Box2d - Pointentity and add local force

BlitzMax Forums/Brucey's Modules/Box2d - Pointentity and add local force

Volker

(Posted 2010) [#1]

Hi,

I want to make a body (shot) move to to a specified point.
So I need the body to' look' at the point and then
add some local force to make him move 'forward'.
But I can't figure out which of my functions fails.

Function ApplyLocalForce(body:b2Body, force:Float)
	Local vec:b2Vec2 = body.GetWorldVector(New b2Vec2.Create(0, force))
	Local pos:b2Vec2 = body.GetWorldPoint(New b2Vec2.Create(0, 0))
	body.ApplyImpulse(vec, pos)
End Function

Function PointtoVector(entity:b2Body, vec:b2Vec2)
	Local pos:b2Vec2 = entity.GetPosition()
	Local angle:Float = GetAngle(pos.X(), pos.Y(), vec.X(), vec.Y())
	
	entity.SetXForm(entity.GetPosition(), angle * -1)
End Function

Armitage 1982

(Posted 2010) [#2]

Impulse require a target vector and don't rely on the object angle.

I don't have BM on this machine but try to work with something like this :

Function ApplyLocalForce(body:b2Body, force:Float)

	Local VXP:float,VYP:float
	Local angle:float = body.GetAngle()

	VXP = Sin(angle) * force
	VYP = Cos(angle) * force

	body.ApplyImpulse(Vec2(VXP, VYP), body.GetPosition())

End Function

Vec2(0, 0) is a good shortcut for New b2Vec2.Create(0, 0) ;-)
body.GetPosition() will always return a World Vector.

Don't forget to add continuous collision detection (CCD) on your body in order to prevent "Tunneling".

Volker

(Posted 2010) [#3]

Thanks a lot, will give it a try tomorrow.