Add egui_wgpu crate (#1564)

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>

examples/custom_3d_glow/Cargo.toml

@@ -9,6 +9,6 @@ publish = false
 
 
 [dependencies]
-eframe = { path = "../../eframe" }
+eframe = { path = "../../eframe", features = ["glow"] }
 egui_glow = { path = "../../egui_glow" }
 glow = "0.11"

examples/custom_3d_glow/src/main.rs

@@ -10,6 +10,7 @@ fn main() {
     let options = eframe::NativeOptions {
         initial_window_size: Some(egui::vec2(350.0, 380.0)),
         multisampling: 8,
+        renderer: eframe::Renderer::Glow,
         ..Default::default()
     };
     eframe::run_native(
@@ -27,8 +28,12 @@ struct MyApp {
 
 impl MyApp {
     fn new(cc: &eframe::CreationContext<'_>) -> Self {
+        let gl = cc
+            .gl
+            .as_ref()
+            .expect("You need to run eframe with the glow backend");
         Self {
-            rotating_triangle: Arc::new(Mutex::new(RotatingTriangle::new(&cc.gl))),
+            rotating_triangle: Arc::new(Mutex::new(RotatingTriangle::new(gl))),
             angle: 0.0,
         }
     }
@@ -51,8 +56,10 @@ impl eframe::App for MyApp {
         });
     }
 
-    fn on_exit(&mut self, gl: &glow::Context) {
-        self.rotating_triangle.lock().destroy(gl);
+    fn on_exit(&mut self, gl: Option<&glow::Context>) {
+        if let Some(gl) = gl {
+            self.rotating_triangle.lock().destroy(gl);
+        }
     }
 }
 

examples/custom_3d_three-d/Cargo.toml

@@ -9,7 +9,7 @@ publish = false
 
 
 [dependencies]
-eframe = { path = "../../eframe" }
+eframe = { path = "../../eframe", features = ["glow"] }
 egui_glow = { path = "../../egui_glow" }
 glow = "0.11"
 three-d = { version = "0.11", default-features = false }

examples/custom_3d_three-d/src/main.rs

@@ -6,6 +6,7 @@ fn main() {
     let options = eframe::NativeOptions {
         initial_window_size: Some(egui::vec2(550.0, 610.0)),
         multisampling: 8,
+        renderer: eframe::Renderer::Glow,
         ..Default::default()
     };
     eframe::run_native(