[gameprogrammer] Re: Spring model

[straver@apollo.nu]

Here's the code for the spring calculations. The gravity isn't applied=20
in this code but it just sets the force.y to some value. And when a =20
objects hit the ground the veloc.y get inverted.=20
=20
I read this gamasutra tutorial when I wrote this code:=20
http://www.gamasutra.com/features/20011005/oliveira_01.htm=20
=20
/* calculate spring forces */=20
for (int i =3D 0; i < (int)springs.size(); i++) {=20
	double distance;=20
	double intensity;=20
	double delta;=20
	point force;=20
		=20
	// calc distance=20
	double dx =3D springs.at(i).attach1->pos.x -=20
		    springs.at(i).attach2->pos.x;=20
	double dy =3D springs.at(i).attach1->pos.y - =20
		    springs.at(i).attach2->pos.y;=20
	distance =3D sqrt ((dx*dx)+(dy*dy));=20
		=20
	if (distance < SPRING_TOLERANCE) {=20
		springs.at(i).attach1->force.x =3D 0.0;=20
		springs.at(i).attach1->force.y =3D 0.0;=20
		springs.at(i).attach2->force.x =3D 0.0;=20
		springs.at(i).attach2->force.y =3D 0.0;=20
	}else {=20
		force.x =3D dx;=20
		force.y =3D dy;=20
			=20
		// normalize=20
		force.x /=3D distance;=20
		force.y /=3D distance;=20
			=20
		// force=20
		delta =3D springs.at(i).length - distance;=20
		intensity =3D springness * delta;=20
		=20
		// store=20
		springs.at(i).attach1->veloc.x +=3D  (force.x * intensity);=20
		springs.at(i).attach1->veloc.y +=3D  (force.y * intensity);=20
		springs.at(i).attach2->veloc.x +=3D  -(force.x * intensity);=20
		springs.at(i).attach2->veloc.y +=3D  -(force.y * intensity);=20
	}=20
}=20
	=20
/* apply forces */=20
for (int i =3D 0; i < (int)points.size(); i++) {=20
	point accel;=20
	=20
	// acceleration=20
	accel.x =3D points.at(i).force.x / weight;=20
	accel.y =3D points.at(i).force.y / weight;=20
		=20
	// velocity=20
	points.at(i).veloc.x +=3D accel.x * frametime;=20
	points.at(i).veloc.y +=3D accel.y * frametime;=20
		=20
	// position=20
	points.at(i).pos.x +=3D (points.at(i).veloc.x * frametime);=20
	points.at(i).pos.y +=3D (points.at(i).veloc.y * frametime);=20
		=20
	// energy loss=20
	points.at(i).veloc.x *=3D 1.0 * frametime;=20
	points.at(i).veloc.y *=3D 1.0 * frametime;=20
		=20
	// reset force=20
	points.at(i).force.x =3D 0.0;=20
	points.at(i).force.y =3D 0.0;		=20
}=20
=20
=20
Quoting Alan Wolfe <atrix2@cox.net>:=20
=20
> Heya,=20
> =20
> whats the equation (and/or code) for how your springs behave?  maybe th=
at=20
> will inspire some ideas (:=20
> =20
> ----- Original Message ----- =20
> From: <straver@apollo.nu>=20
> To: <gameprogrammer@freelists.org>=20
> Sent: Thursday, April 01, 2004 1:53 PM=20
> Subject: [gameprogrammer] Spring model=20
> =20
> =20
> > I'm playing with a spring model but I have run into a trouble.=3D20=20
> > The trouble is that I want a dampning effect on the springs so=3D20=20
> > they don't go all crazy but I don't want any damping effect on=3D20=20
> > the gravity movement for example.=3D20=20
> > =3D20=20
> > I can't think of any way to seperate them.=3D20=20
> >=20
> > -------------------------------------------------=20
> > This mail sent through IMP: http://horde.org/imp/=20
> >=20
> =20
> =20
=20
=20
=20

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