objects with outlines

I'm curious if it's possible to create an object and add an outline around it, to make a cell shaded look. How would this be done, or can it?

It can be done and it is very easy for spheres (and other ovoids) and possible for other shapes.

I can show you in-world if you'd like. You basically just have to do some texturing tricks to generate a pretty satisfying effect.

The simplest way is to double every prim. You'll use an "outline prim" and a "fill prim". The outline prim should be hollow with a completely transparent texture on the outside, and a solid black texture on the inside. The fill prim should be a solid color, set to full bright to eliminate shading, and sized slightly smaller than the outline prim. Put the fill prim inside the outline prim and you're all set. Because the outline prim is transparent on the outside, you'll see the fill prim through it, and because it's black on the inside, you'll see the black surronunding the fill prim, forming an outline.

For spheres, there is a trick to do it with just one prim. If you hollow it, and then twist the top and bottom all the way in opposite directions, you'll see that the outside appears to outline the inside. As long as the inside and outside are different colors, it will look cell shaded. Again, using full bright to eliminate shading is recommended to complete the illusion. Note that this is likely a bug in how the twist affects the normal mapping of the sphere, so it might not be a permanent solution (could be "fixed" at any time), but it has been around for a long time, and it works at the moment.