Move examples out of eframe/examples into examples/ (#1486)

* 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

examples/custom_font/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "custom_font"
+version = "0.1.0"
+authors = ["Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2021"
+rust-version = "1.60"
+publish = false
+
+
+[dependencies]
+eframe = { path = "../../eframe" }

examples/custom_font/README.md

@@ -0,0 +1,3 @@
+```sh
+cargo run -p custom_font
+```

examples/custom_font/src/main.rs

@@ -0,0 +1,63 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use eframe::egui;
+
+fn main() {
+    let options = eframe::NativeOptions::default();
+    eframe::run_native(
+        "egui example: custom font",
+        options,
+        Box::new(|cc| Box::new(MyApp::new(cc))),
+    );
+}
+
+fn setup_custom_fonts(ctx: &egui::Context) {
+    // Start with the default fonts (we will be adding to them rather than replacing them).
+    let mut fonts = egui::FontDefinitions::default();
+
+    // Install my own font (maybe supporting non-latin characters).
+    // .ttf and .otf files supported.
+    fonts.font_data.insert(
+        "my_font".to_owned(),
+        egui::FontData::from_static(include_bytes!("../../../epaint/fonts/Hack-Regular.ttf")),
+    );
+
+    // Put my font first (highest priority) for proportional text:
+    fonts
+        .families
+        .entry(egui::FontFamily::Proportional)
+        .or_default()
+        .insert(0, "my_font".to_owned());
+
+    // Put my font as last fallback for monospace:
+    fonts
+        .families
+        .entry(egui::FontFamily::Monospace)
+        .or_default()
+        .push("my_font".to_owned());
+
+    // Tell egui to use these fonts:
+    ctx.set_fonts(fonts);
+}
+
+struct MyApp {
+    text: String,
+}
+
+impl MyApp {
+    fn new(cc: &eframe::CreationContext<'_>) -> Self {
+        setup_custom_fonts(&cc.egui_ctx);
+        Self {
+            text: "Edit this text field if you want".to_owned(),
+        }
+    }
+}
+
+impl eframe::App for MyApp {
+    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        egui::CentralPanel::default().show(ctx, |ui| {
+            ui.heading("egui using custom fonts");
+            ui.text_edit_multiline(&mut self.text);
+        });
+    }
+}