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       u32 idx = node->start+i;
  73       bh->system->expand_bound( bh->user, node->bbx, idx );
  74    }
  75 }
  76
  77 VG_STATIC void bh_subdivide( bh_tree *bh, u32 inode )
  78 {
  79    bh_node *node = &bh->nodes[ inode ];
  80
  81    if( node->count <= bh->max_per_leaf )
  82       return;
  83
  84    v3f extent;
  85    v3_sub( node->bbx[1], node->bbx[0], extent );
  86
  87    int axis = 0;
  88    if( extent[1] > extent[0] ) axis = 1;
  89    if( extent[2] > extent[axis] ) axis = 2;
  90
  91    float split = node->bbx[0][axis] + extent[axis]*0.5f;
  92    float avg = 0.0;
  93    for( u32 t=0; t<node->count; t++ )
  94    {
  95       u32 idx = node->start+t;
  96       avg += bh->system->item_centroid( bh->user, idx, axis );
  97    }
  98    avg /= (float)node->count;
  99    split = avg;
 100
 101
 102    i32 i = node->start,
 103        j = i + node->count-1;
 104
 105    while( i <= j ){
 106       if( bh->system->item_centroid( bh->user, i, axis ) < split )
 107          i ++;
 108       else{
 109          bh->system->item_swap( bh->user, i, j );
 110          j --;
 111       }
 112    }
 113
 114    u32 left_count = i - node->start;
 115    if( left_count == 0 || left_count == node->count ) return;
 116
 117    u32 il = bh->node_count ++,
 118        ir = bh->node_count ++;
 119
 120    bh_node *lnode = &bh->nodes[il],
 121            *rnode = &bh->nodes[ir];
 122
 123    lnode->start = node->start;
 124    lnode->count = left_count;
 125    rnode->start = i;
 126    rnode->count = node->count - left_count;
 127
 128    node->il = il;
 129    node->ir = ir;
 130    node->count = 0;
 131
 132    bh_update_bounds( bh, il );
 133    bh_update_bounds( bh, ir );
 134    bh_subdivide( bh, il );
 135    bh_subdivide( bh, ir );
 136 }
 137
 138 VG_STATIC bh_tree *bh_create( void *lin_alloc, bh_system *system,
 139                               void *user, u32 item_count, u32 max_per_leaf )
 140 {
 141    assert( max_per_leaf > 0 );
 142
 143    u32 alloc_count = VG_MAX( 1, item_count );
 144
 145    u32 totsize = sizeof(bh_tree) + sizeof(bh_node)*(alloc_count*2-1);
 146    bh_tree *bh = vg_linear_alloc( lin_alloc, vg_align8(totsize) );
 147    bh->system = system;
 148    bh->user = user;
 149    bh->max_per_leaf = max_per_leaf;
 150
 151    bh_node *root = &bh->nodes[0];
 152    bh->node_count = 1;
 153
 154    root->il = 0;
 155    root->ir = 0;
 156    root->count = item_count;
 157    root->start = 0;
 158
 159    bh_update_bounds( bh, 0 );
 160
 161    if( item_count > 2 )
 162       bh_subdivide( bh, 0 );
 163
 164    totsize = vg_align8(sizeof(bh_tree) + sizeof(bh_node) * bh->node_count);
 165    bh = vg_linear_resize( lin_alloc, bh, totsize );
 166
 167    vg_success( "BVH done, size: %u/%u\n", bh->node_count, (alloc_count*2-1) );
 168    return bh;
 169 }
 170
 171 /*
 172  * Draw items in this leaf node.
 173  * *item_debug() must be set!
 174  */
 175 VG_STATIC void bh_debug_leaf( bh_tree *bh, bh_node *node )
 176 {
 177    vg_line_boxf( node->bbx, 0xff00ff00 );
 178
 179    if( bh->system->item_debug ){
 180       for( u32 i=0; i<node->count; i++ ){
 181          u32 idx = node->start+i;
 182          bh->system->item_debug( bh->user, idx );
 183       }
 184    }
 185 }
 186
 187 /*
 188  * Trace the bh tree all the way down to the leaf nodes where pos is inside
 189  */
 190 VG_STATIC void bh_debug_trace( bh_tree *bh, u32 inode, v3f pos, u32 colour )
 191 {
 192    bh_node *node = &bh->nodes[ inode ];
 193
 194    if( (pos[0] >= node->bbx[0][0] && pos[0] <= node->bbx[1][0]) &&
 195        (pos[2] >= node->bbx[0][2] && pos[2] <= node->bbx[1][2]) )
 196    {
 197       if( !node->count ){
 198          vg_line_boxf( node->bbx, colour );
 199
 200          bh_debug_trace( bh, node->il, pos, colour );
 201          bh_debug_trace( bh, node->ir, pos, colour );
 202       }
 203       else{
 204          if( bh->system->item_debug )
 205             bh_debug_leaf( bh, node );
 206       }
 207    }
 208 }
 209
 210 VG_STATIC int bh_ray( bh_tree *bh, v3f co, v3f dir, ray_hit *hit )
 211 {
 212    if( bh->node_count < 2 )
 213       return 0;
 214
 215    int count = 0;
 216    u32 stack[100];
 217    u32 depth = 2;
 218
 219    stack[0] = 0;
 220    stack[1] = bh->nodes[0].il;
 221    stack[2] = bh->nodes[0].ir;
 222
 223    v3f dir_inv;
 224    dir_inv[0] = 1.0f/dir[0];
 225    dir_inv[1] = 1.0f/dir[1];
 226    dir_inv[2] = 1.0f/dir[2];
 227
 228    while(depth){
 229       bh_node *inode = &bh->nodes[ stack[depth] ];
 230       if( ray_aabb1( inode->bbx, co, dir_inv, hit->dist ) ){
 231          if( inode->count ){
 232             for( u32 i=0; i<inode->count; i++ ){
 233                u32 idx = inode->start+i;
 234
 235                if( bh->system->cast_ray )
 236                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 237                else
 238                   count ++;
 239             }
 240
 241             depth --;
 242          }
 243          else{
 244             if( depth+1 >= vg_list_size(stack) ){
 245                vg_error( "Maximum stack reached!\n" );
 246                return count;
 247             }
 248
 249             stack[depth] = inode->il;
 250             stack[depth+1] = inode->ir;
 251             depth ++;
 252          }
 253       }
 254       else{
 255          depth --;
 256       }
 257    }
 258
 259    return count;
 260 }
 261
 262 typedef struct bh_iter bh_iter;
 263 struct bh_iter
 264 {
 265    struct
 266    {
 267       int id, depth;
 268    }
 269    stack[64];
 270
 271    int depth, i;
 272 };
 273
 274 VG_STATIC void bh_iter_init( int root, bh_iter *it )
 275 {
 276    it->stack[0].id = root;
 277    it->stack[0].depth = 0;
 278    it->depth = 0;
 279    it->i = 0;
 280 }
 281
 282 VG_STATIC int bh_next( bh_tree *bh, bh_iter *it, boxf box, int *em )
 283 {
 284    while( it->depth >= 0 ){
 285       bh_node *inode = &bh->nodes[ it->stack[it->depth].id ];
 286
 287       /* Only process overlapping nodes */
 288       if( !box_overlap( inode->bbx, box ) ){
 289          it->depth --;
 290          continue;
 291       }
 292
 293       if( inode->count ){
 294          if( it->i < inode->count ){
 295             *em = inode->start+it->i;
 296             it->i ++;
 297             return 1;
 298          }
 299          else{
 300             it->depth --;
 301             it->i = 0;
 302          }
 303       }
 304       else{
 305          if( it->depth+1 >= vg_list_size(it->stack) ){
 306             vg_error( "Maximum stack reached!\n" );
 307             return 0;
 308          }
 309
 310          it->stack[it->depth  ].id = inode->il;
 311          it->stack[it->depth+1].id = inode->ir;
 312          it->depth ++;
 313          it->i = 0;
 314       }
 315    }
 316
 317    return 0;
 318 }
 319
 320 VG_STATIC int bh_closest_point( bh_tree *bh, v3f pos,
 321                                 v3f closest, float max_dist )
 322 {
 323    if( bh->node_count < 2 )
 324       return -1;
 325
 326    max_dist = max_dist*max_dist;
 327
 328    int queue[ 128 ],
 329        depth = 0,
 330        best_item = -1;
 331
 332    queue[0] = 0;
 333
 334    while( depth >= 0 ){
 335       bh_node *inode = &bh->nodes[ queue[depth] ];
 336
 337       v3f p1;
 338       closest_point_aabb( pos, inode->bbx, p1 );
 339
 340       /* branch into node if its closer than current best */
 341       float node_dist = v3_dist2( pos, p1 );
 342       if( node_dist < max_dist ){
 343          if( inode->count ){
 344             for( int i=0; i<inode->count; i++ ){
 345                v3f p2;
 346                bh->system->item_closest( bh->user, inode->start+i, pos, p2 );
 347
 348                float item_dist = v3_dist2( pos, p2 );
 349                if( item_dist < max_dist ){
 350                   max_dist = item_dist;
 351                   v3_copy( p2, closest );
 352                   best_item = inode->start+i;
 353                }
 354             }
 355
 356             depth --;
 357          }
 358          else{
 359             queue[depth] = inode->il;
 360             queue[depth+1] = inode->ir;
 361
 362             depth ++;
 363          }
 364       }
 365       else
 366          depth --;
 367    }
 368
 369    return best_item;
 370 }
 371
 372 #endif /* BVH_H */