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    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       bh_node *inode = &bh->nodes[ stack[depth] ];
 237       if( ray_aabb1( inode->bbx, co, dir_inv, hit->dist ) ){
 238          if( inode->count ){
 239             for( u32 i=0; i<inode->count; i++ ){
 240                u32 idx = inode->start+i;
 241
 242                if( bh->system->cast_ray )
 243                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 244                else
 245                   count ++;
 246             }
 247
 248             depth --;
 249          }
 250          else{
 251             if( depth+1 >= vg_list_size(stack) ){
 252                vg_error( "Maximum stack reached!\n" );
 253                return count;
 254             }
 255
 256             stack[depth] = inode->il;
 257             stack[depth+1] = inode->ir;
 258             depth ++;
 259          }
 260       }
 261       else{
 262          depth --;
 263       }
 264    }
 265
 266    return count;
 267 }
 268
 269 typedef struct bh_iter bh_iter;
 270 struct bh_iter
 271 {
 272    struct
 273    {
 274       int id, depth;
 275    }
 276    stack[64];
 277
 278    int depth, i;
 279 };
 280
 281 VG_STATIC void bh_iter_init( int root, bh_iter *it )
 282 {
 283    it->stack[0].id = root;
 284    it->stack[0].depth = 0;
 285    it->depth = 0;
 286    it->i = 0;
 287 }
 288
 289 VG_STATIC int bh_next( bh_tree *bh, bh_iter *it, boxf box, int *em )
 290 {
 291    while( it->depth >= 0 ){
 292       bh_node *inode = &bh->nodes[ it->stack[it->depth].id ];
 293
 294       /* Only process overlapping nodes */
 295       if( !box_overlap( inode->bbx, box ) ){
 296          it->depth --;
 297          continue;
 298       }
 299
 300       if( inode->count ){
 301          if( it->i < inode->count ){
 302             *em = inode->start+it->i;
 303             it->i ++;
 304             return 1;
 305          }
 306          else{
 307             it->depth --;
 308             it->i = 0;
 309          }
 310       }
 311       else{
 312          if( it->depth+1 >= vg_list_size(it->stack) ){
 313             vg_error( "Maximum stack reached!\n" );
 314             return 0;
 315          }
 316
 317          it->stack[it->depth  ].id = inode->il;
 318          it->stack[it->depth+1].id = inode->ir;
 319          it->depth ++;
 320          it->i = 0;
 321       }
 322    }
 323
 324    return 0;
 325 }
 326
 327 VG_STATIC int bh_closest_point( bh_tree *bh, v3f pos,
 328                                 v3f closest, float max_dist )
 329 {
 330    if( bh->node_count < 2 )
 331       return -1;
 332
 333    max_dist = max_dist*max_dist;
 334
 335    int queue[ 128 ],
 336        depth = 0,
 337        best_item = -1;
 338
 339    queue[0] = 0;
 340
 341    while( depth >= 0 ){
 342       bh_node *inode = &bh->nodes[ queue[depth] ];
 343
 344       v3f p1;
 345       closest_point_aabb( pos, inode->bbx, p1 );
 346
 347       /* branch into node if its closer than current best */
 348       float node_dist = v3_dist2( pos, p1 );
 349       if( node_dist < max_dist ){
 350          if( inode->count ){
 351             for( int i=0; i<inode->count; i++ ){
 352                v3f p2;
 353                bh->system->item_closest( bh->user, inode->start+i, pos, p2 );
 354
 355                float item_dist = v3_dist2( pos, p2 );
 356                if( item_dist < max_dist ){
 357                   max_dist = item_dist;
 358                   v3_copy( p2, closest );
 359                   best_item = inode->start+i;
 360                }
 361             }
 362
 363             depth --;
 364          }
 365          else{
 366             queue[depth] = inode->il;
 367             queue[depth+1] = inode->ir;
 368
 369             depth ++;
 370          }
 371       }
 372       else
 373          depth --;
 374    }
 375
 376    return best_item;
 377 }
 378
 379 #endif /* BVH_H */