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