/// <summary>
/// Returns a sorted list of intersection points for a line segment with a (closed) polygon.
/// </summary>
/// <param name="v1">Start of line segment</param>
/// <param name="v2">End of line segment</param>
/// <param name="polygon">Polygon to be intersected</param>
/// <returns>All intersection points sorted to their distance on the line segment</returns>
public static List <IntersectionPoint> IntersectionLinePolygon(Vec2d v1, Vec2d v2, List <Vec2d> polygon)
{
List <IntersectionPoint> ips = new List <IntersectionPoint>(2);
Vec2d ip;
double fA, fB;
// Intersect with all polygon edges
for (int i = 0; i < polygon.Count; ++i)
{
Vec2d v3 = polygon[i];
Vec2d v4 = polygon[(i + 1) % polygon.Count];
if (MathUtilD.IntersectionLines(v1, v2, v3, v4, out fA, out fB, out ip))
{
ips.Add(new IntersectionPoint(ip, fA));
}
}
// Sort the list
ips.Sort();
return(ips);
}
public static bool LineIntersectsPolygon(List <Vec2d> poly, Vec2d a, Vec2d b)
{
bool found = false;
double fA, fB;
Vec2d ip;
if (poly.Count == 0)
{
return(found);
}
if (MathUtilD.IntersectionLines(a, b, poly[0], poly[poly.Count - 1], out fA, out fB, out ip))
{
found = true;
}
for (int i = 0; !found && i < poly.Count - 1; i++)
{
if (MathUtilD.IntersectionLines(a, b, poly[i], poly[i + 1], out fA, out fB, out ip))
{
found = true;
}
}
return(found);
}
/// <summary>
/// Returns a list of sub-polygons resulting from a split of a (closed) polygon by a line.
/// </summary>
/// <param name="v1">Start of line</param>
/// <param name="v2">End of line</param>
/// <param name="polygon">Polygon to be split</param>
/// <returns>All resulting polygons, or the original polygon if the line does not intersect the polygon</returns>
public static List <SubPolygon> SplitPolygonByLine(Vec2d v1, Vec2d v2, SubPolygon polygon)
{
// TODO cleanup and rewrite this to perform no unneeded line intersections
List <SubPolygon> result = new List <SubPolygon>(2);
Vec2d ip;
double fA, fB;
// Intersect with all polygon edges
List <Vec2d> points = new List <Vec2d>();
List <bool> onEdge = new List <bool>();
List <Vec2d> finalRun = new List <Vec2d>();
List <bool> finalRunOnEdge = new List <bool>();
for (int i = 0; i < polygon.Count; ++i)
{
Vec2d v3 = polygon[i];
// Run in progress
if (points.Count > 0)
{
points.Add(v3);
onEdge.Add(polygon.IsOnEdge(i));
}
else
{
finalRun.Add(v3);
finalRunOnEdge.Add(polygon.IsOnEdge(i));
}
Vec2d v4 = polygon[(i + 1) % polygon.Count];
MathUtilD.IntersectionLines(v1, v2, v3, v4, out fA, out fB, out ip);
// If intersection of line with polygon segment
if (0.0 <= fB && fB <= 1.0)
{
if (points.Count == 0)
{
// Start of new run
points.Add(ip);
onEdge.Add(polygon.IsOnEdge(i));
if (fB > 0.0)
{
// ip != v3
finalRun.Add(ip);
finalRunOnEdge.Add(false);
}
}
else
{
// End of run
if (fB < 1.0)
{
points.Add(ip);
// Last edge from ip2 to ip1 is not on original polygon edge
onEdge.Add(false);
}
List <Vec2d> r = new List <Vec2d>(points.Count);
r.AddRange(points);
if (!Polygon.IsClockWise(r))
{
result.Add(new SubPolygon(r, onEdge.ToArray()));
}
else
{
finalRun.AddRange(r);
finalRunOnEdge.AddRange(onEdge);
}
points.Clear();
onEdge.Clear();
// Next run
points.Add(ip);
onEdge.Add(polygon.IsOnEdge(i));
}
}
}
if (points.Count > 0)
{
finalRun.InsertRange(0, points);
finalRunOnEdge.InsertRange(0, onEdge);
}
if (finalRun.Count > 0 && !Polygon.IsClockWise(finalRun))
{
result.Add(new SubPolygon(finalRun, finalRunOnEdge.ToArray()));
}
return(result);
}
