silhouette of a cylinder

hi everyone,

i have a solid cylinder and my task is to draw the silhouettes.

if i rotate the cylinder around the z-axis, it should still show the right silhouettes from my point of view.

has anybody an idea how to do this?

i am thankful for any kind of help.

You need to check triangles sides and draw the ones that have normals almost perpendicular to the view direction.