{
	cyl.cal - 2d coordinate mapping onto cylinder.

	Unit radius cylinder with axis along z.

	A1 = picture height/width
	A2 = unit scale for pattern
}

cyl_u = (atan2(Py,Px)+PI)/A2;
cyl_v = Pz/A2;

cyl_tile_u = mod(cyl_u,pic_width);
cyl_tile_v = mod(cyl_v,pic_height);

cyl_match_u = tri(cyl_u,pic_width);
cyl_match_v = tri(cyl_v,pic_height);

pic_width = max(1,1/A1);
pic_height = max(1,A1);