public void CanDeterminePointInPolygon_Square_NegativeCoords_NearBottomLeft()
{
// Arrange
var points = new List<Vertex>() { new Vertex(0, 0), new Vertex(1, 0), new Vertex(1, -1), new Vertex(0, -1) };
var test = new Vertex(0.1, -0.1);
// Act
var b = Polygon.PointInPolygon(points, test);
// Assert
Assert.IsTrue(b);
}
public void CanDeterminePointInPolygon_Square_NearTopRightCorner()
{
// Arrange
var points = new List<Vertex>() { new Vertex(0, 0), new Vertex(0, 1), new Vertex(1, 1), new Vertex(1, 0) };
var test = new Vertex(0.9, 0.9);
// Act
var b = Polygon.PointInPolygon(points, test);
// Assert
Assert.IsTrue(b);
}
public void CanDeterminePointOutsidePolygon_Square()
{
// Arrange
var points = new List<Vertex>() { new Vertex(0, 0), new Vertex(0, 1), new Vertex(1, 1), new Vertex(1, 0) };
var test = new Vertex(1.5, 0.5);
// Act
var b = Polygon.PointInPolygon(points, test);
// Assert
Assert.IsFalse(b);
}
public void CanDeterminePointNotInPolygon_Square_NegativeCoords()
{
// Arrange
var points = new List<Vertex>() { new Vertex(0, 0), new Vertex(1, 0), new Vertex(1, 1), new Vertex(0, 1) };
var test = new Vertex(-0.9, -0.9);
// Act
var b = Polygon.PointInPolygon(points, test);
// Assert
Assert.IsFalse(b);
}
/// <summary>
/// Test if a 2D point is inside a 2D polygon.
/// </summary>
/// <param name="polygon"></param>
/// <param name="testPoint"></param>
/// <returns></returns>
public static bool PointInPolygon(IList<Vertex> polygon, Vertex testPoint)
{
Vertex p1, p2;
bool inside = false;
int vertices = polygon.Count;
if (vertices < 3)
{
return false;
}
// This algo doesnt work with negative co-ordinates, so we need to shift everything into the positive
// quadrant before running the test.
double minX = 0, minY = 0;
for (int i = 0; i < vertices; i++)
{
minX = Math.Min(minX, polygon[i].X);
minY = Math.Min(minY, polygon[i].Y);
}
// Not sure we need to do this
var shiftedPolygon = new List<Vertex>();
var shiftedTestPoint = new Vertex();
minX = (minX < 0) ? Math.Abs(minX) : 0;
minY = (minY < 0) ? Math.Abs(minY) : 0;
// Shift the test point
shiftedTestPoint.X = testPoint.X + minX;
shiftedTestPoint.Y = testPoint.Y + minY;
// Shift the vertices
foreach (var v in polygon)
{
shiftedPolygon.Add(new Vertex(v.X + minX, v.Y + minY));
}
// Now we've adjusted, lets do the test
if (shiftedTestPoint.X < 0 || shiftedTestPoint.Y < 0)
{
return false;
}
var oldPoint = new Vertex(shiftedPolygon[vertices - 1].X, shiftedPolygon[vertices - 1].Y);
for (int i = 0; i < vertices; i++)
{
var newPoint = new Vertex(shiftedPolygon[i].X, shiftedPolygon[i].Y);
// Make p1 the left-most vertex
if (newPoint.X > oldPoint.X)
{
p1 = oldPoint;
p2 = newPoint;
}
else
{
p1 = newPoint;
p2 = oldPoint;
}
if ((newPoint.X < shiftedTestPoint.X) == (shiftedTestPoint.X <= oldPoint.X)
&& ((long)shiftedTestPoint.Y - (long)p1.Y) * (long)(p2.X - p1.X) < ((long)p2.Y - (long)p1.Y) * (long)(shiftedTestPoint.X - p1.X))
{
inside = !inside;
}
oldPoint = newPoint;
}
return inside;
}
/// <summary>
/// Calculate the point of intersection between the plane and a ray
/// </summary>
/// <param name="ray">The ray to test</param>
/// <returns>The point of intersection or null</returns>
public override Intersection Intersect(Ray ray)
{
var PoI = this.GetPointOfIntersectionWithPlane(ray);
if (PoI == null)
{
return null;
}
// Create an ortho-normal basis
var u = (this.Points[1] - this.Points[0]).Normalise;
var v = u.Cross(this.Norm).Normalise;
// Set the plane's origin to a known point
var p1 = this.Points[0];
// Convert the PoI to 2D
var x = (PoI - p1).Dot(u);
var y = (PoI - p1).Dot(v);
var PoI_2d = new Vertex(x, y);
// Convert the vertices of the polygon to 2D using the same basis
IList<Vertex> vertices = new List<Vertex>();
foreach (var p in this.Points)
{
var Px = (p - p1).Dot(u);
var Py = (p - p1).Dot(v);
vertices.Add(new Vertex(Px, Py));
}
if (Polygon.PointInPolygon(vertices, PoI_2d))
{
return new Intersection()
{
Element = this,
Ray = ray,
Distance = (PoI - ray.Start).Magnitude
};
}
return null;
}