/// <summary>
/// This clips the subject polygon against the clip polygon (gets the intersection of the two polygons)
/// </summary>
public static void GetIntersectedPolygon(StructList <Vector2> subjectPoly, StructList <Vector2> clipPoly, StructList <Vector2> outputList)
{
if (subjectPoly.size < 3 || clipPoly.size < 3)
{
throw new ArgumentException(string.Format("The polygons passed in must have at least 3 Vector2s: subject={0}, clip={1}", subjectPoly.size.ToString(), clipPoly.size.ToString()));
}
outputList.size = 0;
outputList.AddRange(subjectPoly);
// Make sure it's clockwise
if (!IsClockwise(subjectPoly, out bool invalid))
{
outputList.Reverse();
}
if (invalid)
{
return;
}
s_EdgeList = s_EdgeList ?? new StructList <Edge>();
s_InputList = s_InputList ?? new StructList <Vector2>(subjectPoly.size);
IterateEdgesClockwise(clipPoly, s_EdgeList);
// Walk around the clip polygon clockwise
for (int i = 0; i < s_EdgeList.size; i++)
{
ref Edge clipEdge = ref s_EdgeList.array[i];
s_InputList.size = 0;
s_InputList.AddRange(outputList);
outputList.size = 0;
// Sometimes when the polygons don't intersect, this list goes to zero. Jump out to avoid an index out of range exception
if (s_InputList.size == 0)
{
break;
}
Vector2 S = s_InputList.array[s_InputList.size - 1];
for (int index = 0; index < s_InputList.size; index++)
{
ref Vector2 E = ref s_InputList.array[index];
if (IsInside(clipEdge, E))
{
if (!IsInside(clipEdge, S))
{
Vector2?v = GetIntersect(S, E, clipEdge.from, clipEdge.to);
if (v == null)
{
throw new ApplicationException("Line segments don't intersect"); // may be colinear, or may be a bug
}
else
{
outputList.Add(v.Value);
}
}
outputList.Add(E);
}
else if (IsInside(clipEdge, S))
{
Vector2?Vector2 = GetIntersect(S, E, clipEdge.from, clipEdge.to);
if (Vector2 == null)
{
throw new ApplicationException("Line segments don't intersect"); // may be colinear, or may be a bug
}
else
{
outputList.Add(Vector2.Value);
}
}
S = E;
}