bvh.h

   1 /*
   2  * Copyright (C) 2021-2022 Mt.ZERO Software, Harry Godden - All Rights Reserved
   3  */
   4
   5 #ifndef BVH_H
   6 #define BVH_H
   7 #include "common.h"
   8
   9 /*
  10  * Usage:
  11  *
  12  * create a bh_system with functions filled out for expand, centroid, and swap.
  13  * optionally include item_debug and cast_ray functions if needed, otherwise,
  14  *   set them to null
  15  *
  16  * create a bh_tree struct with:
  17  *   user: a pointer back the base of the data you are ordering
  18  *   system: the system we created above which will deal with the data
  19  *
  20  * call bh_create( bh_tree *bh, u32 item_count )
  21  * VG_STATIC int bh_ray( bh_tree *bh, u32 inode, v3f co, v3f dir, ray_hit *hit )
  22  * VG_STATIC int bh_select( bh_tree *bh, boxf box, u32 *buffer, int len )
  23  */
  24
  25 typedef struct bh_node bh_node;
  26 typedef struct bh_tree bh_tree;
  27 typedef struct bh_system bh_system;
  28
  29 struct bh_tree
  30 {
  31    u32 node_count;
  32
  33    bh_system *system;
  34    void *user;
  35    u32 max_per_leaf;
  36
  37    struct bh_node
  38    {
  39       boxf bbx;
  40
  41       /* if il is 0, this is a leaf */
  42       int il, count;
  43       union{ int ir, start; };
  44    }
  45    nodes[];
  46 };
  47
  48 struct bh_system
  49 {
  50    void  (*expand_bound)( void *user, boxf bound, u32 item_index );
  51    float (*item_centroid)( void *user, u32 item_index, int axis );
  52    void  (*item_closest)( void *user, u32 item_index, v3f point, v3f closest );
  53    void  (*item_swap)( void *user, u32 ia, u32 ib );
  54
  55    /*
  56     * Optional:
  57     *   item_debug   - draw this item quickly usually with lines
  58     *   cast_ray     - shoot a ray against the object, if this is not set,
  59     *                  raycasts will simply return the hit on the bvh node
  60     */
  61
  62    void  (*item_debug)( void *user, u32 item_index );
  63    int   (*cast_ray)( void *user, u32 index, v3f co, v3f dir, ray_hit *hit );
  64 };
  65
  66 VG_STATIC void bh_update_bounds( bh_tree *bh, u32 inode )
  67 {
  68    bh_node *node = &bh->nodes[ inode ];
  69
  70    box_init_inf( node->bbx );
  71    for( u32 i=0; i<node->count; i++ )
  72    {
  73       u32 idx = node->start+i;
  74       bh->system->expand_bound( bh->user, node->bbx, idx );
  75    }
  76 }
  77
  78 VG_STATIC void bh_subdivide( bh_tree *bh, u32 inode )
  79 {
  80    bh_node *node = &bh->nodes[ inode ];
  81
  82    if( node->count <= bh->max_per_leaf )
  83       return;
  84
  85    v3f extent;
  86    v3_sub( node->bbx[1], node->bbx[0], extent );
  87
  88    int axis = 0;
  89    if( extent[1] > extent[0] ) axis = 1;
  90    if( extent[2] > extent[axis] ) axis = 2;
  91
  92    float split = node->bbx[0][axis] + extent[axis]*0.5f;
  93    float avg = 0.0;
  94    for( u32 t=0; t<node->count; t++ )
  95    {
  96       u32 idx = node->start+t;
  97       avg += bh->system->item_centroid( bh->user, idx, axis );
  98    }
  99    avg /= (float)node->count;
 100    split = avg;
 101
 102
 103    i32 i = node->start,
 104        j = i + node->count-1;
 105
 106    while( i <= j )
 107    {
 108       if( bh->system->item_centroid( bh->user, i, axis ) < split )
 109          i ++;
 110       else
 111       {
 112          bh->system->item_swap( bh->user, i, j );
 113          j --;
 114       }
 115    }
 116
 117    u32 left_count = i - node->start;
 118    if( left_count == 0 || left_count == node->count ) return;
 119
 120    u32 il = bh->node_count ++,
 121        ir = bh->node_count ++;
 122
 123    bh_node *lnode = &bh->nodes[il],
 124            *rnode = &bh->nodes[ir];
 125
 126    lnode->start = node->start;
 127    lnode->count = left_count;
 128    rnode->start = i;
 129    rnode->count = node->count - left_count;
 130
 131    node->il = il;
 132    node->ir = ir;
 133    node->count = 0;
 134
 135    bh_update_bounds( bh, il );
 136    bh_update_bounds( bh, ir );
 137    bh_subdivide( bh, il );
 138    bh_subdivide( bh, ir );
 139 }
 140
 141 VG_STATIC bh_tree *bh_create( void *lin_alloc, bh_system *system,
 142                               void *user, u32 item_count, u32 max_per_leaf )
 143 {
 144    assert( max_per_leaf > 0 );
 145
 146    if( item_count == 0 )
 147    {
 148       bh_tree *bh = vg_linear_alloc( lin_alloc, sizeof(bh_tree) );
 149       bh->node_count = 0;
 150       bh->system = system;
 151       bh->user = user;
 152       return bh;
 153    }
 154
 155    u32 totsize = sizeof(bh_tree) + sizeof(bh_node)*(item_count*2-1);
 156    bh_tree *bh = vg_linear_alloc( lin_alloc, vg_align8(totsize) );
 157    bh->system = system;
 158    bh->user = user;
 159    bh->max_per_leaf = max_per_leaf;
 160
 161    bh_node *root = &bh->nodes[0];
 162    bh->node_count = 1;
 163
 164    root->il = 0;
 165    root->ir = 0;
 166    root->count = item_count;
 167    root->start = 0;
 168
 169    bh_update_bounds( bh, 0 );
 170    bh_subdivide( bh, 0 );
 171
 172    totsize = sizeof(bh_tree) + sizeof(bh_node) * bh->node_count;
 173    bh = vg_linear_resize( lin_alloc, bh, totsize );
 174
 175    vg_success( "BVH done, size: %u/%u\n", bh->node_count, (item_count*2-1) );
 176    return bh;
 177 }
 178
 179 /*
 180  * Draw items in this leaf node.
 181  * *item_debug() must be set!
 182  */
 183 VG_STATIC void bh_debug_leaf( bh_tree *bh, bh_node *node )
 184 {
 185    vg_line_boxf( node->bbx, 0xff00ff00 );
 186
 187    if( bh->system->item_debug )
 188    {
 189       for( u32 i=0; i<node->count; i++ )
 190       {
 191          u32 idx = node->start+i;
 192          bh->system->item_debug( bh->user, idx );
 193       }
 194    }
 195 }
 196
 197 /*
 198  * Trace the bh tree all the way down to the leaf nodes where pos is inside
 199  */
 200 VG_STATIC void bh_debug_trace( bh_tree *bh, u32 inode, v3f pos, u32 colour )
 201 {
 202    bh_node *node = &bh->nodes[ inode ];
 203
 204    if( (pos[0] >= node->bbx[0][0] && pos[0] <= node->bbx[1][0]) &&
 205        (pos[2] >= node->bbx[0][2] && pos[2] <= node->bbx[1][2]) )
 206    {
 207       if( !node->count )
 208       {
 209          vg_line_boxf( node->bbx, colour );
 210
 211          bh_debug_trace( bh, node->il, pos, colour );
 212          bh_debug_trace( bh, node->ir, pos, colour );
 213       }
 214       else
 215       {
 216          if( bh->system->item_debug )
 217             bh_debug_leaf( bh, node );
 218       }
 219    }
 220 }
 221
 222 VG_STATIC int bh_ray( bh_tree *bh, v3f co, v3f dir, ray_hit *hit )
 223 {
 224    if( bh->node_count < 2 )
 225       return 0;
 226
 227    int count = 0;
 228    u32 stack[100];
 229    u32 depth = 2;
 230
 231    stack[0] = 0;
 232    stack[1] = bh->nodes[0].il;
 233    stack[2] = bh->nodes[0].ir;
 234
 235    v3f dir_inv;
 236    dir_inv[0] = 1.0f/dir[0];
 237    dir_inv[1] = 1.0f/dir[1];
 238    dir_inv[2] = 1.0f/dir[2];
 239
 240    while(depth)
 241    {
 242       bh_node *inode = &bh->nodes[ stack[depth] ];
 243       if( ray_aabb1( inode->bbx, co, dir_inv, hit->dist ) )
 244       {
 245          if( inode->count )
 246          {
 247             for( u32 i=0; i<inode->count; i++ )
 248             {
 249                u32 idx = inode->start+i;
 250
 251                if( bh->system->cast_ray )
 252                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 253                else
 254                   count ++;
 255             }
 256
 257             depth --;
 258          }
 259          else
 260          {
 261             if( depth+1 >= vg_list_size(stack) )
 262             {
 263                vg_error( "Maximum stack reached!\n" );
 264                return count;
 265             }
 266
 267             stack[depth] = inode->il;
 268             stack[depth+1] = inode->ir;
 269             depth ++;
 270          }
 271       }
 272       else
 273       {
 274          depth --;
 275       }
 276    }
 277
 278    return count;
 279 }
 280
 281 typedef struct bh_iter bh_iter;
 282 struct bh_iter
 283 {
 284    struct
 285    {
 286       int id, depth;
 287    }
 288    stack[64];
 289
 290    int depth, i;
 291 };
 292
 293 VG_STATIC void bh_iter_init( int root, bh_iter *it )
 294 {
 295    it->stack[0].id = root;
 296    it->stack[0].depth = 0;
 297    it->depth = 0;
 298    it->i = 0;
 299 }
 300
 301 VG_STATIC int bh_next( bh_tree *bh, bh_iter *it, boxf box, int *em )
 302 {
 303    while( it->depth >= 0 )
 304    {
 305       bh_node *inode = &bh->nodes[ it->stack[it->depth].id ];
 306
 307       /* Only process overlapping nodes */
 308       if( !box_overlap( inode->bbx, box ) )
 309       {
 310          it->depth --;
 311          continue;
 312       }
 313
 314       if( inode->count )
 315       {
 316          if( it->i < inode->count )
 317          {
 318             *em = inode->start+it->i;
 319             it->i ++;
 320             return 1;
 321          }
 322          else
 323          {
 324             it->depth --;
 325             it->i = 0;
 326          }
 327       }
 328       else
 329       {
 330          if( it->depth+1 >= vg_list_size(it->stack) )
 331          {
 332             vg_error( "Maximum stack reached!\n" );
 333             return 0;
 334          }
 335
 336          it->stack[it->depth  ].id = inode->il;
 337          it->stack[it->depth+1].id = inode->ir;
 338          it->depth ++;
 339          it->i = 0;
 340       }
 341    }
 342
 343    return 0;
 344 }
 345
 346 VG_STATIC int bh_closest_point( bh_tree *bh, v3f pos,
 347                                 v3f closest, float max_dist )
 348 {
 349    if( bh->node_count < 2 )
 350       return -1;
 351
 352    max_dist = max_dist*max_dist;
 353
 354    int queue[ 128 ],
 355        depth = 0,
 356        best_item = -1;
 357
 358    queue[0] = 0;
 359
 360    while( depth >= 0 )
 361    {
 362       bh_node *inode = &bh->nodes[ queue[depth] ];
 363
 364       v3f p1;
 365       closest_point_aabb( pos, inode->bbx, p1 );
 366
 367       /* branch into node if its closer than current best */
 368       float node_dist = v3_dist2( pos, p1 );
 369       if( node_dist < max_dist )
 370       {
 371          if( inode->count )
 372          {
 373             for( int i=0; i<inode->count; i++ )
 374             {
 375                v3f p2;
 376                bh->system->item_closest( bh->user, inode->start+i, pos, p2 );
 377
 378                float item_dist = v3_dist2( pos, p2 );
 379                if( item_dist < max_dist )
 380                {
 381                   max_dist = item_dist;
 382                   v3_copy( p2, closest );
 383                   best_item = inode->start+i;
 384                }
 385             }
 386
 387             depth --;
 388          }
 389          else
 390          {
 391             queue[depth] = inode->il;
 392             queue[depth+1] = inode->ir;
 393
 394             depth ++;
 395          }
 396       }
 397       else
 398          depth --;
 399    }
 400
 401    return best_item;
 402 }
 403
 404 #endif /* BVH_H */