Added example for android (#368)

examples/minimal-winit-android/Cargo.toml

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+[package]
+name = "minimal-winit-android"
+version = "0.1.0"
+authors = ["Randommist <andreq11s@gmail.com>"]
+edition = "2021"
+publish = false
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+log = "0.4.19"
+pixels = { path = "../.." }
+winit = { version = "0.28.6", features = ["android-native-activity"] }
+
+[target.'cfg(not(target_os = "android"))'.dependencies]
+env_logger = "0.10.0"
+
+[target.'cfg(target_os = "android")'.dependencies]
+android_logger = "0.11.0"
+
+[lib]
+crate_type = ["cdylib"]
+
+
+[package.metadata.android.signing.release]
+path = "./path/to/KeyStoreFile.jks"
+keystore_password = "password"

examples/minimal-winit-android/README.md

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+# Hello Android
+
+![Hello Android](../../img/minimal-winit-android.png)
+
+Minimal example to run on android using `winit` with `android-native-activity` feature
+
+## Running
+```
+export ANDROID_HOME="path/to/sdk"
+export ANDROID_NDK_HOME="path/to/ndk"
+
+rustup target add aarch64-linux-android
+cargo install cargo-apk
+```
+Connect your Android device via USB cable to your computer in debug mode and run the following command
+```
+cargo apk run
+```

examples/minimal-winit-android/src/lib.rs

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+#[cfg(target_os = "android")]
+use winit::platform::android::activity::AndroidApp;
+
+use pixels::{Pixels, SurfaceTexture};
+use winit::event::Event;
+use winit::event_loop::{ControlFlow, EventLoop, EventLoopBuilder};
+use winit::window::Window;
+
+const WIDTH: u32 = 320;
+const HEIGHT: u32 = 240;
+const BOX_SIZE: i16 = 64;
+
+/// Representation of the application state. In this example, a box will bounce around the screen.
+struct World {
+    box_x: i16,
+    box_y: i16,
+    velocity_x: i16,
+    velocity_y: i16,
+}
+
+fn _main(event_loop: EventLoop<()>) {
+    let mut window: Option<Window> = None;
+    let mut pixels: Option<Pixels> = None;
+
+    let mut world = World::new();
+
+    event_loop.run(move |event, event_loop, control_flow| {
+        *control_flow = ControlFlow::Wait;
+        match event {
+            Event::Resumed => {
+                let _window = Window::new(event_loop).unwrap();
+                let _pixels = {
+                    let window_size = _window.inner_size();
+                    let surface_texture =
+                        SurfaceTexture::new(window_size.width, window_size.height, &_window);
+                    Pixels::new(WIDTH, HEIGHT, surface_texture).unwrap()
+                };
+                _window.request_redraw();
+                window = Some(_window);
+                pixels = Some(_pixels);
+            }
+            Event::Suspended => {
+                pixels = None;
+                window = None;
+            }
+            Event::RedrawRequested(_) => {
+                if let (Some(pixels), Some(window)) = (&mut pixels, &window) {
+                    world.draw(pixels.frame_mut());
+                    pixels.render().unwrap();
+                    window.request_redraw();
+                }
+            }
+            _ => {}
+        }
+        if window.is_some() {
+            world.update();
+        }
+    });
+}
+
+impl World {
+    /// Create a new `World` instance that can draw a moving box.
+    fn new() -> Self {
+        Self {
+            box_x: 24,
+            box_y: 16,
+            velocity_x: 1,
+            velocity_y: 1,
+        }
+    }
+
+    /// Update the `World` internal state; bounce the box around the screen.
+    fn update(&mut self) {
+        if self.box_x <= 0 || self.box_x + BOX_SIZE > WIDTH as i16 {
+            self.velocity_x *= -1;
+        }
+        if self.box_y <= 0 || self.box_y + BOX_SIZE > HEIGHT as i16 {
+            self.velocity_y *= -1;
+        }
+
+        self.box_x += self.velocity_x;
+        self.box_y += self.velocity_y;
+    }
+
+    /// Draw the `World` state to the frame buffer.
+    ///
+    /// Assumes the default texture format: `wgpu::TextureFormat::Rgba8UnormSrgb`
+    fn draw(&self, frame: &mut [u8]) {
+        for (i, pixel) in frame.chunks_exact_mut(4).enumerate() {
+            let x = (i % WIDTH as usize) as i16;
+            let y = (i / WIDTH as usize) as i16;
+
+            let inside_the_box = x >= self.box_x
+                && x < self.box_x + BOX_SIZE
+                && y >= self.box_y
+                && y < self.box_y + BOX_SIZE;
+
+            let rgba = if inside_the_box {
+                [0x5e, 0x48, 0xe8, 0xff]
+            } else {
+                [0x48, 0xb2, 0xe8, 0xff]
+            };
+
+            pixel.copy_from_slice(&rgba);
+        }
+    }
+}
+
+#[allow(dead_code)]
+#[cfg(target_os = "android")]
+#[no_mangle]
+fn android_main(app: AndroidApp) {
+    use winit::platform::android::EventLoopBuilderExtAndroid;
+    android_logger::init_once(android_logger::Config::default().with_min_level(log::Level::Info));
+    let event_loop = EventLoopBuilder::new().with_android_app(app).build();
+    log::info!("Hello from android!");
+    _main(event_loop);
+}
+
+#[allow(dead_code)]
+#[cfg(not(target_os = "android"))]
+fn main() {
+    env_logger::builder()
+        .filter_level(log::LevelFilter::Info) // Default Log Level
+        .parse_default_env()
+        .init();
+    let event_loop = EventLoopBuilder::new().build();
+    log::info!("Hello from desktop!");
+    _main(event_loop);
+}