can i set the position of a body in box2d?

cocos2d for iPhone » Programming » physics

can i set the position of a body in box2d?

(9 posts) (7 voices)

Started 2 years ago by jharkey
Latest reply from mahmud

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jharkey
Member

hello everyone. this is my first post ever. i just found cocos2s and box2d last weekend. it's awesome! just what i was looking for.

i've been playing around with chipmunk and box2d. i'm not new to programming or even iphone game programming, but i'm just starting out with physics engines. i was wondering if it's possible to manually control a body in box2d. i know this seems pointless but i want my game character to be controlled without gravity and the rest of the world to be simulated but still interact. i know i could just keep the character out of box2d but i want to benefits of collision detection and everything else.

i found that box2d used to have a SetXForm() function but it appears to be taken out of the version that comes with cocos2d. also, chipmunk seems to have that feature but it is said to be risky to use. also, i prefer box2d already greatly so i want to keep using that.

i found the mouse points, but they seem to be just for dragging bodys around the world. maybe i'm just not seeing how i could use it for that.

does anyone know if that functionality is built in to box2d and i'm just overlooking it, or does anyone have any ideas of how i could get those kind of results?

thanks in advance,
JT

Posted 2 years ago #
badawe
Member

I have the same question, i think this is not possible, becouse you can't set any of these properts, but, if someone know something I interessed to!

Posted 2 years ago #
riq
Key Master
```
body.SetTransform( position, angle);
```
Posted 2 years ago #
Joao Caxaria
Member

yeah there's a method in box2d to do that as well.. Don't remember what it's called but check the xForm method in the body header.

Posted 2 years ago #
pabloruiz55
Member

Although you can do it, it is not adviced... You should be careful when doing so.

Posted 2 years ago #
jharkey
Member

thanks riq, i'll check that function out. and thanks everyone else for the quick answers.

Posted 2 years ago #
patrickC
Member

in chipmunk:
you need to create a body, attach the collision shape to it, add the collision shape to world BUT NOT the body (this way it isn't simulated).
You can then move your body manually and everything seems to work fine.

in box2d:
the new changes to the api should allow you to do exactly what you're after.
I remember reading a post about it, mentioning that with the new way of creating shapes by fixtures, you should be able to create a shape that isn't linked to a body, but that can be used to generate collisions, although I haven't tried that personally.

My two cents!
cheers

Posted 2 years ago #
badawe
Member

If have some joint with one of these objects? Whats happen?

Posted 2 years ago #
mahmud
Member

-(void) ccTouchEnded:(UITouch *)touch withEvent:(UIEvent *)event{

CGPoint location;
location = [touch locationInView: [touch view]];
location = [[CCDirector sharedDirector] convertToGL: location];

//here selSprite is set when user touched the sprite in the ccTouchBegan method
if (selSprite != nil){
selSprite.position.x = location.x;
selSprite.position.y = location.y;

ball->SetTransform(b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO), ball->GetAngle());
ball->SetAwake(true);

}
}

Posted 9 months ago #

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