* Re-implement PaintCallbacks With Support for WGPU
This makes breaking changes to the PaintCallback system, but makes it
flexible enough to support both the WGPU and glow backends with custom
rendering.
Also adds a WGPU equivalent to the glow demo for custom painting.
Based on https://github.com/hasenbanck/egui_wgpu_backend
`egui-wgpu` is now an official backend for `eframe` (opt-in).
Use the `wgpu` feature flag on `eframe` and the `NativeOptions::renderer` settings to pick it.
Co-authored-by: Nils Hasenbanck <nils@hasenbanck.de>
Co-authored-by: Sven Niederberger <niederberger@embotech.com>
Co-authored-by: Sven Niederberger <73159570+s-nie@users.noreply.github.com>
* Move examples out of eframe/examples into examples/
Give each example a `Cargo.toml` and `src/main.rs`.
This makes it easier for people to use as templates.
* Update README.md with more deps needed on vanilla Ubuntu
* Install libgtk-3-dev on CI, hoping that will fix something
