void physics_apply_whack(vec3d *impulse, vec3d *pos, physics_info *pi, matrix *orient, float mass)
{
	vec3d	local_torque, torque;
//	vec3d	npos;

	//	Detect null vector.
	if ((fl_abs(impulse->xyz.x) <= WHACK_LIMIT) && (fl_abs(impulse->xyz.y) <= WHACK_LIMIT) && (fl_abs(impulse->xyz.z) <= WHACK_LIMIT))
		return;

	// first do the rotational velocity
	// calculate the torque on the body based on the point on the
	// object that was hit and the momentum being applied to the object

	vm_vec_crossprod(&torque, pos, impulse);
	vm_vec_rotate ( &local_torque, &torque, orient );

	vec3d delta_rotvel;
	vm_vec_rotate( &delta_rotvel, &local_torque, &pi->I_body_inv );
	vm_vec_scale ( &delta_rotvel, (float) ROTVEL_WHACK_CONST );
	vm_vec_add2( &pi->rotvel, &delta_rotvel );

	//mprintf(("Whack: %7.3f %7.3f %7.3f\n", pi->rotvel.xyz.x, pi->rotvel.xyz.y, pi->rotvel.xyz.z));

	// instant whack on the velocity
	// reduce damping on all axes
	pi->flags |= PF_REDUCED_DAMP;
	update_reduced_damp_timestamp( pi, vm_vec_mag(impulse) );

	// find time for shake from weapon to end
	int dtime = timestamp_until(pi->afterburner_decay);
	if (dtime < WEAPON_SHAKE_TIME) {
		pi->afterburner_decay = timestamp( WEAPON_SHAKE_TIME );
	}

	// Goober5000 - pi->mass should probably be just mass, as specified in the header
	vm_vec_scale_add2( &pi->vel, impulse, 1.0f / mass );
	if (!(pi->flags & PF_USE_VEL) && (vm_vec_mag_squared(&pi->vel) > MAX_SHIP_SPEED*MAX_SHIP_SPEED)) {
		// Get DaveA
		nprintf(("Physics", "speed reset in physics_apply_whack [speed: %f]\n", vm_vec_mag(&pi->vel)));
		vm_vec_normalize(&pi->vel);
		vm_vec_scale(&pi->vel, (float)RESET_SHIP_SPEED);
	}
	vm_vec_rotate( &pi->prev_ramp_vel, &pi->vel, orient );		// set so velocity will ramp starting from current speed
																					// ramped velocity is now affected by collision
}
void physics_collide_whack( vec3d *impulse, vec3d *world_delta_rotvel, physics_info *pi, matrix *orient, bool is_landing )
{
	vec3d	body_delta_rotvel;

	//	Detect null vector.
	if ((fl_abs(impulse->xyz.x) <= WHACK_LIMIT) && (fl_abs(impulse->xyz.y) <= WHACK_LIMIT) && (fl_abs(impulse->xyz.z) <= WHACK_LIMIT))
		return;

	vm_vec_rotate( &body_delta_rotvel, world_delta_rotvel, orient );
//	vm_vec_scale( &body_delta_rotvel, (float)	ROTVEL_COLLIDE_WHACK_CONST );
	vm_vec_add2( &pi->rotvel, &body_delta_rotvel );

	update_reduced_damp_timestamp( pi, vm_vec_mag(impulse) );

	// find time for shake from weapon to end
	if (!is_landing) {
		int dtime = timestamp_until(pi->afterburner_decay);
		if (dtime < WEAPON_SHAKE_TIME) {
			pi->afterburner_decay = timestamp( WEAPON_SHAKE_TIME );
		}
	}

	pi->flags |= PF_REDUCED_DAMP;
	vm_vec_scale_add2( &pi->vel, impulse, 1.0f / pi->mass );
	// check that collision does not give ship too much speed
	// reset if too high
	if (!(pi->flags & PF_USE_VEL) && (vm_vec_mag_squared(&pi->vel) > MAX_SHIP_SPEED*MAX_SHIP_SPEED)) {
		// Get DaveA
		nprintf(("Physics", "speed reset in physics_collide_whack [speed: %f]\n", vm_vec_mag(&pi->vel)));
		vm_vec_normalize(&pi->vel);
		vm_vec_scale(&pi->vel, (float)RESET_SHIP_SPEED);
	}
	vm_vec_rotate( &pi->prev_ramp_vel, &pi->vel, orient );		// set so velocity will ramp starting from current speed
																					// ramped velocity is now affected by collision
	// rotate previous ramp velocity (in model coord) to be same as vel (in world coords)
}
void physics_apply_shock(vec3d *direction_vec, float pressure, physics_info *pi, matrix *orient, vec3d *min, vec3d *max, float radius)
{
	vec3d normal;
	vec3d local_torque, temp_torque, torque;
	vec3d impact_vec;
	vec3d area;
	vec3d sin;

	if (radius > MAX_RADIUS) {
		return;
	}

	vm_vec_normalize_safe ( direction_vec );

	area.xyz.x = (max->xyz.y - min->xyz.z) * (max->xyz.z - min->xyz.z);
	area.xyz.y = (max->xyz.x - min->xyz.x) * (max->xyz.z - min->xyz.z);
	area.xyz.z = (max->xyz.x - min->xyz.x) * (max->xyz.y - min->xyz.y);

	normal.xyz.x = vm_vec_dotprod( direction_vec, &orient->vec.rvec );
	normal.xyz.y = vm_vec_dotprod( direction_vec, &orient->vec.uvec );
	normal.xyz.z = vm_vec_dotprod( direction_vec, &orient->vec.fvec );

	sin.xyz.x = fl_sqrt( fl_abs(1.0f - normal.xyz.x*normal.xyz.x) );
	sin.xyz.y = fl_sqrt( fl_abs(1.0f - normal.xyz.y*normal.xyz.y) );
	sin.xyz.z = fl_sqrt( fl_abs(1.0f - normal.xyz.z*normal.xyz.z) );

	vm_vec_make( &torque, 0.0f, 0.0f, 0.0f );

	// find the torque exerted due to the shockwave hitting each face
	//  model the effect of the shockwave as if the shockwave were a plane of projectiles,
	//  all moving in the direction direction_vec.  then find the torque as the cross prod
	//  of the force (pressure * area * normal * sin * scale * mass)
	//  normal takes account the fraction of the surface exposed to the shockwave
	//  the sin term is not technically needed but "feels" better
	//  scale factors out the increase in area with larger objects
	//  more massive objects get less rotation

	// find torque due to forces on the right/left face
	if ( normal.xyz.x < 0.0f )		// normal < 0, hits the right face
		vm_vec_copy_scale( &impact_vec, &orient->vec.rvec, max->xyz.x * pressure * area.xyz.x *  normal.xyz.x * sin.xyz.x / pi->mass );
	else								// normal > 0, hits the left face
		vm_vec_copy_scale( &impact_vec, &orient->vec.rvec, min->xyz.x * pressure * area.xyz.x * -normal.xyz.x * sin.xyz.x / pi->mass );

	vm_vec_crossprod( &temp_torque, &impact_vec, direction_vec );
	vm_vec_add2( &torque, &temp_torque );

	// find torque due to forces on the up/down face
	if ( normal.xyz.y < 0.0f )
		vm_vec_copy_scale( &impact_vec, &orient->vec.uvec, max->xyz.y * pressure * area.xyz.y *  normal.xyz.y * sin.xyz.y / pi->mass );
	else
		vm_vec_copy_scale( &impact_vec, &orient->vec.uvec, min->xyz.y * pressure * area.xyz.y * -normal.xyz.y * sin.xyz.y / pi->mass );

	vm_vec_crossprod( &temp_torque, &impact_vec, direction_vec );
	vm_vec_add2( &torque, &temp_torque );

	// find torque due to forces on the forward/backward face
	if ( normal.xyz.z < 0.0f )
		vm_vec_copy_scale( &impact_vec, &orient->vec.fvec, max->xyz.z * pressure * area.xyz.z *  normal.xyz.z * sin.xyz.z / pi->mass );
	else
		vm_vec_copy_scale( &impact_vec, &orient->vec.fvec, min->xyz.z * pressure * area.xyz.z * -normal.xyz.z * sin.xyz.z / pi->mass );

	vm_vec_crossprod( &temp_torque, &impact_vec, direction_vec );
	vm_vec_add2( &torque, &temp_torque );

	// compute delta rotvel, scale according to blast and radius
	float scale;

	if (radius < MIN_RADIUS) {
		scale = 1.0f;
	} else {
		scale = (MAX_RADIUS - radius)/(MAX_RADIUS-MIN_RADIUS);
	}

	// set shockwave shake amplitude, duration, flag
	pi->shockwave_shake_amp = (float)(MAX_SHAKE*(pressure/STD_PRESSURE)*scale);
	pi->shockwave_decay = timestamp( SW_BLAST_DURATION );
	pi->flags |= PF_IN_SHOCKWAVE;

	// safety dance
	if (!(IS_VEC_NULL_SQ_SAFE(&torque))) {
		vec3d delta_rotvel;
		vm_vec_rotate( &local_torque, &torque, orient );
		vm_vec_copy_normalize(&delta_rotvel, &local_torque);
		
		vm_vec_scale(&delta_rotvel, (float)(MAX_ROTVEL*(pressure/STD_PRESSURE)*scale));
		// nprintf(("Physics", "rotvel scale %f\n", (MAX_ROTVEL*(pressure/STD_PRESSURE)*scale)));
		vm_vec_add2(&pi->rotvel, &delta_rotvel);
	}

	// set reduced translational damping, set flags
	float velocity_scale = (float)MAX_VEL*scale;
	pi->flags |= PF_REDUCED_DAMP;
	update_reduced_damp_timestamp( pi, velocity_scale*pi->mass );
	vm_vec_scale_add2( &pi->vel, direction_vec, velocity_scale );
	vm_vec_rotate(&pi->prev_ramp_vel, &pi->vel, orient);	// set so velocity will ramp starting from current speed

	// check that kick from shockwave is not too large
	if (!(pi->flags & PF_USE_VEL) && (vm_vec_mag_squared(&pi->vel) > MAX_SHIP_SPEED*MAX_SHIP_SPEED)) {
		// Get DaveA
		nprintf(("Physics", "speed reset in physics_apply_shock [speed: %f]\n", vm_vec_mag(&pi->vel)));
		vm_vec_normalize(&pi->vel);
		vm_vec_scale(&pi->vel, (float)RESET_SHIP_SPEED);
	}
}
// Returns TRUE if the weapon will never hit the other object.
// If it can it predicts how long until these two objects need
// to be checked and fills the time in in current_pair.
int weapon_will_never_hit( object *obj_weapon, object *other, obj_pair * current_pair )
{

	Assert( obj_weapon->type == OBJ_WEAPON );
	weapon *wp = &Weapons[obj_weapon->instance];
	weapon_info *wip = &Weapon_info[wp->weapon_info_index];

//	mprintf(( "Frame: %d,  Weapon=%d, Other=%d, pair=$%08x\n", G3_frame_count, OBJ_INDEX(weapon), OBJ_INDEX(other), current_pair ));
	

	// Do some checks for weapons that don't turn
	if ( !(wip->wi_flags & WIF_TURNS) )	{

		// This first check is to see if a weapon is behind an object, and they
		// are heading in opposite directions.   If so, we don't need to ever check	
		// them again.   This is only valid for weapons that don't turn. 

		float vdot;
		if (wip->subtype == WP_LASER) {
			vec3d velocity_rel_weapon;
			vm_vec_sub(&velocity_rel_weapon, &obj_weapon->phys_info.vel, &other->phys_info.vel);
			vdot = -vm_vec_dot(&velocity_rel_weapon, &obj_weapon->orient.vec.fvec);
		} else {
			vdot = vm_vec_dot( &other->phys_info.vel, &obj_weapon->phys_info.vel);
		}
		if ( vdot <= 0.0f )	{
			// They're heading in opposite directions...
			// check their positions
			vec3d weapon2other;
			vm_vec_sub( &weapon2other, &other->pos, &obj_weapon->pos );
			float pdot = vm_vec_dot( &obj_weapon->orient.vec.fvec, &weapon2other );
			if ( pdot <= -other->radius )	{
				// The other object is behind the weapon by more than
				// its radius, so it will never hit...
				return 1;
			}
		}

		// FUTURE ENHANCEMENT IDEAS 

		// Given a laser does it hit a slow or not moving object
		// in its life or the next n seconds?  We'd actually need to check the 
		// model for this.
				
	}


	// This check doesn't care about orient, only looks at the maximum speed
	// of the two objects, so it knows that in the next n seconds, they can't
	// go further than some distance, so don't bother checking collisions for 
	// that time.   This is very rough, but is so general that it works for
	// everything and immidiately gets rid of a lot of cases.
	
	if ( current_pair )	{
		// Find the time it will take before these get within each others distances.
		// tmp->next_check_time = timestamp(500);
		//vector	max_vel;			//maximum foward velocity in x,y,z

		float max_vel_weapon, max_vel_other;

		//SUSHI: Fix bug where additive weapon velocity screws up collisions
		//Assumes that weapons which don't home don't change speed, which is currently the case.
		if (!(wip->wi_flags & WIF_TURNS))
			max_vel_weapon = obj_weapon->phys_info.speed;
		else if (wp->lssm_stage==5)
			max_vel_weapon = wip->lssm_stage5_vel;
		else
			max_vel_weapon = wp->weapon_max_vel;

		max_vel_other = other->phys_info.max_vel.xyz.z;
		if (max_vel_other < 10.0f) {
			if ( vm_vec_mag_squared( &other->phys_info.vel ) > 100 ) {
				// bump up velocity from collision
				max_vel_other = vm_vec_mag( &other->phys_info.vel ) + 10.0f;
			} else {
				max_vel_other = 10.0f;		// object may move from collision
			}
		}

		// check weapon that does not turn against sphere expanding at ship maxvel
		// compare (weeapon) ray with expanding sphere (ship) to find earliest possible collision time
		// look for two time solutions to Xw = Xs, where Xw = Xw0 + Vwt*t  Xs = Xs + Vs*(t+dt), where Vs*dt = radius of ship 
		// Since direction of Vs is unknown, solve for (Vs*t) and find norm of both sides
		if ( !(wip->wi_flags & WIF_TURNS) ) {
			vec3d delta_x, laser_vel;
			float a,b,c, delta_x_dot_vl, delta_t;
			float root1, root2, root, earliest_time;

			if (max_vel_weapon == max_vel_other) {
				// this will give us NAN using the below formula, so check every frame
				current_pair->next_check_time = timestamp(0);
				return 0;
			}

			vm_vec_sub( &delta_x, &obj_weapon->pos, &other->pos );
			laser_vel = obj_weapon->phys_info.vel;
			// vm_vec_copy_scale( &laser_vel, &weapon->orient.vec.fvec, max_vel_weapon );
			delta_t = (other->radius + 10.0f) / max_vel_other;		// time to get from center to radius of other obj
			delta_x_dot_vl = vm_vec_dotprod( &delta_x, &laser_vel );

			a = max_vel_weapon*max_vel_weapon - max_vel_other*max_vel_other;
			b = 2.0f * (delta_x_dot_vl - max_vel_other*max_vel_other*delta_t);
			c = vm_vec_mag_squared( &delta_x ) - max_vel_other*max_vel_other*delta_t*delta_t;

			float discriminant = b*b - 4.0f*a*c;
			if ( discriminant < 0) {
				// never hit
				return 1;
			} else {
				root = fl_sqrt( discriminant );
				root1 = (-b + root) / (2.0f * a) * 1000.0f;	// get time in ms
				root2 = (-b - root) / (2.0f * a) * 1000.0f;	// get time in ms
			}

			// standard algorithm
			if (max_vel_weapon > max_vel_other) {
				// find earliest positive time
				if ( root1 > root2 ) {
					float temp = root1;
					root1 = root2;
					root2 = temp;
				}

				if (root1 > 0) {
					earliest_time = root1;
				} else if (root2 > 0) {
					// root1 < 0 and root2 > 0, so we're inside sphere and next check should be next frame
					current_pair->next_check_time = timestamp(0);	// check next time
					return 0;
				} else {
					// both times negative, so never collides
					return 1;
				}
			}
			// need to modify it for weapons that are slower than ships
			else {
				if (root2 > 0) {
					earliest_time = root2;
				} else {
					current_pair->next_check_time = timestamp(0);
					return 0;
				}
			}



			// check if possible collision occurs after weapon expires
			if ( earliest_time > 1000*wp->lifeleft )
				return 1;

			// Allow one worst case frametime to elapse (~5 fps)
			earliest_time -= 200.0f;

			if (earliest_time > 100) {
				current_pair->next_check_time = timestamp( fl2i(earliest_time) );
				return 0;
			} else {
				current_pair->next_check_time = timestamp(0);	// check next time
				return 0;
			}

		} else {

			float dist, max_vel, time;

			max_vel = max_vel_weapon + max_vel_other;

			// suggest that fudge factor for other radius be changed to other_radius + const (~10)
			dist = vm_vec_dist( &other->pos, &obj_weapon->pos ) - (other->radius + 10.0f);
			if ( dist > 0.0f )	{
				time = (dist*1000.0f) / max_vel;
				int time_ms = fl2i(time);

				// check if possible collision occurs after weapon expires
				if ( time_ms > 1000*wp->lifeleft )
					return 1;

				time_ms -= 200;	// Allow at least one worst case frametime to elapse (~5 fps)
						
				if ( time_ms > 100 )	{		// If it takes longer than 1/10th of a second, then delay it
					current_pair->next_check_time = timestamp(time_ms);
					//mprintf(( "Delaying %d ms\n", time_ms ));
					return 0;
				}
			}
			current_pair->next_check_time = timestamp(0);	// check next time

		}
	}

	return 0;
}
// Adds the pair to the pair list
void obj_add_pair( object *A, object *B, int check_time, int add_to_end )
{
	uint ctype;
	int (*check_collision)( obj_pair *pair );
	int swapped = 0;	
	
	check_collision = NULL;

	if ( Num_pairs_allocated == 0 ) return;		// don't have anything to add the pair too

	if ( A==B ) return;		// Don't check collisions with yourself

	if ( !(A->flags&OF_COLLIDES) ) return;		// This object doesn't collide with anything
	if ( !(B->flags&OF_COLLIDES) ) return;		// This object doesn't collide with anything
	
	// Make sure you're not checking a parent with it's kid or vicy-versy
//	if ( A->parent_sig == B->signature && !(A->type == OBJ_SHIP && B->type == OBJ_DEBRIS) ) return;
//	if ( B->parent_sig == A->signature && !(A->type == OBJ_DEBRIS && B->type == OBJ_SHIP) ) return;
	if ( reject_obj_pair_on_parent(A,B) ) {
		return;
	}

	Assert( A->type < 127 );
	Assert( B->type < 127 );

	ctype = COLLISION_OF(A->type,B->type);
	switch( ctype )	{
	case COLLISION_OF(OBJ_WEAPON,OBJ_SHIP):
		swapped = 1;
		check_collision = collide_ship_weapon;
		break;
	case COLLISION_OF(OBJ_SHIP, OBJ_WEAPON):
		check_collision = collide_ship_weapon;
		break;
	case COLLISION_OF(OBJ_DEBRIS, OBJ_WEAPON):
		check_collision = collide_debris_weapon;
		break;
	case COLLISION_OF(OBJ_WEAPON, OBJ_DEBRIS):
		swapped = 1;
		check_collision = collide_debris_weapon;
		break;
	case COLLISION_OF(OBJ_DEBRIS, OBJ_SHIP):
		check_collision = collide_debris_ship;		
		break;
	case COLLISION_OF(OBJ_SHIP, OBJ_DEBRIS):
		check_collision = collide_debris_ship;
		swapped = 1;
		break;
	case COLLISION_OF(OBJ_ASTEROID, OBJ_WEAPON):
		// Only check collision's with player weapons
//		if ( Objects[B->parent].flags & OF_PLAYER_SHIP ) {
			check_collision = collide_asteroid_weapon;
//		}
		break;
	case COLLISION_OF(OBJ_WEAPON, OBJ_ASTEROID):
		swapped = 1;
		// Only check collision's with player weapons
//		if ( Objects[A->parent].flags & OF_PLAYER_SHIP ) {
			check_collision = collide_asteroid_weapon;
//		}
		break;
	case COLLISION_OF(OBJ_ASTEROID, OBJ_SHIP):
		// Only check collisions with player ships
//		if ( B->flags & OF_PLAYER_SHIP )	{
			check_collision = collide_asteroid_ship;
//		}
		break;
	case COLLISION_OF(OBJ_SHIP, OBJ_ASTEROID):
		// Only check collisions with player ships
//		if ( A->flags & OF_PLAYER_SHIP )	{
			check_collision = collide_asteroid_ship;
//		}
		swapped = 1;
		break;
	case COLLISION_OF(OBJ_SHIP,OBJ_SHIP):
		check_collision = collide_ship_ship;
		break;	
	
	case COLLISION_OF(OBJ_BEAM, OBJ_SHIP):
		if(beam_collide_early_out(A, B)){
			return;
		}
		check_collision = beam_collide_ship;
		break;

	case COLLISION_OF(OBJ_BEAM, OBJ_ASTEROID):
		if(beam_collide_early_out(A, B)){
			return;
		}
		check_collision = beam_collide_asteroid;
		break;

	case COLLISION_OF(OBJ_BEAM, OBJ_DEBRIS):
		if(beam_collide_early_out(A, B)){
			return;
		}
		check_collision = beam_collide_debris;
		break;

	case COLLISION_OF(OBJ_BEAM, OBJ_WEAPON):
		if(beam_collide_early_out(A, B)){
			return;
		}		
		check_collision = beam_collide_missile;
		break;

	case COLLISION_OF(OBJ_WEAPON, OBJ_WEAPON): {
		weapon_info *awip, *bwip;
		awip = &Weapon_info[Weapons[A->instance].weapon_info_index];
		bwip = &Weapon_info[Weapons[B->instance].weapon_info_index];

		if ((awip->weapon_hitpoints > 0) || (bwip->weapon_hitpoints > 0)) {
			if (bwip->weapon_hitpoints == 0) {
				check_collision = collide_weapon_weapon;
				swapped=1;
			} else {
				check_collision = collide_weapon_weapon;
			}
		}
/*

		if (awip->subtype != WP_LASER || bwip->subtype != WP_LASER) {
			if (awip->subtype == WP_LASER) {
				if ( bwip->wi_flags & WIF_BOMB ) {
					check_collision = collide_weapon_weapon;
				}
			} else if (bwip->subtype == WP_LASER) {
				if ( awip->wi_flags & WIF_BOMB ) {
					check_collision = collide_weapon_weapon;
					swapped=1;			
				}
			} else {
				if ( (awip->wi_flags&WIF_BOMB) || (bwip->wi_flags&WIF_BOMB) ) {
					check_collision = collide_weapon_weapon;
				}
			}
		}
*/
/*
		int	atype, btype;

		atype = Weapon_info[Weapons[A->instance].weapon_info_index].subtype;
		btype = Weapon_info[Weapons[B->instance].weapon_info_index].subtype;

		if ((atype == WP_LASER) && (btype == WP_MISSILE))
			check_collision = collide_weapon_weapon;
		else if ((atype == WP_MISSILE) && (btype == WP_LASER)) {
			check_collision = collide_weapon_weapon;
			swapped = 1;
		} else if ((atype == WP_MISSILE) && (btype == WP_MISSILE))
			check_collision = collide_weapon_weapon;
*/

		break;
	}

	default:
		return;
	}

	// Swap them if needed
	if ( swapped )	{
		object *tmp = A;
		A = B;
		B = tmp;
	}

	// if there are any more obj_pair checks
	// we should then add function int maybe_not_add_obj_pair()
	// MWA -- 4/1/98 -- I'd do it, but I don't want to bust anything, so I'm doing my stuff here instead :-)
	//if ( MULTIPLAYER_CLIENT && !(Netgame.debug_flags & NETD_FLAG_CLIENT_NODAMAGE)){
		// multiplayer clients will only do ship/ship collisions, and their own ship to boot
	//	if ( check_collision != collide_ship_ship ){
	//		return;
	//	}

	//	if ( (A != Player_obj) && (B != Player_obj) ){
	//		return;
	//	}
	//}	

	// only check debris:weapon collisions for player
	if (check_collision == collide_debris_weapon) {
		// weapon is B
		if ( !(Weapon_info[Weapons[B->instance].weapon_info_index].wi_flags & WIF_TURNS) ) {
		// check for dumbfire weapon
			// check if debris is behind laser
			float vdot;
			if (Weapon_info[Weapons[B->instance].weapon_info_index].subtype == WP_LASER) {
				vec3d velocity_rel_weapon;
				vm_vec_sub(&velocity_rel_weapon, &B->phys_info.vel, &A->phys_info.vel);
				vdot = -vm_vec_dot(&velocity_rel_weapon, &B->orient.vec.fvec);
			} else {
				vdot = vm_vec_dot( &A->phys_info.vel, &B->phys_info.vel);
			}
			if ( vdot <= 0.0f )	{
				// They're heading in opposite directions...
				// check their positions
				vec3d weapon2other;
				vm_vec_sub( &weapon2other, &A->pos, &B->pos );
				float pdot = vm_vec_dot( &B->orient.vec.fvec, &weapon2other );
				if ( pdot <= -A->radius )	{
					// The other object is behind the weapon by more than
					// its radius, so it will never hit...
					return;
				}
			}

			// check dist vs. dist moved during weapon lifetime
			vec3d delta_v;
			vm_vec_sub(&delta_v, &B->phys_info.vel, &A->phys_info.vel);
			if (vm_vec_dist_squared(&A->pos, &B->pos) > (vm_vec_mag_squared(&delta_v)*Weapons[B->instance].lifeleft*Weapons[B->instance].lifeleft)) {
				return;
			}

			// for nonplayer ships, only create collision pair if close enough
			if ( (B->parent >= 0) && !(Objects[B->parent].flags & OF_PLAYER_SHIP) && (vm_vec_dist(&B->pos, &A->pos) < (4.0f*A->radius + 200.0f)) )
				return;
		}
	}

	// don't check same team laser:ship collisions on small ships if not player
	if (check_collision == collide_ship_weapon) {
		// weapon is B
		if ( (B->parent >= 0)
			&& !(Objects[B->parent].flags & OF_PLAYER_SHIP)
			&& (Ships[Objects[B->parent].instance].team == Ships[A->instance].team) 
			&& (Ship_info[Ships[A->instance].ship_info_index].flags & SIF_SMALL_SHIP) 
			&& (Weapon_info[Weapons[B->instance].weapon_info_index].subtype == WP_LASER) ) {
			pairs_not_created++;
			return;
		}
	}

	if ( !check_collision ) return;
	Pairs_created++;

	// At this point, we have determined that collisions between
	// these two should be checked, so add the pair to the
	// collision pair list.

	if ( pair_free_list.next == NULL )	{
		nprintf(( "collision", "Out of object pairs!! Not all collisions will work!\n" ));
		return;
	}

	Num_pairs++;
/*	if (Num_pairs > Num_pairs_hwm) {
		Num_pairs_hwm = Num_pairs;
		//nprintf(("AI", "Num_pairs high water mark = %i\n", Num_pairs_hwm));
	}
*/

	if ( Num_pairs >= (Num_pairs_allocated - 20) ) {
		int i;

		Assert( Obj_pairs != NULL );

		int old_pair_count = Num_pairs_allocated;
		obj_pair *old_pairs_ptr = Obj_pairs;

		// determine where we need to update the "previous" ptrs to
		int prev_free_mark = (pair_free_list.next - old_pairs_ptr);
		int prev_used_mark = (pair_used_list.next - old_pairs_ptr);

		Obj_pairs = (obj_pair*) vm_realloc_q( Obj_pairs, sizeof(obj_pair) * (Num_pairs_allocated + PAIRS_BUMP) );

		// allow us to fail here and only if we don't do we setup the new pairs

		if (Obj_pairs == NULL) {
			// failed, just go back to the way we were and use only the pairs we have already
			Obj_pairs = old_pairs_ptr;
		} else {
			Num_pairs_allocated += PAIRS_BUMP;

			Assert( Obj_pairs != NULL );

			// have to reset all of the "next" ptrs for the old set and handle the new set
			for (i = 0; i < Num_pairs_allocated; i++) {
				if (i >= old_pair_count) {
					memset( &Obj_pairs[i], 0, sizeof(obj_pair) );
					Obj_pairs[i].next = &Obj_pairs[i+1];
				} else {
					if (Obj_pairs[i].next != NULL) {
						// the "next" ptr will end up going backwards for used pairs so we have
						// to allow for that with this craziness...
						int next_mark = (Obj_pairs[i].next - old_pairs_ptr);
						Obj_pairs[i].next = &Obj_pairs[next_mark];
					}

					// catch that last NULL from the previously allocated set
					if ( i == (old_pair_count-1) ) {
						Obj_pairs[i].next = &Obj_pairs[i+1];
					}
				}
			}

			Obj_pairs[Num_pairs_allocated-1].next = NULL;

			// reset the "previous" ptrs
			pair_free_list.next = &Obj_pairs[prev_free_mark];
			pair_used_list.next = &Obj_pairs[prev_used_mark];
		}
	}

	// get a new obj_pair from the free list
	obj_pair * new_pair = pair_free_list.next;
	pair_free_list.next = new_pair->next;

	if ( add_to_end ) {
		obj_pair *last, *tmp;

		last = tmp = pair_used_list.next;
		while( tmp != NULL )	{
			if ( tmp->next == NULL )
				last = tmp;

			tmp = tmp->next;
		}

		if ( last == NULL )
			last = &pair_used_list;
			
		last->next = new_pair;
		Assert(new_pair != NULL);
		new_pair->next = NULL;
	}
	else {
		new_pair->next = pair_used_list.next;
		pair_used_list.next = new_pair;
	}

	A->num_pairs++;
	B->num_pairs++;
	
	new_pair->a = A;
	new_pair->b = B;
	new_pair->check_collision = check_collision;

	if ( check_time == -1 ){
		new_pair->next_check_time = timestamp(0);	// 0 means instantly time out
	} else {
		new_pair->next_check_time = check_time;
	}

}
void obj_collide_pair(object *A, object *B)
{
	uint ctype;
	int (*check_collision)( obj_pair *pair );
	int swapped = 0;	
	
	check_collision = NULL;

	if ( A==B ) return;		// Don't check collisions with yourself

	if ( !(A->flags&OF_COLLIDES) ) return;		// This object doesn't collide with anything
	if ( !(B->flags&OF_COLLIDES) ) return;		// This object doesn't collide with anything
	
	// Make sure you're not checking a parent with it's kid or vicy-versy
//	if ( A->parent_sig == B->signature && !(A->type == OBJ_SHIP && B->type == OBJ_DEBRIS) ) return;
//	if ( B->parent_sig == A->signature && !(A->type == OBJ_DEBRIS && B->type == OBJ_SHIP) ) return;
	if ( reject_obj_pair_on_parent(A,B) ) {
		return;
	}

	Assert( A->type < 127 );
	Assert( B->type < 127 );

	ctype = COLLISION_OF(A->type,B->type);
	switch( ctype )	{
	case COLLISION_OF(OBJ_WEAPON,OBJ_SHIP):
		swapped = 1;
		check_collision = collide_ship_weapon;
		break;
	case COLLISION_OF(OBJ_SHIP, OBJ_WEAPON):
		check_collision = collide_ship_weapon;
		break;
	case COLLISION_OF(OBJ_DEBRIS, OBJ_WEAPON):
		check_collision = collide_debris_weapon;
		break;
	case COLLISION_OF(OBJ_WEAPON, OBJ_DEBRIS):
		swapped = 1;
		check_collision = collide_debris_weapon;
		break;
	case COLLISION_OF(OBJ_DEBRIS, OBJ_SHIP):
		check_collision = collide_debris_ship;		
		break;
	case COLLISION_OF(OBJ_SHIP, OBJ_DEBRIS):
		check_collision = collide_debris_ship;
		swapped = 1;
		break;
	case COLLISION_OF(OBJ_ASTEROID, OBJ_WEAPON):
		// Only check collision's with player weapons
//		if ( Objects[B->parent].flags & OF_PLAYER_SHIP ) {
			check_collision = collide_asteroid_weapon;
//		}
		break;
	case COLLISION_OF(OBJ_WEAPON, OBJ_ASTEROID):
		swapped = 1;
		// Only check collision's with player weapons
//		if ( Objects[A->parent].flags & OF_PLAYER_SHIP ) {
			check_collision = collide_asteroid_weapon;
//		}
		break;
	case COLLISION_OF(OBJ_ASTEROID, OBJ_SHIP):
		// Only check collisions with player ships
//		if ( B->flags & OF_PLAYER_SHIP )	{
			check_collision = collide_asteroid_ship;
//		}
		break;
	case COLLISION_OF(OBJ_SHIP, OBJ_ASTEROID):
		// Only check collisions with player ships
//		if ( A->flags & OF_PLAYER_SHIP )	{
			check_collision = collide_asteroid_ship;
//		}
		swapped = 1;
		break;
	case COLLISION_OF(OBJ_SHIP,OBJ_SHIP):
		check_collision = collide_ship_ship;
		break;	
	
	case COLLISION_OF(OBJ_SHIP, OBJ_BEAM):
		if(beam_collide_early_out(B, A)){
			return;
		}
		swapped = 1;
		check_collision = beam_collide_ship;
		break;

	case COLLISION_OF(OBJ_BEAM, OBJ_SHIP):
		if(beam_collide_early_out(A, B)){
			return;
		}
		check_collision = beam_collide_ship;
		break;

	case COLLISION_OF(OBJ_ASTEROID, OBJ_BEAM):
		if(beam_collide_early_out(B, A)) {
			return;
		}
		swapped = 1;
		check_collision = beam_collide_asteroid;
		break;

	case COLLISION_OF(OBJ_BEAM, OBJ_ASTEROID):
		if(beam_collide_early_out(A, B)){
			return;
		}
		check_collision = beam_collide_asteroid;
		break;
	case COLLISION_OF(OBJ_DEBRIS, OBJ_BEAM):
		if(beam_collide_early_out(B, A)) {
			return;
		}
		swapped = 1;
		check_collision = beam_collide_debris;
		break;
	case COLLISION_OF(OBJ_BEAM, OBJ_DEBRIS):
		if(beam_collide_early_out(A, B)){
			return;
		}
		check_collision = beam_collide_debris;
		break;
	case COLLISION_OF(OBJ_WEAPON, OBJ_BEAM):
		if(beam_collide_early_out(B, A)) {
			return;
		}
		swapped = 1;
		check_collision = beam_collide_missile;
		break;

	case COLLISION_OF(OBJ_BEAM, OBJ_WEAPON):
		if(beam_collide_early_out(A, B)){
			return;
		}		
		check_collision = beam_collide_missile;
		break;

	case COLLISION_OF(OBJ_WEAPON, OBJ_WEAPON): {
		weapon_info *awip, *bwip;
		awip = &Weapon_info[Weapons[A->instance].weapon_info_index];
		bwip = &Weapon_info[Weapons[B->instance].weapon_info_index];

		if ((awip->weapon_hitpoints > 0) || (bwip->weapon_hitpoints > 0)) {
			if (bwip->weapon_hitpoints == 0) {
				check_collision = collide_weapon_weapon;
				swapped=1;
			} else {
				check_collision = collide_weapon_weapon;
			}
		}

		break;
	}

	default:
		return;
	}

	if ( !check_collision ) return;

	// Swap them if needed
	if ( swapped )	{
		object *tmp = A;
		A = B;
		B = tmp;
	}

	collider_pair *collision_info = NULL;
	bool valid = false;
	uint key = (OBJ_INDEX(A) << 12) + OBJ_INDEX(B);

	collision_info = &Collision_cached_pairs[key];

	if ( collision_info->initialized ) {
		// make sure we're referring to the correct objects in case the original pair was deleted
		if ( collision_info->signature_a == collision_info->a->signature && 
			collision_info->signature_b == collision_info->b->signature ) {
			valid = true;
		} else {
			collision_info->a = A;
			collision_info->b = B;
			collision_info->signature_a = A->signature;
			collision_info->signature_b = B->signature;
			collision_info->next_check_time = timestamp(0);
		}
	} else {
		collision_info->a = A;
		collision_info->b = B;
		collision_info->signature_a = A->signature;
		collision_info->signature_b = B->signature;
		collision_info->initialized = true;
		collision_info->next_check_time = timestamp(0);
	}

	if ( valid &&  A->type != OBJ_BEAM ) {
		// if this signature is valid, make the necessary checks to see if we need to collide check
		if ( collision_info->next_check_time == -1 ) {
			return;
		} else {
			if ( !timestamp_elapsed(collision_info->next_check_time) ) {
				return;
			}
		}
	} else {
		//if ( A->type == OBJ_BEAM ) {
			//if(beam_collide_early_out(A, B)){
				//collision_info->next_check_time = -1;
				//return;
			//}
		//}

		// only check debris:weapon collisions for player
		if (check_collision == collide_debris_weapon) {
			// weapon is B
			if ( !(Weapon_info[Weapons[B->instance].weapon_info_index].wi_flags & WIF_TURNS) ) {
				// check for dumbfire weapon
				// check if debris is behind laser
				float vdot;
				if (Weapon_info[Weapons[B->instance].weapon_info_index].subtype == WP_LASER) {
					vec3d velocity_rel_weapon;
					vm_vec_sub(&velocity_rel_weapon, &B->phys_info.vel, &A->phys_info.vel);
					vdot = -vm_vec_dot(&velocity_rel_weapon, &B->orient.vec.fvec);
				} else {
					vdot = vm_vec_dot( &A->phys_info.vel, &B->phys_info.vel);
				}
				if ( vdot <= 0.0f )	{
					// They're heading in opposite directions...
					// check their positions
					vec3d weapon2other;
					vm_vec_sub( &weapon2other, &A->pos, &B->pos );
					float pdot = vm_vec_dot( &B->orient.vec.fvec, &weapon2other );
					if ( pdot <= -A->radius )	{
						// The other object is behind the weapon by more than
						// its radius, so it will never hit...
						collision_info->next_check_time = -1;
						return;
					}
				}

				// check dist vs. dist moved during weapon lifetime
				vec3d delta_v;
				vm_vec_sub(&delta_v, &B->phys_info.vel, &A->phys_info.vel);
				if (vm_vec_dist_squared(&A->pos, &B->pos) > (vm_vec_mag_squared(&delta_v)*Weapons[B->instance].lifeleft*Weapons[B->instance].lifeleft)) {
					collision_info->next_check_time = -1;
					return;
				}

				// for nonplayer ships, only create collision pair if close enough
				if ( (B->parent >= 0) && !(Objects[B->parent].flags & OF_PLAYER_SHIP) && (vm_vec_dist(&B->pos, &A->pos) < (4.0f*A->radius + 200.0f)) ) {
					collision_info->next_check_time = -1;
					return;
				}
			}
		}

		// don't check same team laser:ship collisions on small ships if not player
		if (check_collision == collide_ship_weapon) {
			// weapon is B
			if ( (B->parent >= 0)
				&& !(Objects[B->parent].flags & OF_PLAYER_SHIP)
				&& (Ships[Objects[B->parent].instance].team == Ships[A->instance].team) 
				&& (Ship_info[Ships[A->instance].ship_info_index].flags & SIF_SMALL_SHIP) 
				&& (Weapon_info[Weapons[B->instance].weapon_info_index].subtype == WP_LASER) ) {
				collision_info->next_check_time = -1;
				return;
			}
		}
	}

	obj_pair new_pair;	

	new_pair.a = A;
	new_pair.b = B;
	new_pair.check_collision = check_collision;
	new_pair.next_check_time = collision_info->next_check_time;

	if ( check_collision(&new_pair) ) {
		// don't have to check ever again
		collision_info->next_check_time = -1;
	} else {
		collision_info->next_check_time = new_pair.next_check_time;
	}
}