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 #ifdef __FAST_MATH__
  36 #warning "-ffast-math is known to cause bugs in collision code, do not use!"
  37 #endif
  38
  39 struct NearbyCollisionInfo {
  40         // node
  41         NearbyCollisionInfo(bool is_ul, int bouncy, const v3s16 &pos,
  42                         const aabb3f &box) :
  43                 is_unloaded(is_ul),
  44                 obj(nullptr),
  45                 bouncy(bouncy),
  46                 position(pos),
  47                 box(box)
  48         {}
  49
  50         // object
  51         NearbyCollisionInfo(ActiveObject *obj, int bouncy,
  52                         const aabb3f &box) :
  53                 is_unloaded(false),
  54                 obj(obj),
  55                 bouncy(bouncy),
  56                 box(box)
  57         {}
  58
  59         inline bool isObject() const { return obj != nullptr; }
  60
  61         bool is_unloaded;
  62         bool is_step_up = false;
  63         ActiveObject *obj;
  64         int bouncy;
  65         v3s16 position;
  66         aabb3f box;
  67 };
  68
  69 // Helper functions:
  70 // Truncate floating point numbers to specified number of decimal places
  71 // in order to move all the floating point error to one side of the correct value
  72 static inline f32 truncate(const f32 val, const f32 factor)
  73 {
  74         return truncf(val * factor) / factor;
  75 }
  76
  77 static inline v3f truncate(const v3f& vec, const f32 factor)
  78 {
  79         return v3f(
  80                 truncate(vec.X, factor),
  81                 truncate(vec.Y, factor),
  82                 truncate(vec.Z, factor)
  83         );
  84 }
  85
  86 // Helper function:
  87 // Checks for collision of a moving aabbox with a static aabbox
  88 // Returns -1 if no collision, 0 if X collision, 1 if Y collision, 2 if Z collision
  89 // The time after which the collision occurs is stored in dtime.
  90 CollisionAxis axisAlignedCollision(
  91                 const aabb3f &staticbox, const aabb3f &movingbox,
  92                 const v3f &speed, f32 *dtime)
  93 {
  94         //TimeTaker tt("axisAlignedCollision");
  95
  96         aabb3f relbox(
  97                         (movingbox.MaxEdge.X - movingbox.MinEdge.X) + (staticbox.MaxEdge.X - staticbox.MinEdge.X),                                              // sum of the widths
  98                         (movingbox.MaxEdge.Y - movingbox.MinEdge.Y) + (staticbox.MaxEdge.Y - staticbox.MinEdge.Y),
  99                         (movingbox.MaxEdge.Z - movingbox.MinEdge.Z) + (staticbox.MaxEdge.Z - staticbox.MinEdge.Z),
 100                         std::max(movingbox.MaxEdge.X, staticbox.MaxEdge.X) - std::min(movingbox.MinEdge.X, staticbox.MinEdge.X),        //outer bounding 'box' dimensions
 101                         std::max(movingbox.MaxEdge.Y, staticbox.MaxEdge.Y) - std::min(movingbox.MinEdge.Y, staticbox.MinEdge.Y),
 102                         std::max(movingbox.MaxEdge.Z, staticbox.MaxEdge.Z) - std::min(movingbox.MinEdge.Z, staticbox.MinEdge.Z)
 103         );
 104
 105         const f32 dtime_max = *dtime;
 106         f32 inner_margin;               // the distance of clipping recovery
 107         f32 distance;
 108         f32 time;
 109
 110
 111         if (speed.Y) {
 112                 distance = relbox.MaxEdge.Y - relbox.MinEdge.Y;
 113                 *dtime = distance / std::abs(speed.Y);
 114                 time = std::max(*dtime, 0.0f);
 115
 116                 if (*dtime <= dtime_max) {
 117                         inner_margin = std::max(-0.5f * (staticbox.MaxEdge.Y - staticbox.MinEdge.Y), -2.0f);
 118
 119                         if ((speed.Y > 0 && staticbox.MinEdge.Y - movingbox.MaxEdge.Y > inner_margin) ||
 120                                 (speed.Y < 0 && movingbox.MinEdge.Y - staticbox.MaxEdge.Y > inner_margin)) {
 121                                 if (
 122                                         (std::max(movingbox.MaxEdge.X + speed.X * time, staticbox.MaxEdge.X)
 123                                                 - std::min(movingbox.MinEdge.X + speed.X * time, staticbox.MinEdge.X)
 124                                                 - relbox.MinEdge.X < 0) &&
 125                                                 (std::max(movingbox.MaxEdge.Z + speed.Z * time, staticbox.MaxEdge.Z)
 126                                                         - std::min(movingbox.MinEdge.Z + speed.Z * time, staticbox.MinEdge.Z)
 127                                                         - relbox.MinEdge.Z < 0)
 128                                         )
 129                                         return COLLISION_AXIS_Y;
 130                         }
 131                 }
 132                 else {
 133                         return COLLISION_AXIS_NONE;
 134                 }
 135         }
 136
 137         // NO else if here
 138
 139         if (speed.X) {
 140                 distance = relbox.MaxEdge.X - relbox.MinEdge.X;
 141                 *dtime = distance / std::abs(speed.X);
 142                 time = std::max(*dtime, 0.0f);
 143
 144                 if (*dtime <= dtime_max) {
 145                         inner_margin = std::max(-0.5f * (staticbox.MaxEdge.X - staticbox.MinEdge.X), -2.0f);
 146
 147                         if ((speed.X > 0 && staticbox.MinEdge.X - movingbox.MaxEdge.X > inner_margin) ||
 148                                 (speed.X < 0 && movingbox.MinEdge.X - staticbox.MaxEdge.X > inner_margin)) {
 149                                 if (
 150                                         (std::max(movingbox.MaxEdge.Y + speed.Y * time, staticbox.MaxEdge.Y)
 151                                                 - std::min(movingbox.MinEdge.Y + speed.Y * time, staticbox.MinEdge.Y)
 152                                                 - relbox.MinEdge.Y < 0) &&
 153                                                 (std::max(movingbox.MaxEdge.Z + speed.Z * time, staticbox.MaxEdge.Z)
 154                                                         - std::min(movingbox.MinEdge.Z + speed.Z * time, staticbox.MinEdge.Z)
 155                                                         - relbox.MinEdge.Z < 0)
 156                                         )
 157                                         return COLLISION_AXIS_X;
 158                         }
 159                 } else {
 160                         return COLLISION_AXIS_NONE;
 161                 }
 162         }
 163
 164         // NO else if here
 165
 166         if (speed.Z) {
 167                 distance = relbox.MaxEdge.Z - relbox.MinEdge.Z;
 168                 *dtime = distance / std::abs(speed.Z);
 169                 time = std::max(*dtime, 0.0f);
 170
 171                 if (*dtime <= dtime_max) {
 172                         inner_margin = std::max(-0.5f * (staticbox.MaxEdge.Z - staticbox.MinEdge.Z), -2.0f);
 173
 174                         if ((speed.Z > 0 && staticbox.MinEdge.Z - movingbox.MaxEdge.Z > inner_margin) ||
 175                                 (speed.Z < 0 && movingbox.MinEdge.Z - staticbox.MaxEdge.Z > inner_margin)) {
 176                                 if (
 177                                         (std::max(movingbox.MaxEdge.X + speed.X * time, staticbox.MaxEdge.X)
 178                                                 - std::min(movingbox.MinEdge.X + speed.X * time, staticbox.MinEdge.X)
 179                                                 - relbox.MinEdge.X < 0) &&
 180                                                 (std::max(movingbox.MaxEdge.Y + speed.Y * time, staticbox.MaxEdge.Y)
 181                                                         - std::min(movingbox.MinEdge.Y + speed.Y * time, staticbox.MinEdge.Y)
 182                                                         - relbox.MinEdge.Y < 0)
 183                                         )
 184                                         return COLLISION_AXIS_Z;
 185                         }
 186                 }
 187         }
 188
 189         return COLLISION_AXIS_NONE;
 190 }
 191
 192 // Helper function:
 193 // Checks if moving the movingbox up by the given distance would hit a ceiling.
 194 bool wouldCollideWithCeiling(
 195                 const std::vector<NearbyCollisionInfo> &cinfo,
 196                 const aabb3f &movingbox,
 197                 f32 y_increase, f32 d)
 198 {
 199         //TimeTaker tt("wouldCollideWithCeiling");
 200
 201         assert(y_increase >= 0);        // pre-condition
 202
 203         for (const auto &it : cinfo) {
 204                 const aabb3f &staticbox = it.box;
 205                 if ((movingbox.MaxEdge.Y - d <= staticbox.MinEdge.Y) &&
 206                                 (movingbox.MaxEdge.Y + y_increase > staticbox.MinEdge.Y) &&
 207                                 (movingbox.MinEdge.X < staticbox.MaxEdge.X) &&
 208                                 (movingbox.MaxEdge.X > staticbox.MinEdge.X) &&
 209                                 (movingbox.MinEdge.Z < staticbox.MaxEdge.Z) &&
 210                                 (movingbox.MaxEdge.Z > staticbox.MinEdge.Z))
 211                         return true;
 212         }
 213
 214         return false;
 215 }
 216
 217 static inline void getNeighborConnectingFace(const v3s16 &p,
 218         const NodeDefManager *nodedef, Map *map, MapNode n, int v, int *neighbors)
 219 {
 220         MapNode n2 = map->getNode(p);
 221         if (nodedef->nodeboxConnects(n, n2, v))
 222                 *neighbors |= v;
 223 }
 224
 225 collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 226                 f32 pos_max_d, const aabb3f &box_0,
 227                 f32 stepheight, f32 dtime,
 228                 v3f *pos_f, v3f *speed_f,
 229                 v3f accel_f, ActiveObject *self,
 230                 bool collideWithObjects)
 231 {
 232         #define PROFILER_NAME(text) (s_env ? ("Server: " text) : ("Client: " text))
 233         static bool time_notification_done = false;
 234         Map *map = &env->getMap();
 235         ServerEnvironment *s_env = dynamic_cast<ServerEnvironment*>(env);
 236
 237         ScopeProfiler sp(g_profiler, PROFILER_NAME("collisionMoveSimple()"), SPT_AVG);
 238
 239         collisionMoveResult result;
 240
 241         /*
 242                 Calculate new velocity
 243         */
 244         if (dtime > 0.5f) {
 245                 if (!time_notification_done) {
 246                         time_notification_done = true;
 247                         infostream << "collisionMoveSimple: maximum step interval exceeded,"
 248                                         " lost movement details!"<<std::endl;
 249                 }
 250                 dtime = 0.5f;
 251         } else {
 252                 time_notification_done = false;
 253         }
 254
 255         v3f dpos_f = (*speed_f + accel_f * 0.5f * dtime) * dtime;
 256         v3f newpos_f = *pos_f + dpos_f;
 257         *speed_f += accel_f * dtime;
 258
 259         // If the object is static, there are no collisions
 260         if (dpos_f == v3f())
 261                 return result;
 262
 263         // Limit speed for avoiding hangs
 264         speed_f->Y = rangelim(speed_f->Y, -5000, 5000);
 265         speed_f->X = rangelim(speed_f->X, -5000, 5000);
 266         speed_f->Z = rangelim(speed_f->Z, -5000, 5000);
 267
 268         *speed_f = truncate(*speed_f, 10000.0f);
 269
 270         /*
 271                 Collect node boxes in movement range
 272         */
 273         std::vector<NearbyCollisionInfo> cinfo;
 274         {
 275         //TimeTaker tt2("collisionMoveSimple collect boxes");
 276         ScopeProfiler sp2(g_profiler, PROFILER_NAME("collision collect boxes"), SPT_AVG);
 277
 278         v3f minpos_f(
 279                 MYMIN(pos_f->X, newpos_f.X),
 280                 MYMIN(pos_f->Y, newpos_f.Y) + 0.01f * BS, // bias rounding, player often at +/-n.5
 281                 MYMIN(pos_f->Z, newpos_f.Z)
 282         );
 283         v3f maxpos_f(
 284                 MYMAX(pos_f->X, newpos_f.X),
 285                 MYMAX(pos_f->Y, newpos_f.Y),
 286                 MYMAX(pos_f->Z, newpos_f.Z)
 287         );
 288         v3s16 min = floatToInt(minpos_f + box_0.MinEdge, BS) - v3s16(1, 1, 1);
 289         v3s16 max = floatToInt(maxpos_f + box_0.MaxEdge, BS) + v3s16(1, 1, 1);
 290
 291         bool any_position_valid = false;
 292
 293         v3s16 p;
 294         for (p.X = min.X; p.X <= max.X; p.X++)
 295         for (p.Y = min.Y; p.Y <= max.Y; p.Y++)
 296         for (p.Z = min.Z; p.Z <= max.Z; p.Z++) {
 297                 bool is_position_valid;
 298                 MapNode n = map->getNode(p, &is_position_valid);
 299
 300                 if (is_position_valid && n.getContent() != CONTENT_IGNORE) {
 301                         // Object collides into walkable nodes
 302
 303                         any_position_valid = true;
 304                         const NodeDefManager *nodedef = gamedef->getNodeDefManager();
 305                         const ContentFeatures &f = nodedef->get(n);
 306
 307                         if (!f.walkable)
 308                                 continue;
 309
 310                         // Negative bouncy may have a meaning, but we need +value here.
 311                         int n_bouncy_value = abs(itemgroup_get(f.groups, "bouncy"));
 312
 313                         int neighbors = 0;
 314                         if (f.drawtype == NDT_NODEBOX &&
 315                                 f.node_box.type == NODEBOX_CONNECTED) {
 316                                 v3s16 p2 = p;
 317
 318                                 p2.Y++;
 319                                 getNeighborConnectingFace(p2, nodedef, map, n, 1, &neighbors);
 320
 321                                 p2 = p;
 322                                 p2.Y--;
 323                                 getNeighborConnectingFace(p2, nodedef, map, n, 2, &neighbors);
 324
 325                                 p2 = p;
 326                                 p2.Z--;
 327                                 getNeighborConnectingFace(p2, nodedef, map, n, 4, &neighbors);
 328
 329                                 p2 = p;
 330                                 p2.X--;
 331                                 getNeighborConnectingFace(p2, nodedef, map, n, 8, &neighbors);
 332
 333                                 p2 = p;
 334                                 p2.Z++;
 335                                 getNeighborConnectingFace(p2, nodedef, map, n, 16, &neighbors);
 336
 337                                 p2 = p;
 338                                 p2.X++;
 339                                 getNeighborConnectingFace(p2, nodedef, map, n, 32, &neighbors);
 340                         }
 341                         std::vector<aabb3f> nodeboxes;
 342                         n.getCollisionBoxes(gamedef->ndef(), &nodeboxes, neighbors);
 343
 344                         // Calculate float position only once
 345                         v3f posf = intToFloat(p, BS);
 346                         for (auto box : nodeboxes) {
 347                                 box.MinEdge += posf;
 348                                 box.MaxEdge += posf;
 349                                 cinfo.emplace_back(false, n_bouncy_value, p, box);
 350                         }
 351                 } else {
 352                         // Collide with unloaded nodes (position invalid) and loaded
 353                         // CONTENT_IGNORE nodes (position valid)
 354                         aabb3f box = getNodeBox(p, BS);
 355                         cinfo.emplace_back(true, 0, p, box);
 356                 }
 357         }
 358
 359         // Do not move if world has not loaded yet, since custom node boxes
 360         // are not available for collision detection.
 361         // This also intentionally occurs in the case of the object being positioned
 362         // solely on loaded CONTENT_IGNORE nodes, no matter where they come from.
 363         if (!any_position_valid) {
 364                 *speed_f = v3f(0, 0, 0);
 365                 return result;
 366         }
 367
 368         } // tt2
 369
 370         if(collideWithObjects)
 371         {
 372                 /* add object boxes to cinfo */
 373
 374                 std::vector<ActiveObject*> objects;
 375 #ifndef SERVER
 376                 ClientEnvironment *c_env = dynamic_cast<ClientEnvironment*>(env);
 377                 if (c_env != 0) {
 378                         // Calculate distance by speed, add own extent and 1.5m of tolerance
 379                         f32 distance = speed_f->getLength() * dtime +
 380                                 box_0.getExtent().getLength() + 1.5f * BS;
 381                         std::vector<DistanceSortedActiveObject> clientobjects;
 382                         c_env->getActiveObjects(*pos_f, distance, clientobjects);
 383
 384                         for (auto &clientobject : clientobjects) {
 385                                 // Do collide with everything but itself and the parent CAO
 386                                 if (!self || (self != clientobject.obj &&
 387                                                 self != clientobject.obj->getParent())) {
 388                                         objects.push_back((ActiveObject*) clientobject.obj);
 389                                 }
 390                         }
 391                 }
 392                 else
 393 #endif
 394                 {
 395                         if (s_env != NULL) {
 396                                 // Calculate distance by speed, add own extent and 1.5m of tolerance
 397                                 f32 distance = speed_f->getLength() * dtime +
 398                                         box_0.getExtent().getLength() + 1.5f * BS;
 399
 400                                 // search for objects which are not us, or we are not its parent
 401                                 // we directly use the callback to populate the result to prevent
 402                                 // a useless result loop here
 403                                 auto include_obj_cb = [self, &objects] (ServerActiveObject *obj) {
 404                                         if (!obj->isGone() &&
 405                                                 (!self || (self != obj && self != obj->getParent()))) {
 406                                                 objects.push_back((ActiveObject *)obj);
 407                                         }
 408                                         return false;
 409                                 };
 410
 411                                 std::vector<ServerActiveObject *> s_objects;
 412                                 s_env->getObjectsInsideRadius(s_objects, *pos_f, distance, include_obj_cb);
 413                         }
 414                 }
 415
 416                 for (std::vector<ActiveObject*>::const_iterator iter = objects.begin();
 417                                 iter != objects.end(); ++iter) {
 418                         ActiveObject *object = *iter;
 419
 420                         if (object && object->collideWithObjects()) {
 421                                 aabb3f object_collisionbox;
 422                                 if (object->getCollisionBox(&object_collisionbox))
 423                                         cinfo.emplace_back(object, 0, object_collisionbox);
 424                         }
 425                 }
 426 #ifndef SERVER
 427                 if (self && c_env) {
 428                         LocalPlayer *lplayer = c_env->getLocalPlayer();
 429                         if (lplayer->getParent() == nullptr) {
 430                                 aabb3f lplayer_collisionbox = lplayer->getCollisionbox();
 431                                 v3f lplayer_pos = lplayer->getPosition();
 432                                 lplayer_collisionbox.MinEdge += lplayer_pos;
 433                                 lplayer_collisionbox.MaxEdge += lplayer_pos;
 434                                 ActiveObject *obj = (ActiveObject*) lplayer->getCAO();
 435                                 cinfo.emplace_back(obj, 0, lplayer_collisionbox);
 436                         }
 437                 }
 438 #endif
 439         } //tt3
 440
 441         /*
 442                 Collision detection
 443         */
 444
 445         f32 d = 0.0f;
 446
 447         int loopcount = 0;
 448
 449         while(dtime > BS * 1e-10f) {
 450                 // Avoid infinite loop
 451                 loopcount++;
 452                 if (loopcount >= 100) {
 453                         warningstream << "collisionMoveSimple: Loop count exceeded, aborting to avoid infiniite loop" << std::endl;
 454                         break;
 455                 }
 456
 457                 aabb3f movingbox = box_0;
 458                 movingbox.MinEdge += *pos_f;
 459                 movingbox.MaxEdge += *pos_f;
 460
 461                 CollisionAxis nearest_collided = COLLISION_AXIS_NONE;
 462                 f32 nearest_dtime = dtime;
 463                 int nearest_boxindex = -1;
 464
 465                 /*
 466                         Go through every nodebox, find nearest collision
 467                 */
 468                 for (u32 boxindex = 0; boxindex < cinfo.size(); boxindex++) {
 469                         const NearbyCollisionInfo &box_info = cinfo[boxindex];
 470                         // Ignore if already stepped up this nodebox.
 471                         if (box_info.is_step_up)
 472                                 continue;
 473
 474                         // Find nearest collision of the two boxes (raytracing-like)
 475                         f32 dtime_tmp = nearest_dtime;
 476                         CollisionAxis collided = axisAlignedCollision(box_info.box,
 477                                         movingbox, *speed_f, &dtime_tmp);
 478
 479                         if (collided == -1 || dtime_tmp >= nearest_dtime)
 480                                 continue;
 481
 482                         nearest_dtime = dtime_tmp;
 483                         nearest_collided = collided;
 484                         nearest_boxindex = boxindex;
 485                 }
 486
 487                 if (nearest_collided == COLLISION_AXIS_NONE) {
 488                         // No collision with any collision box.
 489                         *pos_f += truncate(*speed_f * dtime, 100.0f);
 490                         dtime = 0;  // Set to 0 to avoid "infinite" loop due to small FP numbers
 491                 } else {
 492                         // Otherwise, a collision occurred.
 493                         NearbyCollisionInfo &nearest_info = cinfo[nearest_boxindex];
 494                         const aabb3f& cbox = nearest_info.box;
 495
 496                         //movingbox except moved to the horizontal position it would be after step up
 497                         aabb3f stepbox = movingbox;
 498                         stepbox.MinEdge.X += speed_f->X * dtime;
 499                         stepbox.MinEdge.Z += speed_f->Z * dtime;
 500                         stepbox.MaxEdge.X += speed_f->X * dtime;
 501                         stepbox.MaxEdge.Z += speed_f->Z * dtime;
 502                         // Check for stairs.
 503                         bool step_up = (nearest_collided != COLLISION_AXIS_Y) && // must not be Y direction
 504                                         (movingbox.MinEdge.Y < cbox.MaxEdge.Y) &&
 505                                         (movingbox.MinEdge.Y + stepheight > cbox.MaxEdge.Y) &&
 506                                         (!wouldCollideWithCeiling(cinfo, stepbox,
 507                                                         cbox.MaxEdge.Y - movingbox.MinEdge.Y,
 508                                                         d));
 509
 510                         // Get bounce multiplier
 511                         float bounce = -(float)nearest_info.bouncy / 100.0f;
 512
 513                         // Move to the point of collision and reduce dtime by nearest_dtime
 514                         if (nearest_dtime < 0) {
 515                                 // Handle negative nearest_dtime
 516                                 if (!step_up) {
 517                                         if (nearest_collided == COLLISION_AXIS_X)
 518                                                 pos_f->X += speed_f->X * nearest_dtime;
 519                                         if (nearest_collided == COLLISION_AXIS_Y)
 520                                                 pos_f->Y += speed_f->Y * nearest_dtime;
 521                                         if (nearest_collided == COLLISION_AXIS_Z)
 522                                                 pos_f->Z += speed_f->Z * nearest_dtime;
 523                                 }
 524                         } else {
 525                                 *pos_f += truncate(*speed_f * nearest_dtime, 100.0f);
 526                                 dtime -= nearest_dtime;
 527                         }
 528
 529                         bool is_collision = true;
 530                         if (nearest_info.is_unloaded)
 531                                 is_collision = false;
 532
 533                         CollisionInfo info;
 534                         if (nearest_info.isObject())
 535                                 info.type = COLLISION_OBJECT;
 536                         else
 537                                 info.type = COLLISION_NODE;
 538
 539                         info.node_p = nearest_info.position;
 540                         info.object = nearest_info.obj;
 541                         info.old_speed = *speed_f;
 542                         info.plane = nearest_collided;
 543
 544                         // Set the speed component that caused the collision to zero
 545                         if (step_up) {
 546                                 // Special case: Handle stairs
 547                                 nearest_info.is_step_up = true;
 548                                 is_collision = false;
 549                         } else if (nearest_collided == COLLISION_AXIS_X) {
 550                                 if (fabs(speed_f->X) > BS * 3)
 551                                         speed_f->X *= bounce;
 552                                 else
 553                                         speed_f->X = 0;
 554                                 result.collides = true;
 555                         } else if (nearest_collided == COLLISION_AXIS_Y) {
 556                                 if(fabs(speed_f->Y) > BS * 3)
 557                                         speed_f->Y *= bounce;
 558                                 else
 559                                         speed_f->Y = 0;
 560                                 result.collides = true;
 561                         } else if (nearest_collided == COLLISION_AXIS_Z) {
 562                                 if (fabs(speed_f->Z) > BS * 3)
 563                                         speed_f->Z *= bounce;
 564                                 else
 565                                         speed_f->Z = 0;
 566                                 result.collides = true;
 567                         }
 568
 569                         info.new_speed = *speed_f;
 570                         if (info.new_speed.getDistanceFrom(info.old_speed) < 0.1f * BS)
 571                                 is_collision = false;
 572
 573                         if (is_collision) {
 574                                 info.axis = nearest_collided;
 575                                 result.collisions.push_back(info);
 576                         }
 577                 }
 578         }
 579
 580         /*
 581                 Final touches: Check if standing on ground, step up stairs.
 582         */
 583         aabb3f box = box_0;
 584         box.MinEdge += *pos_f;
 585         box.MaxEdge += *pos_f;
 586         for (const auto &box_info : cinfo) {
 587                 const aabb3f &cbox = box_info.box;
 588
 589                 /*
 590                         See if the object is touching ground.
 591
 592                         Object touches ground if object's minimum Y is near node's
 593                         maximum Y and object's X-Z-area overlaps with the node's
 594                         X-Z-area.
 595                 */
 596
 597                 if (cbox.MaxEdge.X - d > box.MinEdge.X && cbox.MinEdge.X + d < box.MaxEdge.X &&
 598                                 cbox.MaxEdge.Z - d > box.MinEdge.Z &&
 599                                 cbox.MinEdge.Z + d < box.MaxEdge.Z) {
 600                         if (box_info.is_step_up) {
 601                                 pos_f->Y += cbox.MaxEdge.Y - box.MinEdge.Y;
 602                                 box = box_0;
 603                                 box.MinEdge += *pos_f;
 604                                 box.MaxEdge += *pos_f;
 605                         }
 606                         if (std::fabs(cbox.MaxEdge.Y - box.MinEdge.Y) < 0.05f) {
 607                                 result.touching_ground = true;
 608
 609                                 if (box_info.isObject())
 610                                         result.standing_on_object = true;
 611                         }
 612                 }
 613         }
 614
 615         return result;
 616 }