src/collision.cpp

   1 /*
   2 Minetest
   3 Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
   4
   5 This program is free software; you can redistribute it and/or modify
   6 it under the terms of the GNU Lesser General Public License as published by
   7 the Free Software Foundation; either version 2.1 of the License, or
   8 (at your option) any later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU Lesser General Public License for more details.
  14
  15 You should have received a copy of the GNU Lesser General Public License along
  16 with this program; if not, write to the Free Software Foundation, Inc.,
  17 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #include "collision.h"
  21 #include "mapblock.h"
  22 #include "map.h"
  23 #include "nodedef.h"
  24 #include "gamedef.h"
  25 #include "log.h"
  26 #include "environment.h"
  27 #include "serverobject.h"
  28 #include <vector>
  29 #include <set>
  30 #include "util/timetaker.h"
  31 #include "main.h" // g_profiler
  32 #include "profiler.h"
  33
  34 // float error is 10 - 9.96875 = 0.03125
  35 //#define COLL_ZERO 0.032 // broken unit tests
  36 #define COLL_ZERO 0
  37
  38 // Helper function:
  39 // Checks for collision of a moving aabbox with a static aabbox
  40 // Returns -1 if no collision, 0 if X collision, 1 if Y collision, 2 if Z collision
  41 // The time after which the collision occurs is stored in dtime.
  42 int axisAlignedCollision(
  43                 const aabb3f &staticbox, const aabb3f &movingbox,
  44                 const v3f &speed, f32 d, f32 &dtime)
  45 {
  46         //TimeTaker tt("axisAlignedCollision");
  47
  48         f32 xsize = (staticbox.MaxEdge.X - staticbox.MinEdge.X) - COLL_ZERO;     // reduce box size for solve collision stuck (flying sand)
  49         f32 ysize = (staticbox.MaxEdge.Y - staticbox.MinEdge.Y); // - COLL_ZERO; // Y - no sense for falling, but maybe try later
  50         f32 zsize = (staticbox.MaxEdge.Z - staticbox.MinEdge.Z) - COLL_ZERO;
  51
  52         aabb3f relbox(
  53                         movingbox.MinEdge.X - staticbox.MinEdge.X,
  54                         movingbox.MinEdge.Y - staticbox.MinEdge.Y,
  55                         movingbox.MinEdge.Z - staticbox.MinEdge.Z,
  56                         movingbox.MaxEdge.X - staticbox.MinEdge.X,
  57                         movingbox.MaxEdge.Y - staticbox.MinEdge.Y,
  58                         movingbox.MaxEdge.Z - staticbox.MinEdge.Z
  59         );
  60
  61         if(speed.X > 0) // Check for collision with X- plane
  62         {
  63                 if(relbox.MaxEdge.X <= d)
  64                 {
  65                         dtime = - relbox.MaxEdge.X / speed.X;
  66                         if((relbox.MinEdge.Y + speed.Y * dtime < ysize) &&
  67                                         (relbox.MaxEdge.Y + speed.Y * dtime > COLL_ZERO) &&
  68                                         (relbox.MinEdge.Z + speed.Z * dtime < zsize) &&
  69                                         (relbox.MaxEdge.Z + speed.Z * dtime > COLL_ZERO))
  70                                 return 0;
  71                 }
  72                 else if(relbox.MinEdge.X > xsize)
  73                 {
  74                         return -1;
  75                 }
  76         }
  77         else if(speed.X < 0) // Check for collision with X+ plane
  78         {
  79                 if(relbox.MinEdge.X >= xsize - d)
  80                 {
  81                         dtime = (xsize - relbox.MinEdge.X) / speed.X;
  82                         if((relbox.MinEdge.Y + speed.Y * dtime < ysize) &&
  83                                         (relbox.MaxEdge.Y + speed.Y * dtime > COLL_ZERO) &&
  84                                         (relbox.MinEdge.Z + speed.Z * dtime < zsize) &&
  85                                         (relbox.MaxEdge.Z + speed.Z * dtime > COLL_ZERO))
  86                                 return 0;
  87                 }
  88                 else if(relbox.MaxEdge.X < 0)
  89                 {
  90                         return -1;
  91                 }
  92         }
  93
  94         // NO else if here
  95
  96         if(speed.Y > 0) // Check for collision with Y- plane
  97         {
  98                 if(relbox.MaxEdge.Y <= d)
  99                 {
 100                         dtime = - relbox.MaxEdge.Y / speed.Y;
 101                         if((relbox.MinEdge.X + speed.X * dtime < xsize) &&
 102                                         (relbox.MaxEdge.X + speed.X * dtime > COLL_ZERO) &&
 103                                         (relbox.MinEdge.Z + speed.Z * dtime < zsize) &&
 104                                         (relbox.MaxEdge.Z + speed.Z * dtime > COLL_ZERO))
 105                                 return 1;
 106                 }
 107                 else if(relbox.MinEdge.Y > ysize)
 108                 {
 109                         return -1;
 110                 }
 111         }
 112         else if(speed.Y < 0) // Check for collision with Y+ plane
 113         {
 114                 if(relbox.MinEdge.Y >= ysize - d)
 115                 {
 116                         dtime = (ysize - relbox.MinEdge.Y) / speed.Y;
 117                         if((relbox.MinEdge.X + speed.X * dtime < xsize) &&
 118                                         (relbox.MaxEdge.X + speed.X * dtime > COLL_ZERO) &&
 119                                         (relbox.MinEdge.Z + speed.Z * dtime < zsize) &&
 120                                         (relbox.MaxEdge.Z + speed.Z * dtime > COLL_ZERO))
 121                                 return 1;
 122                 }
 123                 else if(relbox.MaxEdge.Y < 0)
 124                 {
 125                         return -1;
 126                 }
 127         }
 128
 129         // NO else if here
 130
 131         if(speed.Z > 0) // Check for collision with Z- plane
 132         {
 133                 if(relbox.MaxEdge.Z <= d)
 134                 {
 135                         dtime = - relbox.MaxEdge.Z / speed.Z;
 136                         if((relbox.MinEdge.X + speed.X * dtime < xsize) &&
 137                                         (relbox.MaxEdge.X + speed.X * dtime > COLL_ZERO) &&
 138                                         (relbox.MinEdge.Y + speed.Y * dtime < ysize) &&
 139                                         (relbox.MaxEdge.Y + speed.Y * dtime > COLL_ZERO))
 140                                 return 2;
 141                 }
 142                 //else if(relbox.MinEdge.Z > zsize)
 143                 //{
 144                 //      return -1;
 145                 //}
 146         }
 147         else if(speed.Z < 0) // Check for collision with Z+ plane
 148         {
 149                 if(relbox.MinEdge.Z >= zsize - d)
 150                 {
 151                         dtime = (zsize - relbox.MinEdge.Z) / speed.Z;
 152                         if((relbox.MinEdge.X + speed.X * dtime < xsize) &&
 153                                         (relbox.MaxEdge.X + speed.X * dtime > COLL_ZERO) &&
 154                                         (relbox.MinEdge.Y + speed.Y * dtime < ysize) &&
 155                                         (relbox.MaxEdge.Y + speed.Y * dtime > COLL_ZERO))
 156                                 return 2;
 157                 }
 158                 //else if(relbox.MaxEdge.Z < 0)
 159                 //{
 160                 //      return -1;
 161                 //}
 162         }
 163
 164         return -1;
 165 }
 166
 167 // Helper function:
 168 // Checks if moving the movingbox up by the given distance would hit a ceiling.
 169 bool wouldCollideWithCeiling(
 170                 const std::vector<aabb3f> &staticboxes,
 171                 const aabb3f &movingbox,
 172                 f32 y_increase, f32 d)
 173 {
 174         //TimeTaker tt("wouldCollideWithCeiling");
 175
 176         assert(y_increase >= 0);        // pre-condition
 177
 178         for(std::vector<aabb3f>::const_iterator
 179                         i = staticboxes.begin();
 180                         i != staticboxes.end(); i++)
 181         {
 182                 const aabb3f& staticbox = *i;
 183                 if((movingbox.MaxEdge.Y - d <= staticbox.MinEdge.Y) &&
 184                                 (movingbox.MaxEdge.Y + y_increase > staticbox.MinEdge.Y) &&
 185                                 (movingbox.MinEdge.X < staticbox.MaxEdge.X) &&
 186                                 (movingbox.MaxEdge.X > staticbox.MinEdge.X) &&
 187                                 (movingbox.MinEdge.Z < staticbox.MaxEdge.Z) &&
 188                                 (movingbox.MaxEdge.Z > staticbox.MinEdge.Z))
 189                         return true;
 190         }
 191
 192         return false;
 193 }
 194
 195
 196 collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 197                 f32 pos_max_d, const aabb3f &box_0,
 198                 f32 stepheight, f32 dtime,
 199                 v3f &pos_f, v3f &speed_f,
 200                 v3f &accel_f,ActiveObject* self,
 201                 bool collideWithObjects)
 202 {
 203         Map *map = &env->getMap();
 204         //TimeTaker tt("collisionMoveSimple");
 205     ScopeProfiler sp(g_profiler, "collisionMoveSimple avg", SPT_AVG);
 206
 207         collisionMoveResult result;
 208
 209         /*
 210                 Calculate new velocity
 211         */
 212         if( dtime > 0.5 ) {
 213                 infostream<<"collisionMoveSimple: WARNING: maximum step interval exceeded, lost movement details!"<<std::endl;
 214                 dtime = 0.5;
 215         }
 216         speed_f += accel_f * dtime;
 217
 218         // If there is no speed, there are no collisions
 219         if(speed_f.getLength() == 0)
 220                 return result;
 221
 222         // Limit speed for avoiding hangs
 223         speed_f.Y=rangelim(speed_f.Y,-5000,5000);
 224         speed_f.X=rangelim(speed_f.X,-5000,5000);
 225         speed_f.Z=rangelim(speed_f.Z,-5000,5000);
 226
 227         /*
 228                 Collect node boxes in movement range
 229         */
 230         std::vector<aabb3f> cboxes;
 231         std::vector<bool> is_unloaded;
 232         std::vector<bool> is_step_up;
 233         std::vector<bool> is_object;
 234         std::vector<int> bouncy_values;
 235         std::vector<v3s16> node_positions;
 236         {
 237         //TimeTaker tt2("collisionMoveSimple collect boxes");
 238     ScopeProfiler sp(g_profiler, "collisionMoveSimple collect boxes avg", SPT_AVG);
 239
 240         v3s16 oldpos_i = floatToInt(pos_f, BS);
 241         v3s16 newpos_i = floatToInt(pos_f + speed_f * dtime, BS);
 242         s16 min_x = MYMIN(oldpos_i.X, newpos_i.X) + (box_0.MinEdge.X / BS) - 1;
 243         s16 min_y = MYMIN(oldpos_i.Y, newpos_i.Y) + (box_0.MinEdge.Y / BS) - 1;
 244         s16 min_z = MYMIN(oldpos_i.Z, newpos_i.Z) + (box_0.MinEdge.Z / BS) - 1;
 245         s16 max_x = MYMAX(oldpos_i.X, newpos_i.X) + (box_0.MaxEdge.X / BS) + 1;
 246         s16 max_y = MYMAX(oldpos_i.Y, newpos_i.Y) + (box_0.MaxEdge.Y / BS) + 1;
 247         s16 max_z = MYMAX(oldpos_i.Z, newpos_i.Z) + (box_0.MaxEdge.Z / BS) + 1;
 248
 249         for(s16 x = min_x; x <= max_x; x++)
 250         for(s16 y = min_y; y <= max_y; y++)
 251         for(s16 z = min_z; z <= max_z; z++)
 252         {
 253                 v3s16 p(x,y,z);
 254
 255                 bool is_position_valid;
 256                 MapNode n = map->getNodeNoEx(p, &is_position_valid);
 257
 258                 if (is_position_valid) {
 259                         // Object collides into walkable nodes
 260
 261                         const ContentFeatures &f = gamedef->getNodeDefManager()->get(n);
 262                         if(f.walkable == false)
 263                                 continue;
 264                         int n_bouncy_value = itemgroup_get(f.groups, "bouncy");
 265
 266                         std::vector<aabb3f> nodeboxes = n.getCollisionBoxes(gamedef->ndef());
 267                         for(std::vector<aabb3f>::iterator
 268                                         i = nodeboxes.begin();
 269                                         i != nodeboxes.end(); i++)
 270                         {
 271                                 aabb3f box = *i;
 272                                 box.MinEdge += v3f(x, y, z)*BS;
 273                                 box.MaxEdge += v3f(x, y, z)*BS;
 274                                 cboxes.push_back(box);
 275                                 is_unloaded.push_back(false);
 276                                 is_step_up.push_back(false);
 277                                 bouncy_values.push_back(n_bouncy_value);
 278                                 node_positions.push_back(p);
 279                                 is_object.push_back(false);
 280                         }
 281                 }
 282                 else {
 283                         // Collide with unloaded nodes
 284                         aabb3f box = getNodeBox(p, BS);
 285                         cboxes.push_back(box);
 286                         is_unloaded.push_back(true);
 287                         is_step_up.push_back(false);
 288                         bouncy_values.push_back(0);
 289                         node_positions.push_back(p);
 290                         is_object.push_back(false);
 291                 }
 292         }
 293         } // tt2
 294
 295         if(collideWithObjects)
 296         {
 297                 ScopeProfiler sp(g_profiler, "collisionMoveSimple objects avg", SPT_AVG);
 298                 //TimeTaker tt3("collisionMoveSimple collect object boxes");
 299
 300                 /* add object boxes to cboxes */
 301
 302
 303                 std::vector<ActiveObject*> objects;
 304 #ifndef SERVER
 305                 ClientEnvironment *c_env = dynamic_cast<ClientEnvironment*>(env);
 306                 if (c_env != 0) {
 307                         f32 distance = speed_f.getLength();
 308                         std::vector<DistanceSortedActiveObject> clientobjects;
 309                         c_env->getActiveObjects(pos_f,distance * 1.5,clientobjects);
 310                         for (size_t i=0; i < clientobjects.size(); i++) {
 311                                 if ((self == 0) || (self != clientobjects[i].obj)) {
 312                                         objects.push_back((ActiveObject*)clientobjects[i].obj);
 313                                 }
 314                         }
 315                 }
 316                 else
 317 #endif
 318                 {
 319                         ServerEnvironment *s_env = dynamic_cast<ServerEnvironment*>(env);
 320                         if (s_env != 0) {
 321                                 f32 distance = speed_f.getLength();
 322                                 std::set<u16> s_objects = s_env->getObjectsInsideRadius(pos_f,distance * 1.5);
 323                                 for (std::set<u16>::iterator iter = s_objects.begin(); iter != s_objects.end(); iter++) {
 324                                         ServerActiveObject *current = s_env->getActiveObject(*iter);
 325                                         if ((self == 0) || (self != current)) {
 326                                                 objects.push_back((ActiveObject*)current);
 327                                         }
 328                                 }
 329                         }
 330                 }
 331
 332                 for (std::vector<ActiveObject*>::const_iterator iter = objects.begin();
 333                                 iter != objects.end(); ++iter) {
 334                         ActiveObject *object = *iter;
 335
 336                         if (object != NULL) {
 337                                 aabb3f object_collisionbox;
 338                                 if (object->getCollisionBox(&object_collisionbox) &&
 339                                                 object->collideWithObjects()) {
 340                                         cboxes.push_back(object_collisionbox);
 341                                         is_unloaded.push_back(false);
 342                                         is_step_up.push_back(false);
 343                                         bouncy_values.push_back(0);
 344                                         node_positions.push_back(v3s16(0,0,0));
 345                                         is_object.push_back(true);
 346                                 }
 347                         }
 348                 }
 349         } //tt3
 350
 351         assert(cboxes.size() == is_unloaded.size());    // post-condition
 352         assert(cboxes.size() == is_step_up.size());     // post-condition
 353         assert(cboxes.size() == bouncy_values.size());  // post-condition
 354         assert(cboxes.size() == node_positions.size()); // post-condition
 355         assert(cboxes.size() == is_object.size());      // post-condition
 356
 357         /*
 358                 Collision detection
 359         */
 360
 361         /*
 362                 Collision uncertainty radius
 363                 Make it a bit larger than the maximum distance of movement
 364         */
 365         f32 d = pos_max_d * 1.1;
 366         // A fairly large value in here makes moving smoother
 367         //f32 d = 0.15*BS;
 368
 369         // This should always apply, otherwise there are glitches
 370         assert(d > pos_max_d);  // invariant
 371
 372         int loopcount = 0;
 373
 374         while(dtime > BS*1e-10)
 375         {
 376                 //TimeTaker tt3("collisionMoveSimple dtime loop");
 377         ScopeProfiler sp(g_profiler, "collisionMoveSimple dtime loop avg", SPT_AVG);
 378
 379                 // Avoid infinite loop
 380                 loopcount++;
 381                 if(loopcount >= 100)
 382                 {
 383                         infostream<<"collisionMoveSimple: WARNING: Loop count exceeded, aborting to avoid infiniite loop"<<std::endl;
 384                         dtime = 0;
 385                         break;
 386                 }
 387
 388                 aabb3f movingbox = box_0;
 389                 movingbox.MinEdge += pos_f;
 390                 movingbox.MaxEdge += pos_f;
 391
 392                 int nearest_collided = -1;
 393                 f32 nearest_dtime = dtime;
 394                 u32 nearest_boxindex = -1;
 395
 396                 /*
 397                         Go through every nodebox, find nearest collision
 398                 */
 399                 for(u32 boxindex = 0; boxindex < cboxes.size(); boxindex++)
 400                 {
 401                         // Ignore if already stepped up this nodebox.
 402                         if(is_step_up[boxindex])
 403                                 continue;
 404
 405                         // Find nearest collision of the two boxes (raytracing-like)
 406                         f32 dtime_tmp;
 407                         int collided = axisAlignedCollision(
 408                                         cboxes[boxindex], movingbox, speed_f, d, dtime_tmp);
 409
 410                         if(collided == -1 || dtime_tmp >= nearest_dtime)
 411                                 continue;
 412
 413                         nearest_dtime = dtime_tmp;
 414                         nearest_collided = collided;
 415                         nearest_boxindex = boxindex;
 416                 }
 417
 418                 if(nearest_collided == -1)
 419                 {
 420                         // No collision with any collision box.
 421                         pos_f += speed_f * dtime;
 422                         dtime = 0;  // Set to 0 to avoid "infinite" loop due to small FP numbers
 423                 }
 424                 else
 425                 {
 426                         // Otherwise, a collision occurred.
 427
 428                         const aabb3f& cbox = cboxes[nearest_boxindex];
 429
 430                         // Check for stairs.
 431                         bool step_up = (nearest_collided != 1) && // must not be Y direction
 432                                         (movingbox.MinEdge.Y < cbox.MaxEdge.Y) &&
 433                                         (movingbox.MinEdge.Y + stepheight > cbox.MaxEdge.Y) &&
 434                                         (!wouldCollideWithCeiling(cboxes, movingbox,
 435                                                         cbox.MaxEdge.Y - movingbox.MinEdge.Y,
 436                                                         d));
 437
 438                         // Get bounce multiplier
 439                         bool bouncy = (bouncy_values[nearest_boxindex] >= 1);
 440                         float bounce = -(float)bouncy_values[nearest_boxindex] / 100.0;
 441
 442                         // Move to the point of collision and reduce dtime by nearest_dtime
 443                         if(nearest_dtime < 0)
 444                         {
 445                                 // Handle negative nearest_dtime (can be caused by the d allowance)
 446                                 if(!step_up)
 447                                 {
 448                                         if(nearest_collided == 0)
 449                                                 pos_f.X += speed_f.X * nearest_dtime;
 450                                         if(nearest_collided == 1)
 451                                                 pos_f.Y += speed_f.Y * nearest_dtime;
 452                                         if(nearest_collided == 2)
 453                                                 pos_f.Z += speed_f.Z * nearest_dtime;
 454                                 }
 455                         }
 456                         else
 457                         {
 458                                 pos_f += speed_f * nearest_dtime;
 459                                 dtime -= nearest_dtime;
 460                         }
 461
 462                         bool is_collision = true;
 463                         if(is_unloaded[nearest_boxindex])
 464                                 is_collision = false;
 465
 466                         CollisionInfo info;
 467                         if (is_object[nearest_boxindex]) {
 468                                 info.type = COLLISION_OBJECT;
 469                         }
 470                         else {
 471                                 info.type = COLLISION_NODE;
 472                         }
 473                         info.node_p = node_positions[nearest_boxindex];
 474                         info.bouncy = bouncy;
 475                         info.old_speed = speed_f;
 476
 477                         // Set the speed component that caused the collision to zero
 478                         if(step_up)
 479                         {
 480                                 // Special case: Handle stairs
 481                                 is_step_up[nearest_boxindex] = true;
 482                                 is_collision = false;
 483                         }
 484                         else if(nearest_collided == 0) // X
 485                         {
 486                                 if(fabs(speed_f.X) > BS*3)
 487                                         speed_f.X *= bounce;
 488                                 else
 489                                         speed_f.X = 0;
 490                                 result.collides = true;
 491                                 result.collides_xz = true;
 492                         }
 493                         else if(nearest_collided == 1) // Y
 494                         {
 495                                 if(fabs(speed_f.Y) > BS*3)
 496                                         speed_f.Y *= bounce;
 497                                 else
 498                                         speed_f.Y = 0;
 499                                 result.collides = true;
 500                         }
 501                         else if(nearest_collided == 2) // Z
 502                         {
 503                                 if(fabs(speed_f.Z) > BS*3)
 504                                         speed_f.Z *= bounce;
 505                                 else
 506                                         speed_f.Z = 0;
 507                                 result.collides = true;
 508                                 result.collides_xz = true;
 509                         }
 510
 511                         info.new_speed = speed_f;
 512                         if(info.new_speed.getDistanceFrom(info.old_speed) < 0.1*BS)
 513                                 is_collision = false;
 514
 515                         if(is_collision){
 516                                 result.collisions.push_back(info);
 517                         }
 518                 }
 519         }
 520
 521         /*
 522                 Final touches: Check if standing on ground, step up stairs.
 523         */
 524         aabb3f box = box_0;
 525         box.MinEdge += pos_f;
 526         box.MaxEdge += pos_f;
 527         for(u32 boxindex = 0; boxindex < cboxes.size(); boxindex++)
 528         {
 529                 const aabb3f& cbox = cboxes[boxindex];
 530
 531                 /*
 532                         See if the object is touching ground.
 533
 534                         Object touches ground if object's minimum Y is near node's
 535                         maximum Y and object's X-Z-area overlaps with the node's
 536                         X-Z-area.
 537
 538                         Use 0.15*BS so that it is easier to get on a node.
 539                 */
 540                 if(
 541                                 cbox.MaxEdge.X-d > box.MinEdge.X &&
 542                                 cbox.MinEdge.X+d < box.MaxEdge.X &&
 543                                 cbox.MaxEdge.Z-d > box.MinEdge.Z &&
 544                                 cbox.MinEdge.Z+d < box.MaxEdge.Z
 545                 ){
 546                         if(is_step_up[boxindex])
 547                         {
 548                                 pos_f.Y += (cbox.MaxEdge.Y - box.MinEdge.Y);
 549                                 box = box_0;
 550                                 box.MinEdge += pos_f;
 551                                 box.MaxEdge += pos_f;
 552                         }
 553                         if(fabs(cbox.MaxEdge.Y-box.MinEdge.Y) < 0.15*BS)
 554                         {
 555                                 result.touching_ground = true;
 556                                 if(is_unloaded[boxindex])
 557                                         result.standing_on_unloaded = true;
 558                         }
 559                 }
 560         }
 561
 562         return result;
 563 }
 564
 565 #if 0
 566 // This doesn't seem to work and isn't used
 567 collisionMoveResult collisionMovePrecise(Map *map, IGameDef *gamedef,
 568                 f32 pos_max_d, const aabb3f &box_0,
 569                 f32 stepheight, f32 dtime,
 570                 v3f &pos_f, v3f &speed_f, v3f &accel_f)
 571 {
 572         //TimeTaker tt("collisionMovePrecise");
 573     ScopeProfiler sp(g_profiler, "collisionMovePrecise avg", SPT_AVG);
 574
 575         collisionMoveResult final_result;
 576
 577         // If there is no speed, there are no collisions
 578         if(speed_f.getLength() == 0)
 579                 return final_result;
 580
 581         // Don't allow overly huge dtime
 582         if(dtime > 2.0)
 583                 dtime = 2.0;
 584
 585         f32 dtime_downcount = dtime;
 586
 587         u32 loopcount = 0;
 588         do
 589         {
 590                 loopcount++;
 591
 592                 // Maximum time increment (for collision detection etc)
 593                 // time = distance / speed
 594                 f32 dtime_max_increment = 1.0;
 595                 if(speed_f.getLength() != 0)
 596                         dtime_max_increment = pos_max_d / speed_f.getLength();
 597
 598                 // Maximum time increment is 10ms or lower
 599                 if(dtime_max_increment > 0.01)
 600                         dtime_max_increment = 0.01;
 601
 602                 f32 dtime_part;
 603                 if(dtime_downcount > dtime_max_increment)
 604                 {
 605                         dtime_part = dtime_max_increment;
 606                         dtime_downcount -= dtime_part;
 607                 }
 608                 else
 609                 {
 610                         dtime_part = dtime_downcount;
 611                         /*
 612                                 Setting this to 0 (no -=dtime_part) disables an infinite loop
 613                                 when dtime_part is so small that dtime_downcount -= dtime_part
 614                                 does nothing
 615                         */
 616                         dtime_downcount = 0;
 617                 }
 618
 619                 collisionMoveResult result = collisionMoveSimple(map, gamedef,
 620                                 pos_max_d, box_0, stepheight, dtime_part,
 621                                 pos_f, speed_f, accel_f);
 622
 623                 if(result.touching_ground)
 624                         final_result.touching_ground = true;
 625                 if(result.collides)
 626                         final_result.collides = true;
 627                 if(result.collides_xz)
 628                         final_result.collides_xz = true;
 629                 if(result.standing_on_unloaded)
 630                         final_result.standing_on_unloaded = true;
 631         }
 632         while(dtime_downcount > 0.001);
 633
 634         return final_result;
 635 }
 636 #endif