Back faced culling error?

Hello fellow blender users!
I need some help. I’mm trying to make some character models turn out looking similar to those used in RWBY (http://www.creativebloq.com/animation/rbwy-anime-action-dynamic-3d-twist-9134477) and I need help with a certain part… Namely the outline. Notice how the characters have this black line outlining them even though they are 3D models? Yeah, I have no idea how to do that. In the article linked above it states “On RWBY, lines are drawn by exploiting an error with back-faced culling: Wherever there needs to be a line, there is a second set of the same geometry slightly extruded and often coloured black to simulate a line. Having the two sets of geometry adjacent and occluding each other gives the perception of a line.”

What does that even mean? Any help is apreciated!

The attached blend file shows the method that I think you’re looking for. Press P to play the animations and show the outlines.

Here’s how to recreate the effect:

  1. Make a duplicate of the object you want to outline, and fatten the duplicate using Alt+S. The more fattening you do, the thicker the outline.
  2. Completely cover the duplicate object with a black material that has its diffuse and specular properties set to zero.
  3. Use the W menu to flip the normals of the duplicate object. This causes the duplicate object to “turn inside out.”
  4. Set the original object as the parent of the duplicate object.

The above process typically makes pretty good outlines, as seen on the blend file’s blue cylinder. If it works well for your object, then the outlining is done! Sometimes though, this method can produce strange looking results, as seen on the inner part of the green torus. However, as long as your outlines are relatively thin, the problems aren’t especially noticeable and often don’t need to be fixed, as seen on the red torus. There are alternative methods to do outlining that fix some problems that might pop up with this method, but those other methods would require scripts (to my knowledge, anyway).

Here’s the simplified explanation for why this method works, if you’re interested: The duplicate object’s surfaces nearest to the camera often face the camera and obscure (occlude) the original object. By flipping the duplicate object inside out, those surfaces that are near to the camera now face away from the camera and become invisible(they are culled). Because the surfaces are invisible, you can once again see the original object that’s inside the duplicate object. Meanwhile, the duplicate object’s surfaces furthest from the camera would normally face away from the camera and be invisible, but flipping those surfaces toward the camera makes them visible and creates the outline around the original object.

Hope that helps.

Attachments

Objects with Outlines.blend (743 KB)

That is exactly what I wanted! Thank you very much!