public double energy() {
double dx, dy, dz, distance;
double e = 0.0;
for (int i = 0; i < bodies.length; ++i) {
Body iBody = bodies[i];
e +=
0.5
* iBody.getMass()
* (iBody.getVX() * iBody.getVX()
+ iBody.getVY() * iBody.getVY()
+ iBody.getVZ() * iBody.getVZ());
for (int j = i + 1; j < bodies.length; ++j) {
Body jBody = bodies[j];
dx = iBody.getX() - jBody.getX();
dy = iBody.getY() - jBody.getY();
dz = iBody.getZ() - jBody.getZ();
distance = Math.sqrt(dx * dx + dy * dy + dz * dz);
e -= (iBody.getMass() * jBody.getMass()) / distance;
}
}
return e;
}
public void advance(final double dt) {
for (int i = 0; i < bodies.length; ++i) {
Body iBody = bodies[i];
for (int j = i + 1; j < bodies.length; ++j) {
Body jBody = bodies[j];
double dx = iBody.getX() - jBody.getX();
double dy = iBody.getY() - jBody.getY();
double dz = iBody.getZ() - jBody.getZ();
double dSquared = dx * dx + dy * dy + dz * dz;
double distance = Math.sqrt(dSquared);
double mag = dt / (dSquared * distance);
iBody.setVX(iBody.getVX() - (dx * jBody.getMass() * mag));
iBody.setVY(iBody.getVY() - (dy * jBody.getMass() * mag));
iBody.setVZ(iBody.getVZ() - (dz * jBody.getMass() * mag));
jBody.setVX(jBody.getVX() + (dx * iBody.getMass() * mag));
jBody.setVY(jBody.getVY() + (dy * iBody.getMass() * mag));
jBody.setVZ(jBody.getVZ() + (dz * iBody.getMass() * mag));
}
}
for (Body body : bodies) {
body.setX(body.getX() + dt * body.getVX());
body.setY(body.getY() + dt * body.getVY());
body.setZ(body.getZ() + dt * body.getVZ());
}
}
/**
* Fires the weapon, if it has passed it's cooldown interval.
*
* @param body the body of the firing entity.
*/
public void fire(Body body, EntityType whoFired) {
if (System.currentTimeMillis() - lastFireTime >= FIRE_INTERVAL) {
lastFireTime = System.currentTimeMillis();
Bullet bullet = new Bullet(whoFired);
bullet.body.setPos(body.getX(), body.getY());
bullet.body.setVectorX(0);
if (whoFired == EntityType.PLAYER) {
bullet.body.setVectorY(10);
} else {
bullet.body.setVectorY(-10);
}
EntityManager.addBullet(bullet);
}
}
@Test
public void testMovement() throws Exception {
int iterationCountPerStep = Defaults.ITERATION_COUNT_PER_STEP;
int stepCountPerTimeUnit = 10;
World world = new World(iterationCountPerStep, stepCountPerTimeUnit);
Body body = new Body();
body.setForm(new CircularForm(1.0D));
body.setMass(1.0D);
world.addBody(body);
body.setPosition(0.0D, 0.0D);
body.setVelocity(1.0D, 0.0D);
for (int i = 1; i <= 1000; ++i) {
world.proceed();
Assert.assertEquals(
"Simple movement. Illegal 'x' after step " + i + '.',
0.1D * i,
body.getX(),
world.getEpsilon());
Assert.assertEquals(
"Simple movement. Illegal 'y' after step " + i + '.',
0.0D,
body.getY(),
world.getEpsilon());
}
body.setPosition(0.0D, 0.0D);
body.setVelocity(1.0D, 0.0D);
body.setMovementFrictionFactor(0.1D);
double expectedPositionX = 0.0D;
double expectedVelocityX = 1.0D;
for (int i = 1; i <= 1000; ++i) {
for (int j = 0; j < stepCountPerTimeUnit; ++j) {
expectedPositionX += 0.01D * expectedVelocityX;
expectedVelocityX = max(expectedVelocityX - 0.001D, 0.0D);
}
world.proceed();
Assert.assertEquals(
"Movement with ground friction. Illegal 'x' after step " + i + '.',
expectedPositionX,
body.getX(),
world.getEpsilon());
Assert.assertEquals(
"Movement with ground friction. Illegal 'y' after step " + i + '.',
0.0D,
body.getY(),
world.getEpsilon());
}
body.setPosition(0.0D, 0.0D);
body.setVelocity(1.0D, 0.0D);
body.setMovementFrictionFactor(0.0D);
body.setMovementAirFrictionFactor(0.1D);
expectedPositionX = 0.0D;
expectedVelocityX = 1.0D;
for (int i = 1; i <= 1000; ++i) {
for (int j = 0; j < stepCountPerTimeUnit; ++j) {
expectedPositionX += 0.01D * expectedVelocityX;
expectedVelocityX *= pow(1.0D - 0.1D, 0.01D);
}
world.proceed();
Assert.assertEquals(
"Movement with air friction. Illegal 'x' after step " + i + '.',
expectedPositionX,
body.getX(),
world.getEpsilon());
Assert.assertEquals(
"Movement with air friction. Illegal 'y' after step " + i + '.',
0.0D,
body.getY(),
world.getEpsilon());
}
}