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 <cmath>
  22 #include "mapblock.h"
  23 #include "map.h"
  24 #include "nodedef.h"
  25 #include "gamedef.h"
  26 #ifndef SERVER
  27 #include "client/clientenvironment.h"
  28 #include "client/localplayer.h"
  29 #endif
  30 #include "serverenvironment.h"
  31 #include "server/serveractiveobject.h"
  32 #include "util/timetaker.h"
  33 #include "profiler.h"
  34
  35
  36 struct NearbyCollisionInfo {
  37         NearbyCollisionInfo(bool is_ul, bool is_obj, int bouncy,
  38                         const v3s16 &pos, const aabb3f &box) :
  39                 is_unloaded(is_ul),
  40                 is_object(is_obj),
  41                 bouncy(bouncy),
  42                 position(pos),
  43                 box(box)
  44         {}
  45
  46         bool is_unloaded;
  47         bool is_step_up = false;
  48         bool is_object;
  49         int bouncy;
  50         v3s16 position;
  51         aabb3f box;
  52 };
  53
  54
  55 // Helper function:
  56 // Checks for collision of a moving aabbox with a static aabbox
  57 // Returns -1 if no collision, 0 if X collision, 1 if Y collision, 2 if Z collision
  58 // The time after which the collision occurs is stored in dtime.
  59 CollisionAxis axisAlignedCollision(
  60                 const aabb3f &staticbox, const aabb3f &movingbox,
  61                 const v3f &speed, f32 *dtime)
  62 {
  63         //TimeTaker tt("axisAlignedCollision");
  64
  65         aabb3f relbox(
  66                         movingbox.MaxEdge.X - movingbox.MinEdge.X + staticbox.MaxEdge.X - staticbox.MinEdge.X,                                          // sum of the widths
  67                         movingbox.MaxEdge.Y - movingbox.MinEdge.Y + staticbox.MaxEdge.Y - staticbox.MinEdge.Y,
  68                         movingbox.MaxEdge.Z - movingbox.MinEdge.Z + staticbox.MaxEdge.Z - staticbox.MinEdge.Z,
  69                         std::max(movingbox.MaxEdge.X, staticbox.MaxEdge.X) - std::min(movingbox.MinEdge.X, staticbox.MinEdge.X),        //outer bounding 'box' dimensions
  70                         std::max(movingbox.MaxEdge.Y, staticbox.MaxEdge.Y) - std::min(movingbox.MinEdge.Y, staticbox.MinEdge.Y),
  71                         std::max(movingbox.MaxEdge.Z, staticbox.MaxEdge.Z) - std::min(movingbox.MinEdge.Z, staticbox.MinEdge.Z)
  72         );
  73
  74         const f32 dtime_max = *dtime;
  75         const f32 inner_margin = -1.5f;
  76         f32 distance;
  77         f32 time;
  78
  79         if (speed.X) {
  80                 distance = relbox.MaxEdge.X - relbox.MinEdge.X;
  81
  82                 *dtime = distance >= 0 ? std::abs(distance / speed.X) : -std::abs(distance / speed.X);
  83                 time = std::max(*dtime, 0.0f);
  84
  85                 if (distance > inner_margin) {
  86                         if (*dtime <= dtime_max) {
  87                                 if ((speed.X > 0 && staticbox.MaxEdge.X > movingbox.MaxEdge.X) ||
  88                                                 (speed.X < 0 && staticbox.MinEdge.X < movingbox.MinEdge.X)) {
  89                                         if (
  90                                                 (std::max(movingbox.MaxEdge.Y + speed.Y * time, staticbox.MaxEdge.Y)
  91                                                         - std::min(movingbox.MinEdge.Y + speed.Y * time, staticbox.MinEdge.Y)
  92                                                         - relbox.MinEdge.Y < 0) &&
  93                                                 (std::max(movingbox.MaxEdge.Z + speed.Z * time, staticbox.MaxEdge.Z)
  94                                                         - std::min(movingbox.MinEdge.Z + speed.Z * time, staticbox.MinEdge.Z)
  95                                                         - relbox.MinEdge.Z < 0)
  96                                                 )
  97                                                 return COLLISION_AXIS_X;
  98                                 }
  99                         } else {
 100                                 return COLLISION_AXIS_NONE;
 101                         }
 102                 }
 103         }
 104
 105         // NO else if here
 106
 107         if (speed.Y) {
 108                 distance = relbox.MaxEdge.Y - relbox.MinEdge.Y;
 109
 110                 *dtime = distance >= 0 ? std::abs(distance / speed.Y) : -std::abs(distance / speed.Y);
 111                 time = std::max(*dtime, 0.0f);
 112
 113                 if (distance > inner_margin) {
 114                         if (*dtime <= dtime_max) {
 115                                 if ((speed.Y > 0 && staticbox.MaxEdge.Y > movingbox.MaxEdge.Y) ||
 116                                                 (speed.Y < 0 && staticbox.MinEdge.Y < movingbox.MinEdge.Y)) {
 117                                         if (
 118                                                 (std::max(movingbox.MaxEdge.X + speed.X * time, staticbox.MaxEdge.X)
 119                                                         - std::min(movingbox.MinEdge.X + speed.X * time, staticbox.MinEdge.X)
 120                                                         - relbox.MinEdge.X < 0) &&
 121                                                 (std::max(movingbox.MaxEdge.Z + speed.Z * time, staticbox.MaxEdge.Z)
 122                                                         - std::min(movingbox.MinEdge.Z + speed.Z * time, staticbox.MinEdge.Z)
 123                                                         - relbox.MinEdge.Z < 0)
 124                                                 )
 125                                                 return COLLISION_AXIS_Y;
 126                                 }
 127                         } else {
 128                                 return COLLISION_AXIS_NONE;
 129                         }
 130                 }
 131         }
 132
 133         // NO else if here
 134
 135         if (speed.Z) {
 136                 distance = relbox.MaxEdge.Z - relbox.MinEdge.Z;
 137
 138                 *dtime = distance >= 0 ? std::abs(distance / speed.Z) : -std::abs(distance / speed.Z);
 139                 time = std::max(*dtime, 0.0f);
 140
 141                 if (distance > inner_margin) {
 142                         if (*dtime <= dtime_max) {
 143                                 if ((speed.Z > 0 && staticbox.MaxEdge.Z > movingbox.MaxEdge.Z) ||
 144                                                 (speed.Z < 0 && staticbox.MinEdge.Z < movingbox.MinEdge.Z)) {
 145                                         if (
 146                                                 (std::max(movingbox.MaxEdge.X + speed.X * time, staticbox.MaxEdge.X)
 147                                                         - std::min(movingbox.MinEdge.X + speed.X * time, staticbox.MinEdge.X)
 148                                                         - relbox.MinEdge.X < 0) &&
 149                                                 (std::max(movingbox.MaxEdge.Y + speed.Y * time, staticbox.MaxEdge.Y)
 150                                                         - std::min(movingbox.MinEdge.Y + speed.Y * time, staticbox.MinEdge.Y)
 151                                                         - relbox.MinEdge.Y < 0)
 152                                                 )
 153                                                 return COLLISION_AXIS_Z;
 154                                 }
 155                         }
 156                 }
 157         }
 158
 159         return COLLISION_AXIS_NONE;
 160 }
 161
 162 // Helper function:
 163 // Checks if moving the movingbox up by the given distance would hit a ceiling.
 164 bool wouldCollideWithCeiling(
 165                 const std::vector<NearbyCollisionInfo> &cinfo,
 166                 const aabb3f &movingbox,
 167                 f32 y_increase, f32 d)
 168 {
 169         //TimeTaker tt("wouldCollideWithCeiling");
 170
 171         assert(y_increase >= 0);        // pre-condition
 172
 173         for (const auto &it : cinfo) {
 174                 const aabb3f &staticbox = it.box;
 175                 if ((movingbox.MaxEdge.Y - d <= staticbox.MinEdge.Y) &&
 176                                 (movingbox.MaxEdge.Y + y_increase > staticbox.MinEdge.Y) &&
 177                                 (movingbox.MinEdge.X < staticbox.MaxEdge.X) &&
 178                                 (movingbox.MaxEdge.X > staticbox.MinEdge.X) &&
 179                                 (movingbox.MinEdge.Z < staticbox.MaxEdge.Z) &&
 180                                 (movingbox.MaxEdge.Z > staticbox.MinEdge.Z))
 181                         return true;
 182         }
 183
 184         return false;
 185 }
 186
 187 static inline void getNeighborConnectingFace(const v3s16 &p,
 188         const NodeDefManager *nodedef, Map *map, MapNode n, int v, int *neighbors)
 189 {
 190         MapNode n2 = map->getNode(p);
 191         if (nodedef->nodeboxConnects(n, n2, v))
 192                 *neighbors |= v;
 193 }
 194
 195 collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 196                 f32 pos_max_d, const aabb3f &box_0,
 197                 f32 stepheight, f32 dtime,
 198                 v3f *pos_f, v3f *speed_f,
 199                 v3f accel_f, ActiveObject *self,
 200                 bool collideWithObjects)
 201 {
 202         static bool time_notification_done = false;
 203         Map *map = &env->getMap();
 204
 205         ScopeProfiler sp(g_profiler, "collisionMoveSimple()", SPT_AVG);
 206
 207         collisionMoveResult result;
 208
 209         /*
 210                 Calculate new velocity
 211         */
 212         if (dtime > 0.5f) {
 213                 if (!time_notification_done) {
 214                         time_notification_done = true;
 215                         infostream << "collisionMoveSimple: maximum step interval exceeded,"
 216                                         " lost movement details!"<<std::endl;
 217                 }
 218                 dtime = 0.5f;
 219         } else {
 220                 time_notification_done = false;
 221         }
 222         *speed_f += accel_f * dtime;
 223
 224         // If there is no speed, there are no collisions
 225         if (speed_f->getLength() == 0)
 226                 return result;
 227
 228         // Limit speed for avoiding hangs
 229         speed_f->Y = rangelim(speed_f->Y, -5000, 5000);
 230         speed_f->X = rangelim(speed_f->X, -5000, 5000);
 231         speed_f->Z = rangelim(speed_f->Z, -5000, 5000);
 232
 233         /*
 234                 Collect node boxes in movement range
 235         */
 236         std::vector<NearbyCollisionInfo> cinfo;
 237         {
 238         //TimeTaker tt2("collisionMoveSimple collect boxes");
 239         ScopeProfiler sp2(g_profiler, "collisionMoveSimple(): collect boxes", SPT_AVG);
 240
 241         v3f newpos_f = *pos_f + *speed_f * dtime;
 242         v3f minpos_f(
 243                 MYMIN(pos_f->X, newpos_f.X),
 244                 MYMIN(pos_f->Y, newpos_f.Y) + 0.01f * BS, // bias rounding, player often at +/-n.5
 245                 MYMIN(pos_f->Z, newpos_f.Z)
 246         );
 247         v3f maxpos_f(
 248                 MYMAX(pos_f->X, newpos_f.X),
 249                 MYMAX(pos_f->Y, newpos_f.Y),
 250                 MYMAX(pos_f->Z, newpos_f.Z)
 251         );
 252         v3s16 min = floatToInt(minpos_f + box_0.MinEdge, BS) - v3s16(1, 1, 1);
 253         v3s16 max = floatToInt(maxpos_f + box_0.MaxEdge, BS) + v3s16(1, 1, 1);
 254
 255         bool any_position_valid = false;
 256
 257         v3s16 p;
 258         for (p.X = min.X; p.X <= max.X; p.X++)
 259         for (p.Y = min.Y; p.Y <= max.Y; p.Y++)
 260         for (p.Z = min.Z; p.Z <= max.Z; p.Z++) {
 261                 bool is_position_valid;
 262                 MapNode n = map->getNode(p, &is_position_valid);
 263
 264                 if (is_position_valid && n.getContent() != CONTENT_IGNORE) {
 265                         // Object collides into walkable nodes
 266
 267                         any_position_valid = true;
 268                         const NodeDefManager *nodedef = gamedef->getNodeDefManager();
 269                         const ContentFeatures &f = nodedef->get(n);
 270
 271                         if (!f.walkable)
 272                                 continue;
 273
 274                         int n_bouncy_value = itemgroup_get(f.groups, "bouncy");
 275
 276                         int neighbors = 0;
 277                         if (f.drawtype == NDT_NODEBOX &&
 278                                 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
 307                         // Calculate float position only once
 308                         v3f posf = intToFloat(p, BS);
 309                         for (auto box : nodeboxes) {
 310                                 box.MinEdge += posf;
 311                                 box.MaxEdge += posf;
 312                                 cinfo.emplace_back(false, false, n_bouncy_value, p, box);
 313                         }
 314                 } else {
 315                         // Collide with unloaded nodes (position invalid) and loaded
 316                         // CONTENT_IGNORE nodes (position valid)
 317                         aabb3f box = getNodeBox(p, BS);
 318                         cinfo.emplace_back(true, false, 0, p, box);
 319                 }
 320         }
 321
 322         // Do not move if world has not loaded yet, since custom node boxes
 323         // are not available for collision detection.
 324         // This also intentionally occurs in the case of the object being positioned
 325         // solely on loaded CONTENT_IGNORE nodes, no matter where they come from.
 326         if (!any_position_valid) {
 327                 *speed_f = v3f(0, 0, 0);
 328                 return result;
 329         }
 330
 331         } // tt2
 332
 333         if(collideWithObjects)
 334         {
 335                 /* add object boxes to cinfo */
 336
 337                 std::vector<ActiveObject*> objects;
 338 #ifndef SERVER
 339                 ClientEnvironment *c_env = dynamic_cast<ClientEnvironment*>(env);
 340                 if (c_env != 0) {
 341                         // Calculate distance by speed, add own extent and 1.5m of tolerance
 342                         f32 distance = speed_f->getLength() * dtime +
 343                                 box_0.getExtent().getLength() + 1.5f * BS;
 344                         std::vector<DistanceSortedActiveObject> clientobjects;
 345                         c_env->getActiveObjects(*pos_f, distance, clientobjects);
 346
 347                         for (auto &clientobject : clientobjects) {
 348                                 // Do collide with everything but itself and the parent CAO
 349                                 if (!self || (self != clientobject.obj &&
 350                                                 self != clientobject.obj->getParent())) {
 351                                         objects.push_back((ActiveObject*) clientobject.obj);
 352                                 }
 353                         }
 354                 }
 355                 else
 356 #endif
 357                 {
 358                         ServerEnvironment *s_env = dynamic_cast<ServerEnvironment*>(env);
 359                         if (s_env != NULL) {
 360                                 // Calculate distance by speed, add own extent and 1.5m of tolerance
 361                                 f32 distance = speed_f->getLength() * dtime +
 362                                         box_0.getExtent().getLength() + 1.5f * BS;
 363                                 std::vector<u16> s_objects;
 364                                 s_env->getObjectsInsideRadius(s_objects, *pos_f, distance);
 365
 366                                 for (u16 obj_id : s_objects) {
 367                                         ServerActiveObject *current = s_env->getActiveObject(obj_id);
 368
 369                                         if (!self || (self != current &&
 370                                                         self != current->getParent())) {
 371                                                 objects.push_back((ActiveObject*)current);
 372                                         }
 373                                 }
 374                         }
 375                 }
 376
 377                 for (std::vector<ActiveObject*>::const_iterator iter = objects.begin();
 378                                 iter != objects.end(); ++iter) {
 379                         ActiveObject *object = *iter;
 380
 381                         if (object) {
 382                                 aabb3f object_collisionbox;
 383                                 if (object->getCollisionBox(&object_collisionbox) &&
 384                                                 object->collideWithObjects()) {
 385                                         cinfo.emplace_back(false, true, 0, v3s16(), object_collisionbox);
 386                                 }
 387                         }
 388                 }
 389 #ifndef SERVER
 390                 if (self && c_env) {
 391                         LocalPlayer *lplayer = c_env->getLocalPlayer();
 392                         if (lplayer->getParent() == nullptr) {
 393                                 aabb3f lplayer_collisionbox = lplayer->getCollisionbox();
 394                                 v3f lplayer_pos = lplayer->getPosition();
 395                                 lplayer_collisionbox.MinEdge += lplayer_pos;
 396                                 lplayer_collisionbox.MaxEdge += lplayer_pos;
 397                                 cinfo.emplace_back(false, true, 0, v3s16(), lplayer_collisionbox);
 398                         }
 399                 }
 400 #endif
 401         } //tt3
 402
 403         /*
 404                 Collision detection
 405         */
 406
 407         f32 d = 0.0f;
 408
 409         int loopcount = 0;
 410
 411         while(dtime > BS * 1e-10f) {
 412                 // Avoid infinite loop
 413                 loopcount++;
 414                 if (loopcount >= 100) {
 415                         warningstream << "collisionMoveSimple: Loop count exceeded, aborting to avoid infiniite loop" << std::endl;
 416                         break;
 417                 }
 418
 419                 aabb3f movingbox = box_0;
 420                 movingbox.MinEdge += *pos_f;
 421                 movingbox.MaxEdge += *pos_f;
 422
 423                 CollisionAxis nearest_collided = COLLISION_AXIS_NONE;
 424                 f32 nearest_dtime = dtime;
 425                 int nearest_boxindex = -1;
 426
 427                 /*
 428                         Go through every nodebox, find nearest collision
 429                 */
 430                 for (u32 boxindex = 0; boxindex < cinfo.size(); boxindex++) {
 431                         const NearbyCollisionInfo &box_info = cinfo[boxindex];
 432                         // Ignore if already stepped up this nodebox.
 433                         if (box_info.is_step_up)
 434                                 continue;
 435
 436                         // Find nearest collision of the two boxes (raytracing-like)
 437                         f32 dtime_tmp = nearest_dtime;
 438                         CollisionAxis collided = axisAlignedCollision(box_info.box,
 439                                         movingbox, *speed_f, &dtime_tmp);
 440
 441                         if (collided == -1 || dtime_tmp >= nearest_dtime)
 442                                 continue;
 443
 444                         nearest_dtime = dtime_tmp;
 445                         nearest_collided = collided;
 446                         nearest_boxindex = boxindex;
 447                 }
 448
 449                 if (nearest_collided == COLLISION_AXIS_NONE) {
 450                         // No collision with any collision box.
 451                         *pos_f += *speed_f * dtime;
 452                         dtime = 0;  // Set to 0 to avoid "infinite" loop due to small FP numbers
 453                 } else {
 454                         // Otherwise, a collision occurred.
 455                         NearbyCollisionInfo &nearest_info = cinfo[nearest_boxindex];
 456                         const aabb3f& cbox = nearest_info.box;
 457
 458                         //movingbox except moved to the horizontal position it would be after step up
 459                         aabb3f stepbox = movingbox;
 460                         stepbox.MinEdge.X += speed_f->X * dtime;
 461                         stepbox.MinEdge.Z += speed_f->Z * dtime;
 462                         stepbox.MaxEdge.X += speed_f->X * dtime;
 463                         stepbox.MaxEdge.Z += speed_f->Z * dtime;
 464                         // Check for stairs.
 465                         bool step_up = (nearest_collided != COLLISION_AXIS_Y) && // must not be Y direction
 466                                         (movingbox.MinEdge.Y < cbox.MaxEdge.Y) &&
 467                                         (movingbox.MinEdge.Y + stepheight > cbox.MaxEdge.Y) &&
 468                                         (!wouldCollideWithCeiling(cinfo, stepbox,
 469                                                         cbox.MaxEdge.Y - movingbox.MinEdge.Y,
 470                                                         d));
 471
 472                         // Get bounce multiplier
 473                         float bounce = -(float)nearest_info.bouncy / 100.0f;
 474
 475                         // Move to the point of collision and reduce dtime by nearest_dtime
 476                         if (nearest_dtime < 0) {
 477                                 // Handle negative nearest_dtime
 478                                 if (!step_up) {
 479                                         if (nearest_collided == COLLISION_AXIS_X)
 480                                                 pos_f->X += speed_f->X * nearest_dtime;
 481                                         if (nearest_collided == COLLISION_AXIS_Y)
 482                                                 pos_f->Y += speed_f->Y * nearest_dtime;
 483                                         if (nearest_collided == COLLISION_AXIS_Z)
 484                                                 pos_f->Z += speed_f->Z * nearest_dtime;
 485                                 }
 486                         } else {
 487                                 *pos_f += *speed_f * nearest_dtime;
 488                                 dtime -= nearest_dtime;
 489                         }
 490
 491                         bool is_collision = true;
 492                         if (nearest_info.is_unloaded)
 493                                 is_collision = false;
 494
 495                         CollisionInfo info;
 496                         if (nearest_info.is_object)
 497                                 info.type = COLLISION_OBJECT;
 498                         else
 499                                 info.type = COLLISION_NODE;
 500
 501                         info.node_p = nearest_info.position;
 502                         info.old_speed = *speed_f;
 503                         info.plane = nearest_collided;
 504
 505                         // Set the speed component that caused the collision to zero
 506                         if (step_up) {
 507                                 // Special case: Handle stairs
 508                                 nearest_info.is_step_up = true;
 509                                 is_collision = false;
 510                         } else if (nearest_collided == COLLISION_AXIS_X) {
 511                                 if (fabs(speed_f->X) > BS * 3)
 512                                         speed_f->X *= bounce;
 513                                 else
 514                                         speed_f->X = 0;
 515                                 result.collides = true;
 516                         } else if (nearest_collided == COLLISION_AXIS_Y) {
 517                                 if(fabs(speed_f->Y) > BS * 3)
 518                                         speed_f->Y *= bounce;
 519                                 else
 520                                         speed_f->Y = 0;
 521                                 result.collides = true;
 522                         } else if (nearest_collided == COLLISION_AXIS_Z) {
 523                                 if (fabs(speed_f->Z) > BS * 3)
 524                                         speed_f->Z *= bounce;
 525                                 else
 526                                         speed_f->Z = 0;
 527                                 result.collides = true;
 528                         }
 529
 530                         info.new_speed = *speed_f;
 531                         if (info.new_speed.getDistanceFrom(info.old_speed) < 0.1f * BS)
 532                                 is_collision = false;
 533
 534                         if (is_collision) {
 535                                 info.axis = nearest_collided;
 536                                 result.collisions.push_back(info);
 537                         }
 538                 }
 539         }
 540
 541         /*
 542                 Final touches: Check if standing on ground, step up stairs.
 543         */
 544         aabb3f box = box_0;
 545         box.MinEdge += *pos_f;
 546         box.MaxEdge += *pos_f;
 547         for (const auto &box_info : cinfo) {
 548                 const aabb3f &cbox = box_info.box;
 549
 550                 /*
 551                         See if the object is touching ground.
 552
 553                         Object touches ground if object's minimum Y is near node's
 554                         maximum Y and object's X-Z-area overlaps with the node's
 555                         X-Z-area.
 556                 */
 557
 558                 if (cbox.MaxEdge.X - d > box.MinEdge.X && cbox.MinEdge.X + d < box.MaxEdge.X &&
 559                                 cbox.MaxEdge.Z - d > box.MinEdge.Z &&
 560                                 cbox.MinEdge.Z + d < box.MaxEdge.Z) {
 561                         if (box_info.is_step_up) {
 562                                 pos_f->Y += cbox.MaxEdge.Y - box.MinEdge.Y;
 563                                 box = box_0;
 564                                 box.MinEdge += *pos_f;
 565                                 box.MaxEdge += *pos_f;
 566                         }
 567                         if (std::fabs(cbox.MaxEdge.Y - box.MinEdge.Y) < 0.05f) {
 568                                 result.touching_ground = true;
 569
 570                                 if (box_info.is_object)
 571                                         result.standing_on_object = true;
 572                         }
 573                 }
 574         }
 575
 576         return result;
 577 }