// This checks if a vertex is reflex (corner > 180 deg) or convex (corner < 180 deg)
private static bool IsReflex(EarClipVertex[] t)
{
// Return true when corner is > 180 deg
return(Line2D.GetSideOfLine(t[0].Position, t[2].Position, t[1].Position) < 0.0f);
}
// 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// pick the wrong one, the polygon is no longer valid and triangulation will fail.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 clips a polygon and returns the triangles
// The polygon may not have any holes or islands
// See: http://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf
private int DoEarClip(EarClipPolygon poly, List <Vector2D> verticeslist, List <Sidedef> sidedefslist)
{
LinkedList <EarClipVertex> verts = new LinkedList <EarClipVertex>();
List <EarClipVertex> convexes = new List <EarClipVertex>(poly.Count);
LinkedList <EarClipVertex> reflexes = new LinkedList <EarClipVertex>();
LinkedList <EarClipVertex> eartips = new LinkedList <EarClipVertex>();
LinkedListNode <EarClipVertex> n1, n2;
EarClipVertex v, v1, v2;
EarClipVertex[] t, t1, t2;
int countvertices = 0;
// Go for all vertices to fill list
foreach (EarClipVertex vec in poly)
{
vec.SetVertsLink(verts.AddLast(vec));
}
// Remove any zero-length lines, these will give problems
n1 = verts.First;
do
{
// Continue until adjacent zero-length lines are removed
n2 = n1.Next ?? verts.First;
Vector2D d = n1.Value.Position - n2.Value.Position;
while ((Math.Abs(d.x) < 0.00001f) && (Math.Abs(d.y) < 0.00001f))
{
n2.Value.Remove();
n2 = n1.Next ?? verts.First;
if (n2 != null)
{
d = n1.Value.Position - n2.Value.Position;
}
else
{
break;
}
}
// Next!
n1 = n2;
}while(n1 != verts.First);
// Optimization: Vertices which have lines with the
// same angle are useless. Remove them!
n1 = verts.First;
while (n1 != null)
{
// Get the next vertex
n2 = n1.Next;
// Get triangle for v
t = GetTriangle(n1.Value);
// Check if both lines have the same angle
Line2D a = new Line2D(t[0].Position, t[1].Position);
Line2D b = new Line2D(t[1].Position, t[2].Position);
if (Math.Abs(Angle2D.Difference(a.GetAngle(), b.GetAngle())) < 0.00001f)
{
// Same angles, remove vertex
n1.Value.Remove();
}
// Next!
n1 = n2;
}
// Go for all vertices to determine reflex or convex
foreach (EarClipVertex vv in verts)
{
// Add to reflex or convex list
if (IsReflex(GetTriangle(vv)))
{
vv.AddReflex(reflexes);
}
else
{
convexes.Add(vv);
}
}
// Go for all convex vertices to see if they are ear tips
foreach (EarClipVertex cv in convexes)
{
// Add when this is a valid ear
t = GetTriangle(cv);
if (CheckValidEar(t, reflexes))
{
cv.AddEarTip(eartips);
}
}
#if DEBUG
if (OnShowPolygon != null)
{
OnShowPolygon(verts);
}
#endif
// Process ears until done
while ((eartips.Count > 0) && (verts.Count > 2))
{
// Get next ear
v = eartips.First.Value;
t = GetTriangle(v);
// Only save this triangle when it has an area
if (TriangleHasArea(t))
{
// Add ear as triangle
AddTriangleToList(t, verticeslist, sidedefslist, (verts.Count == 3));
countvertices += 3;
}
// Remove this ear from all lists
v.Remove();
v1 = t[0];
v2 = t[2];
#if DEBUG
if (TriangleHasArea(t))
{
if (OnShowEarClip != null)
{
OnShowEarClip(t, verts);
}
}
#endif
// Test first neighbour
t1 = GetTriangle(v1);
if (IsReflex(t1))
{
// List as reflex if not listed yet
if (!v1.IsReflex)
{
v1.AddReflex(reflexes);
}
v1.RemoveEarTip();
}
else
{
// Remove from reflexes
v1.RemoveReflex();
}
// Test second neighbour
t2 = GetTriangle(v2);
if (IsReflex(t2))
{
// List as reflex if not listed yet
if (!v2.IsReflex)
{
v2.AddReflex(reflexes);
}
v2.RemoveEarTip();
}
else
{
// Remove from reflexes
v2.RemoveReflex();
}
// Check if any neightbour have become a valid or invalid ear
if (!v1.IsReflex && (CheckValidEar(t1, reflexes)))
{
v1.AddEarTip(eartips);
}
else
{
v1.RemoveEarTip();
}
if (!v2.IsReflex && (CheckValidEar(t2, reflexes)))
{
v2.AddEarTip(eartips);
}
else
{
v2.RemoveEarTip();
}
}
#if DEBUG
if (OnShowRemaining != null)
{
OnShowRemaining(verts);
}
#endif
// Dispose remaining vertices
foreach (EarClipVertex ecv in verts)
{
ecv.Dispose();
}
// Return the number of vertices in the result
return(countvertices);
}
// 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);
}