New to writing shaders, please forgive any naivety in the question!

Parallax mapping in any of its ray-marchy variants (e.g. steep parallax, cone step mapping, POM) generates fake geometry on a material, generally nearly indistinguishable from real geometry and at a much higher resolution than is practical using GPU tessellation. However, the geometry created does not extend outside the initial bounds of the triangle being rendered (unlike with GPU tessellation) - so e.g. a parallax mapped sphere still has circular edges.

I'm want to try adapting a parallax shader (preferably OpenGL, any high quality variation of parallax mapping will do though I gather cone stepping is pretty much the state of the art) to write outside of the poly bounds using gl_FragDepth (and enabling conservative depth output).

This seems to be theoretically possible (see this Unity example https://forum.unity.com/threads/modifying-depth-when-parallax-mapping.364037/). However that post did not include any shader code and got no responses.

Is anyone aware of an existing implementation of this (with source available), or else could give me a good idea of how I should proceed with implementing it?

Many thanks.