Combine demo_glium and demo_web into one egui_demo crate

egui_demo/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "egui_demo"
+version = "0.1.0"
+authors = ["Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2018"
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+egui = { path = "../egui", features = ["serde", "serde_json"] }
+serde = { version = "1", features = ["derive"] }
+
+# For compiling natively:
+[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
+egui_glium = { path = "../egui_glium" }
+
+# For compiling to web:
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+egui_web = { path = "../egui_web" }
+js-sys = "0.3"
+wasm-bindgen = "0.2"

egui_demo/src/lib.rs

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+#![forbid(unsafe_code)]
+#![cfg_attr(not(debug_assertions), deny(warnings))] // Forbid warnings in release builds
+#![warn(clippy::all)]
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen::prelude::*;
+
+/// This is the entry-point for all the web-assembly.
+/// This is called once from the HTML.
+/// It loads the app, installs some callbacks, then returns.
+/// You can add more callbacks like this if you want to call in to your code.
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen]
+pub fn start(canvas_id: &str) -> Result<(), wasm_bindgen::JsValue> {
+    let app = egui::DemoApp::default();
+    egui_web::start(canvas_id, Box::new(app))?;
+    Ok(())
+}

egui_demo/src/main.rs

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+#![forbid(unsafe_code)]
+#![cfg_attr(not(debug_assertions), deny(warnings))] // Forbid warnings in release builds
+#![warn(clippy::all)]
+
+// When compiling natively:
+fn main() {
+    let app = egui::DemoApp::default();
+    egui_glium::run(Box::new(app));
+}