How can i achieve an outline effect?

Question

I have a small shader that does the following things:

(First cgprogram block)

1. Copy the current mesh and scales it along the normals
2. Assign a color to the inflated mesh
3. Draw the inflated mesh

(Second cgprogram block)

1. Assign a color to the original mesh
2. Draw the original mesh

In-game you can only see the inflated mesh because the smaller one gets inglobated.

Is there a way to re-order the rendering order, by drawing first the inflated mesh and then the original mesh, resulting in a sort of outline effect?

What I tried

1. Setting Cull Front on the inflated mesh and Cull Back on the original mesh

   I copied this approach from an outline shader. Unfortunately it leads to other problems such as bad intersecting between inflated mesh in-game.

2. Changing the Queue in the shader between the two CGPROGRAM blocks

   I set the first CGPROGRAM block on "Queue" = "Geometry-10" and the second on "Queue" = "Geometry+0" but.. no effect.

Is there a way to obtain the desired effect? Thanks in advance.

Here are some images to make the question a bit clearer:

Current wireframe situation

Original mesh inside, inflated mesh outside

Current shaded situation

Desired outcome

Inflated mesh set on Cull Front

This is the aforementioned problems between intersecting meshes. The inflated meshes have z-fighting going on.

Answer 1

Your problem here isn't rendering order. Since your regular colour mesh pass is second, it will come after the outline blob.

But, if your outline blob is writing to the z-buffer, then every fragment of your regular mesh will fail the depth test, because there's some part of the outline blob sitting between it and the camera.

You can turn off depth writes for the outline pass with

ZWrite Off

in the same section where you do your culling settings. This will prevent the blob from writing to the depth buffer, so by the time the regular mesh draws the depth buffer will still be in the state it was in before you even started drawing this material & mesh.

Note though that this will increase overdraw. In the typical case, we draw the outline inside-out, second, so that it's the outline mesh that fails the depth test and is discarded, and we only need to blend the smaller region of pixels making up the outline. By rendering the blob first, every pixel on the interior of the model is going to get written into at least twice, and more if the model has concave shapes. For just this one effect it won't be a big cost, but watch out for using this "painter's algorithm" for lots of effects all over your game.