ScenegraphLayer show object border: custom shader for inverse hull method

[carlos-vl]

I want to be able to highlight the border of a 3D model loaded in a ScenegraphLayer.
My idea is to use the inverse hull technique:

• Render two ScenegraphLayer instances for the same object: one with the model, another one for the outline.
• The one for the outline is black (or any other color), uses front face culling to show only the back of the object set and is slightly bigger.
• That way we have the model + the outline.

This partly works out of the box, setting these props for the second ScenegraphLayer (the one used for the outline)

{
  ...
  getColor: () => [0, 0, 0, 255],
  sizeScale: 1.05,
  parameters: {
    cullMode: "front",
  },
}

However, even if this kinda works, the border is not ok, as using the sizeScale prop to make the solid layer bigger is not the right approach. Instead, the vertices should be extruded along their normals. I try to do this with a custom shader, injecting the following code on vs:DECKGL_FILTER_GL_POSITION

vec3 extrudedPosition = geometry.position.xyz + geometry.normal * 0.01;
position = project_common_position_to_clipspace(vec4(extrudedPosition, 1.0));

However, this seems to move the model upwards, not make it bigger.
Can someone help me to understand why this is happening?

[carlos-vl]

Ok I got this to work, it seems if lightning is not set to pbr, the normals are then always (0, 0, 1), that is why it was moving upwards instead of extruding as expected. I now can get this effect.

As a final step, I would like to be able to show just the outline of the model, without the model itself, so that I can move the model silhouette along the map. Anyone knows how I could do this? I would like to get some similar result to what can be seen in this CesiumJS examples