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
  94    float avg = 0.0;
  95    for( u32 t=0; t<node->count; t++ )
  96    {
  97       u32 idx = node->start+t;
  98       avg += bh->system->item_centroid( bh->user, idx, axis );
  99    }
 100    avg /= (float)node->count;
 101
 102    split = avg;
 103
 104    i32 i = node->start,
 105        j = i + node->count-1;
 106
 107    while( i <= j )
 108    {
 109       if( bh->system->item_centroid( bh->user, i, axis ) < split )
 110          i ++;
 111       else
 112       {
 113          bh->system->item_swap( bh->user, i, j );
 114          j --;
 115       }
 116    }
 117
 118    u32 left_count = i - node->start;
 119    if( left_count == 0 || left_count == node->count ) return;
 120
 121    u32 il = bh->node_count ++,
 122        ir = bh->node_count ++;
 123
 124    bh_node *lnode = &bh->nodes[il],
 125            *rnode = &bh->nodes[ir];
 126
 127    lnode->start = node->start;
 128    lnode->count = left_count;
 129    rnode->start = i;
 130    rnode->count = node->count - left_count;
 131
 132    node->il = il;
 133    node->ir = ir;
 134    node->count = 0;
 135
 136    bh_update_bounds( bh, il );
 137    bh_update_bounds( bh, ir );
 138    bh_subdivide( bh, il );
 139    bh_subdivide( bh, ir );
 140 }
 141
 142 VG_STATIC bh_tree *bh_create( void *lin_alloc, bh_system *system,
 143                               void *user, u32 item_count, u32 max_per_leaf )
 144 {
 145    assert( max_per_leaf > 0 );
 146
 147    if( item_count == 0 )
 148    {
 149       bh_tree *bh = vg_linear_alloc( lin_alloc, sizeof(bh_tree) );
 150       bh->node_count = 0;
 151       bh->system = system;
 152       bh->user = user;
 153       return bh;
 154    }
 155
 156    u32 totsize = sizeof(bh_tree) + sizeof(bh_node)*(item_count*2-1);
 157    bh_tree *bh = vg_linear_alloc( lin_alloc, vg_align8(totsize) );
 158    bh->system = system;
 159    bh->user = user;
 160    bh->max_per_leaf = max_per_leaf;
 161
 162    bh_node *root = &bh->nodes[0];
 163    bh->node_count = 1;
 164
 165    root->il = 0;
 166    root->ir = 0;
 167    root->count = item_count;
 168    root->start = 0;
 169
 170    bh_update_bounds( bh, 0 );
 171    bh_subdivide( bh, 0 );
 172
 173    totsize = sizeof(bh_tree) + sizeof(bh_node) * bh->node_count;
 174    bh = vg_linear_resize( lin_alloc, bh, totsize );
 175
 176    vg_success( "BVH done, size: %u/%u\n", bh->node_count, (item_count*2-1) );
 177    return bh;
 178 }
 179
 180 /*
 181  * Draw items in this leaf node.
 182  * *item_debug() must be set!
 183  */
 184 VG_STATIC void bh_debug_leaf( bh_tree *bh, bh_node *node )
 185 {
 186    vg_line_boxf( node->bbx, 0xff00ff00 );
 187
 188    if( bh->system->item_debug )
 189    {
 190       for( u32 i=0; i<node->count; i++ )
 191       {
 192          u32 idx = node->start+i;
 193          bh->system->item_debug( bh->user, idx );
 194       }
 195    }
 196 }
 197
 198 /*
 199  * Trace the bh tree all the way down to the leaf nodes where pos is inside
 200  */
 201 VG_STATIC void bh_debug_trace( bh_tree *bh, u32 inode, v3f pos, u32 colour )
 202 {
 203    bh_node *node = &bh->nodes[ inode ];
 204
 205    if( (pos[0] >= node->bbx[0][0] && pos[0] <= node->bbx[1][0]) &&
 206        (pos[2] >= node->bbx[0][2] && pos[2] <= node->bbx[1][2]) )
 207    {
 208       if( !node->count )
 209       {
 210          vg_line_boxf( node->bbx, colour );
 211
 212          bh_debug_trace( bh, node->il, pos, colour );
 213          bh_debug_trace( bh, node->ir, pos, colour );
 214       }
 215       else
 216       {
 217          if( bh->system->item_debug )
 218             bh_debug_leaf( bh, node );
 219       }
 220    }
 221 }
 222
 223 VG_STATIC int bh_ray( bh_tree *bh, v3f co, v3f dir, ray_hit *hit )
 224 {
 225    if( bh->node_count < 2 )
 226       return 0;
 227
 228    int count = 0;
 229    u32 stack[100];
 230    u32 depth = 2;
 231
 232    stack[0] = 0;
 233    stack[1] = bh->nodes[0].il;
 234    stack[2] = bh->nodes[0].ir;
 235
 236    while(depth)
 237    {
 238       bh_node *inode = &bh->nodes[ stack[depth] ];
 239       if( ray_aabb( inode->bbx, co, dir, hit->dist ) )
 240       {
 241          if( inode->count )
 242          {
 243             for( u32 i=0; i<inode->count; i++ )
 244             {
 245                u32 idx = inode->start+i;
 246
 247                if( bh->system->cast_ray )
 248                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 249                else
 250                   count ++;
 251             }
 252
 253             depth --;
 254          }
 255          else
 256          {
 257             if( depth+1 >= vg_list_size(stack) )
 258             {
 259                vg_error( "Maximum stack reached!\n" );
 260                return count;
 261             }
 262
 263             stack[depth] = inode->il;
 264             stack[depth+1] = inode->ir;
 265             depth ++;
 266          }
 267       }
 268       else
 269       {
 270          depth --;
 271       }
 272    }
 273
 274    return count;
 275 }
 276
 277 typedef struct bh_iter bh_iter;
 278 struct bh_iter
 279 {
 280    struct
 281    {
 282       int id, depth;
 283    }
 284    stack[64];
 285
 286    int depth, i;
 287 };
 288
 289 VG_STATIC void bh_iter_init( int root, bh_iter *it )
 290 {
 291    it->stack[0].id = root;
 292    it->stack[0].depth = 0;
 293    it->depth = 0;
 294    it->i = 0;
 295 }
 296
 297 VG_STATIC int bh_next( bh_tree *bh, bh_iter *it, boxf box, int *em )
 298 {
 299    while( it->depth >= 0 )
 300    {
 301       bh_node *inode = &bh->nodes[ it->stack[it->depth].id ];
 302
 303       /* Only process overlapping nodes */
 304       if( !box_overlap( inode->bbx, box ) )
 305       {
 306          it->depth --;
 307          continue;
 308       }
 309
 310       if( inode->count )
 311       {
 312          if( it->i < inode->count )
 313          {
 314             *em = inode->start+it->i;
 315             it->i ++;
 316             return 1;
 317          }
 318          else
 319          {
 320             it->depth --;
 321             it->i = 0;
 322          }
 323       }
 324       else
 325       {
 326          if( it->depth+1 >= vg_list_size(it->stack) )
 327          {
 328             vg_error( "Maximum stack reached!\n" );
 329             return 0;
 330          }
 331
 332          it->stack[it->depth  ].id = inode->il;
 333          it->stack[it->depth+1].id = inode->ir;
 334          it->depth ++;
 335          it->i = 0;
 336       }
 337    }
 338
 339    return 0;
 340 }
 341
 342 VG_STATIC int bh_closest_point( bh_tree *bh, v3f pos,
 343                                 v3f closest, float max_dist )
 344 {
 345    if( bh->node_count < 2 )
 346       return -1;
 347
 348    max_dist = max_dist*max_dist;
 349
 350    int queue[ 128 ],
 351        depth = 0,
 352        best_item = -1;
 353
 354    queue[0] = 0;
 355
 356    while( depth >= 0 )
 357    {
 358       bh_node *inode = &bh->nodes[ queue[depth] ];
 359
 360       v3f p1;
 361       closest_point_aabb( pos, inode->bbx, p1 );
 362
 363       /* branch into node if its closer than current best */
 364       float node_dist = v3_dist2( pos, p1 );
 365       if( node_dist < max_dist )
 366       {
 367          if( inode->count )
 368          {
 369             for( int i=0; i<inode->count; i++ )
 370             {
 371                v3f p2;
 372                bh->system->item_closest( bh->user, inode->start+i, pos, p2 );
 373
 374                float item_dist = v3_dist2( pos, p2 );
 375                if( item_dist < max_dist )
 376                {
 377                   max_dist = item_dist;
 378                   v3_copy( p2, closest );
 379                   best_item = inode->start+i;
 380                }
 381             }
 382
 383             depth --;
 384          }
 385          else
 386          {
 387             queue[depth] = inode->il;
 388             queue[depth+1] = inode->ir;
 389
 390             depth ++;
 391          }
 392       }
 393       else
 394          depth --;
 395    }
 396
 397    return best_item;
 398 }
 399
 400 #endif /* BVH_H */