That's pretty clever or an outline. Load the mesh with textures, then load the mesh again without textures, change color to black, flip, the scale. Pretty damn clever.
But an outline has nothing to do with Cel-Shading. Cel-Shading requires vast knowledge of normals, lighting, shading, and some other stuff.
But an outline has nothing to do with Cel-Shading. Cel-Shading requires vast knowledge of normals, lighting, shading, and some other stuff.