made rtbuild object_heuristic_spliter faster

I think its something like:
	old was:  4*nlogn + 3*(n*6)
	new is:  (2*nlogn + 3*(n*6)) * f, with f<1

Still missing changing the sorting function to an introsort instead of qsort
Other options like bucketing sort may be worth trying (for very large trees)

source/blender/blenkernel/BKE_utildefines.h

@@ -80,6 +80,14 @@
 
 #define INIT_MINMAX2(min, max) { (min)[0]= (min)[1]= 1.0e30f; (max)[0]= (max)[1]= -1.0e30f; }
 
+#define DO_MIN(vec, min) { if( (min)[0]>(vec)[0] ) (min)[0]= (vec)[0];      \
+							  if( (min)[1]>(vec)[1] ) (min)[1]= (vec)[1];   \
+							  if( (min)[2]>(vec)[2] ) (min)[2]= (vec)[2]; } \
+
+#define DO_MAX(vec, max) { if( (max)[0]<(vec)[0] ) (max)[0]= (vec)[0];		\
+							  if( (max)[1]<(vec)[1] ) (max)[1]= (vec)[1];	\
+							  if( (max)[2]<(vec)[2] ) (max)[2]= (vec)[2]; } \
+
 #define DO_MINMAX(vec, min, max) { if( (min)[0]>(vec)[0] ) (min)[0]= (vec)[0]; \
 							  if( (min)[1]>(vec)[1] ) (min)[1]= (vec)[1]; \
 							  if( (min)[2]>(vec)[2] ) (min)[2]= (vec)[2]; \

source/blender/render/intern/include/rayobject_rtbuild.h

@@ -53,6 +53,8 @@ typedef struct RTBuilder
 	/* child partitions calculated during splitting */
 	int child_offset[RTBUILD_MAX_CHILDS+1];
 	
+	int child_sorted_axis; /* -1 if not sorted */
+
 } RTBuilder;
 
 /* used during creation */

source/blender/render/intern/source/rayobject_bih.c

@@ -102,9 +102,8 @@ static void bih_free(BIHTree *obj)
 
 static void bih_bb(BIHTree *obj, float *min, float *max)
 {
-	//TODO only half operations needed
+	DO_MIN(obj->bb[0], min);
-	DO_MINMAX(obj->bb[0], min, max);
+	DO_MAX(obj->bb[1], max);
-	DO_MINMAX(obj->bb[1], min, max);
 }
 
 /*
@@ -213,8 +212,8 @@ static BIHNode *bih_rearrange(BIHTree *tree, RTBuilder *builder, int nid, float
 			parent->bi[i][0] = cbb[parent->split_axis];
 			parent->bi[i][1] = cbb[parent->split_axis+3];
 
-			DO_MINMAX(cbb  , bb, bb+3);
+			DO_MIN(cbb  , bb);
-			DO_MINMAX(cbb+3, bb, bb+3);
+			DO_MAX(cbb+3, bb+3);
 		}
 		for(; i<BIH_NCHILDS; i++)
 		{

source/blender/render/intern/source/rayobject_blibvh.c

@@ -110,8 +110,8 @@ static void RayObject_blibvh_add(RayObject *o, RayObject *ob)
 	INIT_MINMAX(min_max, min_max+3);
 	RE_rayobject_merge_bb(ob, min_max, min_max+3);
 
-	DO_MINMAX(min_max  , obj->bb[0], obj->bb[1]);
+	DO_MIN(min_max  , obj->bb[0]);
-	DO_MINMAX(min_max+3, obj->bb[0], obj->bb[1]);
+	DO_MAX(min_max+3, obj->bb[1]);
 	
 	BLI_bvhtree_insert(obj->bvh, (int)ob, min_max, 2 );	
 }
@@ -135,6 +135,6 @@ static void RayObject_blibvh_free(RayObject *o)
 static void RayObject_blibvh_bb(RayObject *o, float *min, float *max)
 {
 	BVHObject *obj = (BVHObject*)o;
-	DO_MINMAX( obj->bb[0], min, max );
+	DO_MIN( obj->bb[0], min );
-	DO_MINMAX( obj->bb[1], min, max );
+	DO_MAX( obj->bb[1], max );
 }

source/blender/render/intern/source/rayobject_bvh.c

@@ -133,9 +133,8 @@ static void bvh_merge_bb(BVHNode *node, float *min, float *max)
 {
 	if(RayObject_isAligned(node))
 	{
-		//TODO only half operations needed
+		DO_MIN(node->bb  , min);
-		DO_MINMAX(node->bb  , min, max);
+		DO_MAX(node->bb+3, max);
-		DO_MINMAX(node->bb+3, min, max);
 	}
 	else
 	{

source/blender/render/intern/source/rayobject_rtbuild.c

@@ -19,6 +19,7 @@ static void rtbuild_init(RTBuilder *b, RayObject **begin, RayObject **end)
 	b->begin = begin;
 	b->end   = end;
 	b->split_axis = 0;
+	b->child_sorted_axis = -1;
 	
 	for(i=0; i<RTBUILD_MAX_CHILDS; i++)
 		b->child_offset[i] = 0;
@@ -46,6 +47,7 @@ void rtbuild_add(RTBuilder *b, RayObject *o)
 RTBuilder* rtbuild_get_child(RTBuilder *b, int child, RTBuilder *tmp)
 {
 	rtbuild_init( tmp, b->begin + b->child_offset[child], b->begin + b->child_offset[child+1] );
+	tmp->child_sorted_axis = b->child_sorted_axis;
 	return tmp;
 }
 
@@ -254,12 +256,14 @@ float bb_volume(float *min, float *max)
 
 float bb_area(float *min, float *max)
 {
-	float sub[3];
+	float sub[3], a;
 	sub[0] = max[0]-min[0];
 	sub[1] = max[1]-min[1];
 	sub[2] = max[2]-min[2];
 
-	return (sub[0]*sub[1] + sub[0]*sub[2] + sub[1]*sub[2])*2;
+	a = (sub[0]*sub[1] + sub[0]*sub[2] + sub[1]*sub[2])*2;
+	assert(a >= 0.0);
+	return a;
 }
 
 int rtbuild_heuristic_object_split(RTBuilder *b, int nchilds)
@@ -274,7 +278,7 @@ int rtbuild_heuristic_object_split(RTBuilder *b, int nchilds)
 	else
 	{
 		float bcost = FLT_MAX;
-		int i, axis, baxis, boffset;
+		int i, axis, baxis, boffset, k, try_axis[3];
 		CostObject *cost   = MEM_mallocN( sizeof(CostObject)*size, "RTBuilder.HeuristicObjectSplitter" );
 		float      *acc_bb = MEM_mallocN( sizeof(float)*6*size, "RTBuilder.HeuristicObjectSplitterBB" );
 
@@ -285,7 +289,20 @@ int rtbuild_heuristic_object_split(RTBuilder *b, int nchilds)
 			RE_rayobject_merge_bb(b->begin[i], cost[i].bb, cost[i].bb+3);
 		}
 		
-		for(axis=0; axis<3; axis++)
+		if(b->child_sorted_axis >= 0 && b->child_sorted_axis < 3)
+		{
+			try_axis[0] = b->child_sorted_axis;
+			try_axis[1] = (b->child_sorted_axis+1)%3;
+			try_axis[2] = (b->child_sorted_axis+2)%3;
+		}
+		else
+		{
+			try_axis[0] = 0;
+			try_axis[1] = 1;
+			try_axis[2] = 2;
+		}
+		
+		for(axis=try_axis[k=0]; k<3; axis=try_axis[++k])
 		{
 			float other_bb[6];
 
@@ -295,37 +312,54 @@ int rtbuild_heuristic_object_split(RTBuilder *b, int nchilds)
 				float *bb = acc_bb+i*6;
 				if(i == size-1)
 				{
-					INIT_MINMAX( bb, bb+3 );
+					VECCOPY(bb, cost[i].bb);
+					VECCOPY(bb+3, cost[i].bb+3);
 				}
 				else
 				{
-					VECCOPY( bb, bb+6 );
+					bb[0] = MIN2(cost[i].bb[0], bb[6+0]);
-					VECCOPY( bb+3, bb+6+3 );
+					bb[1] = MIN2(cost[i].bb[1], bb[6+1]);
+					bb[2] = MIN2(cost[i].bb[2], bb[6+2]);
+
+					bb[3] = MAX2(cost[i].bb[3], bb[6+3]);
+					bb[4] = MAX2(cost[i].bb[4], bb[6+4]);
+					bb[5] = MAX2(cost[i].bb[5], bb[6+5]);
 				}
-				RE_rayobject_merge_bb( cost[i].obj, bb, bb+3 );
 			}
 			
 			INIT_MINMAX(other_bb, other_bb+3);
-			DO_MINMAX( cost[0].bb, other_bb, other_bb+3 );
+			DO_MIN( cost[0].bb,   other_bb   );
-			DO_MINMAX( cost[0].bb+3, other_bb, other_bb+3 );
+			DO_MAX( cost[0].bb+3, other_bb+3 );
 
 			for(i=1; i<size; i++)
 			{
 				//Worst case heuristic (cost of each child is linear)
-				float hcost = bb_area(other_bb, other_bb+3)*(i+log(i)) + bb_area(acc_bb+i*6, acc_bb+i*6+3)*(size-i+log(size-i));
+				float hcost, left_side, right_side;
-				if(hcost < bcost)
+				
+				left_side = bb_area(other_bb, other_bb+3)*(i+logf(i));
+				right_side= bb_area(acc_bb+i*6, acc_bb+i*6+3)*(size-i+logf(size-i));
+				
+				if(left_side > bcost) break;	//No way we can find a better heuristic in this axis
+
+				hcost = left_side+right_side;
+				if( hcost < bcost
+				|| (hcost == bcost && axis < baxis)) //this makes sure the tree built is the same whatever is the order of the sorting axis
 				{
 					bcost = hcost;
 					baxis = axis;
 					boffset = i;
 				}
-				DO_MINMAX( cost[i].bb, other_bb, other_bb+3 );
+				DO_MIN( cost[i].bb,   other_bb   );
-				DO_MINMAX( cost[i].bb+3, other_bb, other_bb+3 );
+				DO_MAX( cost[i].bb+3, other_bb+3 );
 			}
-		}
+			
-		costobject_sort(cost, cost+size, baxis);
+			if(baxis == axis)
+			{
 				for(i=0; i<size; i++)
 					b->begin[i] = cost[i].obj;
+				b->child_sorted_axis = axis;
+			}
+		}
 			
 		b->child_offset[0] = 0;
 		b->child_offset[1] = boffset;