bih.c

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// This code written in 2010 by Ashley Rose Hale (LadyHavoc) (darkplacesengine gmail 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;
}