Mesh in front of Grease Pencil: how to remove the outline? In my current project I have a GP character whose mouth is a mesh animated with shape keys. Problem is that the mesh has an outline around it when rendered that shows the background through. It looks like the same artefact as when compositing a transparent image without the alpha multiplied.
Here's a simple example I made to illustrate the problem:

The red blob is a grease pencil fill and the blue square is a plane. Here the outline is white because the world background is white but it would be the colour of whatever object is behind the GP object.
I'm using 2.93 alpha, but also tested with 2.82 and the problem was the same (if not worst).
It is a known issue: https://developer.blender.org/T78795
The workaround mentioned on the bug report is to disable anti-aliasing for EEVEE (Film &gt; Filter Size = 0) and for Grease Pencil (Anti-Aliasing Threshold = 0). Which in turn means you'd have to render double the size then downscale the result to get anti-aliasing back.
EDIT: I came across a way to do this without losing GPencil anti-aliasing. Basically it requires isolating GP and Meshes in different View Layers and compositing them back together with a Z Combine node (as explained in my answer here), and disabling the node's &quot;Z anti-aliasing&quot;. You still have to set EEVEE's Filter Size to zero but at least the edges of GPencil objects stay smooth without doubling render size.