/// <summary>Adds a point to DragState with a filtering algorithm. The
/// default filtering algorithm supports "backing up the mouse" for erasure.</summary>
/// <returns>true if a point was added, false if not.</returns>
protected virtual bool AddFiltered(DragState state, DragPoint dp)
{
var points = state.MousePoints;
if (points.Count < 2)
{
return(AddIfFarEnough(points, dp));
}
var newSeg = (LineSegment <float>)points.Last.Point.To(dp.Point);
// Strategy:
// 1. Stroke the new segment with a simple rectangle with no endcap.
// The rectangle will be a thin box around the point (halfwidth
// is 1..2)
var newRect = SimpleStroke(newSeg, EraseThreshold1);
var newRectBB = newRect.ToBoundingBox();
// 2. Identify the most recent intersection point between this rectangle
// (newRect) and the line being drawn. (if there is no such point,
// there is no erasure. Done.)
// 2b. That intersection point is the one _entering_ the rectangle. Find
// the previous intersection point, the one that exits the rectangle.
// this is the beginning of the region to potentially erase.
var older = points.Reverse().AdjacentPairs().Select(pair => pair.B.Point.To(pair.A.Point));
Point <float> beginning = default(Point <float>);
bool keepLooking = false;
int offs = 0;
var e = older.GetEnumerator();
for (; e.MoveNext(); offs++)
{
var seg = e.Current;
var list = FindIntersectionsWith(seg, newRect, true).ToList();
if (list.Count != 0)
{
var min = list.MinOrDefault(p => p.A);
beginning = min.B;
if (!(offs == 0 && min.A == 1))
{
if (keepLooking || !PolygonMath.IsPointInPolygon(newRect, seg.A))
{
break;
}
keepLooking = true;
}
}
else if (offs == 0)
{
} // todo: use IsPointInPolygon if itscs unstable
}
int iFirst = points.Count - 1 - offs; // index of the first point inside the region (iFirst-1 is outside)
if (iFirst > 0)
{
// 3. Between here and there, identify the farthest point away from the
// new point (dp.Point).
var region = ((IList <DragPoint>)points).Slice(iFirst);
int offsFarthest = region.IndexOfMax(p => (p.Point.Sub(dp.Point)).Quadrance());
int iFarthest = iFirst + offsFarthest;
// 4. Make sure that all the points between here and there are close to
// this line (within, say... 8 pixels). If so, we have erasure.
var seg = dp.Point.To(points[iFarthest].Point);
if (region.All(p => p.Point.DistanceTo(seg) < EraseThreshold2))
{
// 5. Respond to erasure by deleting all the points between there
// and here, not including the first or last point.
// 5b. Consider adding the intersection point found in step 2b to
// the point list, before adding the new point.
points.Resize(iFirst);
if (points.Count == 0 || (points.Last.Point.Sub(beginning)).Length() >= MinDistBetweenDragPoints)
{
points.Add(new DragPoint(beginning, 10, points));
}
}
}
return(AddIfFarEnough(points, dp));
}