fix positionfromvelocity

// does nothing if parameter chan doesn't give CoordsEvent's

func PositionFromVelocity(c chan Event) chan Event{

	extra := make(chan Event)

	var x,y float32

	var x,y,vx,vy float32

	var startTime time.Time

	var startMoment time.Duration

	var m time.Duration

	ticker:=time.NewTicker(VelocityRepeat)

	go func(){

		e:= <-c

		startTime=time.Now()

		startMoment=e.Moment()

		lm:=startMoment

		for e:=range c{

			m:=e.Moment()

			if ce,ok:=e.(CoordsEvent);ok{

				dt:=(m-lm).Seconds()

				x+=float32(float64(ce.X)*dt)

				y+=float32(float64(ce.Y)*dt)

				m=e.Moment()

				vx,vy=ce.X,ce.Y

				dt:=float32((m-lm).Seconds())

				x+=vx*dt

				y+=vy*dt

				lm=	m

			}

		}

		ticker.Stop()

	}()

	go func(){

		ticker:=time.NewTicker(VelocityRepeat)

		var nx,ny float32

		lt:=time.Now()

		for t:=range ticker.C{

			extra <-CoordsEvent{when{startMoment+t.Sub(startTime)},x,y}			

			nx,ny=x,y

			dt:=float32(t.Sub(lt).Seconds())

			extra <-CoordsEvent{when{startMoment+t.Sub(startTime)},nx+dt*vx,ny+dt*vy}			

		}

		ticker.Stop()

	}()

	return extra