Because Shaders are connected to Materials that effect 1 mesh at a time, we had to combine all those meshes into one outline-able mesh. Now we just need the outline.
Though shaders are a fairly deep hole to jump into, the Unity Community is there for us with a few commonly desired shaders. I found several useful resources Here. Select Silhouette-Outlined Diffuse and copy the variant that's right for you. There's Standard, Bumped, and Outline Only. I like Outline Only but you may have other needs.
Copy the Shader script. In Unity, make yourself a new Shader, open, and paste shader script.
Now The Outline
This part's super simple
- Make yourself a new Material.
- Assign the new Outline Shader
- Adjust color to preference. I like bright greens and blues.
Finally, we combine these two techniques into a complex outline.
- Take your original multi-mesh object, with it's "empty" parent-object
- From there make an empty game-object child with scaled about 1 to 1.
- Assign the Mesh you made earlier
- Assign your new Outline Material
- Adjust to preference
With these steps we've completed the Multi-Mesh Object Outline path. I hope you enjoy your outlines derived from this method.