public static IPrimitive CreateNewHierachy(List <IPrimitive> traceableItems, int maxRecursion = int.MaxValue, int recursionDepth = 0, SortingAccelerator accelerator = null) { if (accelerator == null) { accelerator = new SortingAccelerator(); } int numItems = traceableItems.Count; if (numItems == 0) { return(null); } if (numItems == 1) { return(traceableItems[0]); } int bestAxis = -1; int bestIndexToSplitOn = -1; var axisSorter = new CompareCentersOnAxis(0); if (recursionDepth < maxRecursion) { if (numItems > 50) { bestAxis = accelerator.NextAxis; bestIndexToSplitOn = numItems / 2; } else { double totalIntersectCost = 0; int skipInterval = 1; for (int i = 0; i < numItems; i += skipInterval) { IPrimitive item = traceableItems[i]; totalIntersectCost += item.GetIntersectCost(); } // get the bounding box of all the items we are going to consider. AxisAlignedBoundingBox OverallBox = traceableItems[0].GetAxisAlignedBoundingBox(); for (int i = skipInterval; i < numItems; i += skipInterval) { OverallBox += traceableItems[i].GetAxisAlignedBoundingBox(); } double areaOfTotalBounds = OverallBox.GetSurfaceArea(); double bestCost = totalIntersectCost; var totalDeviationOnAxis = default(Vector3); double[] surfaceArreaOfItem = new double[numItems - 1]; double[] rightBoundsAtItem = new double[numItems - 1]; for (int axis = 0; axis < 3; axis++) { double intersectCostOnLeft = 0; axisSorter.WhichAxis = axis; traceableItems.Sort(axisSorter); // Get all left bounds AxisAlignedBoundingBox currentLeftBounds = traceableItems[0].GetAxisAlignedBoundingBox(); surfaceArreaOfItem[0] = currentLeftBounds.GetSurfaceArea(); for (int itemIndex = 1; itemIndex < numItems - 1; itemIndex += skipInterval) { currentLeftBounds += traceableItems[itemIndex].GetAxisAlignedBoundingBox(); surfaceArreaOfItem[itemIndex] = currentLeftBounds.GetSurfaceArea(); totalDeviationOnAxis[axis] += Math.Abs(traceableItems[itemIndex].GetCenter()[axis] - traceableItems[itemIndex - 1].GetCenter()[axis]); } // Get all right bounds if (numItems > 1) { AxisAlignedBoundingBox currentRightBounds = traceableItems[numItems - 1].GetAxisAlignedBoundingBox(); rightBoundsAtItem[numItems - 2] = currentRightBounds.GetSurfaceArea(); for (int itemIndex = numItems - 1; itemIndex > 1; itemIndex -= skipInterval) { currentRightBounds += traceableItems[itemIndex - 1].GetAxisAlignedBoundingBox(); rightBoundsAtItem[itemIndex - 2] = currentRightBounds.GetSurfaceArea(); } } // Sweep from left for (int itemIndex = 0; itemIndex < numItems - 1; itemIndex += skipInterval) { double thisCost = 0; { // Evaluate Surface Cost Equation double costOfTwoAABB = 2 * AxisAlignedBoundingBox.GetIntersectCost(); // the cost of the two children AABB tests // do the left cost intersectCostOnLeft += traceableItems[itemIndex].GetIntersectCost(); double leftCost = (surfaceArreaOfItem[itemIndex] / areaOfTotalBounds) * intersectCostOnLeft; // do the right cost double intersectCostOnRight = totalIntersectCost - intersectCostOnLeft; double rightCost = (rightBoundsAtItem[itemIndex] / areaOfTotalBounds) * intersectCostOnRight; thisCost = costOfTwoAABB + leftCost + rightCost; } if (thisCost < bestCost + .000000001) // if it is less within some tiny error { if (thisCost > bestCost - .000000001) { // they are the same within the error if (axis > 0 && bestAxis != axis) // we have changed axis since last best and we need to decide if this is better than the last axis best { if (totalDeviationOnAxis[axis] > totalDeviationOnAxis[axis - 1]) { // this new axis is better and we'll switch to it. Otherwise don't switch. bestCost = thisCost; bestIndexToSplitOn = itemIndex; bestAxis = axis; } } } else // this is just better { bestCost = thisCost; bestIndexToSplitOn = itemIndex; bestAxis = axis; } } } } } } if (bestAxis == -1) { // No better partition found return(new UnboundCollection(traceableItems)); } else { var leftItems = new List <IPrimitive>(bestIndexToSplitOn + 1); var rightItems = new List <IPrimitive>(numItems - bestIndexToSplitOn + 1); if (numItems > 100) { // there are lots of items, lets find a sampled bounds and then choose a center var totalBounds = AxisAlignedBoundingBox.Empty(); for (int i = 0; i < 50; i++) { totalBounds.ExpandToInclude(traceableItems[i * numItems / 50].GetCenter()); } bestAxis = totalBounds.XSize > totalBounds.YSize ? 0 : 1; bestAxis = totalBounds.Size[bestAxis] > totalBounds.ZSize ? bestAxis : 2; var axisCenter = totalBounds.Center[bestAxis]; for (int i = 0; i < numItems; i++) { if (traceableItems[i].GetAxisCenter(bestAxis) <= axisCenter) { leftItems.Add(traceableItems[i]); } else { rightItems.Add(traceableItems[i]); } } } else // sort them and find the center { axisSorter.WhichAxis = bestAxis; traceableItems.Sort(axisSorter); for (int i = 0; i <= bestIndexToSplitOn; i++) { leftItems.Add(traceableItems[i]); } for (int i = bestIndexToSplitOn + 1; i < numItems; i++) { rightItems.Add(traceableItems[i]); } } IPrimitive leftGroup = CreateNewHierachy(leftItems, maxRecursion, recursionDepth + 1, accelerator); IPrimitive rightGroup = CreateNewHierachy(rightItems, maxRecursion, recursionDepth + 1, accelerator); var newBVHNode = new BoundingVolumeHierarchy(leftGroup, rightGroup, bestAxis); return(newBVHNode); } }
public double GetSurfaceArea() { return(Aabb.GetSurfaceArea()); }