//The original algorithm calculates the intersection between two polygons, this will instead get the outside
//Assumes the polygons are oriented counter clockwise
//poly is the polygon we want to cut
//Assumes the polygon we want to remove from the other polygon is convex, so clipPolygon has to be convex
//We will end up with the !intersection of the polygons
public static List <List <MyVector2> > ClipPolygonInverted(List <MyVector2> poly, List <Plane2> clippingPlanes)
{
//The result may be more than one polygons
List <List <MyVector2> > finalPolygons = new List <List <MyVector2> >();
List <MyVector2> vertices = new List <MyVector2>(poly);
//The remaining polygon after each cut
List <MyVector2> vertices_tmp = new List <MyVector2>();
//Clip the polygon
for (int i = 0; i < clippingPlanes.Count; i++)
{
Plane2 plane = clippingPlanes[i];
//A new polygon which is the part of the polygon which is outside of this plane
List <MyVector2> outsidePolygon = new List <MyVector2>();
for (int j = 0; j < vertices.Count; j++)
{
int jPlusOne = MathUtility.ClampListIndex(j + 1, vertices.Count);
MyVector2 v1 = vertices[j];
MyVector2 v2 = vertices[jPlusOne];
//Calculate the distance to the plane from each vertex
//This is how we will know if they are inside or outside
//If they are inside, the distance is positive, which is why the planes normals have to be oriented to the inside
float dist_to_v1 = Geometry.DistanceFromPointToPlane(plane.normal, plane.pos, v1);
float dist_to_v2 = Geometry.DistanceFromPointToPlane(plane.normal, plane.pos, v2);
//TODO: What will happen if they are exactly 0?
//Case 1. Both are inside (= to the left), save v2 to the other polygon
if (dist_to_v1 >= 0f && dist_to_v2 >= 0f)
{
vertices_tmp.Add(v2);
}
//Case 2. Both are outside (= to the right), save v1
else if (dist_to_v1 < 0f && dist_to_v2 < 0f)
{
outsidePolygon.Add(v2);
}
//Case 3. Outside -> Inside, save intersection point
else if (dist_to_v1 < 0f && dist_to_v2 >= 0f)
{
MyVector2 rayDir = MyVector2.Normalize(v2 - v1);
MyVector2 intersectionPoint = Intersections.GetRayPlaneIntersectionPoint(plane.pos, plane.normal, v1, rayDir);
outsidePolygon.Add(intersectionPoint);
vertices_tmp.Add(intersectionPoint);
vertices_tmp.Add(v2);
}
//Case 4. Inside -> Outside, save intersection point and v2
else if (dist_to_v1 >= 0f && dist_to_v2 < 0f)
{
MyVector2 rayDir = MyVector2.Normalize(v2 - v1);
MyVector2 intersectionPoint = Intersections.GetRayPlaneIntersectionPoint(plane.pos, plane.normal, v1, rayDir);
outsidePolygon.Add(intersectionPoint);
outsidePolygon.Add(v2);
vertices_tmp.Add(intersectionPoint);
}
}
//Add the polygon outside of this plane to the list of all polygons that are outside of all planes
if (outsidePolygon.Count > 0)
{
finalPolygons.Add(outsidePolygon);
}
//Add the polygon which was inside of this and previous planes to the polygon we want to test
vertices.Clear();
vertices.AddRange(vertices_tmp);
vertices_tmp.Clear();
}
return(finalPolygons);
}
//Assumes the polygons are oriented counter clockwise
//poly is the polygon we want to cut
//Assumes the polygon we want to remove from the other polygon is convex, so clipPolygon has to be convex
//We will end up with the intersection of the polygons
public static List <MyVector2> ClipPolygon(List <MyVector2> poly, List <Plane2> clippingPlanes)
{
//Clone the vertices because we will remove vertices from this list
List <MyVector2> vertices = new List <MyVector2>(poly);
//Save the new vertices temporarily in this list before transfering them to vertices
List <MyVector2> vertices_tmp = new List <MyVector2>();
//Clip the polygon
for (int i = 0; i < clippingPlanes.Count; i++)
{
Plane2 plane = clippingPlanes[i];
for (int j = 0; j < vertices.Count; j++)
{
int jPlusOne = MathUtility.ClampListIndex(j + 1, vertices.Count);
MyVector2 v1 = vertices[j];
MyVector2 v2 = vertices[jPlusOne];
//Calculate the distance to the plane from each vertex
//This is how we will know if they are inside or outside
//If they are inside, the distance is positive, which is why the planes normals have to be oriented to the inside
float dist_to_v1 = Geometry.DistanceFromPointToPlane(plane.normal, plane.pos, v1);
float dist_to_v2 = Geometry.DistanceFromPointToPlane(plane.normal, plane.pos, v2);
//TODO: What will happen if they are exactly 0? Should maybe use a tolerance of 0.001
//Case 1. Both are outside (= to the right), do nothing
//Case 2. Both are inside (= to the left), save v2
if (dist_to_v1 >= 0f && dist_to_v2 >= 0f)
{
vertices_tmp.Add(v2);
}
//Case 3. Outside -> Inside, save intersection point and v2
else if (dist_to_v1 < 0f && dist_to_v2 >= 0f)
{
MyVector2 rayDir = MyVector2.Normalize(v2 - v1);
MyVector2 intersectionPoint = Intersections.GetRayPlaneIntersectionPoint(plane.pos, plane.normal, v1, rayDir);
vertices_tmp.Add(intersectionPoint);
vertices_tmp.Add(v2);
}
//Case 4. Inside -> Outside, save intersection point
else if (dist_to_v1 >= 0f && dist_to_v2 < 0f)
{
MyVector2 rayDir = MyVector2.Normalize(v2 - v1);
MyVector2 intersectionPoint = Intersections.GetRayPlaneIntersectionPoint(plane.pos, plane.normal, v1, rayDir);
vertices_tmp.Add(intersectionPoint);
}
}
//Add the new vertices to the list of vertices
vertices.Clear();
vertices.AddRange(vertices_tmp);
vertices_tmp.Clear();
}
return(vertices);
}