Add GamepadButtonInput event (#9008)

# Objective

Add `GamepadButtonInput` event
Resolves #8988

## Solution

- Add `GamepadButtonInput` type
- Emit `GamepadButtonInput` events whenever `Input<GamepadButton>` is
written to
- Update example

---------

Co-authored-by: François <mockersf@gmail.com>

crates/bevy_input/src/gamepad.rs

@@ -1,4 +1,4 @@
-use crate::{Axis, Input};
+use crate::{Axis, ButtonState, Input};
 use bevy_ecs::event::{Event, EventReader, EventWriter};
 use bevy_ecs::{
     change_detection::DetectChangesMut,
@@ -265,6 +265,21 @@ impl GamepadButton {
     }
 }
 
+/// A gamepad button input event.
+#[derive(Event, Debug, Clone, Copy, PartialEq, Eq, Reflect)]
+#[reflect(Debug, PartialEq)]
+#[cfg_attr(
+    feature = "serialize",
+    derive(serde::Serialize, serde::Deserialize),
+    reflect(Serialize, Deserialize)
+)]
+pub struct GamepadButtonInput {
+    /// The gamepad button assigned to the event.
+    pub button: GamepadButton,
+    /// The pressed state of the button.
+    pub state: ButtonState,
+}
+
 /// A type of a [`GamepadAxis`].
 ///
 /// ## Usage
@@ -1159,20 +1174,35 @@ pub fn gamepad_axis_event_system(
 
 /// Uses [`GamepadButtonChangedEvent`]s to update the relevant [`Input`] and [`Axis`] values.
 pub fn gamepad_button_event_system(
-    mut button_events: EventReader<GamepadButtonChangedEvent>,
+    mut button_changed_events: EventReader<GamepadButtonChangedEvent>,
     mut button_input: ResMut<Input<GamepadButton>>,
+    mut button_input_events: EventWriter<GamepadButtonInput>,
     settings: Res<GamepadSettings>,
 ) {
-    for button_event in button_events.iter() {
+    for button_event in button_changed_events.iter() {
         let button = GamepadButton::new(button_event.gamepad, button_event.button_type);
         let value = button_event.value;
         let button_property = settings.get_button_settings(button);
 
         if button_property.is_released(value) {
-            // We don't have to check if the button was previously pressed
+            // Check if button was previously pressed
+            if button_input.pressed(button) {
+                button_input_events.send(GamepadButtonInput {
+                    button,
+                    state: ButtonState::Released,
+                });
+            }
+            // We don't have to check if the button was previously pressed here
             // because that check is performed within Input<T>::release()
             button_input.release(button);
         } else if button_property.is_pressed(value) {
+            // Check if button was previously not pressed
+            if !button_input.pressed(button) {
+                button_input_events.send(GamepadButtonInput {
+                    button,
+                    state: ButtonState::Pressed,
+                });
+            }
             button_input.press(button);
         };
     }

crates/bevy_input/src/lib.rs

@@ -41,7 +41,7 @@ use gamepad::{
     gamepad_axis_event_system, gamepad_button_event_system, gamepad_connection_system,
     gamepad_event_system, AxisSettings, ButtonAxisSettings, ButtonSettings, Gamepad, GamepadAxis,
     GamepadAxisChangedEvent, GamepadAxisType, GamepadButton, GamepadButtonChangedEvent,
-    GamepadButtonType, GamepadConnection, GamepadConnectionEvent, GamepadEvent,
+    GamepadButtonInput, GamepadButtonType, GamepadConnection, GamepadConnectionEvent, GamepadEvent,
     GamepadRumbleRequest, GamepadSettings, Gamepads,
 };
 
@@ -75,6 +75,7 @@ impl Plugin for InputPlugin {
             // gamepad
             .add_event::<GamepadConnectionEvent>()
             .add_event::<GamepadButtonChangedEvent>()
+            .add_event::<GamepadButtonInput>()
             .add_event::<GamepadAxisChangedEvent>()
             .add_event::<GamepadEvent>()
             .add_event::<GamepadRumbleRequest>()
@@ -131,6 +132,7 @@ impl Plugin for InputPlugin {
             .register_type::<GamepadConnection>()
             .register_type::<GamepadButtonType>()
             .register_type::<GamepadButton>()
+            .register_type::<GamepadButtonInput>()
             .register_type::<GamepadAxisType>()
             .register_type::<GamepadAxis>()
             .register_type::<GamepadSettings>()

examples/input/gamepad_input_events.rs

@@ -2,7 +2,8 @@
 
 use bevy::{
     input::gamepad::{
-        GamepadAxisChangedEvent, GamepadButtonChangedEvent, GamepadConnectionEvent, GamepadEvent,
+        GamepadAxisChangedEvent, GamepadButtonChangedEvent, GamepadButtonInput,
+        GamepadConnectionEvent, GamepadEvent,
     },
     prelude::*,
 };
@@ -15,25 +16,37 @@ fn main() {
 }
 
 fn gamepad_events(
-    mut gamepad_connection_events: EventReader<GamepadConnectionEvent>,
-    mut gamepad_axis_events: EventReader<GamepadAxisChangedEvent>,
-    mut gamepad_button_events: EventReader<GamepadButtonChangedEvent>,
+    mut connection_events: EventReader<GamepadConnectionEvent>,
+    mut axis_changed_events: EventReader<GamepadAxisChangedEvent>,
+    // Handles the continuous measure of how far a button has been pressed down, as measured
+    // by `Axis<GamepadButton>`. Whenever that value changes, this event is emitted.
+    mut button_changed_events: EventReader<GamepadButtonChangedEvent>,
+    // Handles the boolean measure of whether a button is considered pressed or unpressed, as
+    // defined by the thresholds in `GamepadSettings::button_settings` and measured by
+    // `Input<GamepadButton>`. When the threshold is crossed and the button state changes,
+    // this event is emmitted.
+    mut button_input_events: EventReader<GamepadButtonInput>,
 ) {
-    for connection_event in gamepad_connection_events.iter() {
+    for connection_event in connection_events.iter() {
         info!("{:?}", connection_event);
     }
-    for axis_event in gamepad_axis_events.iter() {
+    for axis_changed_event in axis_changed_events.iter() {
         info!(
             "{:?} of {:?} is changed to {}",
-            axis_event.axis_type, axis_event.gamepad, axis_event.value
+            axis_changed_event.axis_type, axis_changed_event.gamepad, axis_changed_event.value
         );
     }
-    for button_event in gamepad_button_events.iter() {
+    for button_changed_event in button_changed_events.iter() {
         info!(
             "{:?} of {:?} is changed to {}",
-            button_event.button_type, button_event.gamepad, button_event.value
+            button_changed_event.button_type,
+            button_changed_event.gamepad,
+            button_changed_event.value
         );
     }
+    for button_input_event in button_input_events.iter() {
+        info!("{:?}", button_input_event);
+    }
 }
 
 // If you require in-frame relative event ordering, you can also read the `Gamepad` event