--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/trunk/tests/ChipmunkDemos/samples/Planet.d	Sat Dec 04 02:02:29 2010 +0100
@@ -0,0 +1,123 @@
+
+// written in the D programming language
+
+module samples.Planet;
+
+import chipmunkd.chipmunk;
+
+import samples.ChipmunkDemo;
+
+static cpSpace *space;
+static cpBody *planetBody;
+
+static cpFloat gravityStrength = 5.0e6f;
+
+static void
+update(int ticks)
+{
+	int steps = 1;
+	cpFloat dt = 1.0f/60.0f/cast(cpFloat)steps;
+	
+	for(int i=0; i<steps; i++){
+		cpSpaceStep(space, dt);
+		
+		// Update the static body spin so that it looks like it's rotating.
+		cpBodyUpdatePosition(planetBody, dt);
+	}
+}
+
+static void
+planetGravityVelocityFunc(cpBody *_body, cpVect gravity, cpFloat damping, cpFloat dt)
+{
+	// Gravitational acceleration is proportional to the inverse square of
+	// distance, and directed toward the origin. The central planet is assumed
+	// to be massive enough that it affects the satellites but not vice versa.
+	cpVect p = _body.p;
+	cpFloat sqdist = cpvlengthsq(p);
+	cpVect g = cpvmult(p, -gravityStrength / (sqdist * cpfsqrt(sqdist)));
+	
+	cpBodyUpdateVelocity(_body, g, damping, dt);
+}
+
+static cpVect
+rand_pos(cpFloat radius)
+{
+	cpVect v;
+	do {
+		v = cpv(frand()*(640 - 2*radius) - (320 - radius), frand()*(480 - 2*radius) - (240 - radius));
+	} while(cpvlength(v) < 85.0f);
+	
+	return v;
+}
+
+static void
+add_box()
+{
+	const cpFloat size = 10.0f;
+	const cpFloat mass = 1.0f;
+	
+	cpVect verts[] = [
+		cpv(-size,-size),
+		cpv(-size, size),
+		cpv( size, size),
+		cpv( size,-size),
+	];
+	
+	cpFloat radius = cpvlength(cpv(size, size));
+
+	cpBody *_body = cpSpaceAddBody(space, cpBodyNew(mass, cpMomentForPoly(mass, 4, verts.ptr, cpvzero)));
+	_body.velocity_func = &planetGravityVelocityFunc;
+	_body.p = rand_pos(radius);
+
+	// Set the box's velocity to put it into a circular orbit from its
+	// starting position.
+	cpFloat r = cpvlength(_body.p);
+	cpFloat v = cpfsqrt(gravityStrength / r) / r;
+	_body.v = cpvmult(cpvperp(_body.p), v);
+
+	// Set the box's angular velocity to match its orbital period and
+	// align its initial angle with its position.
+	_body.w = v;
+	cpBodySetAngle(_body, cpfatan2(_body.p.y, _body.p.x));
+
+	cpShape *shape = cpSpaceAddShape(space, cpPolyShapeNew(_body, 4, verts.ptr, cpvzero));
+	shape.e = 0.0f; shape.u = 0.7f;
+}
+
+static cpSpace *
+init()
+{
+	planetBody = cpBodyNew(INFINITY, INFINITY);
+	planetBody.w = 0.2f;
+	
+	cpResetShapeIdCounter();
+	
+	space = cpSpaceNew();
+	cpSpaceResizeActiveHash(space, 30.0f, 10000);
+	space.iterations = 20;
+	
+	for(int i=0; i<30; i++)
+		add_box();
+	
+	cpShape *shape = cpSpaceAddShape(space, cpCircleShapeNew(planetBody, 70.0f, cpvzero));
+	shape.e = 1.0f; shape.u = 1.0f;
+	shape.layers = NOT_GRABABLE_MASK;
+	
+	return space;
+}
+
+static void
+destroy()
+{
+	cpBodyFree(planetBody);
+	cpSpaceFreeChildren(space);
+	cpSpaceFree(space);
+}
+
+chipmunkDemo Planet = {
+	"Planet",
+	null,
+	&init,
+	&update,
+	&destroy,
+};