/// <summary>
/// Helper function to find out the hit test result
/// </summary>
private void ProduceHitTestResults(
List <LassoCrossing> crossingList, List <StrokeIntersection> strokeIntersections)
{
bool previousSegmentInsideLasso = false;
for (int x = 0; x <= crossingList.Count; x++)
{
bool currentSegmentWithinLasso = false;
bool canMerge = true;
StrokeIntersection si = new StrokeIntersection();
if (x == 0)
{
si.HitBegin = StrokeFIndices.BeforeFirst;
si.InBegin = StrokeFIndices.BeforeFirst;
}
else
{
si.InBegin = crossingList[x - 1].FIndices.EndFIndex;
si.HitBegin = crossingList[x - 1].FIndices.BeginFIndex;
currentSegmentWithinLasso = SegmentWithinLasso(crossingList[x - 1].EndNode, si.InBegin);
}
if (x == crossingList.Count)
{
// For a special case when the last intersection is something like (1.2, AL).
// As a result the last InSegment should be empty.
if (DoubleUtil.AreClose(si.InBegin, StrokeFIndices.AfterLast))
{
si.InEnd = StrokeFIndices.BeforeFirst;
}
else
{
si.InEnd = StrokeFIndices.AfterLast;
}
si.HitEnd = StrokeFIndices.AfterLast;
}
else
{
si.InEnd = crossingList[x].FIndices.BeginFIndex;
// For a speical case when the first intersection is something like (BF, 0.67).
// As a result the first InSegment should be empty
if (DoubleUtil.AreClose(si.InEnd, StrokeFIndices.BeforeFirst))
{
System.Diagnostics.Debug.Assert(DoubleUtil.AreClose(si.InBegin, StrokeFIndices.BeforeFirst));
si.InBegin = StrokeFIndices.AfterLast;
}
si.HitEnd = crossingList[x].FIndices.EndFIndex;
currentSegmentWithinLasso = SegmentWithinLasso(crossingList[x].StartNode, si.InEnd);
// If both the start and end position of the current crossing is
// outside the lasso, the crossing is a hit-only intersection, i.e., the in-segment is empty.
if (!currentSegmentWithinLasso && !SegmentWithinLasso(crossingList[x].EndNode, si.HitEnd))
{
currentSegmentWithinLasso = true;
si.HitBegin = crossingList[x].FIndices.BeginFIndex;
si.InBegin = StrokeFIndices.AfterLast;
si.InEnd = StrokeFIndices.BeforeFirst;
canMerge = false;
}
}
if (currentSegmentWithinLasso)
{
if (x > 0 && previousSegmentInsideLasso && canMerge)
{
// we need to consolidate with the previous segment
StrokeIntersection previousIntersection = strokeIntersections[strokeIntersections.Count - 1];
// For example: previousIntersection = [BF, AL, BF, 0.0027], si = [BF, 0.0027, 0.049, 0.063]
if (previousIntersection.InSegment.IsEmpty)
{
previousIntersection.InBegin = si.InBegin;
}
previousIntersection.InEnd = si.InEnd;
previousIntersection.HitEnd = si.HitEnd;
strokeIntersections[strokeIntersections.Count - 1] = previousIntersection;
}
else
{
strokeIntersections.Add(si);
}
if (DoubleUtil.AreClose(si.HitEnd, StrokeFIndices.AfterLast))
{
// The strokeIntersections already cover the end of the stroke. No need to continue.
return;
}
}
previousSegmentInsideLasso = currentSegmentWithinLasso;
}
}
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());
}