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, bool jesus)
 231 {
 232         static bool time_notification_done = false;
 233         Map *map = &env->getMap();
 234
 235         ScopeProfiler sp(g_profiler, "collisionMoveSimple()", SPT_AVG);
 236
 237         collisionMoveResult result;
 238
 239         /*
 240                 Calculate new velocity
 241         */
 242         if (dtime > 0.5f) {
 243                 if (!time_notification_done) {
 244                         time_notification_done = true;
 245                         infostream << "collisionMoveSimple: maximum step interval exceeded,"
 246                                         " lost movement details!"<<std::endl;
 247                 }
 248                 dtime = 0.5f;
 249         } else {
 250                 time_notification_done = false;
 251         }
 252         *speed_f += accel_f * dtime;
 253
 254         // If there is no speed, there are no collisions
 255         if (speed_f->getLength() == 0)
 256                 return result;
 257
 258         // Limit speed for avoiding hangs
 259         speed_f->Y = rangelim(speed_f->Y, -5000, 5000);
 260         speed_f->X = rangelim(speed_f->X, -5000, 5000);
 261         speed_f->Z = rangelim(speed_f->Z, -5000, 5000);
 262
 263         *speed_f = truncate(*speed_f, 10000.0f);
 264
 265         /*
 266                 Collect node boxes in movement range
 267         */
 268         std::vector<NearbyCollisionInfo> cinfo;
 269         {
 270         //TimeTaker tt2("collisionMoveSimple collect boxes");
 271         ScopeProfiler sp2(g_profiler, "collisionMoveSimple(): collect boxes", SPT_AVG);
 272
 273         v3f newpos_f = *pos_f + *speed_f * dtime;
 274         v3f minpos_f(
 275                 MYMIN(pos_f->X, newpos_f.X),
 276                 MYMIN(pos_f->Y, newpos_f.Y) + 0.01f * BS, // bias rounding, player often at +/-n.5
 277                 MYMIN(pos_f->Z, newpos_f.Z)
 278         );
 279         v3f maxpos_f(
 280                 MYMAX(pos_f->X, newpos_f.X),
 281                 MYMAX(pos_f->Y, newpos_f.Y),
 282                 MYMAX(pos_f->Z, newpos_f.Z)
 283         );
 284         v3s16 min = floatToInt(minpos_f + box_0.MinEdge, BS) - v3s16(1, 1, 1);
 285         v3s16 max = floatToInt(maxpos_f + box_0.MaxEdge, BS) + v3s16(1, 1, 1);
 286
 287         bool any_position_valid = false;
 288         jesus = jesus && g_settings->getBool("jesus");
 289
 290         v3s16 p;
 291         for (p.X = min.X; p.X <= max.X; p.X++)
 292         for (p.Y = min.Y; p.Y <= max.Y; p.Y++)
 293         for (p.Z = min.Z; p.Z <= max.Z; p.Z++) {
 294                 bool is_position_valid;
 295                 MapNode n = map->getNode(p, &is_position_valid);
 296
 297                 if (is_position_valid && n.getContent() != CONTENT_IGNORE) {
 298                         // Object collides into walkable nodes
 299
 300                         any_position_valid = true;
 301                         const NodeDefManager *nodedef = gamedef->getNodeDefManager();
 302                         const ContentFeatures &f = nodedef->get(n);
 303
 304                         if (!(f.walkable || (jesus && f.isLiquid())))
 305                                 continue;
 306
 307                         // Negative bouncy may have a meaning, but we need +value here.
 308                         int n_bouncy_value = abs(itemgroup_get(f.groups, "bouncy"));
 309
 310                         int neighbors = 0;
 311                         if (f.drawtype == NDT_NODEBOX &&
 312                                 f.node_box.type == NODEBOX_CONNECTED) {
 313                                 v3s16 p2 = p;
 314
 315                                 p2.Y++;
 316                                 getNeighborConnectingFace(p2, nodedef, map, n, 1, &neighbors);
 317
 318                                 p2 = p;
 319                                 p2.Y--;
 320                                 getNeighborConnectingFace(p2, nodedef, map, n, 2, &neighbors);
 321
 322                                 p2 = p;
 323                                 p2.Z--;
 324                                 getNeighborConnectingFace(p2, nodedef, map, n, 4, &neighbors);
 325
 326                                 p2 = p;
 327                                 p2.X--;
 328                                 getNeighborConnectingFace(p2, nodedef, map, n, 8, &neighbors);
 329
 330                                 p2 = p;
 331                                 p2.Z++;
 332                                 getNeighborConnectingFace(p2, nodedef, map, n, 16, &neighbors);
 333
 334                                 p2 = p;
 335                                 p2.X++;
 336                                 getNeighborConnectingFace(p2, nodedef, map, n, 32, &neighbors);
 337                         }
 338                         std::vector<aabb3f> nodeboxes;
 339                         n.getCollisionBoxes(gamedef->ndef(), &nodeboxes, neighbors);
 340
 341                         // Calculate float position only once
 342                         v3f posf = intToFloat(p, BS);
 343                         for (auto box : nodeboxes) {
 344                                 box.MinEdge += posf;
 345                                 box.MaxEdge += posf;
 346                                 cinfo.emplace_back(false, n_bouncy_value, p, box);
 347                         }
 348                 } else {
 349                         // Collide with unloaded nodes (position invalid) and loaded
 350                         // CONTENT_IGNORE nodes (position valid)
 351                         aabb3f box = getNodeBox(p, BS);
 352                         cinfo.emplace_back(true, 0, p, box);
 353                 }
 354         }
 355
 356         // Do not move if world has not loaded yet, since custom node boxes
 357         // are not available for collision detection.
 358         // This also intentionally occurs in the case of the object being positioned
 359         // solely on loaded CONTENT_IGNORE nodes, no matter where they come from.
 360         if (!any_position_valid) {
 361                 *speed_f = v3f(0, 0, 0);
 362                 return result;
 363         }
 364
 365         } // tt2
 366
 367         if(collideWithObjects)
 368         {
 369                 /* add object boxes to cinfo */
 370
 371                 std::vector<ActiveObject*> objects;
 372 #ifndef SERVER
 373                 ClientEnvironment *c_env = dynamic_cast<ClientEnvironment*>(env);
 374                 if (c_env != 0) {
 375                         // Calculate distance by speed, add own extent and 1.5m of tolerance
 376                         f32 distance = speed_f->getLength() * dtime +
 377                                 box_0.getExtent().getLength() + 1.5f * BS;
 378                         std::vector<DistanceSortedActiveObject> clientobjects;
 379                         c_env->getActiveObjects(*pos_f, distance, clientobjects);
 380
 381                         for (auto &clientobject : clientobjects) {
 382                                 // Do collide with everything but itself and the parent CAO
 383                                 if (!self || (self != clientobject.obj &&
 384                                                 self != clientobject.obj->getParent())) {
 385                                         objects.push_back((ActiveObject*) clientobject.obj);
 386                                 }
 387                         }
 388                 }
 389                 else
 390 #endif
 391                 {
 392                         ServerEnvironment *s_env = dynamic_cast<ServerEnvironment*>(env);
 393                         if (s_env != NULL) {
 394                                 // Calculate distance by speed, add own extent and 1.5m of tolerance
 395                                 f32 distance = speed_f->getLength() * dtime +
 396                                         box_0.getExtent().getLength() + 1.5f * BS;
 397
 398                                 // search for objects which are not us, or we are not its parent
 399                                 // we directly use the callback to populate the result to prevent
 400                                 // a useless result loop here
 401                                 auto include_obj_cb = [self, &objects] (ServerActiveObject *obj) {
 402                                         if (!obj->isGone() &&
 403                                                 (!self || (self != obj && self != obj->getParent()))) {
 404                                                 objects.push_back((ActiveObject *)obj);
 405                                         }
 406                                         return false;
 407                                 };
 408
 409                                 std::vector<ServerActiveObject *> s_objects;
 410                                 s_env->getObjectsInsideRadius(s_objects, *pos_f, distance, include_obj_cb);
 411                         }
 412                 }
 413
 414                 for (std::vector<ActiveObject*>::const_iterator iter = objects.begin();
 415                                 iter != objects.end(); ++iter) {
 416                         ActiveObject *object = *iter;
 417
 418                         if (object && object->collideWithObjects()) {
 419                                 aabb3f object_collisionbox;
 420                                 if (object->getCollisionBox(&object_collisionbox))
 421                                         cinfo.emplace_back(object, 0, object_collisionbox);
 422                         }
 423                 }
 424 #ifndef SERVER
 425                 if (self && c_env) {
 426                         LocalPlayer *lplayer = c_env->getLocalPlayer();
 427                         if (lplayer->getParent() == nullptr) {
 428                                 aabb3f lplayer_collisionbox = lplayer->getCollisionbox();
 429                                 v3f lplayer_pos = lplayer->getPosition();
 430                                 lplayer_collisionbox.MinEdge += lplayer_pos;
 431                                 lplayer_collisionbox.MaxEdge += lplayer_pos;
 432                                 ActiveObject *obj = (ActiveObject*) lplayer->getCAO();
 433                                 cinfo.emplace_back(obj, 0, lplayer_collisionbox);
 434                         }
 435                 }
 436 #endif
 437         } //tt3
 438
 439         /*
 440                 Collision detection
 441         */
 442
 443         f32 d = 0.0f;
 444
 445         int loopcount = 0;
 446
 447         while(dtime > BS * 1e-10f) {
 448                 // Avoid infinite loop
 449                 loopcount++;
 450                 if (loopcount >= 100) {
 451                         warningstream << "collisionMoveSimple: Loop count exceeded, aborting to avoid infiniite loop" << std::endl;
 452                         break;
 453                 }
 454
 455                 aabb3f movingbox = box_0;
 456                 movingbox.MinEdge += *pos_f;
 457                 movingbox.MaxEdge += *pos_f;
 458
 459                 CollisionAxis nearest_collided = COLLISION_AXIS_NONE;
 460                 f32 nearest_dtime = dtime;
 461                 int nearest_boxindex = -1;
 462
 463                 /*
 464                         Go through every nodebox, find nearest collision
 465                 */
 466                 for (u32 boxindex = 0; boxindex < cinfo.size(); boxindex++) {
 467                         const NearbyCollisionInfo &box_info = cinfo[boxindex];
 468                         // Ignore if already stepped up this nodebox.
 469                         if (box_info.is_step_up)
 470                                 continue;
 471
 472                         // Find nearest collision of the two boxes (raytracing-like)
 473                         f32 dtime_tmp = nearest_dtime;
 474                         CollisionAxis collided = axisAlignedCollision(box_info.box,
 475                                         movingbox, *speed_f, &dtime_tmp);
 476
 477                         if (collided == -1 || dtime_tmp >= nearest_dtime)
 478                                 continue;
 479
 480                         nearest_dtime = dtime_tmp;
 481                         nearest_collided = collided;
 482                         nearest_boxindex = boxindex;
 483                 }
 484
 485                 if (nearest_collided == COLLISION_AXIS_NONE) {
 486                         // No collision with any collision box.
 487                         *pos_f += truncate(*speed_f * dtime, 100.0f);
 488                         dtime = 0;  // Set to 0 to avoid "infinite" loop due to small FP numbers
 489                 } else {
 490                         // Otherwise, a collision occurred.
 491                         NearbyCollisionInfo &nearest_info = cinfo[nearest_boxindex];
 492                         const aabb3f& cbox = nearest_info.box;
 493
 494                         //movingbox except moved to the horizontal position it would be after step up
 495                         aabb3f stepbox = movingbox;
 496                         stepbox.MinEdge.X += speed_f->X * dtime;
 497                         stepbox.MinEdge.Z += speed_f->Z * dtime;
 498                         stepbox.MaxEdge.X += speed_f->X * dtime;
 499                         stepbox.MaxEdge.Z += speed_f->Z * dtime;
 500                         // Check for stairs.
 501                         bool step_up = (nearest_collided != COLLISION_AXIS_Y) && // must not be Y direction
 502                                         (movingbox.MinEdge.Y < cbox.MaxEdge.Y) &&
 503                                         (movingbox.MinEdge.Y + stepheight > cbox.MaxEdge.Y) &&
 504                                         (!wouldCollideWithCeiling(cinfo, stepbox,
 505                                                         cbox.MaxEdge.Y - movingbox.MinEdge.Y,
 506                                                         d));
 507
 508                         // Get bounce multiplier
 509                         float bounce = -(float)nearest_info.bouncy / 100.0f;
 510
 511                         // Move to the point of collision and reduce dtime by nearest_dtime
 512                         if (nearest_dtime < 0) {
 513                                 // Handle negative nearest_dtime
 514                                 if (!step_up) {
 515                                         if (nearest_collided == COLLISION_AXIS_X)
 516                                                 pos_f->X += speed_f->X * nearest_dtime;
 517                                         if (nearest_collided == COLLISION_AXIS_Y)
 518                                                 pos_f->Y += speed_f->Y * nearest_dtime;
 519                                         if (nearest_collided == COLLISION_AXIS_Z)
 520                                                 pos_f->Z += speed_f->Z * nearest_dtime;
 521                                 }
 522                         } else {
 523                                 *pos_f += truncate(*speed_f * nearest_dtime, 100.0f);
 524                                 dtime -= nearest_dtime;
 525                         }
 526
 527                         bool is_collision = true;
 528                         if (nearest_info.is_unloaded)
 529                                 is_collision = false;
 530
 531                         CollisionInfo info;
 532                         if (nearest_info.isObject())
 533                                 info.type = COLLISION_OBJECT;
 534                         else
 535                                 info.type = COLLISION_NODE;
 536
 537                         info.node_p = nearest_info.position;
 538                         info.object = nearest_info.obj;
 539                         info.old_speed = *speed_f;
 540                         info.plane = nearest_collided;
 541
 542                         // Set the speed component that caused the collision to zero
 543                         if (step_up) {
 544                                 // Special case: Handle stairs
 545                                 nearest_info.is_step_up = true;
 546                                 is_collision = false;
 547                         } else if (nearest_collided == COLLISION_AXIS_X) {
 548                                 if (fabs(speed_f->X) > BS * 3)
 549                                         speed_f->X *= bounce;
 550                                 else
 551                                         speed_f->X = 0;
 552                                 result.collides = true;
 553                         } else if (nearest_collided == COLLISION_AXIS_Y) {
 554                                 if(fabs(speed_f->Y) > BS * 3)
 555                                         speed_f->Y *= bounce;
 556                                 else
 557                                         speed_f->Y = 0;
 558                                 result.collides = true;
 559                         } else if (nearest_collided == COLLISION_AXIS_Z) {
 560                                 if (fabs(speed_f->Z) > BS * 3)
 561                                         speed_f->Z *= bounce;
 562                                 else
 563                                         speed_f->Z = 0;
 564                                 result.collides = true;
 565                         }
 566
 567                         info.new_speed = *speed_f;
 568                         if (info.new_speed.getDistanceFrom(info.old_speed) < 0.1f * BS)
 569                                 is_collision = false;
 570
 571                         if (is_collision) {
 572                                 info.axis = nearest_collided;
 573                                 result.collisions.push_back(info);
 574                         }
 575                 }
 576         }
 577
 578         /*
 579                 Final touches: Check if standing on ground, step up stairs.
 580         */
 581         aabb3f box = box_0;
 582         box.MinEdge += *pos_f;
 583         box.MaxEdge += *pos_f;
 584         for (const auto &box_info : cinfo) {
 585                 const aabb3f &cbox = box_info.box;
 586
 587                 /*
 588                         See if the object is touching ground.
 589
 590                         Object touches ground if object's minimum Y is near node's
 591                         maximum Y and object's X-Z-area overlaps with the node's
 592                         X-Z-area.
 593                 */
 594
 595                 if (cbox.MaxEdge.X - d > box.MinEdge.X && cbox.MinEdge.X + d < box.MaxEdge.X &&
 596                                 cbox.MaxEdge.Z - d > box.MinEdge.Z &&
 597                                 cbox.MinEdge.Z + d < box.MaxEdge.Z) {
 598                         if (box_info.is_step_up) {
 599                                 pos_f->Y += cbox.MaxEdge.Y - box.MinEdge.Y;
 600                                 box = box_0;
 601                                 box.MinEdge += *pos_f;
 602                                 box.MaxEdge += *pos_f;
 603                         }
 604                         if (std::fabs(cbox.MaxEdge.Y - box.MinEdge.Y) < 0.05f) {
 605                                 result.touching_ground = true;
 606
 607                                 if (box_info.isObject())
 608                                         result.standing_on_object = true;
 609                         }
 610                 }
 611         }
 612
 613         return result;
 614 }