Add gamepad registration example (#387)

* Create example

* Add `set_gamepad()` doc

* Update RELEASES.md

* invert condition and change to `pressed()`

RELEASES.md

@@ -11,6 +11,7 @@
 
 - Fixed invalid example code in README
 - Added example for setting default controls
+- Added example for registering gamepads in a local multiplayer fashion
 
 ### Enhancements
 - Implement `Reflect` for `InputMap` and most other types.

examples/register_gamepads.rs

@@ -0,0 +1,93 @@
+//! Demonstrates how to register gamepads in local multiplayer fashion
+
+use bevy::{prelude::*, utils::HashMap};
+use leafwing_input_manager::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_plugins(InputManagerPlugin::<Action>::default())
+        .init_resource::<JoinedPlayers>()
+        .add_systems(Update, (join, jump, disconnect))
+        .run()
+}
+
+#[derive(Actionlike, PartialEq, Eq, Clone, Copy, Hash, Debug, Reflect)]
+enum Action {
+    Jump,
+    Disconnect,
+}
+
+// This is used to check if a player already exists and which entity to disconnect
+#[derive(Resource, Default)]
+struct JoinedPlayers(pub HashMap<Gamepad, Entity>);
+
+#[derive(Component)]
+struct Player {
+    // This gamepad is used to index each player
+    gamepad: Gamepad,
+}
+
+fn join(
+    mut commands: Commands,
+    mut joined_players: ResMut<JoinedPlayers>,
+    gamepads: Res<Gamepads>,
+    button_inputs: Res<Input<GamepadButton>>,
+) {
+    for gamepad in gamepads.iter() {
+        // Join the game when both bumpers (L+R) on the controller are pressed
+        // We drop down the Bevy's input to get the input from each gamepad
+        if button_inputs.pressed(GamepadButton::new(gamepad, GamepadButtonType::LeftTrigger))
+            && button_inputs.pressed(GamepadButton::new(gamepad, GamepadButtonType::RightTrigger))
+        {
+            // Make sure a player can not join twice
+            if !joined_players.0.contains_key(&gamepad) {
+                println!("Player {} has joined the game!", gamepad.id);
+
+                let player = commands
+                    .spawn(InputManagerBundle::<Action> {
+                        action_state: ActionState::default(),
+                        input_map: InputMap::default()
+                            .insert(GamepadButtonType::South, Action::Jump)
+                            .insert(GamepadButtonType::Select, Action::Disconnect)
+                            // Make sure to set the gamepad or all gamepads will be used!
+                            .set_gamepad(gamepad)
+                            .build(),
+                    })
+                    .insert(Player { gamepad })
+                    .id();
+
+                // Insert the created player and its gamepad to the hashmap of joined players
+                // Since uniqueness was already checked above, we can insert here unchecked
+                joined_players.0.insert_unique_unchecked(gamepad, player);
+            }
+        }
+    }
+}
+
+fn jump(action_query: Query<(&ActionState<Action>, &Player)>) {
+    // Iterate through each player to see if they jumped
+    for (action_state, player) in action_query.iter() {
+        if action_state.just_pressed(Action::Jump) {
+            println!("Player {} jumped!", player.gamepad.id);
+        }
+    }
+}
+
+fn disconnect(
+    mut commands: Commands,
+    action_query: Query<(&ActionState<Action>, &Player)>,
+    mut joined_players: ResMut<JoinedPlayers>,
+) {
+    for (action_state, player) in action_query.iter() {
+        if action_state.pressed(Action::Disconnect) {
+            let player_entity = *joined_players.0.get(&player.gamepad).unwrap();
+
+            // Despawn the disconnected player and remove them from the joined player list
+            commands.entity(player_entity).despawn();
+            joined_players.0.remove(&player.gamepad);
+
+            println!("Player {} has disconnected!", player.gamepad.id);
+        }
+    }
+}