use a better multi_sw_ok_to_commit() check

[taylor/freespace2.git] / src / object / objcollide.cpp

/*
 * Copyright (C) Volition, Inc. 1999.  All rights reserved.
 *
 * All source code herein is the property of Volition, Inc. You may not sell 
 * or otherwise commercially exploit the source or things you created based on
 * the source.
 */

/*
 * $Logfile: /Freespace2/code/Object/ObjCollide.cpp $
 * $Revision$
 * $Date$
 * $Author$
 *
 * Helper routines for all the collision detection functions
 * Also keeps track of all the object pairs.
 *
 * $Log$
 * Revision 1.5  2003/05/25 02:30:43  taylor
 * Freespace 1 support
 *
 * Revision 1.4  2002/06/17 06:33:10  relnev
 * ryan's struct patch for gcc 2.95
 *
 * Revision 1.3  2002/06/09 04:41:24  relnev
 * added copyright header
 *
 * Revision 1.2  2002/05/07 03:16:48  theoddone33
 * The Great Newline Fix
 *
 * Revision 1.1.1.1  2002/05/03 03:28:10  root
 * Initial import.
 *
 * 
 * 18    7/15/99 9:20a Andsager
 * FS2_DEMO initial checkin
 * 
 * 17    6/14/99 3:21p Andsager
 * Allow collisions between ship and its debris.  Fix up collision pairs
 * when large ship is warping out.
 * 
 * 16    5/08/99 8:25p Dave
 * Upped object pairs. First run of nebula lightning.
 * 
 * 15    4/23/99 12:01p Johnson
 * Added SIF_HUGE_SHIP
 * 
 * 14    4/21/99 6:15p Dave
 * Did some serious housecleaning in the beam code. Made it ready to go
 * for anti-fighter "pulse" weapons. Fixed collision pair creation. Added
 * a handy macro for recalculating collision pairs for a given object.
 * 
 * 13    4/20/99 3:41p Andsager
 * Modify objects_will_collide to use endpoints
 * 
 * 12    3/10/99 6:50p Dave
 * Changed the way we buffer packets for all clients. Optimized turret
 * fired packets. Did some weapon firing optimizations.
 * 
 * 11    3/05/99 3:32p Dan
 * Make out of collision pars message npirntf with "collision"
 * 
 * 10    1/21/99 2:06p Dave
 * Final checkin for multiplayer testing.
 * 
 * 9     1/21/99 10:44a Dave
 * More beam weapon stuff. Put in warmdown time.
 * 
 * 8     1/15/99 5:01p Dave
 * Fix for object collision problem.
 * 
 * 7     1/12/99 5:45p Dave
 * Moved weapon pipeline in multiplayer to almost exclusively client side.
 * Very good results. Bandwidth goes down, playability goes up for crappy
 * connections. Fixed object update problem for ship subsystems.
 * 
 * 6     1/12/99 12:53a Dave
 * More work on beam weapons - made collision detection very efficient -
 * collide against all object types properly - made 3 movement types
 * smooth. Put in test code to check for possible non-darkening pixels on
 * object textures.
 * 
 * 5     11/19/98 11:08p Andsager
 * Check in of physics and collision detection of rotating submodels
 * 
 * 4     11/05/98 5:55p Dave
 * Big pass at reducing #includes
 * 
 * 3     10/26/98 9:42a Dave
 * Early flak gun support.
 * 
 * 2     10/07/98 10:53a Dave
 * Initial checkin.
 * 
 * 1     10/07/98 10:50a Dave
 * 
 * 38    7/29/98 3:24p Allender
 * don't call collision code when either of the object pairs is NULL.
 * 
 * 37    4/08/98 8:38a Mike
 * Make ships avoid player when attacking or guarding a faraway object.
 * 
 * 36    4/02/98 11:40a Lawrance
 * check for #ifdef DEMO instead of #ifdef DEMO_RELEASE
 * 
 * 35    4/01/98 1:48p Allender
 * major changes to ship collision in multiplayer.  Clients now do own
 * ship/ship collisions (with their own ship only)  Modifed the hull
 * update packet to be sent quicker when object is target of player.
 * 
 * 34    4/01/98 10:57a Mike
 * Reduce array sizes to save memory.
 * 
 * 33    3/31/98 5:18p John
 * Removed demo/save/restore.  Made NDEBUG defined compile.  Removed a
 * bunch of debug stuff out of player file.  Made model code be able to
 * unload models and malloc out only however many models are needed.
 *  
 * 
 * 32    3/06/98 12:45a Lawrance
 * Rmove a bogus assert in the object pair save/restore
 * 
 * 31    3/05/98 3:12p Mike
 * Fix bugs in asteroid collisions.  Throw asteroids at Galataea (needs to
 * be made general).  Add skill level support for asteroid throwing.
 * 
 * 30    3/05/98 12:12a Mike
 * Make an asteroid in the way prevent player warpout.
 * 
 * 29    2/27/98 4:48p John
 * Made objects keep track of number of pairs they have associated with
 * them.  Then, I can early out of the obj_remove_all which was 2.5% of
 * frametime at beginning of sm2-2 which then is 0% after this.
 * 
 * 28    2/26/98 10:07p Hoffoss
 * Rewrote state saving and restoring to fix bugs and simplify the code.
 * 
 * 27    2/23/98 9:00a Andsager
 * improved back face culling of object:laser pairs to check relative
 * velocity dot laser forward < 0 vs. v_other dot v_laser < 0
 * 
 * 26    2/19/98 4:34p Lawrance
 * Allow weapon-asteroid collisions
 * 
 * 25    2/19/98 10:52a Sandeep
 * AL: Have asteroids collide with all ships
 * 
 * 24    2/12/98 11:45a Andsager
 * Try to cull debris:weapon collisions before they collisoin pair is
 * created.  Look at movement in lifetime and whether debris is behind
 * laser.
 * 
 * 23    2/07/98 3:54p John
 * Added FVI to show_game_resources
 * 
 * 22    2/06/98 7:29p John
 * Made only players ships and player ship weapons do collisions with
 * asteroids.
 * 
 * 21    2/05/98 11:49p Andsager
 * Don't check laser:ship collisions on same team for small ships if laser
 * source not player
 * 
 * 20    2/05/98 9:21p John
 * Some new Direct3D code.   Added code to monitor a ton of stuff in the
 * game.
 * 
 * 19    2/05/98 12:51a Mike
 * Early asteroid stuff.
 * 
 * 18    2/03/98 9:40a Andsager
 * Modify collision object pair creation code so that pairs between debris
 * and weapons (other than player) are not created.
 * 
 * 17    1/28/98 11:06a Andsager
 * Remove some collision pairs.  Add debug code for displaying collision
 * pair info.  
 * 
 * 16    1/24/98 11:16a Andsager
 * Remove debug  info.
 * 
 * 15    1/24/98 11:09a Andsager
 * Fixed bug that was removing collision pairs when weapon within the
 * radius of object.
 * 
 * 14    1/23/98 5:07p Andsager
 * Added tests for object pairs.  (1)  for weapons that do not turn, find
 * the soonest hit time.  (2)  Check if soonest hit time if after end of
 * weapon lifetime.
 * 
 * 13    1/22/98 6:43p John
 * Took out debug code.
 * 
 * 12    1/22/98 6:42p John
 * Move game_flush out of debug console into freespace.     Made object
 * pair code throw out some weapons that turn.   Added stats for how many
 * object pair are actually checked.
 * 
 * 11    1/17/98 10:06p Lawrance
 * For missiles, only collide if WIF_BOMB flag set.
 * 
 * 10    1/14/98 5:21p Allender
 * system to delete object when buffer is nearly full.  System in place to
 * delete weapons when nearly out of weapons slots
 * 
 * 9     1/13/98 8:09p John
 * Removed the old collision system that checked all pairs.   Added code
 * to disable collisions and particles.
 * 
 * 8     1/13/98 3:11p Allender
 * new code to remove old weapons when no more weapon slots available.
 * Currently not called anywhere pending further testing
 * 
 * 7     1/10/98 3:22p Allender
 * temporary check in to get new code
 * 
 * 6     1/10/98 1:14p John
 * Added explanation to debug console commands
 * 
 * 5     1/09/98 9:29a Mike
 * Enable docked ships to warp out.  Make damage done to a ship not
 * proportional to its own mass.
 * 
 * 4     1/08/98 12:12a Mike
 * Make ships turn before warping out, if necessary, to avoid a collision.
 * Warn player if his warpout will collide.  Abort if in stage1.
 * 
 * 3     12/21/97 4:33p John
 * Made debug console functions a class that registers itself
 * automatically, so you don't need to add the function to
 * debugfunctions.cpp.  
 * 
 * 2     12/16/97 5:23p Allender
 * don't deal with object collision paris on multiplayer clients
 * 
 * 1     9/17/97 2:14p John
 * Initial revision
 *
 * $NoKeywords: $
 */

#include "objcollide.h"
#include "linklist.h"
#include "systemvars.h"
#include "timer.h"
#include "multi.h"
#include "beam.h"

#if defined(FS2_DEMO) || defined(FS1_DEMO)
        #define MAX_PAIRS 3000
#else
        #define MAX_PAIRS 8000  //      Reduced from 10,000 to 6,000 by MK on 4/1/98.
                                                                        //      Most I saw was 3400 in sm1-06a, the asteriod mission.  No other mission came close.
#endif

// the next 3 variables are used for pair statistics
// also in weapon.cpp there is Weapons_created.
int Pairs_created = 0;
int Num_pairs = 0;
int Num_pairs_checked = 0;
int pairs_not_created = 0;

int Num_pairs_hwm = 0;

obj_pair Obj_pairs[MAX_PAIRS];

obj_pair pair_used_list;
obj_pair pair_free_list;

void obj_reset_pairs()
{
        int i;
        
//      mprintf(( "Resetting object pairs...\n" ));

        pair_used_list.a = pair_used_list.b = NULL;             
        pair_used_list.next = NULL;
        pair_free_list.a = pair_free_list.b = NULL;             
        pair_free_list.next = &Obj_pairs[0];
        
        Num_pairs = 0;
        for (i=0; i<MAX_PAIRS; i++ )    {
                Obj_pairs[i].a = Obj_pairs[i].b = NULL;
                Obj_pairs[i].next = &Obj_pairs[i+1];
        }
        Obj_pairs[MAX_PAIRS-1].next = NULL;
}

// returns true if we should reject object pair if one is child of other.
int reject_obj_pair_on_parent(object *A, object *B)
{
        if (A->type == OBJ_SHIP) {
                if (B->type == OBJ_DEBRIS) {
                        if (B->parent_sig == A->signature) {
                                return 0;
                        }
                }
        }

        if (B->type == OBJ_SHIP) {
                if (A->type == OBJ_DEBRIS) {
                        if (A->parent_sig == B->signature) {
                                return 0;
                        }
                }
        }

        if (A->parent_sig == B->signature) {
                return 1;
        }

        if (B->parent_sig == A->signature) {
                return 1;
        }

        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 ( 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;
        }

        SDL_assert( A->type < 127 );
        SDL_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->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) {
                                vector 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.v.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
                                vector weapon2other;
                                vm_vec_sub( &weapon2other, &A->pos, &B->pos );
                                float pdot = vm_vec_dot( &B->orient.v.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
                        vector 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 ( !(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 ( !(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;
        }

        // 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;
                SDL_assert(new_pair != NULL);
                new_pair->next = NULL;
        }
        else {
                new_pair->next = pair_used_list.next;
                pair_used_list.next = new_pair;
        }
        
        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));
        }
*/

        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;
        }

}

MONITOR(NumPairs);
MONITOR(NumPairsChecked);

void obj_check_all_collisions()
{
        if ( !(Game_detail_flags & DETAIL_FLAG_COLLISION) )     return;

        obj_pair *parent, *tmp; 
        // debug info
        float avg_time_to_next_check = 0.0f;
                                                        
        parent = &pair_used_list;
        tmp = parent->next;

        Num_pairs_checked = 0;

        while( tmp != NULL )    {

                int removed = 0;
                if ( (tmp->a != NULL) && (tmp->b != NULL) && timestamp_elapsed(tmp->next_check_time) )  {
                        Num_pairs_checked++;

                        if ((*tmp->check_collision)(tmp))       {
                                // We never need to check this pair again.
                                #if 0   //def DONT_REMOVE_PAIRS
                                        // Never check it again, but keep the pair around
                                        // (useful for debugging)
                                        tmp->next_check_time = timestamp(-1);           
                                #else
                                        // Never check it again, so remove the pair
                                        removed = 1;
                                        tmp->a->num_pairs--;    
                                        SDL_assert( tmp->a->num_pairs > -1 );
                                        tmp->b->num_pairs--;
                                        SDL_assert( tmp->b->num_pairs > -1 );
                                        Num_pairs--;
                                        // SDL_assert(Num_pairs >= 0);
                                        parent->next = tmp->next;
                                        tmp->a = tmp->b = NULL;
                                        tmp->next = pair_free_list.next;
                                        pair_free_list.next = tmp;
                                        tmp = parent->next;
                                #endif
                        }
                } 

                if (!removed)   {
                        parent = tmp;
                        tmp = tmp->next;
                        // debug info
                        if (tmp) {
                                int add_time = timestamp_until( tmp->next_check_time );
                                if (add_time > 0)
                                        avg_time_to_next_check += (float) add_time;
                        }
                }
        }

        MONITOR_INC(NumPairs,Num_pairs);
        MONITOR_INC(NumPairsChecked,Num_pairs_checked);

        // #define PAIR_STATS
        #ifdef PAIR_STATS
        avg_time_to_next_check = avg_time_to_next_check / Num_pairs;
        extern int Num_hull_pieces;
        extern int Weapons_created;
        // mprintf(( "[pairs checked: %d, start_pairs: %d, num obj: %d, avg next time: %f]\n", n, org_pairs, num_objects, avg_time_to_next_check ));
        // mprintf(( "[Num_hull_pieces: %3d, Num_weapons_created: %3d, pairs_not_created: %3d, pairs_created: %3d, percent new saved: %9.5f]\n", Num_hull_pieces, Weapons_created, pairs_not_created, Pairs_created, 100.0f*(float)pairs_not_created/(float)(pairs_not_created + Pairs_created) ));
         mprintf(( "[pairs_created: %3d, pairs_not_created: %3d, percent saved %6.3f]\n", Pairs_created, pairs_not_created, 100.0f*pairs_not_created/(Pairs_created+pairs_not_created) ));
        pairs_not_created = 0;
        Weapons_created = 0;
        Pairs_created = 0;
        #endif

        // What percent of the pairs did we check?
        // FYI: (n*(n-1))/2 is the total number of checks required for comparing n objects.

//      if ( org_pairs > 1 )    {
//              Object_checked_percentage = (i2fl(n)*100.0f) / i2fl(org_pairs);
//      } else {
//              Object_checked_percentage = 0.0f;
//      }

}

//      See if two lines intersect by doing recursive subdivision.
//      Bails out if larger distance traveled is less than sum of radii + 1.0f.
int collide_subdivide(vector *p0, vector *p1, float prad, vector *q0, vector *q1, float qrad)
{
        float   a_dist, b_dist, ab_dist;

        a_dist = vm_vec_dist(p0, p1);
        b_dist = vm_vec_dist(q0, q1);

        ab_dist = vm_vec_dist(p1, q1);

        //      See if their spheres intersect
        if (ab_dist < a_dist + b_dist + prad + qrad) {
                if (ab_dist  < prad + qrad)
                        return 1;
                else if (vm_vec_dist(p0, q0) < prad + qrad)
                        return 1;
                else if (SDL_max(a_dist, b_dist) < prad + qrad + 1.0f)
                        return 0;
                else {
                        int     r1, r2 = 0;
                        vector  pa, qa;

                        vm_vec_avg(&pa, p0, p1);
                        vm_vec_avg(&qa, q0, q1);
                        r1 = collide_subdivide(p0, &pa, prad, q0, &qa, qrad);
                        if (!r1)
                                r2 = collide_subdivide(&pa, p1, prad, &qa, q1, qrad);

                        return r1 | r2;
                }
        } else
                return 0;
}



//      Return true if object A is expected to collide with object B within time duration
//      For purposes of this check, the first object moves from current location to predicted
//      location.  The second object is assumed to be where it will be at time duration, NOT
//      where it currently is.
//      radius_scale is used to control the precision of the check.
//              If 0.0, then use polygon models to perform check, slow and accurate
//              If !0.0, then use as a scale on the radius of the objects.  1.0 is Descent style
//                      collisions.  Larger values can be used to be sloppy about the collisions which
//                      is useful if a moving object wants to prevent a collision.
int objects_will_collide(object *A, object *B, float duration, float radius_scale)
{
        object  A_future;
        vector  hitpos;


        A_future = *A;
        vm_vec_scale_add2(&A_future.pos, &A->phys_info.vel, duration);

        if (radius_scale == 0.0f) {
                return ship_check_collision_fast(B, &A_future, &hitpos );
        } else {
                float           size_A, size_B, dist, r;
                vector  nearest_point;

                size_A = A->radius * radius_scale;
                size_B = B->radius * radius_scale;

                //      If A is moving, check along vector.
                if (A->phys_info.speed != 0.0f) {
                        r = find_nearest_point_on_line(&nearest_point, &A->pos, &A_future.pos, &B->pos);
                        if (r < 0) {
                                nearest_point = A->pos;
                        } else if (r > 1) {
                                nearest_point = A_future.pos;
                        }
                        dist = vm_vec_dist_quick(&B->pos, &nearest_point);
                        return (dist < size_A + size_B);
                } else {
                        return vm_vec_dist_quick(&B->pos, &A->pos) < size_A + size_B;
                }
        }
}

//      Return true if the vector from *start_pos to *end_pos is within objp->radius*radius_scale of *objp
int vector_object_collision(vector *start_pos, vector *end_pos, object *objp, float radius_scale)
{
        float           dist, r;
        vector  nearest_point;

        r = find_nearest_point_on_line(&nearest_point, start_pos, end_pos, &objp->pos);
        if ((r >= 0.0f) && (r <= 1.0f)) {
                dist = vm_vec_dist_quick(&objp->pos, &nearest_point);

                return (dist < objp->radius * radius_scale);
        } else
                return 0;
}

// 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 *weapon, object *other, obj_pair * current_pair )
{

        SDL_assert( weapon->type == OBJ_WEAPON );

//      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 ( !(Weapon_info[Weapons[weapon->instance].weapon_info_index].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 (Weapon_info[Weapons[weapon->instance].weapon_info_index].subtype == WP_LASER) {
                        vector velocity_rel_weapon;
                        vm_vec_sub(&velocity_rel_weapon, &weapon->phys_info.vel, &other->phys_info.vel);
                        vdot = -vm_vec_dot(&velocity_rel_weapon, &weapon->orient.v.fvec);
                } else {
                        vdot = vm_vec_dot( &other->phys_info.vel, &weapon->phys_info.vel);
                }
                if ( vdot <= 0.0f )     {
                        // They're heading in opposite directions...
                        // check their positions
                        vector weapon2other;
                        vm_vec_sub( &weapon2other, &other->pos, &weapon->pos );
                        float pdot = vm_vec_dot( &weapon->orient.v.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;
                max_vel_weapon = weapon->phys_info.max_vel.xyz.z;
                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 ( !(Weapon_info[Weapons[weapon->instance].weapon_info_index].wi_flags & WIF_TURNS) ) {
                        vector delta_x, laser_vel;
                        float a,b,c, delta_x_dot_vl, delta_t;
                        float root1, root2, root, earliest_time;

                        vm_vec_sub( &delta_x, &weapon->pos, &other->pos );
                        vm_vec_copy_scale( &laser_vel, &weapon->orient.v.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
                        }

                        // 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;
                        }



                        // check if possible collision occurs after weapon expires
                        if ( earliest_time > 1000*Weapons[weapon->instance].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, &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*Weapons[weapon->instance].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;
}

//      Return true if vector from *curpos to *goalpos intersects with object *goalobjp
//      Else, return false.
//      radius is radius of object moving from curpos to goalpos.
int pp_collide(vector *curpos, vector *goalpos, object *goalobjp, float radius)
{
        mc_info mc;

        SDL_assert(goalobjp->type == OBJ_SHIP);

        ship_model_start(goalobjp);

        mc.model_num = Ships[goalobjp->instance].modelnum;                      // Fill in the model to check
        mc.orient = &goalobjp->orient;  // The object's orient
        mc.pos = &goalobjp->pos;                        // The object's position
        mc.p0 = curpos;                                 // Point 1 of ray to check
        mc.p1 = goalpos;                                        // Point 2 of ray to check
        mc.flags = MC_CHECK_MODEL | MC_CHECK_SPHERELINE;
        mc.radius = radius;

        model_collide(&mc);

        ship_model_stop(goalobjp);

        return mc.num_hits;
}

//      Setup and call pp_collide for collide_predict_large_ship
//      Returns true if objp will collide with objp2 before it reaches goal_pos.
int cpls_aux(vector *goal_pos, object *objp2, object *objp)
{
        float   radius;
        
        radius = objp->radius;
        if (1.5f * radius < 70.0f)
                radius *= 1.5f;
        else
                radius = 70.0f;

        if (pp_collide(&objp->pos, goal_pos, objp2, radius))
                return 1;
        else
                return 0;
}

//      Return true if objp will collide with some large object.
//      Don't check for an object this ship is docked to.
int collide_predict_large_ship(object *objp, float distance)
{
        object  *objp2;
        vector  cur_pos, goal_pos;
        object  *dock_objp;
        ship_info       *sip;

        sip = &Ship_info[Ships[objp->instance].ship_info_index];

        dock_objp = NULL;
        if (objp->type == OBJ_SHIP) {
                ai_info *aip = &Ai_info[Ships[objp->instance].ai_index];
                if (aip->dock_objnum != -1)
                        dock_objp = &Objects[aip->dock_objnum];
        }

        cur_pos = objp->pos;

        vm_vec_scale_add(&goal_pos, &cur_pos, &objp->orient.v.fvec, distance);

        for ( objp2 = GET_FIRST(&obj_used_list); objp2 != END_OF_LIST(&obj_used_list); objp2 = GET_NEXT(objp2) ) {
                if ((objp != objp2) && (objp2->type == OBJ_SHIP)) {
                        if (Ship_info[Ships[objp2->instance].ship_info_index].flags & (SIF_BIG_SHIP | SIF_HUGE_SHIP)) {
                                if (objp2 == dock_objp)
                                        continue;

                                if (cpls_aux(&goal_pos, objp2, objp))
                                        return 1;
                        }
                } else if (!(sip->flags & (SIF_BIG_SHIP | SIF_HUGE_SHIP)) && (objp2->type == OBJ_ASTEROID)) {
                        if (vm_vec_dist_quick(&objp2->pos, &objp->pos) < (distance + objp2->radius)*2.5f) {
                                vector  pos, delvec;
                                int             count;
                                float           d1;

                                d1 = 2.5f * distance + objp2->radius;
                                count = (int) (d1/(objp2->radius + objp->radius));      //      Scale up distance, else looks like there would be a collision.
                                pos = cur_pos;
                                vm_vec_normalized_dir(&delvec, &goal_pos, &cur_pos);
                                vm_vec_scale(&delvec, d1/count);

                                for (; count>0; count--) {
                                        if (vm_vec_dist_quick(&pos, &objp2->pos) < objp->radius + objp2->radius)
                                                return 1;
                                        vm_vec_add2(&pos, &delvec);
                                }
                        }
                }
        }

        return 0;
}

// function to iterate through all object collision pairs looking for weapons
// which could be deleted since they are not going to hit anything.  Passed into this
// function is a 'time' parameter used as watermark for which weapons to check.

#define CRW_NO_OBJECT           -1
#define CRW_NO_PAIR                     0
#define CRW_IN_PAIR                     1
#define CRW_CAN_DELETE          2

#define CRW_MAX_TO_DELETE       4

char crw_status[MAX_WEAPONS];

void crw_check_weapon( int weapon_num, int collide_next_check )
{
        float next_check_time;
        weapon *wp;

        wp = &Weapons[weapon_num];

        // if this weapons life left > time before next collision, then we cannot remove it
        crw_status[WEAPON_INDEX(wp)] = CRW_IN_PAIR;
        next_check_time = ((float)(timestamp_until(collide_next_check)) / 1000.0f);
        if ( wp->lifeleft < next_check_time )
                crw_status[WEAPON_INDEX(wp)] = CRW_CAN_DELETE;
}

int collide_remove_weapons( )
{
        obj_pair *opp;
        int i, num_deleted, oldest_index, j, loop_count;
        float oldest_time;

        // setup remove_weapon array.  assume we can remove it.
        for (i = 0; i < MAX_WEAPONS; i++ ) {
                if ( Weapons[i].objnum == -1 )
                        crw_status[i] = CRW_NO_OBJECT;
                else
                        crw_status[i] = CRW_NO_PAIR;
        }

        // first pass is to see if any of the weapons don't have collision pairs.

        opp = &pair_used_list;
        opp = opp->next;
        while( opp != NULL )    {
                // for each collide pair, if the two objects can still collide, then set the remove_weapon
                // parameter for the weapon to 0.  need to check both parameters
                if ( opp->a->type == OBJ_WEAPON )
                        crw_check_weapon( opp->a->instance, opp->next_check_time );

                if ( opp->b->type == OBJ_WEAPON )
                        crw_check_weapon( opp->b->instance, opp->next_check_time );

                opp = opp->next;
        }

        // for each weapon which could be removed, delete the object
        num_deleted = 0;
        for ( i = 0; i < MAX_WEAPONS; i++ ) {
                if ( crw_status[i] == CRW_CAN_DELETE ) {
                        SDL_assert( Weapons[i].objnum != -1 );
                        obj_delete( Weapons[i].objnum );
                        num_deleted++;
                }
        }

        if ( num_deleted )
                return num_deleted;

        // if we didn't remove any weapons, try to the N oldest weapons.  first checking for pairs, then
        // checking for oldest weapons in general.  We will go through the loop a max of 2 times.  first time
        // through, we check oldest weapons with pairs, next time through, for oldest weapons.
        loop_count = 0;
        do {
                for ( j = 0; j < CRW_MAX_TO_DELETE; j++ ) {
                        oldest_time = 1000.0f;
                        oldest_index = -1;
                        for (i = 0; i < MAX_WEAPONS; i++ ) {
                                if ( Weapons[i].objnum == -1 )                  // shouldn't happen, but this is the safe thing to do.
                                        continue;
                                if ( ((loop_count || crw_status[i] == CRW_NO_PAIR)) && (Weapons[i].lifeleft < oldest_time) ) {
                                        oldest_time = Weapons[i].lifeleft;
                                        oldest_index = i;
                                }
                        }
                        if ( oldest_index != -1 ) {
                                obj_delete(Weapons[oldest_index].objnum);
                                num_deleted++;
                        }
                }

                // if we deleted some weapons, then we can break
                if ( num_deleted )
                        break;

                loop_count++;
        } while ( loop_count < 2);

        return num_deleted;

}

void set_hit_struct_info(collision_info_struct *hit, mc_info *mc, int submodel_rot_hit)
{
        hit->edge_hit = mc->edge_hit;
        hit->hit_pos = mc->hit_point_world;
        hit->hit_time = mc->hit_dist;
        hit->submodel_num = mc->hit_submodel;

        hit->submodel_rot_hit = submodel_rot_hit;
}