Decompose a GLSL mat4 to original RTS values within vertex shader to calculate a View UV Offset?

Hi All,
So i made this post in stack with a bounty but unable to find a solution.
I need to emulate large number of mirrors for a superposition project and i’m using quads to project slots of a texture grid (spritesheet-like) using billboards,
texture slots should switch according to the the combined viewing angle (view vector) and quad rotation.

I believe azimuth and elevation could be the key but I’m open to options other than cubemap abuse or moving the code to CPU side.

All help is appreciated.



weird case where the elevation is working perfectly as azimuth:

Thank you.