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) });
}
public Polygon Buffer(IList <float> shrinkAmounts)
{
var newPoly = new Polygon();
ForEachEdge((p1, p2, index) =>
{
var amount = shrinkAmounts[index];
if (amount <= 0.01)
{
newPoly.Vertices.Add(p1);
newPoly.Vertices.Add(p2);
}
else
{
var n = GeometryHelpers.Scale(GeometryHelpers.Normalize(GeometryHelpers.Rotate90(p2 - p1)), amount);
newPoly.Vertices.Add(p1 + n);
newPoly.Vertices.Add(p2 + n);
}
});
bool wasCut;
var lastEdge = 0;
do
{
wasCut = false;
var n = newPoly.Vertices.Count;
for (var i = lastEdge; i < n - 2; i++)
{
lastEdge = i;
var p11 = newPoly.Vertices[i];
var p12 = newPoly.Vertices[i + 1];
var x1 = p11.x;
var y1 = p11.y;
var dx1 = p12.x - x1;
var dy1 = p12.y - y1;
var maxJ = i > 0 ? n : n - 1;
for (var j = i + 2; j < maxJ; j++)
{
var p21 = newPoly.Vertices[j];
var p22 = j < n - 1 ? newPoly.Vertices[j + 1] : newPoly.Vertices[0];
var x2 = p21.x;
var y2 = p21.y;
var dx2 = p22.x - x2;
var dy2 = p22.y - y2;
var intersect = GeometryHelpers.IntersectLines(x1, y1, dx1, dy1, x2, y2, dx2, dy2);
if (intersect.x > Delta && intersect.x < (1 - Delta) && intersect.y > Delta && intersect.y < (1 - Delta))
{
var pn = new Vector2(x1 + dx1 * intersect.x, y1 + dy1 * intersect.x);
newPoly.Vertices.Insert(j + 1, pn);
newPoly.Vertices.Insert(i + 1, pn);
wasCut = true;
break;
}
}
}
} while (wasCut);
var regular = Enumerable.Range(0, newPoly.Vertices.Count).ToList();
Polygon bestPart = null;
var bestPartSq = float.MinValue;
while (regular.Count > 0)
{
var indices = new List <int> ();
var start = regular[0];
var i = start;
do
{
indices.Add(i);
regular.Remove(i);
var next = (i + 1) % newPoly.Vertices.Count;
var v = newPoly.Vertices[next];
var next1 = newPoly.Vertices.IndexOf(v);
if (next1 == next)
{
next1 = newPoly.Vertices.LastIndexOf(v);
}
i = next1 == -1 ? next : next1;
} while (i != start && indices.Count < 1000);
if (indices.Count >= 999)
{
indices = indices.Take(4).ToList();
}
var poly = new Polygon(indices.Select(v => newPoly.Vertices[v]));
var s = poly.Area();
if (s > bestPartSq)
{
bestPart = poly;
bestPartSq = s;
}
}
return(bestPart);
}
