protected void BuildFrustum()
{
// save off the composite matrix to the base
base.matrix = Matrix4F.Mult(view, projection);
// compute vectors of frustum edges
float xs = (float)System.Math.Abs(1.0f / projection.Column0.X);
float ys = (float)System.Math.Abs(1.0f / projection.Column1.Y);
edge = new Vector3F[4];
edge[0] = ViewDir - (xs * RightVec) - (ys * Up);
edge[1] = ViewDir + (xs * RightVec) - (ys * Up);
edge[2] = ViewDir + (xs * RightVec) + (ys * Up);
edge[3] = ViewDir - (xs * RightVec) + (ys * Up);
// make frustum planes
this.near.Normal = ViewDir;
this.near.D = -Vector3F.Dot(EyePoint, ViewDir);
makePlane(edge[0], edge[3], EyePoint, ref this.left);
makePlane(edge[2], edge[1], EyePoint, ref this.right);
makePlane(edge[1], edge[0], EyePoint, ref this.bottom);
makePlane(edge[3], edge[2], EyePoint, ref this.top);
this.far.Normal = near.Normal * -1;
this.far.D = near.D + farClip;
CreateCorners();
}