In this context, Overlay simply means a gui application where 1. It has a transparent window surface 2. It can toggle the borders/decorations like title bar. 3. can let the input like mouse clicks to passthrough its window surface.
Here, we will let input passthrough when egui doesn't need input.
The project itself builds upon the egui_backend crate while using egui_window_glfw_passthrough for windowing functionality.
For rendering, we use egui_render_three_d, as three-d will allow you to draw a bunch of things easily.
But, as apple doesn't support opengl, we use egui_render_wgpu on macos.
For advanced usecases, i recommend directly using egui_window_glfw_passthrough from https://github.com/coderedart/etk
Look at the basic example for a rough idea of how to use this crate for normal usecase.
Look at the triangle example (only for linux/windows users), to see how you can draw custom stuff too.
https://github.com/coderedart/egui_overlay/assets/24411704/9f7bab7b-26ec-47d1-b51e-74006dfa7b0d