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 "profiler.h"
  32
  33 // float error is 10 - 9.96875 = 0.03125
  34 //#define COLL_ZERO 0.032 // broken unit tests
  35 #define COLL_ZERO 0
  36
  37 // Helper function:
  38 // Checks for collision of a moving aabbox with a static aabbox
  39 // Returns -1 if no collision, 0 if X collision, 1 if Y collision, 2 if Z collision
  40 // The time after which the collision occurs is stored in dtime.
  41 int axisAlignedCollision(
  42                 const aabb3f &staticbox, const aabb3f &movingbox,
  43                 const v3f &speed, f32 d, f32 *dtime)
  44 {
  45         //TimeTaker tt("axisAlignedCollision");
  46
  47         f32 xsize = (staticbox.MaxEdge.X - staticbox.MinEdge.X) - COLL_ZERO;     // reduce box size for solve collision stuck (flying sand)
  48         f32 ysize = (staticbox.MaxEdge.Y - staticbox.MinEdge.Y); // - COLL_ZERO; // Y - no sense for falling, but maybe try later
  49         f32 zsize = (staticbox.MaxEdge.Z - staticbox.MinEdge.Z) - COLL_ZERO;
  50
  51         aabb3f relbox(
  52                         movingbox.MinEdge.X - staticbox.MinEdge.X,
  53                         movingbox.MinEdge.Y - staticbox.MinEdge.Y,
  54                         movingbox.MinEdge.Z - staticbox.MinEdge.Z,
  55                         movingbox.MaxEdge.X - staticbox.MinEdge.X,
  56                         movingbox.MaxEdge.Y - staticbox.MinEdge.Y,
  57                         movingbox.MaxEdge.Z - staticbox.MinEdge.Z
  58         );
  59
  60         if(speed.X > 0) // Check for collision with X- plane
  61         {
  62                 if (relbox.MaxEdge.X <= d) {
  63                         *dtime = -relbox.MaxEdge.X / speed.X;
  64                         if ((relbox.MinEdge.Y + speed.Y * (*dtime) < ysize) &&
  65                                         (relbox.MaxEdge.Y + speed.Y * (*dtime) > COLL_ZERO) &&
  66                                         (relbox.MinEdge.Z + speed.Z * (*dtime) < zsize) &&
  67                                         (relbox.MaxEdge.Z + speed.Z * (*dtime) > COLL_ZERO))
  68                                 return 0;
  69                 }
  70                 else if(relbox.MinEdge.X > xsize)
  71                 {
  72                         return -1;
  73                 }
  74         }
  75         else if(speed.X < 0) // Check for collision with X+ plane
  76         {
  77                 if (relbox.MinEdge.X >= xsize - d) {
  78                         *dtime = (xsize - relbox.MinEdge.X) / speed.X;
  79                         if ((relbox.MinEdge.Y + speed.Y * (*dtime) < ysize) &&
  80                                         (relbox.MaxEdge.Y + speed.Y * (*dtime) > COLL_ZERO) &&
  81                                         (relbox.MinEdge.Z + speed.Z * (*dtime) < zsize) &&
  82                                         (relbox.MaxEdge.Z + speed.Z * (*dtime) > COLL_ZERO))
  83                                 return 0;
  84                 }
  85                 else if(relbox.MaxEdge.X < 0)
  86                 {
  87                         return -1;
  88                 }
  89         }
  90
  91         // NO else if here
  92
  93         if(speed.Y > 0) // Check for collision with Y- plane
  94         {
  95                 if (relbox.MaxEdge.Y <= d) {
  96                         *dtime = -relbox.MaxEdge.Y / speed.Y;
  97                         if ((relbox.MinEdge.X + speed.X * (*dtime) < xsize) &&
  98                                         (relbox.MaxEdge.X + speed.X * (*dtime) > COLL_ZERO) &&
  99                                         (relbox.MinEdge.Z + speed.Z * (*dtime) < zsize) &&
 100                                         (relbox.MaxEdge.Z + speed.Z * (*dtime) > COLL_ZERO))
 101                                 return 1;
 102                 }
 103                 else if(relbox.MinEdge.Y > ysize)
 104                 {
 105                         return -1;
 106                 }
 107         }
 108         else if(speed.Y < 0) // Check for collision with Y+ plane
 109         {
 110                 if (relbox.MinEdge.Y >= ysize - d) {
 111                         *dtime = (ysize - relbox.MinEdge.Y) / speed.Y;
 112                         if ((relbox.MinEdge.X + speed.X * (*dtime) < xsize) &&
 113                                         (relbox.MaxEdge.X + speed.X * (*dtime) > COLL_ZERO) &&
 114                                         (relbox.MinEdge.Z + speed.Z * (*dtime) < zsize) &&
 115                                         (relbox.MaxEdge.Z + speed.Z * (*dtime) > COLL_ZERO))
 116                                 return 1;
 117                 }
 118                 else if(relbox.MaxEdge.Y < 0)
 119                 {
 120                         return -1;
 121                 }
 122         }
 123
 124         // NO else if here
 125
 126         if(speed.Z > 0) // Check for collision with Z- plane
 127         {
 128                 if (relbox.MaxEdge.Z <= d) {
 129                         *dtime = -relbox.MaxEdge.Z / speed.Z;
 130                         if ((relbox.MinEdge.X + speed.X * (*dtime) < xsize) &&
 131                                         (relbox.MaxEdge.X + speed.X * (*dtime) > COLL_ZERO) &&
 132                                         (relbox.MinEdge.Y + speed.Y * (*dtime) < ysize) &&
 133                                         (relbox.MaxEdge.Y + speed.Y * (*dtime) > COLL_ZERO))
 134                                 return 2;
 135                 }
 136                 //else if(relbox.MinEdge.Z > zsize)
 137                 //{
 138                 //      return -1;
 139                 //}
 140         }
 141         else if(speed.Z < 0) // Check for collision with Z+ plane
 142         {
 143                 if (relbox.MinEdge.Z >= zsize - d) {
 144                         *dtime = (zsize - relbox.MinEdge.Z) / speed.Z;
 145                         if ((relbox.MinEdge.X + speed.X * (*dtime) < xsize) &&
 146                                         (relbox.MaxEdge.X + speed.X * (*dtime) > COLL_ZERO) &&
 147                                         (relbox.MinEdge.Y + speed.Y * (*dtime) < ysize) &&
 148                                         (relbox.MaxEdge.Y + speed.Y * (*dtime) > COLL_ZERO))
 149                                 return 2;
 150                 }
 151                 //else if(relbox.MaxEdge.Z < 0)
 152                 //{
 153                 //      return -1;
 154                 //}
 155         }
 156
 157         return -1;
 158 }
 159
 160 // Helper function:
 161 // Checks if moving the movingbox up by the given distance would hit a ceiling.
 162 bool wouldCollideWithCeiling(
 163                 const std::vector<aabb3f> &staticboxes,
 164                 const aabb3f &movingbox,
 165                 f32 y_increase, f32 d)
 166 {
 167         //TimeTaker tt("wouldCollideWithCeiling");
 168
 169         assert(y_increase >= 0);        // pre-condition
 170
 171         for(std::vector<aabb3f>::const_iterator
 172                         i = staticboxes.begin();
 173                         i != staticboxes.end(); ++i)
 174         {
 175                 const aabb3f& staticbox = *i;
 176                 if((movingbox.MaxEdge.Y - d <= staticbox.MinEdge.Y) &&
 177                                 (movingbox.MaxEdge.Y + y_increase > staticbox.MinEdge.Y) &&
 178                                 (movingbox.MinEdge.X < staticbox.MaxEdge.X) &&
 179                                 (movingbox.MaxEdge.X > staticbox.MinEdge.X) &&
 180                                 (movingbox.MinEdge.Z < staticbox.MaxEdge.Z) &&
 181                                 (movingbox.MaxEdge.Z > staticbox.MinEdge.Z))
 182                         return true;
 183         }
 184
 185         return false;
 186 }
 187
 188 static inline void getNeighborConnectingFace(v3s16 p, INodeDefManager *nodedef,
 189                 Map *map, MapNode n, int v, int *neighbors)
 190 {
 191         MapNode n2 = map->getNodeNoEx(p);
 192         if (nodedef->nodeboxConnects(n, n2, v))
 193                 *neighbors |= v;
 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         static bool time_notification_done = false;
 204         Map *map = &env->getMap();
 205         //TimeTaker tt("collisionMoveSimple");
 206         ScopeProfiler sp(g_profiler, "collisionMoveSimple avg", SPT_AVG);
 207
 208         collisionMoveResult result;
 209
 210         /*
 211                 Calculate new velocity
 212         */
 213         if (dtime > 0.5) {
 214                 if (!time_notification_done) {
 215                         time_notification_done = true;
 216                         infostream << "collisionMoveSimple: maximum step interval exceeded,"
 217                                         " lost movement details!"<<std::endl;
 218                 }
 219                 dtime = 0.5;
 220         } else {
 221                 time_notification_done = false;
 222         }
 223         *speed_f += accel_f * dtime;
 224
 225         // If there is no speed, there are no collisions
 226         if (speed_f->getLength() == 0)
 227                 return result;
 228
 229         // Limit speed for avoiding hangs
 230         speed_f->Y = rangelim(speed_f->Y, -5000, 5000);
 231         speed_f->X = rangelim(speed_f->X, -5000, 5000);
 232         speed_f->Z = rangelim(speed_f->Z, -5000, 5000);
 233
 234         /*
 235                 Collect node boxes in movement range
 236         */
 237         std::vector<aabb3f> cboxes;
 238         std::vector<bool> is_unloaded;
 239         std::vector<bool> is_step_up;
 240         std::vector<bool> is_object;
 241         std::vector<int> bouncy_values;
 242         std::vector<v3s16> node_positions;
 243         {
 244         //TimeTaker tt2("collisionMoveSimple collect boxes");
 245         ScopeProfiler sp(g_profiler, "collisionMoveSimple collect boxes avg", SPT_AVG);
 246
 247         v3s16 oldpos_i = floatToInt(*pos_f, BS);
 248         v3s16 newpos_i = floatToInt(*pos_f + *speed_f * dtime, BS);
 249         s16 min_x = MYMIN(oldpos_i.X, newpos_i.X) + (box_0.MinEdge.X / BS) - 1;
 250         s16 min_y = MYMIN(oldpos_i.Y, newpos_i.Y) + (box_0.MinEdge.Y / BS) - 1;
 251         s16 min_z = MYMIN(oldpos_i.Z, newpos_i.Z) + (box_0.MinEdge.Z / BS) - 1;
 252         s16 max_x = MYMAX(oldpos_i.X, newpos_i.X) + (box_0.MaxEdge.X / BS) + 1;
 253         s16 max_y = MYMAX(oldpos_i.Y, newpos_i.Y) + (box_0.MaxEdge.Y / BS) + 1;
 254         s16 max_z = MYMAX(oldpos_i.Z, newpos_i.Z) + (box_0.MaxEdge.Z / BS) + 1;
 255
 256         bool any_position_valid = false;
 257
 258         for(s16 x = min_x; x <= max_x; x++)
 259         for(s16 y = min_y; y <= max_y; y++)
 260         for(s16 z = min_z; z <= max_z; z++)
 261         {
 262                 v3s16 p(x,y,z);
 263
 264                 bool is_position_valid;
 265                 MapNode n = map->getNodeNoEx(p, &is_position_valid);
 266
 267                 if (is_position_valid) {
 268                         // Object collides into walkable nodes
 269
 270                         any_position_valid = true;
 271                         INodeDefManager *nodedef = gamedef->getNodeDefManager();
 272                         const ContentFeatures &f = nodedef->get(n);
 273                         if(f.walkable == false)
 274                                 continue;
 275                         int n_bouncy_value = itemgroup_get(f.groups, "bouncy");
 276
 277                         int neighbors = 0;
 278                         if (f.drawtype == NDT_NODEBOX && f.node_box.type == NODEBOX_CONNECTED) {
 279                                 v3s16 p2 = p;
 280
 281                                 p2.Y++;
 282                                 getNeighborConnectingFace(p2, nodedef, map, n, 1, &neighbors);
 283
 284                                 p2 = p;
 285                                 p2.Y--;
 286                                 getNeighborConnectingFace(p2, nodedef, map, n, 2, &neighbors);
 287
 288                                 p2 = p;
 289                                 p2.Z--;
 290                                 getNeighborConnectingFace(p2, nodedef, map, n, 4, &neighbors);
 291
 292                                 p2 = p;
 293                                 p2.X--;
 294                                 getNeighborConnectingFace(p2, nodedef, map, n, 8, &neighbors);
 295
 296                                 p2 = p;
 297                                 p2.Z++;
 298                                 getNeighborConnectingFace(p2, nodedef, map, n, 16, &neighbors);
 299
 300                                 p2 = p;
 301                                 p2.X++;
 302                                 getNeighborConnectingFace(p2, nodedef, map, n, 32, &neighbors);
 303                         }
 304                         std::vector<aabb3f> nodeboxes;
 305                         n.getCollisionBoxes(gamedef->ndef(), &nodeboxes, neighbors);
 306                         for(std::vector<aabb3f>::iterator
 307                                         i = nodeboxes.begin();
 308                                         i != nodeboxes.end(); ++i)
 309                         {
 310                                 aabb3f box = *i;
 311                                 box.MinEdge += v3f(x, y, z)*BS;
 312                                 box.MaxEdge += v3f(x, y, z)*BS;
 313                                 cboxes.push_back(box);
 314                                 is_unloaded.push_back(false);
 315                                 is_step_up.push_back(false);
 316                                 bouncy_values.push_back(n_bouncy_value);
 317                                 node_positions.push_back(p);
 318                                 is_object.push_back(false);
 319                         }
 320                 }
 321                 else {
 322                         // Collide with unloaded nodes
 323                         aabb3f box = getNodeBox(p, BS);
 324                         cboxes.push_back(box);
 325                         is_unloaded.push_back(true);
 326                         is_step_up.push_back(false);
 327                         bouncy_values.push_back(0);
 328                         node_positions.push_back(p);
 329                         is_object.push_back(false);
 330                 }
 331         }
 332
 333         // Do not move if world has not loaded yet, since custom node boxes
 334         // are not available for collision detection.
 335         if (!any_position_valid) {
 336                 *speed_f = v3f(0, 0, 0);
 337                 return result;
 338         }
 339
 340         } // tt2
 341
 342         if(collideWithObjects)
 343         {
 344                 ScopeProfiler sp(g_profiler, "collisionMoveSimple objects avg", SPT_AVG);
 345                 //TimeTaker tt3("collisionMoveSimple collect object boxes");
 346
 347                 /* add object boxes to cboxes */
 348
 349                 std::vector<ActiveObject*> objects;
 350 #ifndef SERVER
 351                 ClientEnvironment *c_env = dynamic_cast<ClientEnvironment*>(env);
 352                 if (c_env != 0) {
 353                         f32 distance = speed_f->getLength();
 354                         std::vector<DistanceSortedActiveObject> clientobjects;
 355                         c_env->getActiveObjects(*pos_f, distance * 1.5, clientobjects);
 356                         for (size_t i=0; i < clientobjects.size(); i++) {
 357                                 if ((self == 0) || (self != clientobjects[i].obj)) {
 358                                         objects.push_back((ActiveObject*)clientobjects[i].obj);
 359                                 }
 360                         }
 361                 }
 362                 else
 363 #endif
 364                 {
 365                         ServerEnvironment *s_env = dynamic_cast<ServerEnvironment*>(env);
 366                         if (s_env != 0) {
 367                                 f32 distance = speed_f->getLength();
 368                                 std::vector<u16> s_objects;
 369                                 s_env->getObjectsInsideRadius(s_objects, *pos_f, distance * 1.5);
 370                                 for (std::vector<u16>::iterator iter = s_objects.begin(); iter != s_objects.end(); ++iter) {
 371                                         ServerActiveObject *current = s_env->getActiveObject(*iter);
 372                                         if ((self == 0) || (self != current)) {
 373                                                 objects.push_back((ActiveObject*)current);
 374                                         }
 375                                 }
 376                         }
 377                 }
 378
 379                 for (std::vector<ActiveObject*>::const_iterator iter = objects.begin();
 380                                 iter != objects.end(); ++iter) {
 381                         ActiveObject *object = *iter;
 382
 383                         if (object != NULL) {
 384                                 aabb3f object_collisionbox;
 385                                 if (object->getCollisionBox(&object_collisionbox) &&
 386                                                 object->collideWithObjects()) {
 387                                         cboxes.push_back(object_collisionbox);
 388                                         is_unloaded.push_back(false);
 389                                         is_step_up.push_back(false);
 390                                         bouncy_values.push_back(0);
 391                                         node_positions.push_back(v3s16(0,0,0));
 392                                         is_object.push_back(true);
 393                                 }
 394                         }
 395                 }
 396         } //tt3
 397
 398         assert(cboxes.size() == is_unloaded.size());    // post-condition
 399         assert(cboxes.size() == is_step_up.size());     // post-condition
 400         assert(cboxes.size() == bouncy_values.size());  // post-condition
 401         assert(cboxes.size() == node_positions.size()); // post-condition
 402         assert(cboxes.size() == is_object.size());      // post-condition
 403
 404         /*
 405                 Collision detection
 406         */
 407
 408         /*
 409                 Collision uncertainty radius
 410                 Make it a bit larger than the maximum distance of movement
 411         */
 412         f32 d = pos_max_d * 1.1;
 413         // A fairly large value in here makes moving smoother
 414         //f32 d = 0.15*BS;
 415
 416         // This should always apply, otherwise there are glitches
 417         assert(d > pos_max_d);  // invariant
 418
 419         int loopcount = 0;
 420
 421         while(dtime > BS * 1e-10) {
 422                 //TimeTaker tt3("collisionMoveSimple dtime loop");
 423                 ScopeProfiler sp(g_profiler, "collisionMoveSimple dtime loop avg", SPT_AVG);
 424
 425                 // Avoid infinite loop
 426                 loopcount++;
 427                 if (loopcount >= 100) {
 428                         warningstream << "collisionMoveSimple: Loop count exceeded, aborting to avoid infiniite loop" << std::endl;
 429                         break;
 430                 }
 431
 432                 aabb3f movingbox = box_0;
 433                 movingbox.MinEdge += *pos_f;
 434                 movingbox.MaxEdge += *pos_f;
 435
 436                 int nearest_collided = -1;
 437                 f32 nearest_dtime = dtime;
 438                 int nearest_boxindex = -1;
 439
 440                 /*
 441                         Go through every nodebox, find nearest collision
 442                 */
 443                 for (u32 boxindex = 0; boxindex < cboxes.size(); boxindex++) {
 444                         // Ignore if already stepped up this nodebox.
 445                         if(is_step_up[boxindex])
 446                                 continue;
 447
 448                         // Find nearest collision of the two boxes (raytracing-like)
 449                         f32 dtime_tmp;
 450                         int collided = axisAlignedCollision(
 451                                         cboxes[boxindex], movingbox, *speed_f, d, &dtime_tmp);
 452
 453                         if (collided == -1 || dtime_tmp >= nearest_dtime)
 454                                 continue;
 455
 456                         nearest_dtime = dtime_tmp;
 457                         nearest_collided = collided;
 458                         nearest_boxindex = boxindex;
 459                 }
 460
 461                 if (nearest_collided == -1) {
 462                         // No collision with any collision box.
 463                         *pos_f += *speed_f * dtime;
 464                         dtime = 0;  // Set to 0 to avoid "infinite" loop due to small FP numbers
 465                 } else {
 466                         // Otherwise, a collision occurred.
 467
 468                         const aabb3f& cbox = cboxes[nearest_boxindex];
 469                         // Check for stairs.
 470                         bool step_up = (nearest_collided != 1) && // must not be Y direction
 471                                         (movingbox.MinEdge.Y < cbox.MaxEdge.Y) &&
 472                                         (movingbox.MinEdge.Y + stepheight > cbox.MaxEdge.Y) &&
 473                                         (!wouldCollideWithCeiling(cboxes, movingbox,
 474                                                         cbox.MaxEdge.Y - movingbox.MinEdge.Y,
 475                                                         d));
 476
 477                         // Get bounce multiplier
 478                         bool bouncy = (bouncy_values[nearest_boxindex] >= 1);
 479                         float bounce = -(float)bouncy_values[nearest_boxindex] / 100.0;
 480
 481                         // Move to the point of collision and reduce dtime by nearest_dtime
 482                         if (nearest_dtime < 0) {
 483                                 // Handle negative nearest_dtime (can be caused by the d allowance)
 484                                 if (!step_up) {
 485                                         if (nearest_collided == 0)
 486                                                 pos_f->X += speed_f->X * nearest_dtime;
 487                                         if (nearest_collided == 1)
 488                                                 pos_f->Y += speed_f->Y * nearest_dtime;
 489                                         if (nearest_collided == 2)
 490                                                 pos_f->Z += speed_f->Z * nearest_dtime;
 491                                 }
 492                         } else {
 493                                 *pos_f += *speed_f * nearest_dtime;
 494                                 dtime -= nearest_dtime;
 495                         }
 496
 497                         bool is_collision = true;
 498                         if (is_unloaded[nearest_boxindex])
 499                                 is_collision = false;
 500
 501                         CollisionInfo info;
 502                         if (is_object[nearest_boxindex])
 503                                 info.type = COLLISION_OBJECT;
 504                         else
 505                                 info.type = COLLISION_NODE;
 506
 507                         info.node_p = node_positions[nearest_boxindex];
 508                         info.bouncy = bouncy;
 509                         info.old_speed = *speed_f;
 510
 511                         // Set the speed component that caused the collision to zero
 512                         if (step_up) {
 513                                 // Special case: Handle stairs
 514                                 is_step_up[nearest_boxindex] = true;
 515                                 is_collision = false;
 516                         } else if(nearest_collided == 0) { // X
 517                                 if (fabs(speed_f->X) > BS * 3)
 518                                         speed_f->X *= bounce;
 519                                 else
 520                                         speed_f->X = 0;
 521                                 result.collides = true;
 522                                 result.collides_xz = true;
 523                         }
 524                         else if(nearest_collided == 1) { // Y
 525                                 if (fabs(speed_f->Y) > BS * 3)
 526                                         speed_f->Y *= bounce;
 527                                 else
 528                                         speed_f->Y = 0;
 529                                 result.collides = true;
 530                         } else if(nearest_collided == 2) { // Z
 531                                 if (fabs(speed_f->Z) > BS * 3)
 532                                         speed_f->Z *= bounce;
 533                                 else
 534                                         speed_f->Z = 0;
 535                                 result.collides = true;
 536                                 result.collides_xz = true;
 537                         }
 538
 539                         info.new_speed = *speed_f;
 540                         if (info.new_speed.getDistanceFrom(info.old_speed) < 0.1 * BS)
 541                                 is_collision = false;
 542
 543                         if (is_collision) {
 544                                 result.collisions.push_back(info);
 545                         }
 546                 }
 547         }
 548
 549         /*
 550                 Final touches: Check if standing on ground, step up stairs.
 551         */
 552         aabb3f box = box_0;
 553         box.MinEdge += *pos_f;
 554         box.MaxEdge += *pos_f;
 555         for (u32 boxindex = 0; boxindex < cboxes.size(); boxindex++) {
 556                 const aabb3f& cbox = cboxes[boxindex];
 557
 558                 /*
 559                         See if the object is touching ground.
 560
 561                         Object touches ground if object's minimum Y is near node's
 562                         maximum Y and object's X-Z-area overlaps with the node's
 563                         X-Z-area.
 564
 565                         Use 0.15*BS so that it is easier to get on a node.
 566                 */
 567                 if (cbox.MaxEdge.X - d > box.MinEdge.X && cbox.MinEdge.X + d < box.MaxEdge.X &&
 568                                 cbox.MaxEdge.Z - d > box.MinEdge.Z &&
 569                                 cbox.MinEdge.Z + d < box.MaxEdge.Z) {
 570                         if (is_step_up[boxindex]) {
 571                                 pos_f->Y += (cbox.MaxEdge.Y - box.MinEdge.Y);
 572                                 box = box_0;
 573                                 box.MinEdge += *pos_f;
 574                                 box.MaxEdge += *pos_f;
 575                         }
 576                         if (fabs(cbox.MaxEdge.Y - box.MinEdge.Y) < 0.15 * BS) {
 577                                 result.touching_ground = true;
 578
 579                                 if (is_object[boxindex])
 580                                         result.standing_on_object = true;
 581                                 if (is_unloaded[boxindex])
 582                                         result.standing_on_unloaded = true;
 583                         }
 584                 }
 585         }
 586
 587         return result;
 588 }