first pass at bvh construction (SAH), untested

diff --git a/src/bvh.c b/src/bvh.c
index af6ed45..d6d237e 100644 (file)
--- a/src/bvh.c
+++ b/src/bvh.c
@@ -1,22 +1,36 @@
+#include <stdio.h>
 #include <stdlib.h>
 #include <float.h>
 #include "bvh.h"
 
 #define SPLIT_BUCKETS  8
 
+static float eval_split_cost(struct bvhnode *node, float area, float sp, struct triangle **tribuf, int *part);
+
 int build_bvh_sah(struct bvhnode *tree)
 {
-       int i, j, best;
+       int i, best;
        float sp, sp0, spgap, area, ext[3];
        float spcost[SPLIT_BUCKETS];
        int part[SPLIT_BUCKETS];
-       struct triangle **tribuf, **src;
+       struct triangle **tribuf;
+       struct aabox *aabb = &tree->aabb;
+
+       if(tree->left || tree->right) return 0;
+
+       /* calculate the bounding box for this node */
+       aabox_init(aabb);
+       for(i=0; i<tree->num_faces; i++) {
+               aabox_addface(aabb, tree->faces[i]);
+       }
 
-       if(tree->num_faces < 16 || tree->left || tree->right) return 0;
+       if(tree->num_faces < 16) {
+               return 0;
+       }
 
-       ext[0] = tree->aabb.vmax.x - tree->aabb.vmin.x;
-       ext[1] = tree->aabb.vmax.y - tree->aabb.vmin.y;
-       ext[2] = tree->aabb.vmax.z - tree->aabb.vmin.z;
+       ext[0] = aabb->vmax.x - aabb->vmin.x;
+       ext[1] = aabb->vmax.y - aabb->vmin.y;
+       ext[2] = aabb->vmax.z - aabb->vmin.z;
 
        if((area = surf_area(ext[0], ext[1], ext[2])) <= 0.0f) return 0;
 
@@ -33,7 +47,7 @@ int build_bvh_sah(struct bvhnode *tree)
 
        for(i=0; i<SPLIT_BUCKETS; i++) {
                sp = sp0 + i * spgap;
-               spcost[i] = eval_cost(tree, area, sp, tribuf + i * tree->num_faces, part + i);
+               spcost[i] = eval_split_cost(tree, area, sp, tribuf + i * tree->num_faces, part + i);
        }
 
        best = 0;
@@ -43,6 +57,12 @@ int build_bvh_sah(struct bvhnode *tree)
                }
        }
 
+       if(spcost[best] > tree->num_faces) {
+               /* the best split cost is worst than the no-split case */
+               free(tribuf);
+               return 0;
+       }
+
        /* found the best split, allocate child nodes, split the original array and copy
         * the pointers from tribuf to each part
         */
@@ -54,22 +74,28 @@ int build_bvh_sah(struct bvhnode *tree)
        }
 
        memcpy(tree->faces, tribuf + best * tree->num_faces, tree->num_faces * sizeof *tribuf);
+       free(tribuf);
 
        tree->left->faces = tree->faces;
        tree->left->num_faces = part[best];
        tree->right->faces = tree->faces + part[best];
        tree->right->num_faces = tree->faces - tree->left->faces;
 
-       /* TODO: calc aabox for each child node */
-       free(tribuf);
+       build_bvh_sah(tree->left);
+       build_bvh_sah(tree->right);
+       return 0;
 }
 
-static float eval_cost(struct bvhnode *node, float area, float sp, struct triangle **tribuf, int *part)
+static float eval_split_cost(struct bvhnode *node, float area, float sp, struct triangle **tribuf, int *part)
 {
-       int i;
-       float cost;
+       int i, nleft, nright;
+       float cost, sa_left, sa_right, cost_left, cost_right;
        struct triangle *tri;
        struct triangle **pleft, **pright;
+       struct aabox bbleft, bbright;
+
+       aabox_init(&bbleft);
+       aabox_init(&bbright);
 
        /* partition on sp */
        pleft = tribuf;
@@ -77,16 +103,27 @@ static float eval_cost(struct bvhnode *node, float area, float sp, struct triang
 
        for(i=0; i<node->num_faces; i++) {
                tri = node->faces[i];
-               if(cgm_velem(tri->v, node->axis) < sp) {
+               if(cgm_velem(&tri->v[0].pos, node->axis) < sp) {
+                       aabox_addface(&bbleft, tri);
                        *pleft++ = tri;
                } else {
+                       aabox_addface(&bbright, tri);
                        *pright-- = tri;
                }
        }
 
-       /* TODO calc cost */
+       nleft = pleft - tribuf;
+       nright = node->num_faces - nleft;
+
+       sa_left = aabox_surf_area(&bbleft);
+       sa_right = aabox_surf_area(&bbright);
+
+       /* intersection cost = 1, traversal cost = 0.2 * intesection cost */
+       cost_left = sa_left * nleft;
+       cost_right = sa_right * nright;
+       cost = 0.2f + (cost_left + cost_right) / area;
 
-       *part = pleft - tribuf;
+       *part = nleft;
        return cost;
 }
 

diff --git a/src/geom.c b/src/geom.c
index 07f7a9b..a704bab 100644 (file)
--- a/src/geom.c
+++ b/src/geom.c
@@ -68,6 +68,25 @@ int ray_aabox_any(cgm_ray *ray, struct aabox *box, float tmax)
        return 1;
 }
 
+void aabox_init(struct aabox *box)
+{
+       box->vmin.x = box->vmin.y = box->vmin.z = FLT_MAX;
+       box->vmax.x = box->vmax.y = box->vmax.z = -FLT_MAX;
+}
+
+void aabox_addface(struct aabox *box, struct triangle *tri)
+{
+       int i;
+       for(i=0; i<3; i++) {
+               if(tri->v[i].pos.x < box->vmin.x) box->vmin.x = tri->v[i].pos.x;
+               if(tri->v[i].pos.x > box->vmax.x) box->vmax.x = tri->v[i].pos.x;
+               if(tri->v[i].pos.y < box->vmin.y) box->vmin.y = tri->v[i].pos.y;
+               if(tri->v[i].pos.y > box->vmax.y) box->vmax.y = tri->v[i].pos.y;
+               if(tri->v[i].pos.z < box->vmin.z) box->vmin.z = tri->v[i].pos.z;
+               if(tri->v[i].pos.z > box->vmax.z) box->vmax.z = tri->v[i].pos.z;
+       }
+}
+
 void aabox_union(struct aabox *res, struct aabox *a, struct aabox *b)
 {
        res->vmin.x = a->vmin.x < b->vmin.x ? a->vmin.x : b->vmin.x;

diff --git a/src/geom.h b/src/geom.h
index 2233c67..b0fbb1d 100644 (file)
--- a/src/geom.h
+++ b/src/geom.h
@@ -30,6 +30,8 @@ struct rayhit {
 int ray_triangle(cgm_ray *ray, struct triangle *tri, float tmax, struct rayhit *hit);
 int ray_aabox_any(cgm_ray *ray, struct aabox *box, float tmax);
 
+void aabox_init(struct aabox *box);
+void aabox_addface(struct aabox *box, struct triangle *tri);
 void aabox_union(struct aabox *res, struct aabox *a, struct aabox *b);
 float aabox_surf_area(struct aabox *box);
 float surf_area(float dx, float dy, float dz);