/// <summary>
/// Cuts a hole into a shape.
/// </summary>
/// <param name="shapeVerts">An array of vertices for the primary shape.</param>
/// <param name="holeVerts">An array of vertices for the hole to be cut. It is assumed that these vertices lie completely within the shape verts.</param>
/// <returns>The new array of vertices that can be passed to Triangulate to properly triangulate the shape with the hole.</returns>
public static Vector2[] CutHoleInShape(Vector2[] shapeVerts, Vector2[] holeVerts)
{
Log("\nCutting hole into shape...");
//make sure the shape vertices are wound counter clockwise and the hole vertices clockwise
shapeVerts = EnsureWindingOrder(shapeVerts, WindingOrder.CounterClockwise);
holeVerts = EnsureWindingOrder(holeVerts, WindingOrder.Clockwise);
//clear all of the lists
polygonVertices.Clear();
earVertices.Clear();
convexVertices.Clear();
reflexVertices.Clear();
//generate the cyclical list of vertices in the polygon
for (int i = 0; i < shapeVerts.Length; i++)
{
polygonVertices.AddLast(new Vertex(shapeVerts[i], i));
}
CyclicalList <Vertex> holePolygon = new CyclicalList <Vertex>();
for (int i = 0; i < holeVerts.Length; i++)
{
holePolygon.Add(new Vertex(holeVerts[i], i + polygonVertices.Count));
}
#if DEBUG
StringBuilder vString = new StringBuilder();
foreach (Vertex v in polygonVertices)
{
vString.Append(string.Format("{0}, ", v));
}
Log("Shape Vertices: {0}", vString);
vString = new StringBuilder();
foreach (Vertex v in holePolygon)
{
vString.Append(string.Format("{0}, ", v));
}
Log("Hole Vertices: {0}", vString);
#endif
FindConvexAndReflexVertices();
FindEarVertices();
//find the hole vertex with the largest X value
Vertex rightMostHoleVertex = holePolygon[0];
foreach (Vertex v in holePolygon)
{
if (v.Position.X > rightMostHoleVertex.Position.X)
{
rightMostHoleVertex = v;
}
}
//construct a list of all line segments where at least one vertex
//is to the right of the rightmost hole vertex with one vertex
//above the hole vertex and one below
List <LineSegment> segmentsToTest = new List <LineSegment>();
for (int i = 0; i < polygonVertices.Count; i++)
{
Vertex a = polygonVertices[i].Value;
Vertex b = polygonVertices[i + 1].Value;
if ((a.Position.X > rightMostHoleVertex.Position.X || b.Position.X > rightMostHoleVertex.Position.X) &&
(a.Position.Y >= rightMostHoleVertex.Position.Y && b.Position.Y <= rightMostHoleVertex.Position.Y ||
a.Position.Y <= rightMostHoleVertex.Position.Y && b.Position.Y >= rightMostHoleVertex.Position.Y))
{
segmentsToTest.Add(new LineSegment(a, b));
}
}
//now we try to find the closest intersection point heading to the right from
//our hole vertex.
float? closestPoint = null;
LineSegment closestSegment = new LineSegment();
foreach (LineSegment segment in segmentsToTest)
{
float?intersection = segment.IntersectsWithRay(rightMostHoleVertex.Position, Vector2.UnitX);
if (intersection != null)
{
if (closestPoint == null || closestPoint.Value > intersection.Value)
{
closestPoint = intersection;
closestSegment = segment;
}
}
}
//if closestPoint is null, there were no collisions (likely from improper input data),
//but we'll just return without doing anything else
if (closestPoint == null)
{
return(shapeVerts);
}
//otherwise we can find our mutually visible vertex to split the polygon
Vector2 I = rightMostHoleVertex.Position + Vector2.UnitX * closestPoint.Value;
Vertex P = closestSegment.A.Position.X > closestSegment.B.Position.X
? closestSegment.A
: closestSegment.B;
//construct triangle MIP
Triangle mip = new Triangle(rightMostHoleVertex, new Vertex(I, 1), P);
//see if any of the reflex vertices lie inside of the MIP triangle
List <Vertex> interiorReflexVertices = new List <Vertex>();
foreach (Vertex v in reflexVertices)
{
if (mip.ContainsPoint(v))
{
interiorReflexVertices.Add(v);
}
}
//if there are any interior reflex vertices, find the one that, when connected
//to our rightMostHoleVertex, forms the line closest to Vector2.UnitX
if (interiorReflexVertices.Count > 0)
{
float closestDot = -1f;
foreach (Vertex v in interiorReflexVertices)
{
//compute the dot product of the vector against the UnitX
Vector2 d = Vector2.Normalize(v.Position - rightMostHoleVertex.Position);
float dot = Vector2.Dot(Vector2.UnitX, d);
//if this line is the closest we've found
if (dot > closestDot)
{
//save the value and save the vertex as P
closestDot = dot;
P = v;
}
}
}
//now we just form our output array by injecting the hole vertices into place
//we know we have to inject the hole into the main array after point P going from
//rightMostHoleVertex around and then back to P.
int mIndex = holePolygon.IndexOf(rightMostHoleVertex);
int injectPoint = polygonVertices.IndexOf(P);
Log("Inserting hole at injection point {0} starting at hole vertex {1}.",
P,
rightMostHoleVertex);
for (int i = mIndex; i <= mIndex + holePolygon.Count; i++)
{
Log("Inserting vertex {0} after vertex {1}.", holePolygon[i], polygonVertices[injectPoint].Value);
polygonVertices.AddAfter(polygonVertices[injectPoint++], holePolygon[i]);
}
polygonVertices.AddAfter(polygonVertices[injectPoint], P);
#if DEBUG
vString = new StringBuilder();
foreach (Vertex v in polygonVertices)
{
vString.Append(string.Format("{0}, ", v));
}
Log("New Shape Vertices: {0}\n", vString);
#endif
//finally we write out the new polygon vertices and return them out
Vector2[] newShapeVerts = new Vector2[polygonVertices.Count];
for (int i = 0; i < polygonVertices.Count; i++)
{
newShapeVerts[i] = polygonVertices[i].Value.Position;
}
return(newShapeVerts);
}