Quadtree: correct OpenMP parallelism

The problem is that the STL vector 'array' is being used in multiple threads in
parallel. Give each thread its own vector and merge the result into 'array'.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

source/crisscross/quadtree.h

@@ -112,41 +112,59 @@ namespace CrissCross
 					midY = (llPosition.Y() + trPosition.Y()) / 2.0f;
 
 			#ifdef _OPENMP
+			std::vector<T> v1, v2, v3, v4;
 			#pragma omp parallel sections
-			#endif
 			{
-				#ifdef _OPENMP
 				#pragma omp section
-				#endif
 				if (top > midY && left < midX) {
 					/* need to descend into top left quadtree */
-					tl->ObjectsInCircle(array, circle, radius);
+					tl->ObjectsInCircle(v1, circle, radius);
 				}
 
-				#ifdef _OPENMP
 				#pragma omp section
-				#endif
 				if (top > midY && right > midX)	{
 					/* top right quadtree */
-					tr->ObjectsInCircle(array, circle, radius);
+					tr->ObjectsInCircle(v2, circle, radius);
 				}
 
-				#ifdef _OPENMP
 				#pragma omp section
-				#endif
 				if (bottom < midY && right > midX) {
 					/* lower right quadtree */
-					lr->ObjectsInCircle(array, circle, radius);
+					lr->ObjectsInCircle(v3, circle, radius);
 				}
 
-				#ifdef _OPENMP
 				#pragma omp section
-				#endif
 				if (bottom < midY && left < midX) {
 					/* lower left quadtree */
-					ll->ObjectsInCircle(array, circle, radius);
+					ll->ObjectsInCircle(v4, circle, radius);
 				}
 			}
+			/* Merge the resulting vectors. */
+			array.insert(array.end(), v1.begin(), v1.end());
+			array.insert(array.end(), v2.begin(), v2.end());
+			array.insert(array.end(), v3.begin(), v3.end());
+			array.insert(array.end(), v4.begin(), v4.end());
+			#else
+			if (top > midY && left < midX) {
+				/* need to descend into top left quadtree */
+				tl->ObjectsInCircle(array, circle, radius);
+			}
+
+			if (top > midY && right > midX)	{
+				/* top right quadtree */
+				tr->ObjectsInCircle(array, circle, radius);
+			}
+
+			if (bottom < midY && right > midX) {
+				/* lower right quadtree */
+				lr->ObjectsInCircle(array, circle, radius);
+			}
+
+			if (bottom < midY && left < midX) {
+				/* lower left quadtree */
+				ll->ObjectsInCircle(array, circle, radius);
+			}
+			#endif
 		}
 
 		template <class T, int MaxDepth, int MaxNodesPerLevel>