src/collision.cpp

   1 /*
   2 Minetest-c55
   3 Copyright (C) 2010 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 General Public License as published by
   7 the Free Software Foundation; either version 2 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 General Public License for more details.
  14
  15 You should have received a copy of the GNU 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
  24 collisionMoveResult collisionMoveSimple(Map *map, f32 pos_max_d,
  25                 const core::aabbox3d<f32> &box_0,
  26                 f32 dtime, v3f &pos_f, v3f &speed_f)
  27 {
  28         collisionMoveResult result;
  29
  30         v3f oldpos_f = pos_f;
  31         v3s16 oldpos_i = floatToInt(oldpos_f, BS);
  32
  33         /*
  34                 Calculate new position
  35         */
  36         pos_f += speed_f * dtime;
  37
  38         /*
  39                 Collision detection
  40         */
  41
  42         // position in nodes
  43         v3s16 pos_i = floatToInt(pos_f, BS);
  44
  45         /*
  46                 Collision uncertainty radius
  47                 Make it a bit larger than the maximum distance of movement
  48         */
  49         f32 d = pos_max_d * 1.1;
  50         // A fairly large value in here makes moving smoother
  51         //f32 d = 0.15*BS;
  52
  53         // This should always apply, otherwise there are glitches
  54         assert(d > pos_max_d);
  55
  56         /*
  57                 Calculate collision box
  58         */
  59         core::aabbox3d<f32> box = box_0;
  60         box.MaxEdge += pos_f;
  61         box.MinEdge += pos_f;
  62         core::aabbox3d<f32> oldbox = box_0;
  63         oldbox.MaxEdge += oldpos_f;
  64         oldbox.MinEdge += oldpos_f;
  65
  66         /*
  67                 If the object lies on a walkable node, this is set to true.
  68         */
  69         result.touching_ground = false;
  70
  71         /*
  72                 Go through every node around the object
  73         */
  74         for(s16 y = oldpos_i.Y - 1; y <= oldpos_i.Y + 2; y++)
  75         for(s16 z = oldpos_i.Z - 1; z <= oldpos_i.Z + 1; z++)
  76         for(s16 x = oldpos_i.X - 1; x <= oldpos_i.X + 1; x++)
  77         {
  78                 try{
  79                         // Object collides into walkable nodes
  80                         if(content_walkable(map->getNode(v3s16(x,y,z)).d) == false)
  81                                 continue;
  82                 }
  83                 catch(InvalidPositionException &e)
  84                 {
  85                         // Doing nothing here will block the object from
  86                         // walking over map borders
  87                 }
  88
  89                 core::aabbox3d<f32> nodebox = getNodeBox(v3s16(x,y,z), BS);
  90
  91                 /*
  92                         See if the object is touching ground.
  93
  94                         Object touches ground if object's minimum Y is near node's
  95                         maximum Y and object's X-Z-area overlaps with the node's
  96                         X-Z-area.
  97
  98                         Use 0.15*BS so that it is easier to get on a node.
  99                 */
 100                 if(
 101                                 //fabs(nodebox.MaxEdge.Y-box.MinEdge.Y) < d
 102                                 fabs(nodebox.MaxEdge.Y-box.MinEdge.Y) < 0.15*BS
 103                                 && nodebox.MaxEdge.X-d > box.MinEdge.X
 104                                 && nodebox.MinEdge.X+d < box.MaxEdge.X
 105                                 && nodebox.MaxEdge.Z-d > box.MinEdge.Z
 106                                 && nodebox.MinEdge.Z+d < box.MaxEdge.Z
 107                 ){
 108                         result.touching_ground = true;
 109                 }
 110
 111                 // If object doesn't intersect with node, ignore node.
 112                 if(box.intersectsWithBox(nodebox) == false)
 113                         continue;
 114
 115                 /*
 116                         Go through every axis
 117                 */
 118                 v3f dirs[3] = {
 119                         v3f(0,0,1), // back-front
 120                         v3f(0,1,0), // top-bottom
 121                         v3f(1,0,0), // right-left
 122                 };
 123                 for(u16 i=0; i<3; i++)
 124                 {
 125                         /*
 126                                 Calculate values along the axis
 127                         */
 128                         f32 nodemax = nodebox.MaxEdge.dotProduct(dirs[i]);
 129                         f32 nodemin = nodebox.MinEdge.dotProduct(dirs[i]);
 130                         f32 objectmax = box.MaxEdge.dotProduct(dirs[i]);
 131                         f32 objectmin = box.MinEdge.dotProduct(dirs[i]);
 132                         f32 objectmax_old = oldbox.MaxEdge.dotProduct(dirs[i]);
 133                         f32 objectmin_old = oldbox.MinEdge.dotProduct(dirs[i]);
 134
 135                         /*
 136                                 Check collision for the axis.
 137                                 Collision happens when object is going through a surface.
 138                         */
 139                         bool negative_axis_collides =
 140                                 (nodemax > objectmin && nodemax <= objectmin_old + d
 141                                         && speed_f.dotProduct(dirs[i]) < 0);
 142                         bool positive_axis_collides =
 143                                 (nodemin < objectmax && nodemin >= objectmax_old - d
 144                                         && speed_f.dotProduct(dirs[i]) > 0);
 145                         bool main_axis_collides =
 146                                         negative_axis_collides || positive_axis_collides;
 147
 148                         /*
 149                                 Check overlap of object and node in other axes
 150                         */
 151                         bool other_axes_overlap = true;
 152                         for(u16 j=0; j<3; j++)
 153                         {
 154                                 if(j == i)
 155                                         continue;
 156                                 f32 nodemax = nodebox.MaxEdge.dotProduct(dirs[j]);
 157                                 f32 nodemin = nodebox.MinEdge.dotProduct(dirs[j]);
 158                                 f32 objectmax = box.MaxEdge.dotProduct(dirs[j]);
 159                                 f32 objectmin = box.MinEdge.dotProduct(dirs[j]);
 160                                 if(!(nodemax - d > objectmin && nodemin + d < objectmax))
 161                                 {
 162                                         other_axes_overlap = false;
 163                                         break;
 164                                 }
 165                         }
 166
 167                         /*
 168                                 If this is a collision, revert the pos_f in the main
 169                                 direction.
 170                         */
 171                         if(other_axes_overlap && main_axis_collides)
 172                         {
 173                                 speed_f -= speed_f.dotProduct(dirs[i]) * dirs[i];
 174                                 pos_f -= pos_f.dotProduct(dirs[i]) * dirs[i];
 175                                 pos_f += oldpos_f.dotProduct(dirs[i]) * dirs[i];
 176                         }
 177
 178                 }
 179         } // xyz
 180
 181         return result;
 182 }
 183
 184