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    u32 alloc_count = VG_MAX( 1, item_count );
 147
 148    u32 totsize = sizeof(bh_tree) + sizeof(bh_node)*(alloc_count*2-1);
 149    bh_tree *bh = vg_linear_alloc( lin_alloc, vg_align8(totsize) );
 150    bh->system = system;
 151    bh->user = user;
 152    bh->max_per_leaf = max_per_leaf;
 153
 154    bh_node *root = &bh->nodes[0];
 155    bh->node_count = 1;
 156
 157    root->il = 0;
 158    root->ir = 0;
 159    root->count = item_count;
 160    root->start = 0;
 161
 162    bh_update_bounds( bh, 0 );
 163
 164    if( item_count > 2 )
 165       bh_subdivide( bh, 0 );
 166
 167    totsize = sizeof(bh_tree) + sizeof(bh_node) * bh->node_count;
 168    bh = vg_linear_resize( lin_alloc, bh, totsize );
 169
 170    vg_success( "BVH done, size: %u/%u\n", bh->node_count, (alloc_count*2-1) );
 171    return bh;
 172 }
 173
 174 /*
 175  * Draw items in this leaf node.
 176  * *item_debug() must be set!
 177  */
 178 VG_STATIC void bh_debug_leaf( bh_tree *bh, bh_node *node )
 179 {
 180    vg_line_boxf( node->bbx, 0xff00ff00 );
 181
 182    if( bh->system->item_debug )
 183    {
 184       for( u32 i=0; i<node->count; i++ )
 185       {
 186          u32 idx = node->start+i;
 187          bh->system->item_debug( bh->user, idx );
 188       }
 189    }
 190 }
 191
 192 /*
 193  * Trace the bh tree all the way down to the leaf nodes where pos is inside
 194  */
 195 VG_STATIC void bh_debug_trace( bh_tree *bh, u32 inode, v3f pos, u32 colour )
 196 {
 197    bh_node *node = &bh->nodes[ inode ];
 198
 199    if( (pos[0] >= node->bbx[0][0] && pos[0] <= node->bbx[1][0]) &&
 200        (pos[2] >= node->bbx[0][2] && pos[2] <= node->bbx[1][2]) )
 201    {
 202       if( !node->count )
 203       {
 204          vg_line_boxf( node->bbx, colour );
 205
 206          bh_debug_trace( bh, node->il, pos, colour );
 207          bh_debug_trace( bh, node->ir, pos, colour );
 208       }
 209       else
 210       {
 211          if( bh->system->item_debug )
 212             bh_debug_leaf( bh, node );
 213       }
 214    }
 215 }
 216
 217 VG_STATIC int bh_ray( bh_tree *bh, v3f co, v3f dir, ray_hit *hit )
 218 {
 219    if( bh->node_count < 2 )
 220       return 0;
 221
 222    int count = 0;
 223    u32 stack[100];
 224    u32 depth = 2;
 225
 226    stack[0] = 0;
 227    stack[1] = bh->nodes[0].il;
 228    stack[2] = bh->nodes[0].ir;
 229
 230    v3f dir_inv;
 231    dir_inv[0] = 1.0f/dir[0];
 232    dir_inv[1] = 1.0f/dir[1];
 233    dir_inv[2] = 1.0f/dir[2];
 234
 235    while(depth)
 236    {
 237       bh_node *inode = &bh->nodes[ stack[depth] ];
 238       if( ray_aabb1( inode->bbx, co, dir_inv, hit->dist ) )
 239       {
 240          if( inode->count )
 241          {
 242             for( u32 i=0; i<inode->count; i++ )
 243             {
 244                u32 idx = inode->start+i;
 245
 246                if( bh->system->cast_ray )
 247                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 248                else
 249                   count ++;
 250             }
 251
 252             depth --;
 253          }
 254          else
 255          {
 256             if( depth+1 >= vg_list_size(stack) )
 257             {
 258                vg_error( "Maximum stack reached!\n" );
 259                return count;
 260             }
 261
 262             stack[depth] = inode->il;
 263             stack[depth+1] = inode->ir;
 264             depth ++;
 265          }
 266       }
 267       else
 268       {
 269          depth --;
 270       }
 271    }
 272
 273    return count;
 274 }
 275
 276 typedef struct bh_iter bh_iter;
 277 struct bh_iter
 278 {
 279    struct
 280    {
 281       int id, depth;
 282    }
 283    stack[64];
 284
 285    int depth, i;
 286 };
 287
 288 VG_STATIC void bh_iter_init( int root, bh_iter *it )
 289 {
 290    it->stack[0].id = root;
 291    it->stack[0].depth = 0;
 292    it->depth = 0;
 293    it->i = 0;
 294 }
 295
 296 VG_STATIC int bh_next( bh_tree *bh, bh_iter *it, boxf box, int *em )
 297 {
 298    while( it->depth >= 0 )
 299    {
 300       bh_node *inode = &bh->nodes[ it->stack[it->depth].id ];
 301
 302       /* Only process overlapping nodes */
 303       if( !box_overlap( inode->bbx, box ) )
 304       {
 305          it->depth --;
 306          continue;
 307       }
 308
 309       if( inode->count )
 310       {
 311          if( it->i < inode->count )
 312          {
 313             *em = inode->start+it->i;
 314             it->i ++;
 315             return 1;
 316          }
 317          else
 318          {
 319             it->depth --;
 320             it->i = 0;
 321          }
 322       }
 323       else
 324       {
 325          if( it->depth+1 >= vg_list_size(it->stack) )
 326          {
 327             vg_error( "Maximum stack reached!\n" );
 328             return 0;
 329          }
 330
 331          it->stack[it->depth  ].id = inode->il;
 332          it->stack[it->depth+1].id = inode->ir;
 333          it->depth ++;
 334          it->i = 0;
 335       }
 336    }
 337
 338    return 0;
 339 }
 340
 341 VG_STATIC int bh_closest_point( bh_tree *bh, v3f pos,
 342                                 v3f closest, float max_dist )
 343 {
 344    if( bh->node_count < 2 )
 345       return -1;
 346
 347    max_dist = max_dist*max_dist;
 348
 349    int queue[ 128 ],
 350        depth = 0,
 351        best_item = -1;
 352
 353    queue[0] = 0;
 354
 355    while( depth >= 0 )
 356    {
 357       bh_node *inode = &bh->nodes[ queue[depth] ];
 358
 359       v3f p1;
 360       closest_point_aabb( pos, inode->bbx, p1 );
 361
 362       /* branch into node if its closer than current best */
 363       float node_dist = v3_dist2( pos, p1 );
 364       if( node_dist < max_dist )
 365       {
 366          if( inode->count )
 367          {
 368             for( int i=0; i<inode->count; i++ )
 369             {
 370                v3f p2;
 371                bh->system->item_closest( bh->user, inode->start+i, pos, p2 );
 372
 373                float item_dist = v3_dist2( pos, p2 );
 374                if( item_dist < max_dist )
 375                {
 376                   max_dist = item_dist;
 377                   v3_copy( p2, closest );
 378                   best_item = inode->start+i;
 379                }
 380             }
 381
 382             depth --;
 383          }
 384          else
 385          {
 386             queue[depth] = inode->il;
 387             queue[depth+1] = inode->ir;
 388
 389             depth ++;
 390          }
 391       }
 392       else
 393          depth --;
 394    }
 395
 396    return best_item;
 397 }
 398
 399 #endif /* BVH_H */