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