public MeshPoint IntersectLine(MeshPolygon tri, int lineInd)
{
var points = tri.Points;
var lineInd2 = (lineInd + 1) % points.Count;
var pt1 = tri.Points[lineInd];
var pt2 = tri.Points[lineInd2];
Vector3 a = EdgeVec; //line 1
Vector3 b = pt2.Position - pt1.Position; //line 2
Vector3 c = EdgePos - pt1.Position; //vec between starts
//percent of line 1 where we intersect with line 2
float ip = 1 / (-b.X * a.Z + a.X * b.Z); //projection
float t = (b.X * c.Z - b.Z * c.X) * ip;
//percent of line 2 where we intersect line 1
float ip2 = 1 / (-a.X * b.Z + b.X * a.Z);
float s = (a.X * (-c.Z) - a.Z * (-c.X)) * ip2;
//pos + vec * t = pos2 + vec2 * s
//vec * t - vec2 * s = pos2 - pos1
float[] newTC = new float[pt1.TexCoords.Length];
float ms = 1 - s;
for (int i = 0; i < newTC.Length; i++)
{
newTC[i] = pt1.TexCoords[i] * ms + pt2.TexCoords[i] * s;
}
return(new MeshPoint(
//position from the clip triangle (use t)
EdgePos + EdgeVec * t,
//texcoords from the two points in the poly (use s)
newTC
));
}
private void ClipTriangles(BaseMeshTriangle baseTri, MeshTriangle projTri, List <MeshPoint> outverts, List <int> inds)
{
//Sutherland–Hodgman algorithm
//clip a triangle against another by iteratively clipping each edge of the second one
//we want to clip against base tri
var outputList = new MeshPolygon(projTri);
var basePlane = new Plane(baseTri.Vertices[0], baseTri.Vertices[1], baseTri.Vertices[2]);
for (int i = 0; i < 3; i++)
{
if (outputList.Points.Count == 0)
{
return;
}
var inputList = outputList;
var edge = new ClipEdge(baseTri.Vertices[i], baseTri.Vertices[(i + 1) % 3]);
outputList = new MeshPolygon();
var lastPoint = inputList.Points.Last();
int j = inputList.Points.Count - 1;
foreach (var point in inputList.Points)
{
if (!edge.ShouldClip(point.Position))
{
if (edge.ShouldClip(lastPoint.Position))
{
outputList.Points.Add(edge.IntersectLine(inputList, j));
}
//we still need to project the point onto the surface...
var ray = new Ray(point.Position, new Vector3(0, -1, 0));
var intersect2 = ray.Intersects(basePlane);
if (intersect2 == null)
{
ray.Direction *= -1;
intersect2 = ray.Intersects(basePlane);
if (intersect2 == null)
{
}
intersect2 = -(intersect2 ?? 0f);
}
point.Position.Y -= intersect2.Value;
outputList.Points.Add(point);
}
else
{
if (!edge.ShouldClip(lastPoint.Position))
{
outputList.Points.Add(edge.IntersectLine(inputList, j));
}
}
j = (j + 1) % inputList.Points.Count;
lastPoint = point;
}
}
if (outputList.Points.Count < 3)
{
return; //?
}
outputList.Triangulate(outverts, inds);
}