/// <summary>
/// Create a polygon coplanar with the current plane that extends to the given extent
/// </summary>
/// <param name="fExtent"></param>
/// <returns></returns>
public Polygon3D CreatePolygon(float fExtent)
{
int a, b, c;
float[] n = new float[3] {
Math.Abs(Normal.X),
Math.Abs(Normal.Y),
Math.Abs(Normal.Z)
};
if (n[0] >= n[1] && n[0] >= n[2])
{
a = 1; b = 2; c = 0;
}
else if (n[1] >= n[0] && n[1] >= n[2])
{
a = 0; b = 2; c = 1;
}
else if (n[2] >= n[0] && n[2] >= n[1])
{
a = 0; b = 1; c = 2;
}
else
{
a = b = c = -1;
Debug.Assert(false);
}
//Debug.WriteLine( " normal[" + Normal.ToString() + " a[" + a + "] b[" + b + "] c[" + c + "]" );
int[] aSigns = new int[4] {
1, 1, -1, -1
};
int[] bSigns = new int[4] {
1, -1, -1, 1
};
Polygon3D poly = new Polygon3D();
for (int i = 0; i < 4; i++)
{
Vector3D pt = new Vector3D();
pt[a] = fExtent * aSigns[i];
pt[b] = fExtent * bSigns[i];
pt[c] = (Constant - Normal[a] * pt[a] - Normal[b] * pt[b]) / Normal[c];
//Debug.WriteLine( " pt[" + i + "] = " + pt.ToString() + " dTp = " + DistanceToPlane( pt ) );
poly.Points.Add(pt);
}
//Debug.WriteLine( " plane.Normal = " + Normal );
//Debug.WriteLine( " plane.Constant = " + Constant );
if (Vector3D.Dot(Normal, poly.GetNormal()) < 0)
{
poly.Flip();
}
//Debug.WriteLine( " polygon.Normal = " + poly.Normal().ToString() );
return(poly);
}
//--------------------------------------------------------------------------------
/// <summary>
/// Clip the given polygon by the plane so that only the regions
/// located positive of the plane remain.
/// </summary>
/// <param name="polygon"></param>
public void ClipPolygon(Polygon3D polygon)
{
Vector3D ptNormal = polygon.GetNormal();
Vector3DCollection vNewPoints = new Vector3DCollection();
int iPoints = polygon.Points.Count;
for (int i = 0; i < iPoints; i++)
{
Vector3D pt0 = polygon.Points[(i + iPoints - 1) % iPoints];
Vector3D pt1 = polygon.Points[i];
int sign0 = (int)Math3D.GetSign(this.GetDistanceToPlane(pt0), Math3D.EpsilonF);
int sign1 = (int)Math3D.GetSign(this.GetDistanceToPlane(pt1), Math3D.EpsilonF);
if (sign0 > 0)
{
// line is infront
if (sign1 >= 0)
{
vNewPoints.Add(pt1);
}
// line is entering plane
else if (sign1 < 0)
{
Debug.Assert(sign0 > 0 && sign1 < 0);
vNewPoints.Add(this.GetIntersection(pt0, pt1));
}
}
else if (sign0 == 0)
{
// line is infront
if (sign1 > 0)
{
vNewPoints.Add(pt1);
}
// line is coplanar
else if (sign1 == 0)
{
vNewPoints.Add(pt1);
}
// line is behind
else if (sign1 < 0)
{
}
}
else if (sign0 < 0)
{
// line is leaving plane
if (sign1 > 0)
{
Debug.Assert(sign0 < 0 && sign1 > 0);
vNewPoints.Add(this.GetIntersection(pt0, pt1));
vNewPoints.Add(pt1);
}
// line is leaving plane
else if (sign1 == 0)
{
vNewPoints.Add(pt1);
}
// line is behind
else if (sign1 < 0)
{
}
}
}
// set new points
polygon.Points.Clear();
polygon.Points.AddRange(vNewPoints);
/*if( this.Points.Count >= 3 ) {
* if( Vector3D.Dot( this.GetNormal(), ptNormal ) < 0 ) {
* this.Flip();
* }
* } */
polygon.Optimize();
}