android-activity/examples/agdk-mainloop/src/lib.rs

use android_activity::{AndroidApp, InputStatus, MainEvent, PollEvent};
use log::info;

#[no_mangle]
fn android_main(app: AndroidApp) {
    android_logger::init_once(android_logger::Config::default().with_min_level(log::Level::Info));

    let mut quit = false;
    let mut redraw_pending = true;
    let mut native_window: Option<ndk::native_window::NativeWindow> = None;

    while !quit {
        app.poll_events(
            Some(std::time::Duration::from_secs(1)), /* timeout */
            |event| {
                match event {
                    PollEvent::Wake => {
                        info!("Early wake up");
                    }
                    PollEvent::Timeout => {
                        info!("Timed out");
                        // Real app would probably rely on vblank sync via graphics API...
                        redraw_pending = true;
                    }
                    PollEvent::Main(main_event) => {
                        info!("Main event: {:?}", main_event);
                        match main_event {
                            MainEvent::SaveState { saver, .. } => {
                                saver.store("foo://bar".as_bytes());
                            }
                            MainEvent::Pause => {}
                            MainEvent::Resume { loader, .. } => {
                                if let Some(state) = loader.load() {
                                    if let Ok(uri) = String::from_utf8(state) {
                                        info!("Resumed with saved state = {uri:#?}");
                                    }
                                }
                            }
                            MainEvent::InitWindow { .. } => {
                                native_window = app.native_window();
                                redraw_pending = true;
                            }
                            MainEvent::TerminateWindow { .. } => {
                                native_window = None;
                            }
                            MainEvent::WindowResized { .. } => {
                                redraw_pending = true;
                            }
                            MainEvent::RedrawNeeded { .. } => {
                                redraw_pending = true;
                            }
                            MainEvent::InputAvailable { .. } => {
                                redraw_pending = true;
                            }
                            MainEvent::ConfigChanged { .. } => {
                                info!("Config Changed: {:#?}", app.config());
                            }
                            MainEvent::LowMemory => {}

                            MainEvent::Destroy => quit = true,
                            _ => { /* ... */ }
                        }
                    }
                    _ => {}
                }

                if redraw_pending {
                    if let Some(native_window) = &native_window {
                        redraw_pending = false;

                        // Handle input
                        app.input_events(|event| {
                            info!("Input Event: {event:?}");
                            InputStatus::Unhandled
                        });

                        info!("Render...");
                        dummy_render(native_window);
                    }
                }
            },
        );
    }
}

/// Post a NOP frame to the window
///
/// Since this is a bare minimum test app we don't depend
/// on any GPU graphics APIs but we do need to at least
/// convince Android that we're drawing something and are
/// responsive, otherwise it will stop delivering input
/// events to us.
fn dummy_render(native_window: &ndk::native_window::NativeWindow) {
    unsafe {
        let mut buf: ndk_sys::ANativeWindow_Buffer = std::mem::zeroed();
        let mut rect: ndk_sys::ARect = std::mem::zeroed();
        ndk_sys::ANativeWindow_lock(
            native_window.ptr().as_ptr() as _,
            &mut buf as _,
            &mut rect as _,
        );
        // Note: we don't try and touch the buffer since that
        // also requires us to handle various buffer formats
        ndk_sys::ANativeWindow_unlockAndPost(native_window.ptr().as_ptr() as _);
    }
}