// Return true if the three points form an ear.
private static bool FormsEar(LatLng[] pts, int a, int b, int c)
{
// See if the angle ABC is concave.
if (GetAngle(pts[a].Latitude, pts[a].Longitude, pts[b].Latitude, pts[b].Longitude, pts[c].Latitude, pts[c].Longitude) > 0)
{
// This is a concave corner so the triangle
// cannot be an ear.
return(false);
}
// Make the triangle A, B, C.
Game.Triangle triangle = AddTriangle(pts[a], pts[b], pts[c]);
// Check the other points to see
// if they lie in triangle A, B, C.
for (int i = 0; i < pts.Length; i++)
{
if ((i != a) && (i != b) && (i != c))
{
if (PointInTriangle(triangle, pts[i]))
{
// This point is in the triangle
// do this is not an ear.
return(false);
}
}
}
// This is an ear.
return(true);
}
public static LatLng FindRandomPoint(Game.GameActivity gameActivity)
{
Random random = new Random();
List <Game.Triangle> triangles = Triangulate(gameActivity.gamePlayArea.vertices);
Game.Triangle triangle = triangles[random.Next(0, triangles.Count)];
LatLng v1 = new LatLng(triangle.vertices[1].Latitude - triangle.vertices[0].Latitude, triangle.vertices[1].Longitude - triangle.vertices[0].Longitude);
LatLng v2 = new LatLng(triangle.vertices[2].Latitude - triangle.vertices[0].Latitude, triangle.vertices[2].Longitude - triangle.vertices[0].Longitude);
double a1 = random.NextDouble();
double a2 = random.NextDouble();
v1.Latitude = v1.Latitude * a1;
v1.Longitude = v1.Longitude * a1;
v2.Latitude = v2.Latitude * a2;
v2.Longitude = v2.Longitude * a2;
LatLng x = new LatLng(v1.Latitude + v2.Latitude, v1.Longitude + v2.Longitude);
x.Latitude += triangle.vertices[0].Latitude;
x.Longitude += triangle.vertices[0].Longitude;
return(x);
}
private static Game.Triangle AddTriangle(LatLng a, LatLng b, LatLng c)
{
Game.Triangle triangle = new Game.Triangle();
triangle.vertices = new LatLng[3];
triangle.vertices[0] = a;
triangle.vertices[1] = b;
triangle.vertices[2] = c;
return(triangle);
}
// Return true if the point is in the polygon.
private static bool PointInTriangle(Game.Triangle triangle, LatLng point)
{
// Get the angle between the point and the
// first and last vertices.
int max_point = triangle.vertices.Length - 1;
double total_angle = GetAngle(triangle.vertices[max_point].Latitude, triangle.vertices[max_point].Longitude, point.Latitude, point.Longitude, triangle.vertices[0].Latitude, triangle.vertices[0].Longitude);
// Add the angles from the point
// to each other pair of vertices.
for (int i = 0; i < max_point; i++)
{
total_angle += GetAngle(triangle.vertices[i].Latitude, triangle.vertices[i].Longitude, point.Latitude, point.Longitude, triangle.vertices[i + 1].Latitude, triangle.vertices[i + 1].Longitude);
}
// The total angle should be 2 * PI or -2 * PI if
// the point is in the polygon and close to zero
// if the point is outside the polygon.
return(Math.Abs(total_angle) > 0.000001);
}
