public PolyNode GetRightestConnection(PolyNode incoming)
{
if (NConnected == 0)
{
Debug.Assert(false); // This means the connection graph is inconsistent
}
if (NConnected == 1)
{
//b2Assert(false);
// Because of the possibility of collapsing nearby points,
// we may end up with "spider legs" dangling off of a region.
// The correct behavior here is to turn around.
return(incoming);
}
FVector2 inDir = Position - incoming.Position;
float inLength = inDir.Length();
inDir.Normalize();
Debug.Assert(inLength > Box2D.Settings.b2_epsilon);
PolyNode result = null;
for (int i = 0; i < NConnected; ++i)
{
if (Connected[i] == incoming)
{
continue;
}
FVector2 testDir = Connected[i].Position - Position;
float testLengthSqr = testDir.LengthSquared();
testDir.Normalize();
Debug.Assert(testLengthSqr >= Box2D.Settings.b2_epsilon * Box2D.Settings.b2_epsilon);
float myCos = FVector2.Dot(inDir, testDir);
float mySin = MathUtils.Cross(inDir, testDir);
if (result != null)
{
FVector2 resultDir = result.Position - Position;
resultDir.Normalize();
float resCos = FVector2.Dot(inDir, resultDir);
float resSin = MathUtils.Cross(inDir, resultDir);
if (IsRighter(mySin, myCos, resSin, resCos))
{
result = Connected[i];
}
}
else
{
result = Connected[i];
}
}
Debug.Assert(result != null);
return(result);
}
/// <summary>
/// Triangulates a polygon using simple ear-clipping algorithm. Returns
/// size of Triangle array unless the polygon can't be triangulated.
/// This should only happen if the polygon self-intersects,
/// though it will not _always_ return null for a bad polygon - it is the
/// caller's responsibility to check for self-intersection, and if it
/// doesn't, it should at least check that the return value is non-null
/// before using. You're warned!
///
/// Triangles may be degenerate, especially if you have identical points
/// in the input to the algorithm. Check this before you use them.
///
/// This is totally unoptimized, so for large polygons it should not be part
/// of the simulation loop.
///
/// Warning: Only works on simple polygons.
/// </summary>
/// <returns></returns>
public static List <Triangle> TriangulatePolygon(Vertices vertices)
{
List <Triangle> results = new List <Triangle>();
if (vertices.Count < 3)
{
return(new List <Triangle>());
}
//Recurse and split on pinch points
Vertices pA, pB;
Vertices pin = new Vertices(vertices);
if (ResolvePinchPoint(pin, out pA, out pB))
{
List <Triangle> mergeA = TriangulatePolygon(pA);
List <Triangle> mergeB = TriangulatePolygon(pB);
if (mergeA.Count == -1 || mergeB.Count == -1)
{
throw new Exception("Can't triangulate your polygon.");
}
for (int i = 0; i < mergeA.Count; ++i)
{
results.Add(new Triangle(mergeA[i]));
}
for (int i = 0; i < mergeB.Count; ++i)
{
results.Add(new Triangle(mergeB[i]));
}
return(results);
}
Triangle[] buffer = new Triangle[vertices.Count - 2];
int bufferSize = 0;
float[] xrem = new float[vertices.Count];
float[] yrem = new float[vertices.Count];
for (int i = 0; i < vertices.Count; ++i)
{
xrem[i] = vertices[i].X;
yrem[i] = vertices[i].Y;
}
int vNum = vertices.Count;
while (vNum > 3)
{
// Find an ear
int earIndex = -1;
float earMaxMinCross = -10.0f;
for (int i = 0; i < vNum; ++i)
{
if (IsEar(i, xrem, yrem, vNum))
{
int lower = Remainder(i - 1, vNum);
int upper = Remainder(i + 1, vNum);
FVector2 d1 = new FVector2(xrem[upper] - xrem[i], yrem[upper] - yrem[i]);
FVector2 d2 = new FVector2(xrem[i] - xrem[lower], yrem[i] - yrem[lower]);
FVector2 d3 = new FVector2(xrem[lower] - xrem[upper], yrem[lower] - yrem[upper]);
d1.Normalize();
d2.Normalize();
d3.Normalize();
float cross12;
MathUtils.Cross(ref d1, ref d2, out cross12);
cross12 = Math.Abs(cross12);
float cross23;
MathUtils.Cross(ref d2, ref d3, out cross23);
cross23 = Math.Abs(cross23);
float cross31;
MathUtils.Cross(ref d3, ref d1, out cross31);
cross31 = Math.Abs(cross31);
//Find the maximum minimum angle
float minCross = Math.Min(cross12, Math.Min(cross23, cross31));
if (minCross > earMaxMinCross)
{
earIndex = i;
earMaxMinCross = minCross;
}
}
}
// If we still haven't found an ear, we're screwed.
// Note: sometimes this is happening because the
// remaining points are collinear. Really these
// should just be thrown out without halting triangulation.
if (earIndex == -1)
{
for (int i = 0; i < bufferSize; i++)
{
results.Add(new Triangle(buffer[i]));
}
return(results);
}
// Clip off the ear:
// - remove the ear tip from the list
--vNum;
float[] newx = new float[vNum];
float[] newy = new float[vNum];
int currDest = 0;
for (int i = 0; i < vNum; ++i)
{
if (currDest == earIndex)
{
++currDest;
}
newx[i] = xrem[currDest];
newy[i] = yrem[currDest];
++currDest;
}
// - add the clipped triangle to the triangle list
int under = (earIndex == 0) ? (vNum) : (earIndex - 1);
int over = (earIndex == vNum) ? 0 : (earIndex + 1);
Triangle toAdd = new Triangle(xrem[earIndex], yrem[earIndex], xrem[over], yrem[over], xrem[under],
yrem[under]);
buffer[bufferSize] = toAdd;
++bufferSize;
// - replace the old list with the new one
xrem = newx;
yrem = newy;
}
Triangle tooAdd = new Triangle(xrem[1], yrem[1], xrem[2], yrem[2], xrem[0], yrem[0]);
buffer[bufferSize] = tooAdd;
++bufferSize;
for (int i = 0; i < bufferSize; i++)
{
results.Add(new Triangle(buffer[i]));
}
return(results);
}
