/// <summary>
/// Returns true if vertex j can be seen from vertex i without any obstructions.
/// </summary>
/// <param name="polygon"></param>
/// <param name="i"></param>
/// <param name="j"></param>
/// <returns></returns>
private bool CanSee(Polygon polygon, int i, int j)
{
Microsoft.Xna.Framework.Vector2 prev = polygon.At(i - 1);
Microsoft.Xna.Framework.Vector2 on = polygon.At(i);
Microsoft.Xna.Framework.Vector2 next = polygon.At(i + 1);
if (IsReflex(prev, on, next))
{
if (LeftOrOn(polygon.At(i), polygon.At(i - 1), polygon.At(j)) &&
RightOrOn(polygon.At(i), polygon.At(i + 1), polygon.At(j)))
{
return(false);
}
}
else
{
if (RightOrOn(polygon.At(i), polygon.At(i + 1), polygon.At(j)) ||
LeftOrOn(polygon.At(i), polygon.At(i - 1), polygon.At(j)))
{
return(false);
}
}
Microsoft.Xna.Framework.Vector2 prevj = polygon.At(j - 1);
Microsoft.Xna.Framework.Vector2 onj = polygon.At(j);
Microsoft.Xna.Framework.Vector2 nextj = polygon.At(j + 1);
if (IsReflex(prevj, onj, nextj))
{
if (LeftOrOn(polygon.At(j), polygon.At(j - 1), polygon.At(i)) &&
RightOrOn(polygon.At(j), polygon.At(j + 1), polygon.At(i)))
{
return(false);
}
}
else
{
if (RightOrOn(polygon.At(j), polygon.At(j + 1), polygon.At(i)) ||
LeftOrOn(polygon.At(j), polygon.At(j - 1), polygon.At(i)))
{
return(false);
}
}
for (int k = 0; k < polygon.Count; ++k)
{
// YOGESH : changed from Line-Line intersection to Segment-Segment Intersection
Microsoft.Xna.Framework.Vector2 p1 = polygon.At(i);
Microsoft.Xna.Framework.Vector2 p2 = polygon.At(j);
Microsoft.Xna.Framework.Vector2 q1 = polygon.At(k);
Microsoft.Xna.Framework.Vector2 q2 = polygon.At(k + 1);
// ignore incident edges
if (p1.Equals(q1) || p1.Equals(q2) || p2.Equals(q1) || p2.Equals(q2))
{
continue;
}
var intersection = LineAlgorithms.LineSegmentIntersection(p1, p2, q1, q2);
if (intersection != null &&
intersection.WithinFirstSegment &&
intersection.WithinSecondSegment)
{
Microsoft.Xna.Framework.Vector2 intPoint = intersection.IntersectionPoint;
// intPoint is not any of the j line then false, else continue. Intersection has to be interior to qualify s 'false' from here
if ((!intPoint.Equals(polygon.At(k))) || (!intPoint.Equals(polygon.At(k + 1))))
{
return(false);
}
}
}
return(true);
}
