any ideas ? Thanks

Posted 8 months ago #

EviluS
Member

You want to make the body point to the direction of motion (If I understand correctly)

I'm doing this

CGPoint current = CGPointMake(b->GetPosition().x*PTM_RATIO, b->GetPosition().y*PTM_RATIO);
CGPoint destionation = CGPointMake(shield.position.x+arc4random()%20, shield.position.y+arc4random()%20);
CGPoint vector = ccpSub(destionation, current);
vector = ccpNormalize(vector);
b2Vec2 direction = b2Vec2(vector.x*(arc4random()%5+2), vector.y*(arc4random()%5+2));
float rads = atan2f(direction.y, direction.x);
b->ApplyLinearImpulse(direction, b->GetPosition());
b->SetTransform(b->GetPosition(), rads);

b is the body you move, shield is the end point. This will make the b body to move toward the shield body (location) and also update it angle to match the direction vector.
Here I calculate the new direction and also its angle in radians and then just apply a transform to the b body.

Posted 8 months ago #

iforce2d
Member

You can use SetTransform as pointed out above, and then SetAngularVelocity(0) to stop it from rotating after that.

Posted 8 months ago #
gaurav
Member

@ EviluS what is shield exactly how do i get it ? since i dont know my final position because the object does not move according to some touch location .. Thanks

Posted 8 months ago #
gaurav
Member

@iforce2d right thanks will check it out

Posted 8 months ago #
EviluS
Member

shield is a box2d body (specific for my code) positioned in the center of the screen.

In your case if you do not know the final position you can create a method which on every 0.05 (or some other interval) takes your box2d body position and then run second method with a delay. In that second method you should use my code from above but replace the shield position with the one you took. I think that should do the trick.

Posted 8 months ago #

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