How to apply a shader on the whole screen?

:information_source: Attention Topic was automatically imported from the old Question2Answer platform.
:bust_in_silhouette: Asked By JulioYagami

I need to make a game pause and I want to apply a shader that lets the screen with gray scales

:bust_in_silhouette: Reply From: SIsilicon

Take a look at the official Godot demo that shows off screen-space shaders.