Add Android example

README.md

@@ -32,13 +32,13 @@ cargo run --example window
 
 ## Common issues
 
-Please refer to [ISSUES.md.](ISSUES.md)
+Please refer to [ISSUES.md](ISSUES.md).
 
 ### Usage
 
 Glutin is an OpenGL context creation library and doesn't directly provide OpenGL bindings for you.
 
-For examples, please look [here.](https://github.com/rust-windowing/glutin/tree/master/glutin_examples)
+For examples, please look [here](https://github.com/rust-windowing/glutin/tree/master/glutin_examples).
 
 Note that glutin aims at being a low-level brick in your rendering infrastructure. You are encouraged to write another layer of abstraction between glutin and your application.
 
@@ -48,9 +48,13 @@ Glutin is only officially supported on the latest stable version of the Rust com
 
 ### Android
 
-To compile the examples for android, you have to use the `cargo apk` utility.
+Be sure to handle Android's lifecycle correctly when using a `winit` window by only creating a GL surface (currently entire context) after `winit` raises `Event::Resumed`, and destroy it again upon receiving `Event::Suspended`. See this in action in [the `android.rs` example](./glutin_examples/examples/android.rs).
 
-See [`cargo-apk` in the `android-ndk-rs` repository](https://github.com/rust-windowing/android-ndk-rs/cargo-apk) for instructions.
+To compile and run the Android example on your device, install [`cargo-apk`](https://crates.io/crates/cargo-apk) and start the app using:
+
+```console
+$ cargo apk r -p glutin_examples --example android
+```
 
 ### X11
 

glutin/src/api/egl/mod.rs

@@ -982,7 +982,8 @@ where
         out.push(surface_type as raw::c_int);
 
         match (api, version) {
-            (Api::OpenGlEs, Some((3, _))) => {
+            // TODO: `version` is `None` when GLRequest is Latest
+            (Api::OpenGlEs, None | Some((3, _))) => {
                 if egl_version < &(1, 3) {
                     return Err(CreationError::NoAvailablePixelFormat);
                 }
@@ -1017,7 +1018,7 @@ where
                 out.push(ffi::egl::CONFORMANT as raw::c_int);
                 out.push(ffi::egl::OPENGL_BIT as raw::c_int);
             }
-            (_, _) => unimplemented!(),
+            (api, version) => unimplemented!("{:?} at version {:?}", api, version),
         };
 
         if let Some(hardware_accelerated) = pf_reqs.hardware_accelerated {

glutin/src/api/wgl/mod.rs

@@ -1,4 +1,4 @@
-#![cfg(any(target_os = "windows"))]
+#![cfg(target_os = "windows")]
 
 mod make_current_guard;
 

glutin_examples/Cargo.toml

@@ -17,3 +17,10 @@ image = "0.21"
 
 [build-dependencies]
 gl_generator = "0.14"
+
+[target.'cfg(target_os = "android")'.dependencies]
+ndk-glue = "0.5" # Keep in sync with winit
+
+[[example]]
+name = "android"
+crate-type = ["cdylib"]

glutin_examples/examples/android.rs

@@ -0,0 +1,61 @@
+#![cfg(target_os = "android")]
+
+mod support;
+
+use glutin::event::{Event, WindowEvent};
+use glutin::event_loop::{ControlFlow, EventLoop};
+use glutin::window::WindowBuilder;
+
+#[cfg_attr(target_os = "android", ndk_glue::main(backtrace = "on"))]
+fn main() {
+    println!("App started");
+    let el = EventLoop::new();
+
+    // On Android a window is only available (ndk_glue::native_window() returns Some,
+    // to create an EGL context on) after Resumed is received, and disappears when
+    // Suspended is received.
+
+    let mut state = None;
+
+    el.run(move |event, el, control_flow| {
+        *control_flow = ControlFlow::Wait;
+
+        println!("{:?}", &event);
+
+        match event {
+            Event::Resumed => {
+                println!("Android window available");
+                let wb = WindowBuilder::new().with_title("Hello world!");
+                let windowed_context =
+                    glutin::ContextBuilder::new().build_windowed(wb, el).unwrap();
+
+                let windowed_context = unsafe { windowed_context.make_current().unwrap() };
+
+                let gl = support::load(windowed_context.context());
+
+                state = Some((windowed_context, gl));
+            }
+            Event::Suspended => {
+                println!("Android window removed");
+                // Destroy the GL context before ndk-glue releases the window back to the system
+                state = None;
+            }
+            Event::WindowEvent { event: WindowEvent::CloseRequested, .. } => {
+                *control_flow = ControlFlow::Exit
+            }
+            Event::WindowEvent { event: WindowEvent::Resized(size), .. } => {
+                if let Some((windowed_context, _)) = &state {
+                    windowed_context.resize(size);
+                    windowed_context.window().request_redraw();
+                }
+            }
+            Event::RedrawRequested(_) => {
+                if let Some((windowed_context, gl)) = &state {
+                    gl.draw_frame([1.0, 0.5, 0.7, 1.0]);
+                    windowed_context.swap_buffers().unwrap();
+                }
+            }
+            _ => {}
+        }
+    });
+}

glutin_wgl_sys/src/lib.rs

@@ -1,4 +1,4 @@
-#![cfg(any(target_os = "windows"))]
+#![cfg(target_os = "windows")]
 
 /// WGL bindings
 pub mod wgl {