// This checks if a point is inside a triangle
// When the point is on an edge of the triangle, it depends on the lines
// adjacent to the point if it is considered inside or not
// NOTE: vertices in t must be in clockwise order!
private static bool PointInsideTriangle(EarClipVertex[] t, LinkedListNode <EarClipVertex> p)
{
// If the triangle has no area, there can never be a point inside
if (TriangleHasArea(t))
{
float lineside01 = Line2D.GetSideOfLine(t[0].Position, t[1].Position, p.Value.Position);
float lineside12 = Line2D.GetSideOfLine(t[1].Position, t[2].Position, p.Value.Position);
float lineside20 = Line2D.GetSideOfLine(t[2].Position, t[0].Position, p.Value.Position);
float u_on_line = 0.5f;
// If point p is on the line of an edge, find out where on the edge segment p is.
if (lineside01 == 0.0f)
{
u_on_line = Line2D.GetNearestOnLine(t[0].Position, t[1].Position, p.Value.Position);
}
else if (lineside12 == 0.0f)
{
u_on_line = Line2D.GetNearestOnLine(t[1].Position, t[2].Position, p.Value.Position);
}
else if (lineside20 == 0.0f)
{
u_on_line = Line2D.GetNearestOnLine(t[2].Position, t[0].Position, p.Value.Position);
}
// If any of the lineside results are 0 then that means the point p lies on that edge and we
// need to test if the lines adjacent to the point p are in the triangle or not.
// If the lines are intersecting the triangle, we also consider the point inside.
if ((lineside01 == 0.0f) || (lineside12 == 0.0f) || (lineside20 == 0.0f))
{
// When the point p is outside the edge segment, then it is not inside the triangle
if ((u_on_line < 0.0f) || (u_on_line > 1.0f))
{
return(false);
}
// Point p is on an edge segment. We'll have to decide by it's lines if we call it inside or outside the triangle.
LinkedListNode <EarClipVertex> p1 = p.Previous ?? p.List.Last;
LinkedListNode <EarClipVertex> p2 = p.Next ?? p.List.First;
if (LineInsideTriangle(t, p.Value.Position, p1.Value.Position))
{
return(true);
}
if (LineInsideTriangle(t, p.Value.Position, p2.Value.Position))
{
return(true);
}
return(false);
}
return((lineside01 < 0.0f) && (lineside12 < 0.0f) && (lineside20 < 0.0f));
}
return(false);
}
public float GetNearestOnLine(Vector2D p)
{
return(Line2D.GetNearestOnLine(v1, v2, p));
}
// 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 u, ul, foundu = float.MaxValue;
Vector2D foundpos = new Vector2D();
// 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 Vector2D(endx, start.Value.Position.y));
// Calculate a small bonus (0.1 mappixel)
float bonus = starttoright.GetNearestOnLine(new Vector2D(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);
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);
Vector2D 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));
}
}
}
// This checks if a line is inside a triangle (touching the triangle is allowed)
// NOTE: We already know p1 is on an edge segment of the triangle
private static bool LineInsideTriangle(EarClipVertex[] t, Vector2D p1, Vector2D p2)
{
float s01 = Line2D.GetSideOfLine(t[0].Position, t[1].Position, p2);
float s12 = Line2D.GetSideOfLine(t[1].Position, t[2].Position, p2);
float s20 = Line2D.GetSideOfLine(t[2].Position, t[0].Position, p2);
float p2_on_edge = 2.0f; // somewhere outside the 0 .. 1 range
float p1_on_same_edge = 2.0f;
// Test if p2 is inside the triangle
if ((s01 < 0.0f) && (s12 < 0.0f) && (s20 < 0.0f))
{
// Line is inside triangle, because p2 is
return(true);
}
// Test if p2 is on an edge of the triangle and if it is we would
// like to know where on the edge segment p2 is
if (s01 == 0.0f)
{
p2_on_edge = Line2D.GetNearestOnLine(t[0].Position, t[1].Position, p2);
p1_on_same_edge = Line2D.GetSideOfLine(t[0].Position, t[1].Position, p1);
}
else if (s12 == 0.0f)
{
p2_on_edge = Line2D.GetNearestOnLine(t[1].Position, t[2].Position, p2);
p1_on_same_edge = Line2D.GetSideOfLine(t[1].Position, t[2].Position, p1);
}
else if (s20 == 0.0f)
{
p2_on_edge = Line2D.GetNearestOnLine(t[2].Position, t[0].Position, p2);
p1_on_same_edge = Line2D.GetSideOfLine(t[2].Position, t[0].Position, p1);
}
// Is p2 actually on the edge segment?
if ((p2_on_edge >= 0.0f) && (p2_on_edge <= 1.0f))
{
// If p1 is on the same edge (or the unlimited line of that edge)
// then the line is not inside this triangle.
if (p1_on_same_edge == 0.0f)
{
return(false);
}
}
// Do a complete line-triangle intersection test
// We already know p1 is not inside the triangle (possibly on an edge)
Line2D p = new Line2D(p1, p2);
Line2D t01 = new Line2D(t[0].Position, t[1].Position);
Line2D t12 = new Line2D(t[1].Position, t[2].Position);
Line2D t20 = new Line2D(t[2].Position, t[0].Position);
float pu, pt;
// Test intersections
t01.GetIntersection(p, out pu, out pt);
if (!float.IsNaN(pu) && (pu >= 0.0f) && (pu <= 1.0f) && (pt >= 0.0f) && (pt <= 1.0f))
{
return(true);
}
t12.GetIntersection(p, out pu, out pt);
if (!float.IsNaN(pu) && (pu >= 0.0f) && (pu <= 1.0f) && (pt >= 0.0f) && (pt <= 1.0f))
{
return(true);
}
t20.GetIntersection(p, out pu, out pt);
if (!float.IsNaN(pu) && (pu >= 0.0f) && (pu <= 1.0f) && (pt >= 0.0f) && (pt <= 1.0f))
{
return(true);
}
return(false);
}