Blender 2.91 - Z-fighting with new overlay on unselected objects

[McManning]

Stock 2.91 adds some darkening effect to unselected meshes when you're actively working on one. This still happens even if a custom render engine is used - which is gross.

Probably affects https://github.com/McManning/Coherence as well.

[McManning]

Related change on Blender's end: https://developer.blender.org/D8679

[McManning]

A very slight offset in the vertex shader can solve this - but this isn't a universal solution for all use cases:

void main() {
    gl_Position = ModelViewProjectionMatrix * vec4(Position, 1.0);
    gl_Position.z = gl_Position.z - 0.000001 * gl_Position.w;
    ...
}