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 typedef struct ray_hit ray_hit;
  30 struct ray_hit{
  31    float dist;
  32    u32 *tri;
  33    v3f pos, normal;
  34 };
  35
  36 struct bh_tree
  37 {
  38    u32 node_count;
  39
  40    bh_system *system;
  41    void *user;
  42    u32 max_per_leaf;
  43
  44    struct bh_node
  45    {
  46       boxf bbx;
  47
  48       /* if il is 0, this is a leaf */
  49       int il, count;
  50       union{ int ir, start; };
  51    }
  52    nodes[];
  53 };
  54
  55 struct bh_system
  56 {
  57    void  (*expand_bound)( void *user, boxf bound, u32 item_index );
  58    float (*item_centroid)( void *user, u32 item_index, int axis );
  59    void  (*item_closest)( void *user, u32 item_index, v3f point, v3f closest );
  60    void  (*item_swap)( void *user, u32 ia, u32 ib );
  61
  62    /*
  63     * Optional:
  64     *   item_debug   - draw this item quickly usually with lines
  65     *   cast_ray     - shoot a ray against the object, if this is not set,
  66     *                  raycasts will simply return the hit on the bvh node
  67     */
  68
  69    void  (*item_debug)( void *user, u32 item_index );
  70    int   (*cast_ray)( void *user, u32 index, v3f co, v3f dir, ray_hit *hit );
  71 };
  72
  73 VG_STATIC void bh_update_bounds( bh_tree *bh, u32 inode )
  74 {
  75    bh_node *node = &bh->nodes[ inode ];
  76
  77    box_init_inf( node->bbx );
  78    for( u32 i=0; i<node->count; i++ ){
  79       u32 idx = node->start+i;
  80       bh->system->expand_bound( bh->user, node->bbx, idx );
  81    }
  82 }
  83
  84 VG_STATIC void bh_subdivide( bh_tree *bh, u32 inode )
  85 {
  86    bh_node *node = &bh->nodes[ inode ];
  87
  88    if( node->count <= bh->max_per_leaf )
  89       return;
  90
  91    v3f extent;
  92    v3_sub( node->bbx[1], node->bbx[0], extent );
  93
  94    int axis = 0;
  95    if( extent[1] > extent[0] ) axis = 1;
  96    if( extent[2] > extent[axis] ) axis = 2;
  97
  98    float split = node->bbx[0][axis] + extent[axis]*0.5f;
  99    float avg = 0.0;
 100    for( u32 t=0; t<node->count; t++ )
 101    {
 102       u32 idx = node->start+t;
 103       avg += bh->system->item_centroid( bh->user, idx, axis );
 104    }
 105    avg /= (float)node->count;
 106    split = avg;
 107
 108
 109    i32 i = node->start,
 110        j = i + node->count-1;
 111
 112    while( i <= j ){
 113       if( bh->system->item_centroid( bh->user, i, axis ) < split )
 114          i ++;
 115       else{
 116          bh->system->item_swap( bh->user, i, j );
 117          j --;
 118       }
 119    }
 120
 121    u32 left_count = i - node->start;
 122    if( left_count == 0 || left_count == node->count ) return;
 123
 124    u32 il = bh->node_count ++,
 125        ir = bh->node_count ++;
 126
 127    bh_node *lnode = &bh->nodes[il],
 128            *rnode = &bh->nodes[ir];
 129
 130    lnode->start = node->start;
 131    lnode->count = left_count;
 132    rnode->start = i;
 133    rnode->count = node->count - left_count;
 134
 135    node->il = il;
 136    node->ir = ir;
 137    node->count = 0;
 138
 139    bh_update_bounds( bh, il );
 140    bh_update_bounds( bh, ir );
 141    bh_subdivide( bh, il );
 142    bh_subdivide( bh, ir );
 143 }
 144
 145 VG_STATIC bh_tree *bh_create( void *lin_alloc, bh_system *system,
 146                               void *user, u32 item_count, u32 max_per_leaf )
 147 {
 148    assert( max_per_leaf > 0 );
 149
 150    u32 alloc_count = VG_MAX( 1, item_count );
 151
 152    u32 totsize = sizeof(bh_tree) + sizeof(bh_node)*(alloc_count*2-1);
 153    bh_tree *bh = vg_linear_alloc( lin_alloc, vg_align8(totsize) );
 154    bh->system = system;
 155    bh->user = user;
 156    bh->max_per_leaf = max_per_leaf;
 157
 158    bh_node *root = &bh->nodes[0];
 159    bh->node_count = 1;
 160
 161    root->il = 0;
 162    root->ir = 0;
 163    root->count = item_count;
 164    root->start = 0;
 165
 166    bh_update_bounds( bh, 0 );
 167
 168    if( item_count > 2 )
 169       bh_subdivide( bh, 0 );
 170
 171    totsize = vg_align8(sizeof(bh_tree) + sizeof(bh_node) * bh->node_count);
 172    bh = vg_linear_resize( lin_alloc, bh, totsize );
 173
 174    vg_success( "BVH done, size: %u/%u\n", bh->node_count, (alloc_count*2-1) );
 175    return bh;
 176 }
 177
 178 /*
 179  * Draw items in this leaf node.
 180  * *item_debug() must be set!
 181  */
 182 VG_STATIC void bh_debug_leaf( bh_tree *bh, bh_node *node )
 183 {
 184    vg_line_boxf( node->bbx, 0xff00ff00 );
 185
 186    if( bh->system->item_debug ){
 187       for( u32 i=0; i<node->count; i++ ){
 188          u32 idx = node->start+i;
 189          bh->system->item_debug( bh->user, idx );
 190       }
 191    }
 192 }
 193
 194 /*
 195  * Trace the bh tree all the way down to the leaf nodes where pos is inside
 196  */
 197 VG_STATIC void bh_debug_trace( bh_tree *bh, u32 inode, v3f pos, u32 colour )
 198 {
 199    bh_node *node = &bh->nodes[ inode ];
 200
 201    if( (pos[0] >= node->bbx[0][0] && pos[0] <= node->bbx[1][0]) &&
 202        (pos[2] >= node->bbx[0][2] && pos[2] <= node->bbx[1][2]) )
 203    {
 204       if( !node->count ){
 205          vg_line_boxf( node->bbx, colour );
 206
 207          bh_debug_trace( bh, node->il, pos, colour );
 208          bh_debug_trace( bh, node->ir, pos, colour );
 209       }
 210       else{
 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    v3_div( (v3f){1.0f,1.0f,1.0f}, dir, dir_inv );
 232
 233    while(depth){
 234       bh_node *inode = &bh->nodes[ stack[depth] ];
 235       if( ray_aabb1( inode->bbx, co, dir_inv, hit->dist ) ){
 236          if( inode->count ){
 237             for( u32 i=0; i<inode->count; i++ ){
 238                u32 idx = inode->start+i;
 239
 240                if( bh->system->cast_ray )
 241                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 242                else
 243                   count ++;
 244             }
 245
 246             depth --;
 247          }
 248          else{
 249             if( depth+1 >= vg_list_size(stack) ){
 250                vg_error( "Maximum stack reached!\n" );
 251                return count;
 252             }
 253
 254             stack[depth] = inode->il;
 255             stack[depth+1] = inode->ir;
 256             depth ++;
 257          }
 258       }
 259       else{
 260          depth --;
 261       }
 262    }
 263
 264    return count;
 265 }
 266
 267 typedef struct bh_iter bh_iter;
 268 struct bh_iter
 269 {
 270    struct {
 271       i32 id, depth;
 272    }
 273    stack[64];
 274
 275    enum bh_query_type{
 276       k_bh_query_box,
 277       k_bh_query_ray
 278    }
 279    query;
 280
 281    union{
 282       struct{
 283          boxf box;
 284       }
 285       box;
 286
 287       struct{
 288          v3f co, inv_dir;
 289          f32 max_dist;
 290       }
 291       ray;
 292    };
 293
 294    i32 depth, i;
 295 };
 296
 297 VG_STATIC void bh_iter_init_box( i32 root, bh_iter *it, boxf box )
 298 {
 299    it->query = k_bh_query_box;
 300    it->stack[0].id = root;
 301    it->stack[0].depth = 0;
 302    it->depth = 0;
 303    it->i = 0;
 304
 305    box_copy( box, it->box.box );
 306 }
 307
 308 VG_STATIC void bh_iter_init_ray( i32 root, bh_iter *it, v3f co,
 309                                  v3f dir, f32 max_dist )
 310 {
 311    it->query = k_bh_query_ray;
 312    it->stack[0].id = root;
 313    it->stack[0].depth = 0;
 314    it->depth = 0;
 315    it->i = 0;
 316
 317    v3_div( (v3f){1.0f,1.0f,1.0f}, dir, it->ray.inv_dir );
 318    v3_copy( co, it->ray.co );
 319    it->ray.max_dist = max_dist;
 320 }
 321
 322 VG_STATIC i32 bh_next( bh_tree *bh, bh_iter *it, i32 *em )
 323 {
 324    while( it->depth >= 0 ){
 325       bh_node *inode = &bh->nodes[ it->stack[it->depth].id ];
 326
 327       /* Only process overlapping nodes */
 328       i32 q = 0;
 329
 330       if( it->query == k_bh_query_box )
 331          q = box_overlap( inode->bbx, it->box.box );
 332       else
 333          q = ray_aabb1( inode->bbx, it->ray.co,
 334                         it->ray.inv_dir, it->ray.max_dist );
 335
 336       if( !q ){
 337          it->depth --;
 338          continue;
 339       }
 340
 341       if( inode->count ){
 342          if( it->i < inode->count ){
 343             *em = inode->start+it->i;
 344             it->i ++;
 345             return 1;
 346          }
 347          else{
 348             it->depth --;
 349             it->i = 0;
 350          }
 351       }
 352       else{
 353          if( it->depth+1 >= vg_list_size(it->stack) ){
 354             vg_error( "Maximum stack reached!\n" );
 355             return 0;
 356          }
 357
 358          it->stack[it->depth  ].id = inode->il;
 359          it->stack[it->depth+1].id = inode->ir;
 360          it->depth ++;
 361          it->i = 0;
 362       }
 363    }
 364
 365    return 0;
 366 }
 367
 368 VG_STATIC int bh_closest_point( bh_tree *bh, v3f pos,
 369                                 v3f closest, float max_dist )
 370 {
 371    if( bh->node_count < 2 )
 372       return -1;
 373
 374    max_dist = max_dist*max_dist;
 375
 376    int queue[ 128 ],
 377        depth = 0,
 378        best_item = -1;
 379
 380    queue[0] = 0;
 381
 382    while( depth >= 0 ){
 383       bh_node *inode = &bh->nodes[ queue[depth] ];
 384
 385       v3f p1;
 386       closest_point_aabb( pos, inode->bbx, p1 );
 387
 388       /* branch into node if its closer than current best */
 389       float node_dist = v3_dist2( pos, p1 );
 390       if( node_dist < max_dist ){
 391          if( inode->count ){
 392             for( int i=0; i<inode->count; i++ ){
 393                v3f p2;
 394                bh->system->item_closest( bh->user, inode->start+i, pos, p2 );
 395
 396                float item_dist = v3_dist2( pos, p2 );
 397                if( item_dist < max_dist ){
 398                   max_dist = item_dist;
 399                   v3_copy( p2, closest );
 400                   best_item = inode->start+i;
 401                }
 402             }
 403
 404             depth --;
 405          }
 406          else{
 407             queue[depth] = inode->il;
 408             queue[depth+1] = inode->ir;
 409
 410             depth ++;
 411          }
 412       }
 413       else
 414          depth --;
 415    }
 416
 417    return best_item;
 418 }
 419
 420 #endif /* BVH_H */