Function CheckTrainCollision

src/train_cmd.cpp:3205–3240

* Collision test function. * @param v %Train vehicle to test collision with. * @param t %Train being examined. * @return Number of victims. */

 * @return Number of victims.
 */
static uint CheckTrainCollision(Vehicle *v, Train *t)
{
	/* not a train or in depot */
	if (v->type != VEH_TRAIN || Train::From(v)->track == TRACK_BIT_DEPOT) return 0;

	/* do not crash into trains of another company. */
	if (v->owner != t->owner) return 0;

	/* get first vehicle now to make most usual checks faster */
	Train *coll = Train::From(v)->First();

	/* can't collide with own wagons */
	if (coll == t) return 0;

	int x_diff = v->x_pos - t->x_pos;
	int y_diff = v->y_pos - t->y_pos;

	/* Do fast calculation to check whether trains are not in close vicinity
	 * and quickly reject trains distant enough for any collision.
	 * Differences are shifted by 7, mapping range [-7 .. 8] into [0 .. 15]
	 * Differences are then ORed and then we check for any higher bits */
	uint hash = (y_diff + 7) | (x_diff + 7);
	if (hash & ~15) return 0;

	/* Slower check using multiplication */
	int min_diff = (Train::From(v)->gcache.cached_veh_length + 1) / 2 + (t->gcache.cached_veh_length + 1) / 2 - 1;
	if (x_diff * x_diff + y_diff * y_diff > min_diff * min_diff) return 0;

	/* Happens when there is a train under bridge next to bridge head */
	if (abs(v->z_pos - t->z_pos) > 5) return 0;

	/* Crash both trains. Two statements required to guarantee execution
	 * order because RandomRange() is involved. */
	uint num_victims = TrainCrashed(t);
	return num_victims + TrainCrashed(coll);
}

/**
 * Checks whether the specified train has a collision with another vehicle. If