/// <summary>
/// Static function to convert a list of points into a polygon without having a local object instance
/// </summary>
public static Polygon Get(List<Point2D> data)
{
Polygon p = new Polygon();
p.Import(data);
return p;
}
/// <summary>
/// Merges two convex hulls into one convex hull
/// Finds upper and lower tangents and removes the points in between
/// </summary>
private static Polygon Merge(Polygon polygonA, Polygon polygonB, Boolean stepThrough)
{
//Since a lot of functions require polygons of type List<Point2D>
//Convert them here to save time converting lots later on
var newPolygonA = PolygonManipulation.SortLexographically(polygonA.Convert());
var newPolygonB = PolygonManipulation.SortLexographically(polygonB.Convert());
//Get the rightmost point of polygon A and the leftmost point of polygon B
var tangentPointA = GetRightmostPoint(newPolygonA);
var tangentPointB = GetLeftmostPoint(newPolygonB);
//Find lower tangent
//While Tangent = tangentPointA -> tangentPointB is not a lower tangent to both A and B
while (!(IsLowerTangent(newPolygonA, tangentPointA, tangentPointB) && IsLowerTangent(newPolygonB, tangentPointB,tangentPointA)))
{
//While Tangent = tangentPointA -> tangentPointB is not a lower tangent to A
while (!IsLowerTangent(newPolygonA, tangentPointA,tangentPointB))
{
//Move counter clockwise
tangentPointA = PolygonManipulation.GetNextPoint(newPolygonA, tangentPointA);
}
//While Tangent = tangentPointA -> tangentPointB is not a lower tangent to B
while (!IsLowerTangent(newPolygonB, tangentPointB,tangentPointA))
{
//Move clockwise
tangentPointB = PolygonManipulation.GetPreviousPoint(newPolygonB, tangentPointB);
}
}
//Get the lower tangent
Vector2D lowerTangent = new Vector2D(tangentPointA, tangentPointB);
//Reset the tangent points
tangentPointA = GetRightmostPoint(newPolygonA);
tangentPointB = GetLeftmostPoint(newPolygonB);
//While Tangent = tangentPointA -> tangentPointB is not an upper tangent to both A and B
while (!IsUpperTangent(newPolygonA, tangentPointA, tangentPointB) || !(IsUpperTangent(newPolygonB, tangentPointB, tangentPointA)))
{
//While Tangent = tangentPointA -> tangentPointB is not an upper tangent to A
while (!IsUpperTangent(newPolygonA, tangentPointA, tangentPointB))
{
//Move counter clockwise
tangentPointA = PolygonManipulation.GetPreviousPoint(newPolygonA, tangentPointA);
}
//While Tangent = tangentPointA -> tangentPointB is not an upper tangent to B
while (!IsUpperTangent(newPolygonB, tangentPointB, tangentPointA))
{
//Move clockwise
tangentPointB = PolygonManipulation.GetNextPoint(newPolygonB, tangentPointB);
}
}
//Get the upper tangent
Vector2D upperTangent = new Vector2D(tangentPointA, tangentPointB);
//Draw tangents if in step through mode
if (stepThrough)
{
//Convert the polygons into a format for drawing
var listPolygonA = polygonA.Convert();
var listPolygonB = polygonB.Convert();
//If the polygons have more than two points, fill them in
if (listPolygonA.Count > 2)
{
GraphicalUserInterface.DrawPolygon(listPolygonA, true, XOffset, YOffset, new System.Drawing.SolidBrush(System.Drawing.Color.Coral));
GraphicalUserInterface.DrawPolygon(polygonB.Convert(), true, XOffset, YOffset);
}
GraphicalUserInterface.DrawPolygon(listPolygonA, false, XOffset, YOffset, new System.Drawing.SolidBrush(System.Drawing.Color.Coral));
GraphicalUserInterface.DrawPolygon(polygonB.Convert(), false, XOffset, YOffset);
GraphicalUserInterface.GraphicsObject.DrawLine(new System.Drawing.Pen(System.Drawing.Color.Blue) { Width = 4 },
lowerTangent.Start.Convert(XOffset, YOffset, GraphicalUserInterface.SizeMultiplier),
lowerTangent.Target.Convert(XOffset, YOffset, GraphicalUserInterface.SizeMultiplier));
GraphicalUserInterface.GraphicsObject.DrawLine(new System.Drawing.Pen(System.Drawing.Color.Black) { Width = 4 },
upperTangent.Start.Convert(XOffset, YOffset, GraphicalUserInterface.SizeMultiplier),
upperTangent.Target.Convert(XOffset, YOffset, GraphicalUserInterface.SizeMultiplier));
//Wait for the user to enter a key into the console to continue
Console.ReadKey();
}
//Wire together the polygons by tangent
return Wire(polygonA, polygonB, lowerTangent, upperTangent);
}
/// <summary>
/// This method uses a different method to the Monotone Chain convex hull
/// Instead of storing the vertices of the polygon in lists
/// The vertices are stored as doubly linked lists
/// </summary>
private static Polygon RecursiveSolve(Polygon points, bool stepThrough = false)
{
//If there are few enough points to warrant the Graham Scan algorithm
if (points.Count() <= MinimumSize)
{
return Polygon.Get(ConvexHull.Solve(points.Convert()));
}
//Sort the points by x value and then by y value
var sortedPoints = PolygonManipulation.SortLexographically(points.Convert());
//Split points into two sets
var a = new List<Point2D>();
var b = new List<Point2D>();
a.AddRange(sortedPoints.Take(sortedPoints.Count()/2));
b.AddRange(sortedPoints.Skip(sortedPoints.Count()/2).Take(sortedPoints.Count() - sortedPoints.Count()/2));
//Compute the convex hulls of a and b recursively
var polyA = RecursiveSolve(Polygon.Get(a), stepThrough);
var polyB = RecursiveSolve(Polygon.Get(b), stepThrough);
//Merge the convex hulls together
return Merge(polyA, polyB, stepThrough);
}
/// <summary>
/// Given two polygons, and two tangent which will join together
/// This function will create a polygon which merge the two polygons together using the tangents to bridge between them
/// </summary>
public static Polygon Wire(Polygon polygonA, Polygon polygonB, Vector2D lowerTangent, Vector2D upperTangent)
{
var wiredPolygon = new List<Point2D>();
//If UpperTangent.Start is equal to LowerTangent.Start, we need to end the loop early
Boolean endEarly = PolygonManipulation.Equals(upperTangent.Start, lowerTangent.Start);
//Add the start point to the wired polygon
wiredPolygon.Add(upperTangent.Start);
//Jump across the tangent at set the target at the current vertex
var currentVertex = polygonB.GetVertex(upperTangent.Target);
//Since we need to traverse each polygon in a different direction, this marks what polygon we are on
Boolean leftPolygon = false;
//While we aren't back at start
do
{
//Add the current vertex to the wired polygon
wiredPolygon.Add(currentVertex.Point);
//If we have hit the lower tangent target
if (PolygonManipulation.Equals(currentVertex.Point, lowerTangent.Target))
{
//Jump across the lower tangent onto the other polygon
leftPolygon = true;
currentVertex = polygonA.GetVertex(lowerTangent.Start);
wiredPolygon.Add(currentVertex.Point);
//If we need to end early, break the loop
if (endEarly)
break;
}
//While we haven't find a suitable current vertex
do
{
if (leftPolygon)
{
//Traverse Clockwise
if (currentVertex == null || currentVertex.Point == null)
currentVertex = polygonA.Tail.Prev;
else
currentVertex = currentVertex.Prev;
}
else
{
//Traverse Counterclockwise
if (currentVertex == null || currentVertex.Point == null)
currentVertex = polygonB.Tail.Prev;
else
currentVertex = currentVertex.Prev;
}
} while (currentVertex == null || currentVertex.Point == null);
} while (!PolygonManipulation.Equals(currentVertex.Point, upperTangent.Start));
wiredPolygon = wiredPolygon.Distinct().ToList();
//Since the wired polygon is in clockwise order, we need to reverse it
wiredPolygon.Reverse();
return Polygon.Get(wiredPolygon);
}
