// This calculates the relative angle between two lines
private float CalculateRelativeAngle(Linedef a, Linedef b)
{
// Determine angles
float ana = a.Angle;
if (a.End == basevertex)
{
ana += Angle2D.PI;
}
float anb = b.Angle;
if (b.End == basevertex)
{
anb += Angle2D.PI;
}
// Take the difference from angles
float n = Angle2D.Difference(ana, anb);
// Get line end vertices a and b that are not connected to basevertex
Vector2D va = (a.Start == basevertex ? a.End.Position : a.Start.Position);
Vector2D vb = (b.Start == basevertex ? b.End.Position : b.Start.Position);
// Check to which side the angle goes and adjust angle as needed
float s = Line2D.GetSideOfLine(va, vb, basevertex.Position);
if (((s < 0) && front) || ((s > 0) && !front))
{
n = Angle2D.PI2 - n;
}
// Return result
return(n);
}
// 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 GetSideOfLine(Vector2D p)
{
return(Line2D.GetSideOfLine(v1, v2, p));
}
// 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 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);
}
