{ RCSid $Id: ambpos.cal,v 2.3 2014/05/01 03:00:59 greg Exp $ }
{
	Compute patterns for ambient position markers
}
{ Relative hit point }
rpx = Px - arg(1);
rpy = Py - arg(2);
rpz = Pz - arg(3);

{ Calculation of directional gradient pattern }
ndx = arg(4); ndy = arg(5); ndz = arg(6);
dgx = arg(7); dgy = arg(8); dgz = arg(9);
rdx = ndy*rpz - ndz*rpy;
rdy = ndz*rpx - ndx*rpz;
rdz = ndx*rpy - ndy*rpx;
dgrad = (rdx*dgx + rdy*dgy + rdz*dgz)/sqrt(rpx*rpx + rpy*rpy + rpz*rpz);
dirfunc = bound(0, 1 + dgrad, 2);

{ Calculation of positional gradient pattern }
pgx = arg(4); pgy = arg(5); pgz = arg(6);
posfunc = bound(0, 1 + (pgx*rpx + pgy*rpy + pgz*rpz), 2);

{ Calculation of ellipse stencil for base }
usx = arg(4); usy = arg(5); usz = arg(6);
vsx = arg(7); vsy = arg(8); vsz = arg(9);
ellipstencil = if(1 - sq(usx*rpx + usy*rpy + usz*rpz) - sq(vsx*rpx + vsy*rpy + vsz*rpz),
			1, 0);