/// <summary>
/// Sort and merge the crossing list
/// </summary>
/// <param name="crossingList">The crossing list to sort/merge</param>
private static void SortAndMerge(ref List <LassoCrossing> crossingList)
{
// Sort the crossings based on the BeginFIndex values
crossingList.Sort();
List <LassoCrossing> mergedList = new List <LassoCrossing>();
LassoCrossing mcrossing = LassoCrossing.EmptyCrossing;
foreach (LassoCrossing crossing in crossingList)
{
System.Diagnostics.Debug.Assert(!crossing.IsEmpty && crossing.StartNode.IsValid && crossing.EndNode.IsValid);
if (!mcrossing.Merge(crossing))
{
System.Diagnostics.Debug.Assert(!mcrossing.IsEmpty && mcrossing.StartNode.IsValid && mcrossing.EndNode.IsValid);
mergedList.Add(mcrossing);
mcrossing = crossing;
}
}
if (!mcrossing.IsEmpty)
{
System.Diagnostics.Debug.Assert(!mcrossing.IsEmpty && mcrossing.StartNode.IsValid && mcrossing.EndNode.IsValid);
mergedList.Add(mcrossing);
}
crossingList = mergedList;
}
internal StrokeIntersection[] HitTest(StrokeNodeIterator iterator)
{
System.Diagnostics.Debug.Assert(_points != null);
System.Diagnostics.Debug.Assert(iterator != null);
if (_points.Count < 3)
{
//
// it takes at least 3 points to create a lasso
//
return(Array.Empty <StrokeIntersection>());
}
//
// We're about to perform hit testing with a lasso.
// To do so we need to iterate through each StrokeNode.
// As we do, we calculate the bounding rect between it
// and the previous StrokeNode and store this in 'currentStrokeSegmentBounds'
//
// Next, we check to see if that StrokeNode pair's bounding box intersects
// with the bounding box of the Lasso points. If not, we continue iterating through
// StrokeNode pairs.
//
// If it does, we do a more granular hit test by pairing points in the Lasso, getting
// their bounding box and seeing if that bounding box intersects our current StrokeNode
// pair
//
Point lastNodePosition = new Point();
Point lassoLastPoint = _points[_points.Count - 1];
Rect currentStrokeSegmentBounds = Rect.Empty;
// Initilize the current crossing to be an empty one
LassoCrossing currentCrossing = LassoCrossing.EmptyCrossing;
// Creat a list to hold all the crossings
List <LassoCrossing> crossingList = new List <LassoCrossing>();
for (int i = 0; i < iterator.Count; i++)
{
StrokeNode strokeNode = iterator[i];
Rect nodeBounds = strokeNode.GetBounds();
currentStrokeSegmentBounds.Union(nodeBounds);
// Skip the node if it's outside of the lasso's bounds
if (currentStrokeSegmentBounds.IntersectsWith(_bounds) == true)
{
// currentStrokeSegmentBounds, made up of the bounding box of
// this StrokeNode unioned with the last StrokeNode,
// intersects the lasso bounding box.
//
// Now we need to iterate through the lasso points and find out where they cross
//
Point lastPoint = lassoLastPoint;
foreach (Point point in _points)
{
//
// calculate a segment of the lasso from the last point
// to the current point
//
Rect lassoSegmentBounds = new Rect(lastPoint, point);
//
// see if this lasso segment intersects with the current stroke segment
//
if (!currentStrokeSegmentBounds.IntersectsWith(lassoSegmentBounds))
{
lastPoint = point;
continue;
}
//
// the lasso segment DOES intersect with the current stroke segment
// find out precisely where
//
StrokeFIndices strokeFIndices = strokeNode.CutTest(lastPoint, point);
lastPoint = point;
if (strokeFIndices.IsEmpty)
{
// current lasso segment does not hit the stroke segment, continue with the next lasso point
continue;
}
// Create a potentially new crossing for the current hit testing result.
LassoCrossing potentialNewCrossing = new LassoCrossing(strokeFIndices, strokeNode);
// Try to merge with the current crossing. If the merge is succussful (return true), the new crossing is actually
// continueing the current crossing, so do not start a new crossing. Otherwise, start a new one and add the existing
// one to the list.
if (!currentCrossing.Merge(potentialNewCrossing))
{
// start a new crossing and add the existing on to the list
crossingList.Add(currentCrossing);
currentCrossing = potentialNewCrossing;
}
}
}
// Continue with the next node
currentStrokeSegmentBounds = nodeBounds;
lastNodePosition = strokeNode.Position;
}
// Adding the last crossing to the list, if valid
if (!currentCrossing.IsEmpty)
{
crossingList.Add(currentCrossing);
}
// Handle the special case of no intersection at all
if (crossingList.Count == 0)
{
// the stroke was either completely inside the lasso
// or outside the lasso
if (this.Contains(lastNodePosition))
{
StrokeIntersection[] strokeIntersections = new StrokeIntersection[1];
strokeIntersections[0] = StrokeIntersection.Full;
return(strokeIntersections);
}
else
{
return(Array.Empty <StrokeIntersection>());
}
}
// It is still possible that the current crossing list is not sorted or overlapping.
// Sort the list and merge the overlapping ones.
SortAndMerge(ref crossingList);
// Produce the hit test results and store them in a list
List <StrokeIntersection> strokeIntersectionList = new List <StrokeIntersection>();
ProduceHitTestResults(crossingList, strokeIntersectionList);
return(strokeIntersectionList.ToArray());
}
