main/physics.c

   1 /*
   2 THE COMPUTER CODE CONTAINED HEREIN IS THE SOLE PROPERTY OF PARALLAX
   3 SOFTWARE CORPORATION ("PARALLAX").  PARALLAX, IN DISTRIBUTING THE CODE TO
   4 END-USERS, AND SUBJECT TO ALL OF THE TERMS AND CONDITIONS HEREIN, GRANTS A
   5 ROYALTY-FREE, PERPETUAL LICENSE TO SUCH END-USERS FOR USE BY SUCH END-USERS
   6 IN USING, DISPLAYING,  AND CREATING DERIVATIVE WORKS THEREOF, SO LONG AS
   7 SUCH USE, DISPLAY OR CREATION IS FOR NON-COMMERCIAL, ROYALTY OR REVENUE
   8 FREE PURPOSES.  IN NO EVENT SHALL THE END-USER USE THE COMPUTER CODE
   9 CONTAINED HEREIN FOR REVENUE-BEARING PURPOSES.  THE END-USER UNDERSTANDS
  10 AND AGREES TO THE TERMS HEREIN AND ACCEPTS THE SAME BY USE OF THIS FILE.
  11 COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
  12 */
  13
  14 #ifdef HAVE_CONFIG_H
  15 #include <conf.h>
  16 #endif
  17
  18 #ifdef RCS
  19 static char rcsid[] = "$Id: physics.c,v 1.3 2001-01-31 15:17:57 bradleyb Exp $";
  20 #endif
  21
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24
  25 #include "joy.h"
  26 #include "mono.h"
  27 #include "error.h"
  28
  29 #include "inferno.h"
  30 #include "segment.h"
  31 #include "object.h"
  32 #include "physics.h"
  33 #include "key.h"
  34 #include "game.h"
  35 #include "collide.h"
  36 #include "fvi.h"
  37 #include "newdemo.h"
  38 #include "timer.h"
  39 #include "ai.h"
  40 #include "wall.h"
  41 #include "laser.h"
  42 #include "bm.h"
  43 #include "player.h"
  44
  45 #ifdef TACTILE
  46 #include "tactile.h"
  47 #endif
  48
  49 //Global variables for physics system
  50
  51 #define ROLL_RATE               0x2000
  52 #define DAMP_ANG                        0x400                  //min angle to bank
  53
  54 #define TURNROLL_SCALE  (0x4ec4/2)
  55
  56 #define MAX_OBJECT_VEL i2f(100)
  57
  58 #define BUMP_HACK       1               //if defined, bump player when he gets stuck
  59
  60 //--unused-- int mike_mode=0;
  61
  62 //check point against each side of segment. return bitmask, where bit
  63 //set means behind that side
  64
  65 int Physics_cheat_flag = 0;
  66 extern char BounceCheat;
  67
  68 //##//returns the distance of a point (checkp) from a plane (defined by norm & planep)
  69 //##fix dist_to_plane(vms_vector *checkp,vms_vector *norm,vms_vector *planep)
  70 //##{
  71 //##    vms_vector deltap;
  72 //##
  73 //##    vm_vec_sub(&deltap,checkp,planep);
  74 //##
  75 //##    return vm_vec_dot(&deltap,norm);
  76 //##}
  77
  78 //--unused-- int dpjm_old_joy_x, dpjm_old_joy_y;
  79
  80 int floor_levelling=0;
  81
  82 //--unused-- level_with_floor()
  83 //--unused-- {
  84 //--unused--    floor_levelling=1;
  85 //--unused-- }
  86
  87 //make sure matrix is orthogonal
  88 void check_and_fix_matrix(vms_matrix *m)
  89 {
  90         vms_matrix tempm;
  91
  92         vm_vector_2_matrix(&tempm,&m->fvec,&m->uvec,NULL);
  93         *m  = tempm;
  94 }
  95
  96
  97 void do_physics_align_object( object * obj )
  98 {
  99         vms_vector desired_upvec;
 100         fixang delta_ang,roll_ang;
 101         //vms_vector forvec = {0,0,f1_0};
 102         vms_matrix temp_matrix;
 103         fix d,largest_d=-f1_0;
 104         int i,best_side;
 105
 106         best_side=0;
 107         // bank player according to segment orientation
 108
 109         //find side of segment that player is most alligned with
 110
 111         for (i=0;i<6;i++) {
 112                 #ifdef COMPACT_SEGS
 113                         vms_vector _tv1;
 114                         get_side_normal( &Segments[obj->segnum], i, 0, &_tv1 );
 115                         d = vm_vec_dot(&_tv1,&obj->orient.uvec);
 116                 #else
 117                         d = vm_vec_dot(&Segments[obj->segnum].sides[i].normals[0],&obj->orient.uvec);
 118                 #endif
 119
 120                 if (d > largest_d) {largest_d = d; best_side=i;}
 121         }
 122
 123         if (floor_levelling) {
 124
 125                 // old way: used floor's normal as upvec
 126                 #ifdef COMPACT_SEGS
 127                         get_side_normal(&Segments[obj->segnum], 3, 0, &desired_upvec );
 128                 #else
 129                         desired_upvec = Segments[obj->segnum].sides[3].normals[0];
 130                 #endif
 131
 132         }
 133         else  // new player leveling code: use normal of side closest to our up vec
 134                 if (get_num_faces(&Segments[obj->segnum].sides[best_side])==2) {
 135                         #ifdef COMPACT_SEGS
 136                                 vms_vector normals[2];
 137                                 get_side_normals(&Segments[obj->segnum], best_side, &normals[0], &normals[1] );
 138
 139                                 desired_upvec.x = (normals[0].x + normals[1].x) / 2;
 140                                 desired_upvec.y = (normals[0].y + normals[1].y) / 2;
 141                                 desired_upvec.z = (normals[0].z + normals[1].z) / 2;
 142
 143                                 vm_vec_normalize(&desired_upvec);
 144                         #else
 145                                 side *s = &Segments[obj->segnum].sides[best_side];
 146                                 desired_upvec.x = (s->normals[0].x + s->normals[1].x) / 2;
 147                                 desired_upvec.y = (s->normals[0].y + s->normals[1].y) / 2;
 148                                 desired_upvec.z = (s->normals[0].z + s->normals[1].z) / 2;
 149
 150                                 vm_vec_normalize(&desired_upvec);
 151                         #endif
 152                 }
 153                 else
 154                         #ifdef COMPACT_SEGS
 155                                 get_side_normal(&Segments[obj->segnum], best_side, 0, &desired_upvec );
 156                         #else
 157                                 desired_upvec = Segments[obj->segnum].sides[best_side].normals[0];
 158                         #endif
 159
 160         if (labs(vm_vec_dot(&desired_upvec,&obj->orient.fvec)) < f1_0/2) {
 161                 fixang save_delta_ang;
 162                 vms_angvec tangles;
 163
 164                 vm_vector_2_matrix(&temp_matrix,&obj->orient.fvec,&desired_upvec,NULL);
 165
 166                 save_delta_ang = delta_ang = vm_vec_delta_ang(&obj->orient.uvec,&temp_matrix.uvec,&obj->orient.fvec);
 167
 168                 delta_ang += obj->mtype.phys_info.turnroll;
 169
 170                 if (abs(delta_ang) > DAMP_ANG) {
 171                         vms_matrix rotmat, new_pm;
 172
 173                         roll_ang = fixmul(FrameTime,ROLL_RATE);
 174
 175                         if (abs(delta_ang) < roll_ang) roll_ang = delta_ang;
 176                         else if (delta_ang<0) roll_ang = -roll_ang;
 177
 178                         tangles.p = tangles.h = 0;  tangles.b = roll_ang;
 179                         vm_angles_2_matrix(&rotmat,&tangles);
 180
 181                         vm_matrix_x_matrix(&new_pm,&obj->orient,&rotmat);
 182                         obj->orient = new_pm;
 183                 }
 184                 else floor_levelling=0;
 185         }
 186
 187 }
 188
 189 void set_object_turnroll(object *obj)
 190 {
 191         fixang desired_bank;
 192
 193         desired_bank = -fixmul(obj->mtype.phys_info.rotvel.y,TURNROLL_SCALE);
 194
 195         if (obj->mtype.phys_info.turnroll != desired_bank) {
 196                 fixang delta_ang,max_roll;
 197
 198                 max_roll = fixmul(ROLL_RATE,FrameTime);
 199
 200                 delta_ang = desired_bank - obj->mtype.phys_info.turnroll;
 201
 202                 if (labs(delta_ang) < max_roll)
 203                         max_roll = delta_ang;
 204                 else
 205                         if (delta_ang < 0)
 206                                 max_roll = -max_roll;
 207
 208                 obj->mtype.phys_info.turnroll += max_roll;
 209         }
 210
 211 }
 212
 213 //list of segments went through
 214 int phys_seglist[MAX_FVI_SEGS],n_phys_segs;
 215
 216
 217 #define MAX_IGNORE_OBJS 100
 218
 219 #ifndef NDEBUG
 220 #define EXTRA_DEBUG 1           //no extra debug when NDEBUG is on
 221 #endif
 222
 223 #ifdef EXTRA_DEBUG
 224 object *debug_obj=NULL;
 225 #endif
 226
 227 #define XYZ(v) (v)->x,(v)->y,(v)->z
 228
 229
 230 #ifndef NDEBUG
 231 int     Total_retries=0, Total_sims=0;
 232 int     Dont_move_ai_objects=0;
 233 #endif
 234
 235 #define FT (f1_0/64)
 236
 237 extern int disable_new_fvi_stuff;
 238 //      -----------------------------------------------------------------------------------------------------------
 239 // add rotational velocity & acceleration
 240 void do_physics_sim_rot(object *obj)
 241 {
 242         vms_angvec      tangles;
 243         vms_matrix      rotmat,new_orient;
 244         //fix                   rotdrag_scale;
 245         physics_info *pi;
 246
 247         Assert(FrameTime > 0);  //Get MATT if hit this!
 248
 249         pi = &obj->mtype.phys_info;
 250
 251         if (!(pi->rotvel.x || pi->rotvel.y || pi->rotvel.z || pi->rotthrust.x || pi->rotthrust.y || pi->rotthrust.z))
 252                 return;
 253
 254         if (obj->mtype.phys_info.drag) {
 255                 int count;
 256                 vms_vector accel;
 257                 fix drag,r,k;
 258
 259                 count = FrameTime / FT;
 260                 r = FrameTime % FT;
 261                 k = fixdiv(r,FT);
 262
 263                 drag = (obj->mtype.phys_info.drag*5)/2;
 264
 265                 if (obj->mtype.phys_info.flags & PF_USES_THRUST) {
 266
 267                         vm_vec_copy_scale(&accel,&obj->mtype.phys_info.rotthrust,fixdiv(f1_0,obj->mtype.phys_info.mass));
 268
 269                         while (count--) {
 270
 271                                 vm_vec_add2(&obj->mtype.phys_info.rotvel,&accel);
 272
 273                                 vm_vec_scale(&obj->mtype.phys_info.rotvel,f1_0-drag);
 274                         }
 275
 276                         //do linear scale on remaining bit of time
 277
 278                         vm_vec_scale_add2(&obj->mtype.phys_info.rotvel,&accel,k);
 279                         vm_vec_scale(&obj->mtype.phys_info.rotvel,f1_0-fixmul(k,drag));
 280                 }
 281                 else if (! (obj->mtype.phys_info.flags & PF_FREE_SPINNING)) {
 282                         fix total_drag=f1_0;
 283
 284                         while (count--)
 285                                 total_drag = fixmul(total_drag,f1_0-drag);
 286
 287                         //do linear scale on remaining bit of time
 288
 289                         total_drag = fixmul(total_drag,f1_0-fixmul(k,drag));
 290
 291                         vm_vec_scale(&obj->mtype.phys_info.rotvel,total_drag);
 292                 }
 293
 294         }
 295
 296         //mprintf( (0, "Rot vel = %.3f,%.3f,%.3f\n", f2fl(obj->mtype.phys_info.rotvel.x),f2fl(obj->mtype.phys_info.rotvel.y), f2fl(obj->mtype.phys_info.rotvel.z) ));
 297
 298         //now rotate object
 299
 300         //unrotate object for bank caused by turn
 301         if (obj->mtype.phys_info.turnroll) {
 302                 vms_matrix new_pm;
 303
 304                 tangles.p = tangles.h = 0;
 305                 tangles.b = -obj->mtype.phys_info.turnroll;
 306                 vm_angles_2_matrix(&rotmat,&tangles);
 307                 vm_matrix_x_matrix(&new_pm,&obj->orient,&rotmat);
 308                 obj->orient = new_pm;
 309         }
 310
 311         tangles.p = fixmul(obj->mtype.phys_info.rotvel.x,FrameTime);
 312         tangles.h = fixmul(obj->mtype.phys_info.rotvel.y,FrameTime);
 313         tangles.b  = fixmul(obj->mtype.phys_info.rotvel.z,FrameTime);
 314
 315         vm_angles_2_matrix(&rotmat,&tangles);
 316         vm_matrix_x_matrix(&new_orient,&obj->orient,&rotmat);
 317         obj->orient = new_orient;
 318
 319         if (obj->mtype.phys_info.flags & PF_TURNROLL)
 320                 set_object_turnroll(obj);
 321
 322         //re-rotate object for bank caused by turn
 323         if (obj->mtype.phys_info.turnroll) {
 324                 vms_matrix new_pm;
 325
 326                 tangles.p = tangles.h = 0;
 327                 tangles.b = obj->mtype.phys_info.turnroll;
 328                 vm_angles_2_matrix(&rotmat,&tangles);
 329                 vm_matrix_x_matrix(&new_pm,&obj->orient,&rotmat);
 330                 obj->orient = new_pm;
 331         }
 332
 333         check_and_fix_matrix(&obj->orient);
 334 }
 335
 336 //      -----------------------------------------------------------------------------------------------------------
 337 //Simulate a physics object for this frame
 338 void do_physics_sim(object *obj)
 339 {
 340         int ignore_obj_list[MAX_IGNORE_OBJS],n_ignore_objs;
 341         int iseg;
 342         int try_again;
 343         int fate;
 344         vms_vector frame_vec;                   //movement in this frame
 345         vms_vector new_pos,ipos;                //position after this frame
 346         int count=0;
 347         int objnum;
 348         int WallHitSeg, WallHitSide;
 349         fvi_info hit_info;
 350         fvi_query fq;
 351         vms_vector save_pos;
 352         int save_seg;
 353         fix drag;
 354         fix sim_time,old_sim_time;
 355         vms_vector start_pos;
 356         int obj_stopped=0;
 357         fix moved_time;                 //how long objected moved before hit something
 358         vms_vector save_p0,save_p1;
 359         physics_info *pi;
 360         int orig_segnum = obj->segnum;
 361         int bounced=0;
 362
 363         Assert(obj->type != OBJ_NONE);
 364         Assert(obj->movement_type == MT_PHYSICS);
 365
 366 #ifndef NDEBUG
 367 if (Dont_move_ai_objects)
 368         if (obj->control_type == CT_AI)
 369                 return;
 370 #endif
 371
 372         pi = &obj->mtype.phys_info;
 373
 374         do_physics_sim_rot(obj);
 375
 376         if (!(pi->velocity.x || pi->velocity.y || pi->velocity.z || pi->thrust.x || pi->thrust.y || pi->thrust.z))
 377                 return;
 378
 379         objnum = obj-Objects;
 380
 381         n_phys_segs = 0;
 382
 383         disable_new_fvi_stuff = (obj->type != OBJ_PLAYER);
 384
 385         sim_time = FrameTime;
 386
 387 //debug_obj = obj;
 388
 389         #ifdef EXTRA_DEBUG
 390         if (obj == debug_obj) {
 391                 printf("object %d:\n  start pos = %x %x %x\n",objnum,XYZ(&obj->pos));
 392                 printf("  thrust = %x %x %x\n",XYZ(&obj->mtype.phys_info.thrust));
 393                 printf("  sim_time = %x\n",sim_time);
 394         }
 395
 396         //check for correct object segment
 397         if(!get_seg_masks(&obj->pos,obj->segnum,0).centermask==0) {
 398                 #ifndef NDEBUG
 399                 mprintf((0,"Warning: object %d not in given seg!\n",objnum));
 400                 #endif
 401                 //Int3();  Removed by Rob 10/5/94
 402                 if (!update_object_seg(obj)) {
 403                         #ifndef NDEBUG
 404                         mprintf((0,"Warning: can't find seg for object %d - moving\n",objnum));
 405                         #endif
 406                         if (!(Game_mode & GM_MULTI))
 407                                 Int3();
 408                         compute_segment_center(&obj->pos,&Segments[obj->segnum]);
 409                         obj->pos.x += objnum;
 410                 }
 411         }
 412         #endif
 413
 414         start_pos = obj->pos;
 415
 416         n_ignore_objs = 0;
 417
 418         Assert(obj->mtype.phys_info.brakes==0);         //brakes not used anymore?
 419
 420                 //if uses thrust, cannot have zero drag
 421         Assert(!(obj->mtype.phys_info.flags&PF_USES_THRUST) || obj->mtype.phys_info.drag!=0);
 422
 423 //mprintf((0,"thrust=%x  speed=%x\n",vm_vec_mag(&obj->mtype.phys_info.thrust),vm_vec_mag(&obj->mtype.phys_info.velocity)));
 424
 425         //do thrust & drag
 426
 427         if ((drag = obj->mtype.phys_info.drag) != 0) {
 428
 429                 int count;
 430                 vms_vector accel;
 431                 fix r,k;
 432
 433                 count = sim_time / FT;
 434                 r = sim_time % FT;
 435                 k = fixdiv(r,FT);
 436
 437                 if (obj->mtype.phys_info.flags & PF_USES_THRUST) {
 438
 439                         vm_vec_copy_scale(&accel,&obj->mtype.phys_info.thrust,fixdiv(f1_0,obj->mtype.phys_info.mass));
 440
 441                         while (count--) {
 442
 443                                 vm_vec_add2(&obj->mtype.phys_info.velocity,&accel);
 444
 445                                 vm_vec_scale(&obj->mtype.phys_info.velocity,f1_0-drag);
 446                         }
 447
 448                         //do linear scale on remaining bit of time
 449
 450                         vm_vec_scale_add2(&obj->mtype.phys_info.velocity,&accel,k);
 451
 452                         vm_vec_scale(&obj->mtype.phys_info.velocity,f1_0-fixmul(k,drag));
 453                 }
 454                 else {
 455                         fix total_drag=f1_0;
 456
 457                         while (count--)
 458                                 total_drag = fixmul(total_drag,f1_0-drag);
 459
 460                         //do linear scale on remaining bit of time
 461
 462                         total_drag = fixmul(total_drag,f1_0-fixmul(k,drag));
 463
 464                         vm_vec_scale(&obj->mtype.phys_info.velocity,total_drag);
 465                 }
 466         }
 467
 468         #ifdef EXTRA_DEBUG
 469         if (obj == debug_obj)
 470                 printf("  velocity = %x %x %x\n",XYZ(&obj->mtype.phys_info.velocity));
 471         #endif
 472
 473         do {
 474                 try_again = 0;
 475
 476                 //Move the object
 477                 vm_vec_copy_scale(&frame_vec, &obj->mtype.phys_info.velocity, sim_time);
 478
 479                 #ifdef EXTRA_DEBUG
 480                 if (obj == debug_obj)
 481                         printf("  pass %d, frame_vec = %x %x %x\n",count,XYZ(&frame_vec));
 482                 #endif
 483
 484                 if ( (frame_vec.x==0) && (frame_vec.y==0) && (frame_vec.z==0) )
 485                         break;
 486
 487                 count++;
 488
 489                 //      If retry count is getting large, then we are trying to do something stupid.
 490                 if ( count > 3)         {
 491                         if (obj->type == OBJ_PLAYER) {
 492                                 if (count > 8)
 493                                         break;
 494                         } else
 495                                 break;
 496                 }
 497
 498                 vm_vec_add(&new_pos,&obj->pos,&frame_vec);
 499
 500                 #ifdef EXTRA_DEBUG
 501                 if (obj == debug_obj)
 502                         printf("   desired_pos  = %x %x %x\n",XYZ(&new_pos));
 503                 #endif
 504
 505                 ignore_obj_list[n_ignore_objs] = -1;
 506
 507                 #ifdef EXTRA_DEBUG
 508                 if (obj == debug_obj) {
 509                         printf("   FVI parms: p0 = %8x %8x %8x, segnum=%x, size=%x\n",XYZ(&obj->pos),obj->segnum,obj->size);
 510                         printf("              p1 = %8x %8x %8x\n",XYZ(&new_pos));
 511                 }
 512                 #endif
 513
 514                 fq.p0                                           = &obj->pos;
 515                 fq.startseg                             = obj->segnum;
 516                 fq.p1                                           = &new_pos;
 517                 fq.rad                                  = obj->size;
 518                 fq.thisobjnum                   = objnum;
 519                 fq.ignore_obj_list      = ignore_obj_list;
 520                 fq.flags                                        = FQ_CHECK_OBJS;
 521
 522                 if (obj->type == OBJ_WEAPON)
 523                         fq.flags |= FQ_TRANSPOINT;
 524
 525                 if (obj->type == OBJ_PLAYER)
 526                         fq.flags |= FQ_GET_SEGLIST;
 527
 528 //@@                    if (get_seg_masks(&obj->pos,obj->segnum,0).centermask!=0)
 529 //@@                            Int3();
 530
 531 save_p0 = *fq.p0;
 532 save_p1 = *fq.p1;
 533
 534
 535                 fate = find_vector_intersection(&fq,&hit_info);
 536                 //      Matt: Mike's hack.
 537                 if (fate == HIT_OBJECT) {
 538                         object  *objp = &Objects[hit_info.hit_object];
 539
 540                         if ((objp->type == OBJ_WEAPON) && ((objp->id == PROXIMITY_ID) || (objp->id == SUPERPROX_ID)))
 541                                 count--;
 542                 }
 543
 544                 #ifndef NDEBUG
 545                 if (fate == HIT_BAD_P0) {
 546                         mprintf((0,"Warning: Bad p0 in physics!  Object = %i, type = %i [%s]\n", obj-Objects, obj->type, Object_type_names[obj->type]));
 547                         Int3();
 548                 }
 549                 #endif
 550
 551                 if (obj->type == OBJ_PLAYER) {
 552                         int i;
 553
 554                         if (n_phys_segs && phys_seglist[n_phys_segs-1]==hit_info.seglist[0])
 555                                 n_phys_segs--;
 556
 557                         for (i=0;(i<hit_info.n_segs) && (n_phys_segs<MAX_FVI_SEGS-1);  )
 558                                 phys_seglist[n_phys_segs++] = hit_info.seglist[i++];
 559                 }
 560
 561                 #ifdef EXTRA_DEBUG
 562                 if (obj == debug_obj)
 563                         printf("   fate  = %d, hit_pnt = %8x %8x %8x\n",fate,XYZ(&hit_info.hit_pnt));;
 564                 #endif
 565
 566                 ipos = hit_info.hit_pnt;
 567                 iseg = hit_info.hit_seg;
 568                 WallHitSide = hit_info.hit_side;
 569                 WallHitSeg = hit_info.hit_side_seg;
 570
 571                 if (iseg==-1) {         //some sort of horrible error
 572                         #ifndef NDEBUG
 573                         mprintf((1,"iseg==-1 in physics!  Object = %i, type = %i (%s)\n", obj-Objects, obj->type, Object_type_names[obj->type]));
 574                         #endif
 575                         //Int3();
 576                         //compute_segment_center(&ipos,&Segments[obj->segnum]);
 577                         //ipos.x += objnum;
 578                         //iseg = obj->segnum;
 579                         //fate = HIT_NONE;
 580                         if (obj->type == OBJ_WEAPON)
 581                                 obj->flags |= OF_SHOULD_BE_DEAD;
 582                         break;
 583                 }
 584
 585                 Assert(!((fate==HIT_WALL) && ((WallHitSeg == -1) || (WallHitSeg > Highest_segment_index))));
 586
 587                 //if(!get_seg_masks(&hit_info.hit_pnt,hit_info.hit_seg,0).centermask==0)
 588                 //      Int3();
 589
 590                 save_pos = obj->pos;                    //save the object's position
 591                 save_seg = obj->segnum;
 592
 593                 // update object's position and segment number
 594                 obj->pos = ipos;
 595
 596                 #ifdef EXTRA_DEBUG
 597                 if (obj == debug_obj)
 598                         printf("   new pos = %x %x %x\n",XYZ(&obj->pos));
 599                 #endif
 600
 601                 if ( iseg != obj->segnum )
 602                         obj_relink(objnum, iseg );
 603
 604                 //if start point not in segment, move object to center of segment
 605                 if (get_seg_masks(&obj->pos,obj->segnum,0).centermask!=0) {
 606                         int n;
 607
 608                         if ((n=find_object_seg(obj))==-1) {
 609                                 //Int3();
 610                                 if (obj->type==OBJ_PLAYER && (n=find_point_seg(&obj->last_pos,obj->segnum))!=-1) {
 611                                         obj->pos = obj->last_pos;
 612                                         obj_relink(objnum, n );
 613                                 }
 614                                 else {
 615                                         compute_segment_center(&obj->pos,&Segments[obj->segnum]);
 616                                         obj->pos.x += objnum;
 617                                 }
 618                                 if (obj->type == OBJ_WEAPON)
 619                                         obj->flags |= OF_SHOULD_BE_DEAD;
 620                         }
 621                         return;
 622                 }
 623
 624                 //calulate new sim time
 625                 {
 626                         //vms_vector moved_vec;
 627                         vms_vector moved_vec_n;
 628                         fix attempted_dist,actual_dist;
 629
 630                         old_sim_time = sim_time;
 631
 632                         actual_dist = vm_vec_normalized_dir(&moved_vec_n,&obj->pos,&save_pos);
 633
 634                         if (fate==HIT_WALL && vm_vec_dot(&moved_vec_n,&frame_vec) < 0) {                //moved backwards
 635
 636                                 //don't change position or sim_time
 637
 638 //*******                                       mprintf((0,"Obj %d moved backwards\n",obj-Objects));
 639
 640                                 #ifdef EXTRA_DEBUG
 641                                 if (obj == debug_obj)
 642                                         printf("   Warning: moved backwards!\n");
 643                                 #endif
 644
 645                                 obj->pos = save_pos;
 646
 647                                 //iseg = obj->segnum;           //don't change segment
 648
 649                                 obj_relink(objnum, save_seg );
 650
 651                                 moved_time = 0;
 652                         }
 653                         else {
 654
 655                                 //if (obj == debug_obj)
 656                                 //      printf("   moved_vec = %x %x %x\n",XYZ(&moved_vec));
 657
 658                                 attempted_dist = vm_vec_mag(&frame_vec);
 659
 660                                 sim_time = fixmuldiv(sim_time,attempted_dist-actual_dist,attempted_dist);
 661
 662                                 moved_time = old_sim_time - sim_time;
 663
 664                                 if (sim_time < 0 || sim_time>old_sim_time) {
 665                                         #ifndef NDEBUG
 666                                         mprintf((0,"Bogus sim_time = %x, old = %x\n",sim_time,old_sim_time));
 667                                         if (obj == debug_obj)
 668                                                 printf("   Bogus sim_time = %x, old = %x, attempted_dist = %x, actual_dist = %x\n",sim_time,old_sim_time,attempted_dist,actual_dist);
 669                                         //Int3(); Removed by Rob
 670                                         #endif
 671                                         sim_time = old_sim_time;
 672                                         //WHY DOES THIS HAPPEN??
 673
 674                                         moved_time = 0;
 675                                 }
 676                         }
 677
 678                         #ifdef EXTRA_DEBUG
 679                         if (obj == debug_obj)
 680                                 printf("   new sim_time = %x\n",sim_time);
 681                         #endif
 682
 683                 }
 684
 685
 686                 switch( fate )          {
 687
 688                         case HIT_WALL:          {
 689                                 vms_vector moved_v;
 690                                 //@@fix total_d,moved_d;
 691                                 fix hit_speed,wall_part;
 692
 693                                 // Find hit speed
 694
 695                                 vm_vec_sub(&moved_v,&obj->pos,&save_pos);
 696
 697                                 wall_part = vm_vec_dot(&moved_v,&hit_info.hit_wallnorm);
 698
 699                                 if (wall_part != 0 && moved_time>0 && (hit_speed=-fixdiv(wall_part,moved_time))>0)
 700                                         collide_object_with_wall( obj, hit_speed, WallHitSeg, WallHitSide, &hit_info.hit_pnt );
 701                                 else
 702                                         scrape_object_on_wall(obj, WallHitSeg, WallHitSide, &hit_info.hit_pnt );
 703
 704                                 Assert( WallHitSeg > -1 );
 705                                 Assert( WallHitSide > -1 );
 706
 707                                 if ( !(obj->flags&OF_SHOULD_BE_DEAD) )  {
 708                                         int forcefield_bounce;          //bounce off a forcefield
 709
 710                                         Assert(BounceCheat || !(obj->mtype.phys_info.flags & PF_STICK && obj->mtype.phys_info.flags & PF_BOUNCE));      //can't be bounce and stick
 711
 712                                         forcefield_bounce = (TmapInfo[Segments[WallHitSeg].sides[WallHitSide].tmap_num].flags & TMI_FORCE_FIELD);
 713
 714                                         if (!forcefield_bounce && (obj->mtype.phys_info.flags & PF_STICK)) {            //stop moving
 715
 716                                                 // mprintf((0, "Object %i stuck at %i:%i\n", obj-Objects, WallHitSeg, WallHitSide));
 717                                                 add_stuck_object(obj, WallHitSeg, WallHitSide);
 718
 719                                                 vm_vec_zero(&obj->mtype.phys_info.velocity);
 720                                                 obj_stopped = 1;
 721                                                 try_again = 0;
 722                                         }
 723                                         else {                                  // Slide object along wall
 724                                                 int check_vel=0;
 725
 726                                                 //We're constrained by wall, so subtract wall part from
 727                                                 //velocity vector
 728
 729                                                 wall_part = vm_vec_dot(&hit_info.hit_wallnorm,&obj->mtype.phys_info.velocity);
 730
 731 //                                              mprintf((0, "%d", f2i(vm_vec_mag(&hit_info.hit_wallnorm)) ));
 732
 733                                                 if (forcefield_bounce || (obj->mtype.phys_info.flags & PF_BOUNCE)) {            //bounce off wall
 734                                                         wall_part *= 2; //Subtract out wall part twice to achieve bounce
 735
 736                                                         if (forcefield_bounce) {
 737                                                                 check_vel = 1;                          //check for max velocity
 738                                                                 if (obj->type == OBJ_PLAYER)
 739                                                                         wall_part *= 2;         //player bounce twice as much
 740                                                         }
 741
 742                                                         if ( obj->mtype.phys_info.flags & PF_BOUNCES_TWICE) {
 743                                                                 Assert(obj->mtype.phys_info.flags & PF_BOUNCE);
 744                                                                 if (obj->mtype.phys_info.flags & PF_BOUNCED_ONCE)
 745                                                                         obj->mtype.phys_info.flags &= ~(PF_BOUNCE+PF_BOUNCED_ONCE+PF_BOUNCES_TWICE);
 746                                                                 else
 747                                                                         obj->mtype.phys_info.flags |= PF_BOUNCED_ONCE;
 748                                                         }
 749
 750                                                         bounced = 1;            //this object bounced
 751                                                 }
 752
 753                                                 vm_vec_scale_add2(&obj->mtype.phys_info.velocity,&hit_info.hit_wallnorm,-wall_part);
 754
 755 //                                              mprintf((0, "Velocity at bounce time = %d\n", f2i(vm_vec_mag(&obj->mtype.phys_info.velocity))));
 756
 757 //if (obj==ConsoleObject)
 758 //      mprintf((0,"player vel = %x\n",vm_vec_mag_quick(&obj->mtype.phys_info.velocity)));
 759
 760                                                 if (check_vel) {
 761                                                         fix vel = vm_vec_mag_quick(&obj->mtype.phys_info.velocity);
 762
 763                                                         if (vel > MAX_OBJECT_VEL)
 764                                                                 vm_vec_scale(&obj->mtype.phys_info.velocity,fixdiv(MAX_OBJECT_VEL,vel));
 765                                                 }
 766
 767                                                 if (bounced && obj->type == OBJ_WEAPON)
 768                                                         vm_vector_2_matrix(&obj->orient,&obj->mtype.phys_info.velocity,&obj->orient.uvec,NULL);
 769
 770                                                 #ifdef EXTRA_DEBUG
 771                                                 if (obj == debug_obj) {
 772                                                         printf("   sliding - wall_norm %x %x %x %x\n",wall_part,XYZ(&hit_info.hit_wallnorm));
 773                                                         printf("   wall_part %x, new velocity = %x %x %x\n",wall_part,XYZ(&obj->mtype.phys_info.velocity));
 774                                                 }
 775                                                 #endif
 776
 777                                                 try_again = 1;
 778                                         }
 779                                 }
 780                                 break;
 781                         }
 782
 783                         case HIT_OBJECT:                {
 784                                 vms_vector old_vel;
 785
 786                                 // Mark the hit object so that on a retry the fvi code
 787                                 // ignores this object.
 788
 789                                 Assert(hit_info.hit_object != -1);
 790
 791                                 //      Calculcate the hit point between the two objects.
 792                                 {       vms_vector      *ppos0, *ppos1, pos_hit;
 793                                         fix                     size0, size1;
 794                                         ppos0 = &Objects[hit_info.hit_object].pos;
 795                                         ppos1 = &obj->pos;
 796                                         size0 = Objects[hit_info.hit_object].size;
 797                                         size1 = obj->size;
 798                                         Assert(size0+size1 != 0);       // Error, both sizes are 0, so how did they collide, anyway?!?
 799                                         //vm_vec_scale(vm_vec_sub(&pos_hit, ppos1, ppos0), fixdiv(size0, size0 + size1));
 800                                         //vm_vec_add2(&pos_hit, ppos0);
 801                                         vm_vec_sub(&pos_hit, ppos1, ppos0);
 802                                         vm_vec_scale_add(&pos_hit,ppos0,&pos_hit,fixdiv(size0, size0 + size1));
 803
 804                                         old_vel = obj->mtype.phys_info.velocity;
 805
 806                                         collide_two_objects( obj, &Objects[hit_info.hit_object], &pos_hit);
 807
 808                                 }
 809
 810                                 // Let object continue its movement
 811                                 if ( !(obj->flags&OF_SHOULD_BE_DEAD)  ) {
 812                                         //obj->pos = save_pos;
 813
 814                                         if (obj->mtype.phys_info.flags&PF_PERSISTENT || (old_vel.x == obj->mtype.phys_info.velocity.x && old_vel.y == obj->mtype.phys_info.velocity.y && old_vel.z == obj->mtype.phys_info.velocity.z)) {
 815                                                 //if (Objects[hit_info.hit_object].type == OBJ_POWERUP)
 816                                                         ignore_obj_list[n_ignore_objs++] = hit_info.hit_object;
 817                                                 try_again = 1;
 818                                         }
 819                                 }
 820
 821                                 break;
 822                         }
 823                         case HIT_NONE:
 824                         #ifdef TACTILE
 825                                 if (TactileStick && obj==ConsoleObject && !(FrameCount & 15))
 826                                  Tactile_Xvibrate_clear ();
 827                         #endif
 828                                 break;
 829
 830                         #ifndef NDEBUG
 831                         case HIT_BAD_P0:
 832                                 Int3();         // Unexpected collision type: start point not in specified segment.
 833                                 mprintf((0,"Warning: Bad p0 in physics!!!\n"));
 834                                 break;
 835                         default:
 836                                 // Unknown collision type returned from find_vector_intersection!!
 837                                 Int3();
 838                                 break;
 839                         #endif
 840                 }
 841
 842         } while ( try_again );
 843
 844         //      Pass retry count info to AI.
 845         if (obj->control_type == CT_AI) {
 846                 if (count > 0) {
 847                         Ai_local_info[objnum].retry_count = count-1;
 848                         #ifndef NDEBUG
 849                         Total_retries += count-1;
 850                         Total_sims++;
 851                         #endif
 852                 }
 853         }
 854
 855         //I'm not sure why we do this.  I wish there were a comment that
 856         //explained it.  I think maybe it only needs to be done if the object
 857         //is sliding, but I don't know
 858         if (!obj_stopped && !bounced)   {       //Set velocity from actual movement
 859                 vms_vector moved_vec;
 860
 861                 vm_vec_sub(&moved_vec,&obj->pos,&start_pos);
 862                 vm_vec_copy_scale(&obj->mtype.phys_info.velocity,&moved_vec,fixdiv(f1_0,FrameTime));
 863
 864                 #ifdef BUMP_HACK
 865                 if (obj==ConsoleObject && (obj->mtype.phys_info.velocity.x==0 && obj->mtype.phys_info.velocity.y==0 && obj->mtype.phys_info.velocity.z==0) &&
 866                           !(obj->mtype.phys_info.thrust.x==0 && obj->mtype.phys_info.thrust.y==0 && obj->mtype.phys_info.thrust.z==0)) {
 867                         vms_vector center,bump_vec;
 868
 869                         //bump player a little towards center of segment to unstick
 870
 871                         compute_segment_center(&center,&Segments[obj->segnum]);
 872                         vm_vec_normalized_dir_quick(&bump_vec,&center,&obj->pos);
 873
 874                         //don't bump player toward center of reactor segment
 875                         if (Segment2s[obj->segnum].special == SEGMENT_IS_CONTROLCEN)
 876                                 vm_vec_negate(&bump_vec);
 877
 878                         vm_vec_scale_add2(&obj->pos,&bump_vec,obj->size/5);
 879
 880                         //if moving away from seg, might move out of seg, so update
 881                         if (Segment2s[obj->segnum].special == SEGMENT_IS_CONTROLCEN)
 882                                 update_object_seg(obj);
 883                 }
 884                 #endif
 885         }
 886
 887         //Assert(check_point_in_seg(&obj->pos,obj->segnum,0).centermask==0);
 888
 889         //if (obj->control_type == CT_FLYING)
 890         if (obj->mtype.phys_info.flags & PF_LEVELLING)
 891                 do_physics_align_object( obj );
 892
 893
 894         //hack to keep player from going through closed doors
 895         if (obj->type==OBJ_PLAYER && obj->segnum!=orig_segnum && (Physics_cheat_flag!=0xBADA55) ) {
 896                 int sidenum;
 897
 898                 sidenum = find_connect_side(&Segments[obj->segnum],&Segments[orig_segnum]);
 899
 900                 if (sidenum != -1) {
 901
 902                         if (! (WALL_IS_DOORWAY(&Segments[orig_segnum],sidenum) & WID_FLY_FLAG)) {
 903                                 side *s;
 904                                 int vertnum,num_faces,i;
 905                                 fix dist;
 906                                 int vertex_list[6];
 907
 908                                 //bump object back
 909
 910                                 s = &Segments[orig_segnum].sides[sidenum];
 911
 912                                 if (orig_segnum==-1)
 913                                         Error("orig_segnum == -1 in physics");
 914
 915                                 create_abs_vertex_lists( &num_faces, vertex_list, orig_segnum, sidenum);
 916
 917                                 //let's pretend this wall is not triangulated
 918                                 vertnum = vertex_list[0];
 919                                 for (i=1;i<4;i++)
 920                                         if (vertex_list[i] < vertnum)
 921                                                 vertnum = vertex_list[i];
 922
 923                                 #ifdef COMPACT_SEGS
 924                                         {
 925                                         vms_vector _vn;
 926                                         get_side_normal(&Segments[orig_segnum], sidenum, 0, &_vn );
 927                                         dist = vm_dist_to_plane(&start_pos, &_vn, &Vertices[vertnum]);
 928                                         vm_vec_scale_add(&obj->pos,&start_pos,&_vn,obj->size-dist);
 929                                         }
 930                                 #else
 931                                         dist = vm_dist_to_plane(&start_pos, &s->normals[0], &Vertices[vertnum]);
 932                                         vm_vec_scale_add(&obj->pos,&start_pos,&s->normals[0],obj->size-dist);
 933                                 #endif
 934                                 update_object_seg(obj);
 935
 936                         }
 937                 }
 938         }
 939
 940 //--WE ALWYS WANT THIS IN, MATT AND MIKE DECISION ON 12/10/94, TWO MONTHS AFTER FINAL   #ifndef NDEBUG
 941         //if end point not in segment, move object to last pos, or segment center
 942         if (get_seg_masks(&obj->pos,obj->segnum,0).centermask!=0) {
 943                 if (find_object_seg(obj)==-1) {
 944                         int n;
 945
 946                         //Int3();
 947                         if (obj->type==OBJ_PLAYER && (n=find_point_seg(&obj->last_pos,obj->segnum))!=-1) {
 948                                 obj->pos = obj->last_pos;
 949                                 obj_relink(objnum, n );
 950                         }
 951                         else {
 952                                 compute_segment_center(&obj->pos,&Segments[obj->segnum]);
 953                                 obj->pos.x += objnum;
 954                         }
 955                         if (obj->type == OBJ_WEAPON)
 956                                 obj->flags |= OF_SHOULD_BE_DEAD;
 957                 }
 958         }
 959 //--WE ALWYS WANT THIS IN, MATT AND MIKE DECISION ON 12/10/94, TWO MONTHS AFTER FINAL   #endif
 960
 961
 962 }
 963
 964 //--unused-- //tell us what the given object will do (as far as hiting walls) in
 965 //--unused-- //the given time (in seconds) t.  Igores acceleration (sorry)
 966 //--unused-- //if check_objects is set, check with objects, else just with walls
 967 //--unused-- //returns fate, fills in hit time.  If fate==HIT_NONE, hit_time undefined
 968 //--unused-- int physics_lookahead(object *obj,fix t,int fvi_flags,fix *hit_time, fvi_info *hit_info)
 969 //--unused-- {
 970 //--unused--    vms_vector new_pos;
 971 //--unused--    int objnum,fate;
 972 //--unused--    fvi_query fq;
 973 //--unused--
 974 //--unused--    Assert(obj->movement_type == MT_PHYSICS);
 975 //--unused--
 976 //--unused--    objnum = obj-Objects;
 977 //--unused--
 978 //--unused--    vm_vec_scale_add(&new_pos, &obj->pos, &obj->mtype.phys_info.velocity, t);
 979 //--unused--
 980 //--unused--    fq.p0                                           = &obj->pos;
 981 //--unused--    fq.startseg                             = obj->segnum;
 982 //--unused--    fq.p1                                           = &new_pos;
 983 //--unused--    fq.rad                                  = obj->size;
 984 //--unused--    fq.thisobjnum                   = objnum;
 985 //--unused--    fq.ignore_obj_list      = NULL;
 986 //--unused--    fq.flags                                        = fvi_flags;
 987 //--unused--
 988 //--unused--    fate = find_vector_intersection(&fq,hit_info);
 989 //--unused--
 990 //--unused--    if (fate != HIT_NONE) {
 991 //--unused--            fix dist,speed;
 992 //--unused--
 993 //--unused--            dist = vm_vec_dist(&obj->pos, &hit_info->hit_pnt);
 994 //--unused--
 995 //--unused--            speed = vm_vec_mag(&obj->mtype.phys_info.velocity);
 996 //--unused--
 997 //--unused--            *hit_time = fixdiv(dist,speed);
 998 //--unused--
 999 //--unused--    }
1000 //--unused--
1001 //--unused--    return fate;
1002 //--unused--
1003 //--unused-- }
1004
1005 //Applies an instantaneous force on an object, resulting in an instantaneous
1006 //change in velocity.
1007 void phys_apply_force(object *obj,vms_vector *force_vec)
1008 {
1009
1010         //      Put in by MK on 2/13/96 for force getting applied to Omega blobs, which have 0 mass,
1011         //      in collision with crazy reactor robot thing on d2levf-s.
1012         if (obj->mtype.phys_info.mass == 0)
1013                 return;
1014
1015         if (obj->movement_type != MT_PHYSICS)
1016                 return;
1017
1018 #ifdef TACTILE
1019    if (TactileStick && obj==&Objects[Players[Player_num].objnum])
1020                 Tactile_apply_force (force_vec,&obj->orient);
1021 #endif
1022
1023         //Add in acceleration due to force
1024         vm_vec_scale_add2(&obj->mtype.phys_info.velocity,force_vec,fixdiv(f1_0,obj->mtype.phys_info.mass));
1025
1026
1027 }
1028
1029 //      ----------------------------------------------------------------
1030 //      Do *dest = *delta unless:
1031 //                              *delta is pretty small
1032 //              and     they are of different signs.
1033 void physics_set_rotvel_and_saturate(fix *dest, fix delta)
1034 {
1035         if ((delta ^ *dest) < 0) {
1036                 if (abs(delta) < F1_0/8) {
1037                         // mprintf((0, "D"));
1038                         *dest = delta/4;
1039                 } else
1040                         // mprintf((0, "d"));
1041                         *dest = delta;
1042         } else {
1043                 // mprintf((0, "!"));
1044                 *dest = delta;
1045         }
1046 }
1047
1048 //      ------------------------------------------------------------------------------------------------------
1049 //      Note: This is the old ai_turn_towards_vector code.
1050 //      phys_apply_rot used to call ai_turn_towards_vector until I fixed it, which broke phys_apply_rot.
1051 void physics_turn_towards_vector(vms_vector *goal_vector, object *obj, fix rate)
1052 {
1053         vms_angvec      dest_angles, cur_angles;
1054         fix                     delta_p, delta_h;
1055         vms_vector      *rotvel_ptr = &obj->mtype.phys_info.rotvel;
1056
1057         // Make this object turn towards the goal_vector.  Changes orientation, doesn't change direction of movement.
1058         // If no one moves, will be facing goal_vector in 1 second.
1059
1060         //      Detect null vector.
1061         if ((goal_vector->x == 0) && (goal_vector->y == 0) && (goal_vector->z == 0))
1062                 return;
1063
1064         //      Make morph objects turn more slowly.
1065         if (obj->control_type == CT_MORPH)
1066                 rate *= 2;
1067
1068         vm_extract_angles_vector(&dest_angles, goal_vector);
1069         vm_extract_angles_vector(&cur_angles, &obj->orient.fvec);
1070
1071         delta_p = (dest_angles.p - cur_angles.p);
1072         delta_h = (dest_angles.h - cur_angles.h);
1073
1074         if (delta_p > F1_0/2) delta_p = dest_angles.p - cur_angles.p - F1_0;
1075         if (delta_p < -F1_0/2) delta_p = dest_angles.p - cur_angles.p + F1_0;
1076         if (delta_h > F1_0/2) delta_h = dest_angles.h - cur_angles.h - F1_0;
1077         if (delta_h < -F1_0/2) delta_h = dest_angles.h - cur_angles.h + F1_0;
1078
1079         delta_p = fixdiv(delta_p, rate);
1080         delta_h = fixdiv(delta_h, rate);
1081
1082         if (abs(delta_p) < F1_0/16) delta_p *= 4;
1083         if (abs(delta_h) < F1_0/16) delta_h *= 4;
1084
1085         physics_set_rotvel_and_saturate(&rotvel_ptr->x, delta_p);
1086         physics_set_rotvel_and_saturate(&rotvel_ptr->y, delta_h);
1087         rotvel_ptr->z = 0;
1088 }
1089
1090 //      -----------------------------------------------------------------------------
1091 //      Applies an instantaneous whack on an object, resulting in an instantaneous
1092 //      change in orientation.
1093 void phys_apply_rot(object *obj,vms_vector *force_vec)
1094 {
1095         fix     rate, vecmag;
1096
1097         if (obj->movement_type != MT_PHYSICS)
1098                 return;
1099
1100         vecmag = vm_vec_mag(force_vec)/8;
1101         if (vecmag < F1_0/256)
1102                 rate = 4*F1_0;
1103         else if (vecmag < obj->mtype.phys_info.mass >> 14)
1104                 rate = 4*F1_0;
1105         else {
1106                 rate = fixdiv(obj->mtype.phys_info.mass, vecmag);
1107                 if (obj->type == OBJ_ROBOT) {
1108                         if (rate < F1_0/4)
1109                                 rate = F1_0/4;
1110                         //      Changed by mk, 10/24/95, claw guys should not slow down when attacking!
1111                         if (!Robot_info[obj->id].thief && !Robot_info[obj->id].attack_type) {
1112                                 if (obj->ctype.ai_info.SKIP_AI_COUNT * FrameTime < 3*F1_0/4) {
1113                                         fix     tval = fixdiv(F1_0, 8*FrameTime);
1114                                         int     addval;
1115
1116                                         addval = f2i(tval);
1117
1118                                         if ( (d_rand() * 2) < (tval & 0xffff))
1119                                                 addval++;
1120                                         obj->ctype.ai_info.SKIP_AI_COUNT += addval;
1121                                         // -- mk: too much stuff making hard to see my debug messages...mprintf((0, "FrameTime = %7.3f, addval = %i\n", f2fl(FrameTime), addval));
1122                                 }
1123                         }
1124                 } else {
1125                         if (rate < F1_0/2)
1126                                 rate = F1_0/2;
1127                 }
1128         }
1129
1130         //      Turn amount inversely proportional to mass.  Third parameter is seconds to do 360 turn.
1131         physics_turn_towards_vector(force_vec, obj, rate);
1132
1133
1134 }
1135
1136
1137 //this routine will set the thrust for an object to a value that will
1138 //(hopefully) maintain the object's current velocity
1139 void set_thrust_from_velocity(object *obj)
1140 {
1141         fix k;
1142
1143         Assert(obj->movement_type == MT_PHYSICS);
1144
1145         k = fixmuldiv(obj->mtype.phys_info.mass,obj->mtype.phys_info.drag,(f1_0-obj->mtype.phys_info.drag));
1146
1147         vm_vec_copy_scale(&obj->mtype.phys_info.thrust,&obj->mtype.phys_info.velocity,k);
1148
1149 }
1150
1151