--- /dev/null
+
+// This code written in 2010 by Forest Hale (lordhavoc ghdigital com), and placed into public domain.
+
+#include <stdlib.h>
+#include <string.h>
+#include "bih.h"
+
+static int BIH_BuildNode(bih_t *bih, int numchildren, int *leaflist, float *totalmins, float *totalmaxs)
+{
+ int i;
+ int j;
+ int longestaxis;
+ int axis = 0;
+ int nodenum;
+ int front = 0;
+ int back = 0;
+ bih_node_t *node;
+ bih_leaf_t *child;
+ float splitdist;
+ float d;
+ float mins[3];
+ float maxs[3];
+ float size[3];
+ float frontmins[3];
+ float frontmaxs[3];
+ float backmins[3];
+ float backmaxs[3];
+ // calculate bounds of children
+ child = bih->leafs + leaflist[0];
+ mins[0] = child->mins[0];
+ mins[1] = child->mins[1];
+ mins[2] = child->mins[2];
+ maxs[0] = child->maxs[0];
+ maxs[1] = child->maxs[1];
+ maxs[2] = child->maxs[2];
+ for (i = 1;i < numchildren;i++)
+ {
+ child = bih->leafs + leaflist[i];
+ if (mins[0] > child->mins[0]) mins[0] = child->mins[0];
+ if (mins[1] > child->mins[1]) mins[1] = child->mins[1];
+ if (mins[2] > child->mins[2]) mins[2] = child->mins[2];
+ if (maxs[0] < child->maxs[0]) maxs[0] = child->maxs[0];
+ if (maxs[1] < child->maxs[1]) maxs[1] = child->maxs[1];
+ if (maxs[2] < child->maxs[2]) maxs[2] = child->maxs[2];
+ }
+ size[0] = maxs[0] - mins[0];
+ size[1] = maxs[1] - mins[1];
+ size[2] = maxs[2] - mins[2];
+ // provide bounds to caller
+ totalmins[0] = mins[0];
+ totalmins[1] = mins[1];
+ totalmins[2] = mins[2];
+ totalmaxs[0] = maxs[0];
+ totalmaxs[1] = maxs[1];
+ totalmaxs[2] = maxs[2];
+ // if we run out of nodes it's the caller's fault, but don't crash
+ if (bih->numnodes == bih->maxnodes)
+ {
+ if (!bih->error)
+ bih->error = BIHERROR_OUT_OF_NODES;
+ return 0;
+ }
+ nodenum = bih->numnodes++;
+ node = bih->nodes + nodenum;
+ // store bounds for node
+ node->mins[0] = mins[0];
+ node->mins[1] = mins[1];
+ node->mins[2] = mins[2];
+ node->maxs[0] = maxs[0];
+ node->maxs[1] = maxs[1];
+ node->maxs[2] = maxs[2];
+ node->front = 0;
+ node->back = 0;
+ node->frontmin = 0;
+ node->backmax = 0;
+ memset(node->children, -1, sizeof(node->children));
+ // check if there are few enough children to store an unordered node
+ if (numchildren <= BIH_MAXUNORDEREDCHILDREN)
+ {
+ node->type = BIH_UNORDERED;
+ for (j = 0;j < numchildren;j++)
+ node->children[j] = leaflist[j];
+ return nodenum;
+ }
+ // pick longest axis
+ longestaxis = 0;
+ if (size[0] < size[1]) longestaxis = 1;
+ if (size[longestaxis] < size[2]) longestaxis = 2;
+ // iterate possible split axis choices, starting with the longest axis, if
+ // all fail it means all children have the same bounds and we simply split
+ // the list in half because each node can only have two children.
+ for (j = 0;j < 3;j++)
+ {
+ // pick an axis
+ axis = (longestaxis + j) % 3;
+ // sort children into front and back lists
+ splitdist = (node->mins[axis] + node->maxs[axis]) * 0.5f;
+ front = 0;
+ back = 0;
+ for (i = 0;i < numchildren;i++)
+ {
+ child = bih->leafs + leaflist[i];
+ d = (child->mins[axis] + child->maxs[axis]) * 0.5f;
+ if (d < splitdist)
+ bih->leafsortscratch[back++] = leaflist[i];
+ else
+ leaflist[front++] = leaflist[i];
+ }
+ // now copy the back ones into the space made in the leaflist for them
+ if (back)
+ memcpy(leaflist + front, bih->leafsortscratch, back*sizeof(leaflist[0]));
+ // if both sides have some children, it's good enough for us.
+ if (front && back)
+ break;
+ }
+ if (j == 3)
+ {
+ // somewhat common case: no good choice, divide children arbitrarily
+ axis = 0;
+ back = numchildren >> 1;
+ front = numchildren - back;
+ }
+
+ // we now have front and back children divided in leaflist...
+ node->type = (bih_nodetype_t)((int)BIH_SPLITX + axis);
+ node->front = BIH_BuildNode(bih, front, leaflist, frontmins, frontmaxs);
+ node->frontmin = frontmins[axis];
+ node->back = BIH_BuildNode(bih, back, leaflist + front, backmins, backmaxs);
+ node->backmax = backmaxs[axis];
+ return nodenum;
+}
+
+int BIH_Build(bih_t *bih, int numleafs, bih_leaf_t *leafs, int maxnodes, bih_node_t *nodes, int *temp_leafsort, int *temp_leafsortscratch)
+{
+ int i;
+
+ memset(bih, 0, sizeof(*bih));
+ bih->numleafs = numleafs;
+ bih->leafs = leafs;
+ bih->leafsort = temp_leafsort;
+ bih->leafsortscratch = temp_leafsortscratch;
+ bih->numnodes = 0;
+ bih->maxnodes = maxnodes;
+ bih->nodes = nodes;
+
+ // clear things we intend to rebuild
+ memset(bih->nodes, 0, sizeof(bih->nodes[0]) * bih->maxnodes);
+ for (i = 0;i < bih->numleafs;i++)
+ bih->leafsort[i] = i;
+
+ bih->rootnode = BIH_BuildNode(bih, bih->numleafs, bih->leafsort, bih->mins, bih->maxs);
+ return bih->error;
+}
+
+static void BIH_GetTriangleListForBox_Node(const bih_t *bih, int nodenum, int maxtriangles, int *trianglelist_idx, int *trianglelist_surf, int *numtrianglespointer, const float *mins, const float *maxs)
+{
+ int axis;
+ bih_node_t *node;
+ bih_leaf_t *leaf;
+ for(;;)
+ {
+ node = bih->nodes + nodenum;
+ // check if this is an unordered node (which holds an array of leaf numbers)
+ if (node->type == BIH_UNORDERED)
+ {
+ for (axis = 0;axis < BIH_MAXUNORDEREDCHILDREN && node->children[axis] >= 0;axis++)
+ {
+ leaf = bih->leafs + node->children[axis];
+ if (mins[0] > leaf->maxs[0] || maxs[0] < leaf->mins[0]
+ || mins[1] > leaf->maxs[1] || maxs[1] < leaf->mins[1]
+ || mins[2] > leaf->maxs[2] || maxs[2] < leaf->mins[2])
+ continue;
+ switch(leaf->type)
+ {
+ case BIH_RENDERTRIANGLE:
+ if (*numtrianglespointer >= maxtriangles)
+ {
+ ++*numtrianglespointer; // so the caller can detect overflow
+ break;
+ }
+ if(trianglelist_surf)
+ trianglelist_surf[*numtrianglespointer] = leaf->surfaceindex;
+ trianglelist_idx[*numtrianglespointer] = leaf->itemindex;
+ ++*numtrianglespointer;
+ break;
+ default:
+ break;
+ }
+ }
+ return;
+ }
+ // splitting node
+ axis = node->type - BIH_SPLITX;
+ if (mins[axis] < node->backmax)
+ {
+ if (maxs[axis] > node->frontmin)
+ BIH_GetTriangleListForBox_Node(bih, node->front, maxtriangles, trianglelist_idx, trianglelist_surf, numtrianglespointer, mins, maxs);
+ nodenum = node->back;
+ continue;
+ }
+ if (maxs[axis] > node->frontmin)
+ {
+ nodenum = node->front;
+ continue;
+ }
+ // fell between the child groups, nothing here
+ return;
+ }
+}
+
+int BIH_GetTriangleListForBox(const bih_t *bih, int maxtriangles, int *trianglelist_idx, int *trianglelist_surf, const float *mins, const float *maxs)
+{
+ int numtriangles = 0;
+ BIH_GetTriangleListForBox_Node(bih, bih->rootnode, maxtriangles, trianglelist_idx, trianglelist_surf, &numtriangles, mins, maxs);
+ return numtriangles;
+}
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