cross-platform main function (#847)

Cargo.toml

@@ -82,11 +82,6 @@ tracing = "0.1.21"
 tracing-chrome = "0.2.0"
 tracing-subscriber = "0.2.15"
 
-# bevy (Android)
-[target.'cfg(target_os = "android")'.dependencies]
-android_logger = "0.9"
-ndk-glue = {version = "0.2", features = ["logger"]}
-
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
 console_error_panic_hook = "0.1.6"
 console_log = {version = "0.2", features = ["color"]}

crates/bevy_derive/src/bevy_main.rs

@@ -0,0 +1,36 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, ItemFn};
+
+pub fn bevy_main(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(item as ItemFn);
+    if input.sig.ident != "main" {
+        panic!("bevy_main can only be used on a function called 'main'")
+    }
+
+    TokenStream::from(quote! {
+        #[no_mangle]
+        #[cfg(target_os = "android")]
+        unsafe extern "C" fn ANativeActivity_onCreate(
+            activity: *mut std::os::raw::c_void,
+            saved_state: *mut std::os::raw::c_void,
+            saved_state_size: usize,
+        ) {
+            bevy::ndk_glue::init(
+                activity as _,
+                saved_state as _,
+                saved_state_size as _,
+                main,
+            );
+        }
+
+        #[no_mangle]
+        #[cfg(target_os = "ios")]
+        extern "C" fn main_rs() {
+            main();
+        }
+
+        #[allow(unused)]
+        #input
+    })
+}

crates/bevy_derive/src/lib.rs

@@ -1,6 +1,7 @@
 extern crate proc_macro;
 
 mod app_plugin;
+mod bevy_main;
 mod bytes;
 mod modules;
 mod render_resource;
@@ -60,3 +61,8 @@ pub fn type_uuid_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStre
 pub fn external_type_uuid(tokens: proc_macro::TokenStream) -> proc_macro::TokenStream {
     type_uuid::external_type_uuid(tokens)
 }
+
+#[proc_macro_attribute]
+pub fn bevy_main(attr: TokenStream, item: TokenStream) -> TokenStream {
+    bevy_main::bevy_main(attr, item)
+}

crates/bevy_internal/Cargo.toml

@@ -40,6 +40,7 @@ bevy_app = { path = "../bevy_app", version = "0.3.0" }
 bevy_asset = { path = "../bevy_asset", version = "0.3.0" }
 bevy_type_registry = { path = "../bevy_type_registry", version = "0.3.0" }
 bevy_core = { path = "../bevy_core", version = "0.3.0" }
+bevy_derive = { path = "../bevy_derive", version = "0.3.0" }
 bevy_diagnostic = { path = "../bevy_diagnostic", version = "0.3.0" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.3.0" }
 bevy_input = { path = "../bevy_input", version = "0.3.0" }
@@ -63,3 +64,5 @@ bevy_wgpu = { path = "../bevy_wgpu", optional = true, version = "0.3.0" }
 bevy_winit = { path = "../bevy_winit", optional = true, version = "0.3.0" }
 bevy_gilrs = { path = "../bevy_gilrs", optional = true, version = "0.3.0" }
 
+[target.'cfg(target_os = "android")'.dependencies]
+ndk-glue = {version = "0.2", features = ["logger"]}

crates/bevy_internal/src/lib.rs

@@ -131,3 +131,6 @@ pub mod wgpu {
 pub mod dynamic_plugin {
     pub use bevy_dynamic_plugin::*;
 }
+
+#[cfg(target_os = "android")]
+pub use ndk_glue;

crates/bevy_internal/src/prelude.rs

@@ -4,6 +4,8 @@ pub use crate::{
     type_registry::RegisterType, window::prelude::*, DefaultPlugins, MinimalPlugins,
 };
 
+pub use bevy_derive::bevy_main;
+
 #[cfg(feature = "bevy_audio")]
 pub use crate::audio::prelude::*;
 

examples/android/android.rs

@@ -1,10 +1,45 @@
-// Edit to run any single file example from Bevy.
-include!("../3d/3d_scene.rs");
+use bevy::prelude::*;
 
-#[cfg_attr(
-    target_os = "android",
-    ndk_glue::main(logger(level = "debug", tag = "android"), backtrace = "full")
-)]
-pub fn android_main() {
-    main();
+// the `bevy_main` proc_macro generates the required android boilerplate
+#[bevy_main]
+fn main() {
+    App::build()
+        .add_resource(Msaa { samples: 2 })
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(setup.system())
+        .run();
+}
+
+/// set up a simple 3D scene
+fn setup(
+    commands: &mut Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // add entities to the world
+    commands
+        // plane
+        .spawn(PbrComponents {
+            mesh: meshes.add(Mesh::from(shape::Plane { size: 10.0 })),
+            material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
+            ..Default::default()
+        })
+        // cube
+        .spawn(PbrComponents {
+            mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
+            material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
+            transform: Transform::from_translation(Vec3::new(0.0, 1.0, 0.0)),
+            ..Default::default()
+        })
+        // light
+        .spawn(LightComponents {
+            transform: Transform::from_translation(Vec3::new(4.0, 8.0, 4.0)),
+            ..Default::default()
+        })
+        // camera
+        .spawn(Camera3dComponents {
+            transform: Transform::from_translation(Vec3::new(-3.0, 5.0, 8.0))
+                .looking_at(Vec3::default(), Vec3::unit_y()),
+            ..Default::default()
+        });
 }

examples/ios/src/lib.rs

@@ -1,14 +1,8 @@
-use bevy::{
-    prelude::{
-        shape, App, Assets, Camera3dComponents, Color, Commands, DefaultPlugins, IntoSystem,
-        LightComponents, Mesh, Msaa, PbrComponents, ResMut, StandardMaterial, Transform, Vec3,
-        WindowDescriptor,
-    },
-    window::WindowMode,
-};
+use bevy::{prelude::*, window::WindowMode};
 
-#[no_mangle]
-extern "C" fn main_rs() {
+// the `bevy_main` proc_macro generates the required ios boilerplate
+#[bevy_main]
+fn main() {
     App::build()
         .add_resource(WindowDescriptor {
             vsync: true,