/// <summary>
/// Determines the winding order of a polygon given a set of vertices.
/// </summary>
/// <param name="vertices">The vertices of the polygon.</param>
/// <returns>The calculated winding order of the polygon.</returns>
public static WindingOrder DetermineWindingOrder(TriangulatorVector2[] vertices)
{
int clockWiseCount = 0;
int counterClockWiseCount = 0;
TriangulatorVector2 p1 = vertices[0];
for (int i = 1; i < vertices.Length; i++)
{
TriangulatorVector2 p2 = vertices[i];
TriangulatorVector2 p3 = vertices[(i + 1) % vertices.Length];
TriangulatorVector2 e1 = p1 - p2;
TriangulatorVector2 e2 = p3 - p2;
if (e1.X * e2.Y - e1.Y * e2.X >= 0)
{
clockWiseCount++;
}
else
{
counterClockWiseCount++;
}
p1 = p2;
}
return(clockWiseCount > counterClockWiseCount
? WindingOrder.Clockwise
: WindingOrder.CounterClockwise);
}
/// <summary>
/// Reverses the winding order for a set of vertices.
/// </summary>
/// <param name="vertices">The vertices of the polygon.</param>
/// <returns>The new vertices for the polygon with the opposite winding order.</returns>
public static TriangulatorVector2[] ReverseWindingOrder(TriangulatorVector2[] vertices)
{
Log("\nReversing winding order...");
TriangulatorVector2[] newVerts = new TriangulatorVector2[vertices.Length];
#if DEBUG
StringBuilder vString = new StringBuilder();
foreach (TriangulatorVector2 v in vertices)
{
vString.Append(string.Format("{0}, ", v));
}
Log("Original Vertices: {0}", vString);
#endif
newVerts[0] = vertices[0];
for (int i = 1; i < newVerts.Length; i++)
{
newVerts[i] = vertices[vertices.Length - i];
}
#if DEBUG
vString = new StringBuilder();
foreach (TriangulatorVector2 v in newVerts)
{
vString.Append(string.Format("{0}, ", v));
}
Log("New Vertices After Reversal: {0}\n", vString);
#endif
return(newVerts);
}
private static bool IsConvex(Vertex c)
{
Vertex p = polygonVertices[polygonVertices.IndexOf(c) - 1].Value;
Vertex n = polygonVertices[polygonVertices.IndexOf(c) + 1].Value;
TriangulatorVector2 d1 = TriangulatorVector2.Normalize(c.Position - p.Position);
TriangulatorVector2 d2 = TriangulatorVector2.Normalize(n.Position - c.Position);
TriangulatorVector2 n2 = new TriangulatorVector2(-d2.Y, d2.X);
return(TriangulatorVector2.Dot(d1, n2) <= 0f);
}
