// This finds the cut coordinates and splits the other poly with inner vertices
private static void SplitOuterWithInner(LinkedListNode <EarClipVertex> start, EarClipPolygon p)
{
LinkedListNode <EarClipVertex> insertbefore = null;
float foundu = float.MaxValue;
Vector2 foundpos = new Vector2();
// Create a line from start that goes beyond the right most vertex of p
LinkedListNode <EarClipVertex> pr = FindRightMostVertex(p);
float startx = start.Value.Position.x;
float endx = pr.Value.Position.x + 10.0f;
Line2D starttoright = new Line2D(start.Value.Position, new Vector2(endx, start.Value.Position.y));
// Calculate a small bonus (0.1 mappixel)
float bonus = starttoright.GetNearestOnLine(new Vector2(start.Value.Position.x + 0.1f, start.Value.Position.y));
// Go for all lines in the outer polygon
LinkedListNode <EarClipVertex> v1 = p.Last;
LinkedListNode <EarClipVertex> v2 = p.First;
while (v2 != null)
{
// Check if the line goes between startx and endx
if ((v1.Value.Position.x > startx || v2.Value.Position.x > startx) &&
(v1.Value.Position.x < endx || v2.Value.Position.x < endx))
{
// Find intersection
Line2D pl = new Line2D(v1.Value.Position, v2.Value.Position);
float u, ul;
pl.GetIntersection(starttoright, out u, out ul);
if (float.IsNaN(u))
{
// We have found a line that is perfectly horizontal
// (parallel to the cut scan line) Check if the line
// is overlapping the cut scan line.
if (v1.Value.Position.y == start.Value.Position.y)
{
// This is an exceptional situation which causes a bit of a problem, because
// this could be a previously made cut, which overlaps another line from the
// same cut and we have to determine which of the two we will join with. If we
// pick the wrong one, the polygon is no longer valid and triangulation will fail.
// Calculate distance of each vertex in units
u = starttoright.GetNearestOnLine(v1.Value.Position);
ul = starttoright.GetNearestOnLine(v2.Value.Position);
// Rule out vertices before the scan line
if (u < 0.0f)
{
u = float.MaxValue;
}
if (ul < 0.0f)
{
ul = float.MaxValue;
}
float insert_u = Math.Min(u, ul);
Vector2 inserpos = starttoright.GetCoordinatesAt(insert_u);
// Check in which direction the line goes.
if (v1.Value.Position.x > v2.Value.Position.x)
{
// The line goes from right to left (towards our start point)
// so we must always insert our cut after this line.
// If the next line goes up, we consider this a better candidate than
// a horizontal line that goes from left to right (the other cut line)
// so we give it a small bonus.
LinkedListNode <EarClipVertex> v3 = v2.Next ?? v2.List.First;
if (v3.Value.Position.y < v2.Value.Position.y)
{
insert_u -= bonus;
}
// Remember this when it is a closer match
if (insert_u <= foundu)
{
insertbefore = v2.Next ?? v2.List.First;
foundu = insert_u;
foundpos = inserpos;
}
}
else
{
// The line goes from left to right (away from our start point)
// so we must always insert our cut before this line.
// If the previous line goes down, we consider this a better candidate than
// a horizontal line that goes from right to left (the other cut line)
// so we give it a small bonus.
LinkedListNode <EarClipVertex> v3 = v1.Previous ?? v1.List.Last;
if (v3.Value.Position.y > v1.Value.Position.y)
{
insert_u -= bonus;
}
// Remember this when it is a closer match
if (insert_u <= foundu)
{
insertbefore = v2;
foundu = insert_u;
foundpos = inserpos;
}
}
}
}
// Found a closer match?
else if ((ul >= 0.0f) && (ul <= 1.0f) && (u > 0.0f) && (u <= foundu))
{
// Found a closer intersection
insertbefore = v2;
foundu = u;
foundpos = starttoright.GetCoordinatesAt(u);
}
}
// Next
v1 = v2;
v2 = v2.Next;
}
// Found anything?
if (insertbefore != null)
{
Sidedef sd = (insertbefore.Previous == null) ? insertbefore.List.Last.Value.Sidedef : insertbefore.Previous.Value.Sidedef;
// Find the position where we have to split the outer polygon
EarClipVertex split = new EarClipVertex(foundpos, null);
// Insert manual split vertices
p.AddBefore(insertbefore, new EarClipVertex(split, sd));
// Start inserting from the start (do I make sense this time?)
v1 = start;
do
{
// Insert inner polygon vertex
p.AddBefore(insertbefore, new EarClipVertex(v1.Value));
v1 = (v1.Next ?? v1.List.First);
} while (v1 != start);
// Insert manual split vertices
p.AddBefore(insertbefore, new EarClipVertex(start.Value, sd));
if (split.Position != insertbefore.Value.Position)
{
p.AddBefore(insertbefore, new EarClipVertex(split, sd));
}
}
}
