public static float Cross(Vector2 a, Vector2 b)
{
return(GeometryHelpers.CrossProduct(a.x, a.y, b.x, b.y));
}
public IEnumerable <Polygon> Cut(Vector2 p1, Vector2 p2, float gap)
{
var x1 = p1.x;
var y1 = p1.y;
var dx1 = p2.x - x1;
var dy1 = p2.y - y1;
var len = Vertices.Count;
var edge1 = 0;
var ratio1 = 0.0f;
var edge2 = 0;
var ratio2 = 0.0f;
var count = 0;
for (var i = 0; i < len; i++)
{
var v0 = Vertices[i];
var v1 = Vertices[(i + 1) % len];
var x2 = v0.x;
var y2 = v0.y;
var dx2 = v1.x - x2;
var dy2 = v1.y - y2;
var t = GeometryHelpers.IntersectLines(x1, y1, dx1, dy1, x2, y2, dx2, dy2);
if (t.y >= 0 && t.y <= 1)
{
switch (count)
{
case 0:
edge1 = i;
ratio1 = t.x;
break;
case 1:
edge2 = i;
ratio2 = t.x;
break;
}
count++;
}
}
if (count == 2)
{
var point1 = p1 + GeometryHelpers.Scale(p2 - p1, ratio1);
var point2 = p1 + GeometryHelpers.Scale(p2 - p1, ratio2);
var half1 = new Polygon(Vertices.GetRange(edge1 + 1, edge2 - edge1));
half1.Vertices.Insert(0, point1);
half1.Vertices.Add(point2);
var half2 = new Polygon(Vertices.GetRange(edge2 + 1, Vertices.Count - edge2 - 1).Concat(Vertices.GetRange(0, edge1 + 1)));
half2.Vertices.Insert(0, point2);
half2.Vertices.Add(point1);
if (gap > 0)
{
half1 = half1.Peel(point2, gap / 2);
half2 = half2.Peel(point1, gap / 2);
}
var v = VectorI(edge1);
return(GeometryHelpers.CrossProduct(dx1, dy1, v.x, v.y) > 0 ?
new [] { half1, half2 } :
new [] { half2, half1 });
}
return(new [] { new Polygon(this) });
}
