public int[] getClosestIntersectingPointsToX1Y1OfLineSegment(int x1, int y1, int x2, int y2)
{
double minDistatnce = 999999999;
int[] closestIntersect = new int[] { -1, -1 };
List <int[]> allIntersectingPoints = getAllIntersectionPointsOfLineSegment(x1, y1, x2, y2);
foreach (int[] xy in allIntersectingPoints)
{
double distance = LineSegment.getLength(x1, y1, xy[0], xy[1]);
if (distance < minDistatnce)
{
minDistatnce = distance;
closestIntersect[0] = xy[0];
closestIntersect[1] = xy[1];
}
}
return(closestIntersect);
}
public int[] getClosestPointsOnPolygonToAPoint(int x, int y, out LineSegment closestEdge, out int closestEdgeStartingPointIndex)
{
double closestDistance = double.MaxValue;
int[] closestPointOnPolygonBoundary = new int[] { -1, -1 };
closestEdge = new LineSegment(-1, -1, -1, -1);
closestEdgeStartingPointIndex = -1;
for (int i = 0; i < vertices.Count; i++)
{
int xx1 = vertices[i][0];
int yy1 = vertices[i][1];
int j = (i + 1) % vertices.Count;
int xx2 = vertices[j][0];
int yy2 = vertices[j][1];
LineSegment line = new LineSegment(xx1, yy1, xx2, yy2);
double slope = line.slope();
double perpendicularSlope = 0;
if (!double.IsInfinity(slope))
{
perpendicularSlope = -1 / slope;
}
// find the perpendicular line that cross (x,y) in image.
// assume the line is y=ax+b, a= slope, b = y-ax, b=px0[1]
//double xstart = 0;
//double ystart = (y - perpendicularSlope * (double)x);
//double xend = -(ystart / perpendicularSlope);
//double yend = 0;
double xstart = 0;
double ystart = 0;
double xend = 0;
double yend = 0;
double b = (y - perpendicularSlope * (double)x);
double[] px0 = new double[] { 0, b };
double[] py0 = new double[] { -(b / perpendicularSlope), 0 };
// assume width height less than 10000
int max = 100000;
double[] pxmax = new double[] { max, perpendicularSlope *max + b };
double[] pymax = new double[] { -1, -1 };
if (perpendicularSlope == 0)
{
pymax[0] = max - 1;
pymax[1] = b;
}
else
{
pymax[0] = (max - b) / perpendicularSlope;
pymax[1] = max;
}
// select the 2 far ends
List <double[]> plist = new List <double[]>()
{
px0, py0, pxmax, pymax
};
double minX = double.MaxValue;
double maxX = double.MinValue;
foreach (double[] p in plist)
{
if (p[0] < minX)
{
minX = p[0];
xstart = minX;
ystart = p[1];
}
if (p[0] > maxX)
{
maxX = p[0];
xend = maxX;
yend = p[1];
}
}
// find out whether it intersect, if intersect, since perpendicular, the intersects is the closest distance to that edge
double[] intersect = new double[] { -1, -1 };
List <double[]> candidatePoints = new List <double[]>();
if (LineSegment.Intersect(xstart, ystart, xend, yend, xx1, yy1, xx2, yy2, out intersect))
{
candidatePoints.Add(intersect);
}
else
{
//"Not Intersecting", then the closest point must be one of the 2 ends.
candidatePoints.Add(new double[] { xx1, yy1 });
candidatePoints.Add(new double[] { xx2, yy2 });
}
foreach (double[] p in candidatePoints)
{
double distance = LineSegment.getLength(x, y, (int)p[0], (int)p[1]);
if (distance < closestDistance)
{
closestDistance = distance;
closestPointOnPolygonBoundary[0] = (int)p[0];
closestPointOnPolygonBoundary[1] = (int)p[1];
closestEdge = line;
closestEdgeStartingPointIndex = i;
}
}
}
return(closestPointOnPolygonBoundary);
}