Add gamecube adapter support

src/input/gamecube/mod.rs

@@ -0,0 +1,35 @@
+pub mod bridge;
+pub mod poll;
+
+pub use bridge::{GcPort, GcPorts, GC_PORT_COUNT};
+pub use poll::{GcAdapterSnapshot, GcPortState};
+
+use bevy::input::gamepad::{gamepad_connection_system, gamepad_event_processing_system};
+use bevy::input::InputSystems;
+use bevy::prelude::*;
+
+#[derive(Default)]
+pub struct GamecubeAdapterPlugin;
+
+impl Plugin for GamecubeAdapterPlugin {
+    fn build(&self, app: &mut App) {
+        app.init_resource::<GcPorts>();
+
+        let Ok(snapshot) = poll::spawn_poll_thread() else {
+            // No adapter connected; leave GcPorts empty and skip wiring the
+            // polling systems.
+            return;
+        };
+
+        app.insert_resource(snapshot).add_systems(
+            PreUpdate,
+            (
+                bridge::gc_connection_system.before(gamepad_connection_system),
+                bridge::gc_event_system
+                    .after(gamepad_connection_system)
+                    .before(gamepad_event_processing_system),
+            )
+                .in_set(InputSystems),
+        );
+    }
+}