/// <summary>
/// For a Point, last used Edge and possible Edges, retrieve the best next Edge
/// </summary>
/// <param name="point">The current Point</param>
/// <param name="lastEdge">The last used Edge</param>
/// <param name="possibleEdges">The possible next Edges</param>
/// <returns>Best next Edge</returns>
internal static PolygonEdge BestEdge(PolygonPoint point, PolygonEdge lastEdge, List <PolygonEdge> possibleEdges)
{
// If just Starting, return the first possible Edge of the Point
// If only one possibility, return that
if ((lastEdge.PointOne == null && lastEdge.PointTwo == null) || possibleEdges.Count == 1)
{
return(possibleEdges[0]);
}
// Variables needed to determine the next Edge
var bestEdge = possibleEdges[0];
var bestAngle = (float)Math.PI * 2;
// Vector from last Point to current Point
var lastVector = (lastEdge.PointTwo.Point - lastEdge.PointOne.Point);
lastVector.Normalize();
// Using CCW Point Order, so the left Vector always points towards the Polygon Center
var insideVector = new Point(-lastVector.Y, lastVector.X);
// Check all possible Edges
foreach (var possibleEdge in possibleEdges)
{
// Next Edge Vector
var edgeVector = (possibleEdge.PointTwo.Point - possibleEdge.PointOne.Point);
edgeVector.Normalize();
// Dot determines if the Vector also points towards the Polygon Center or not (> 0, yes, < 0, no)
var dot = insideVector.X * edgeVector.X + insideVector.Y * edgeVector.Y;
// Cos represents the Angle between the last Edge and the next Edge
var cos = lastVector.X * edgeVector.X + lastVector.Y * edgeVector.Y;
var angle = 0f;
// Depending on the Dot-Value, calculate the actual "inner" Angle
if ((insideVector.X * edgeVector.X + insideVector.Y * edgeVector.Y) > 0)
{
angle = (float)Math.PI - (float)Math.Acos(cos);
}
else
{
angle = (float)Math.PI + (float)Math.Acos(cos);
}
// Replace the old Values if a better Edge was found
if (angle < bestAngle)
{
bestAngle = angle;
bestEdge = possibleEdge;
}
}
return(bestEdge);
}
/// <summary>
/// Searches the nearest StatusHelperElement from the given Point
/// </summary>
/// <param name="point">The Point to search a StatusHelperElement for</param>
/// <returns>The nearest StatusHelperElement that is positioned left of the Poin</returns>
internal StatusHelperElement SearchLeft(PolygonPoint point)
{
// The found StatusHelperElement and the Distance Variables
StatusHelperElement result = null;
var dist = Double.PositiveInfinity;
// Search for the right StatusHelperElement
foreach (var she in this.EdgesHelpers)
{
// Calculate the x-Coordinate of the Intersection between
// a horizontal Line from the Point to the Left and the Edge of the StatusHelperElement
Double xValue = Double.NaN;
if (point.Y == she.Edge.PointOne.Y)
{
xValue = she.Edge.PointOne.X;
}
else if (point.Y == she.Edge.PointTwo.Y)
{
xValue = she.Edge.PointTwo.X;
}
else
{
xValue = she.Edge.PointOne.X + ((point.Y - she.Edge.PointOne.Y) / (she.Edge.PointTwo.Y - she.Edge.PointOne.Y)) * (she.Edge.PointTwo.X - she.Edge.PointOne.X);
}
// If the xValue is smaller than or equal to the Point's x-Coordinate
// (i.e. it lies on the left Side of it - allows a small Error)
if (xValue <= (point.X + SweepLinePolygonTriangulator.Epsilon))
{
// Calculate the Distance
var sheDist = point.X - xValue;
// Update, if the Distance is smaller than a previously found Result
if (sheDist < dist)
{
dist = sheDist;
result = she;
}
}
}
// Return the nearest found StatusHelperElement
return(result);
}
/// <summary>
/// Searches the nearest StatusHelperElement from the given Point
/// </summary>
/// <param name="point">The Point to search a StatusHelperElement for</param>
/// <returns>The nearest StatusHelperElement that is positioned left of the Poin</returns>
internal StatusHelperElement SearchLeft(PolygonPoint point)
{
// The found StatusHelperElement and the Distance Variables
StatusHelperElement result = null;
var dist = Double.PositiveInfinity;
var px = point.X;
var py = point.Y;
// Search for the right StatusHelperElement
foreach (var she in this.EdgesHelpers)
{
// No need to calculate the X-Value
if (she.MinX > px)
{
continue;
}
// Calculate the x-Coordinate of the Intersection between
// a horizontal Line from the Point to the Left and the Edge of the StatusHelperElement
var xValue = she.Edge.PointOne.X + (py - she.Edge.PointOne.Y) * she.Factor;
// If the xValue is smaller than or equal to the Point's x-Coordinate
// (i.e. it lies on the left Side of it - allows a small Error)
if (xValue <= (px + SweepLinePolygonTriangulator.Epsilon))
{
// Calculate the Distance
var sheDist = px - xValue;
// Update, if the Distance is smaller than a previously found Result
if (sheDist < dist)
{
dist = sheDist;
result = she;
}
}
}
// Return the nearest found StatusHelperElement
return(result);
}
/// <summary>
/// Constructor that takes both Points of the Edge
/// </summary>
/// <param name="one">The Startpoint</param>
/// <param name="two">The Endpoint</param>
internal PolygonEdge(PolygonPoint one, PolygonPoint two)
{
this.mPointOne = one;
this.mPointTwo = two;
}
/// <summary>
/// Constructor taking an Edge and a Helper
/// </summary>
/// <param name="edge">The Edge of the StatusHelperElement</param>
/// <param name="point">The Helper for the Edge of the StatusHelperElement</param>
internal StatusHelperElement(PolygonEdge edge, PolygonPoint point)
{
this.Edge = edge;
this.Helper = point;
}