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
  36    struct bh_node
  37    {
  38       boxf bbx;
  39
  40       /* if il is 0, this is a leaf */
  41       u32 il, count;
  42       union{ u32 ir, start; };
  43    }
  44    nodes[];
  45 };
  46
  47 struct bh_system
  48 {
  49    void  (*expand_bound)( void *user, boxf bound, u32 item_index );
  50    float (*item_centroid)( void *user, u32 item_index, int axis );
  51    void  (*item_swap)( void *user, u32 ia, u32 ib );
  52
  53    /*
  54     * Optional:
  55     *   item_debug   - draw this item quickly usually with lines
  56     *   cast_ray     - shoot a ray against the object, if this is not set,
  57     *                  raycasts will simply return the hit on the bvh node
  58     */
  59
  60    void  (*item_debug)( void *user, u32 item_index );
  61    int   (*cast_ray)( void *user, u32 index, v3f co, v3f dir, ray_hit *hit );
  62 };
  63
  64 VG_STATIC void bh_update_bounds( bh_tree *bh, u32 inode )
  65 {
  66    bh_node *node = &bh->nodes[ inode ];
  67
  68    box_init_inf( node->bbx );
  69    for( u32 i=0; i<node->count; i++ )
  70    {
  71       u32 idx = node->start+i;
  72       bh->system->expand_bound( bh->user, node->bbx, idx );
  73    }
  74 }
  75
  76 VG_STATIC void bh_subdivide( bh_tree *bh, u32 inode )
  77 {
  78    bh_node *node = &bh->nodes[ inode ];
  79
  80    v3f extent;
  81    v3_sub( node->bbx[1], node->bbx[0], extent );
  82
  83    int axis = 0;
  84    if( extent[1] > extent[0] ) axis = 1;
  85    if( extent[2] > extent[axis] ) axis = 2;
  86
  87    float split = node->bbx[0][axis] + extent[axis]*0.5f;
  88
  89    float avg = 0.0;
  90    for( u32 t=0; t<node->count; t++ )
  91    {
  92       u32 idx = node->start+t;
  93       avg += bh->system->item_centroid( bh->user, idx, axis );
  94    }
  95    avg /= (float)node->count;
  96
  97    split = avg;
  98
  99    i32 i = node->start,
 100        j = i + node->count-1;
 101
 102    while( i <= j )
 103    {
 104       if( bh->system->item_centroid( bh->user, i, axis ) < split )
 105          i ++;
 106       else
 107       {
 108          bh->system->item_swap( bh->user, i, j );
 109          j --;
 110       }
 111    }
 112
 113    u32 left_count = i - node->start;
 114    if( left_count == 0 || left_count == node->count ) return;
 115
 116    u32 il = bh->node_count ++,
 117        ir = bh->node_count ++;
 118
 119    bh_node *lnode = &bh->nodes[il],
 120            *rnode = &bh->nodes[ir];
 121
 122    lnode->start = node->start;
 123    lnode->count = left_count;
 124    rnode->start = i;
 125    rnode->count = node->count - left_count;
 126
 127    node->il = il;
 128    node->ir = ir;
 129    node->count = 0;
 130
 131    bh_update_bounds( bh, il );
 132    bh_update_bounds( bh, ir );
 133    bh_subdivide( bh, il );
 134    bh_subdivide( bh, ir );
 135 }
 136
 137 VG_STATIC bh_tree *bh_create( void *lin_alloc, bh_system *system,
 138                               void *user, u32 item_count )
 139 {
 140    if( item_count == 0 )
 141    {
 142       bh_tree *bh = vg_linear_alloc( lin_alloc, sizeof(bh_tree) );
 143       bh->node_count = 0;
 144       bh->system = system;
 145       bh->user = user;
 146       return bh;
 147    }
 148
 149    u32 totsize = sizeof(bh_tree) + sizeof(bh_node)*(item_count*2-1);
 150    bh_tree *bh = vg_linear_alloc( lin_alloc, totsize );
 151    bh->system = system;
 152    bh->user = user;
 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    bh_subdivide( bh, 0 );
 164
 165    totsize = sizeof(bh_tree) + sizeof(bh_node) * bh->node_count;
 166    bh = vg_linear_resize( lin_alloc, bh, totsize );
 167
 168    vg_success( "BVH done, size: %u/%u\n", bh->node_count, (item_count*2-1) );
 169    return bh;
 170 }
 171
 172 VG_STATIC void bh_debug_node( bh_tree *bh, u32 inode, v3f pos, u32 colour )
 173 {
 174    bh_node *node = &bh->nodes[ inode ];
 175
 176    if( (pos[0] >= node->bbx[0][0] && pos[0] <= node->bbx[1][0]) &&
 177        (pos[2] >= node->bbx[0][2] && pos[2] <= node->bbx[1][2]) )
 178    {
 179       if( !node->count )
 180       {
 181          vg_line_boxf( node->bbx, colour );
 182
 183          bh_debug_node( bh, node->il, pos, colour );
 184          bh_debug_node( bh, node->ir, pos, colour );
 185       }
 186       else
 187       {
 188          vg_line_boxf( node->bbx, 0xff00ff00 );
 189
 190          if( bh->system->item_debug )
 191          {
 192             for( u32 i=0; i<node->count; i++ )
 193             {
 194                u32 idx = node->start+i;
 195                bh->system->item_debug( bh->user, idx );
 196             }
 197          }
 198       }
 199    }
 200 }
 201
 202 VG_STATIC int bh_ray( bh_tree *bh, v3f co, v3f dir, ray_hit *hit )
 203 {
 204    if( bh->node_count < 2 )
 205       return 0;
 206
 207    int count = 0;
 208    u32 stack[100];
 209    u32 depth = 2;
 210
 211    stack[0] = 0;
 212    stack[1] = bh->nodes[0].il;
 213    stack[2] = bh->nodes[0].ir;
 214
 215    while(depth)
 216    {
 217       bh_node *inode = &bh->nodes[ stack[depth] ];
 218       if( ray_aabb( inode->bbx, co, dir, hit->dist ) )
 219       {
 220          if( inode->count )
 221          {
 222             for( u32 i=0; i<inode->count; i++ )
 223             {
 224                u32 idx = inode->start+i;
 225
 226                if( bh->system->cast_ray )
 227                   count += bh->system->cast_ray( bh->user, idx, co, dir, hit );
 228                else
 229                   count ++;
 230             }
 231
 232             depth --;
 233          }
 234          else
 235          {
 236             if( depth+1 >= vg_list_size(stack) )
 237             {
 238                vg_error( "Maximum stack reached!\n" );
 239                return count;
 240             }
 241
 242             stack[depth] = inode->il;
 243             stack[depth+1] = inode->ir;
 244             depth ++;
 245          }
 246       }
 247       else
 248       {
 249          depth --;
 250       }
 251    }
 252
 253    return count;
 254 }
 255
 256 VG_STATIC int bh_select( bh_tree *bh, boxf box, u32 *buffer, int len )
 257 {
 258    if( bh->node_count < 2 )
 259       return 0;
 260
 261    int count = 0;
 262    u32 stack[100];
 263    u32 depth = 2;
 264
 265    stack[0] = 0;
 266    stack[1] = bh->nodes[0].il;
 267    stack[2] = bh->nodes[0].ir;
 268
 269    while(depth)
 270    {
 271       bh_node *inode = &bh->nodes[ stack[depth] ];
 272       if( box_overlap( inode->bbx, box ) )
 273       {
 274          if( inode->count )
 275          {
 276             if( count + inode->count >= len )
 277                return count;
 278
 279             for( u32 i=0; i<inode->count; i++ )
 280                buffer[ count ++ ] = inode->start+i;
 281
 282             depth --;
 283          }
 284          else
 285          {
 286             if( depth+1 >= vg_list_size(stack) )
 287             {
 288                vg_error( "Maximum stack reached!\n" );
 289                return count;
 290             }
 291
 292             stack[depth] = inode->il;
 293             stack[depth+1] = inode->ir;
 294             depth ++;
 295          }
 296       }
 297       else
 298       {
 299          depth --;
 300       }
 301    }
 302
 303    return count;
 304 }
 305
 306 #endif /* BVH_H */