add documentation on Input (bevyengine#1781)

related to bevyengine#1700 

This PR:
* documents all methods on `Input<T>`
* adds documentation on the struct about how to use it, and how to implement it for a new input type
* renames method `update` to a easier to understand `clear`
* adds two methods to check for state and clear it after, allowing easier use in the case of bevyengine#1700 

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

crates/bevy_input/src/gamepad.rs

@@ -209,7 +209,7 @@ pub fn gamepad_event_system(
     mut events: EventWriter<GamepadEvent>,
     settings: Res<GamepadSettings>,
 ) {
-    button_input.update();
+    button_input.clear();
     for event in raw_events.iter() {
         let (gamepad, event) = (event.0, &event.1);
         match event {

crates/bevy_input/src/input.rs

@@ -1,7 +1,33 @@
 use bevy_utils::HashSet;
 use std::hash::Hash;
 
-/// A "press-able" input of type `T`
+// unused import, but needed for intra doc link to work
+#[allow(unused_imports)]
+use bevy_ecs::schedule::State;
+
+/// A "press-able" input of type `T`.
+///
+/// This type can be used as a resource to keep the current state of an input, by reacting to
+/// events from the input. For a given input value:
+///
+/// * [`Input::pressed`] will return `true` between a press and a release event.
+/// * [`Input::just_pressed`] will return `true` for one frame after a press event.
+/// * [`Input::just_released`] will return `true` for one frame after a release event.
+///
+/// In case multiple systems are checking for [`Input::just_pressed`] or [`Input::just_released`]
+/// but only one should react, for example in the case of triggering
+/// [`State`] change, you should consider clearing the input state, either by:
+///
+/// * Using [`Input::just_pressed_and_clear`] or [`Input::just_released_and_clear`] instead.
+/// * Calling [`Input::clear`] or [`Input::reset`] immediately after the state change.
+///
+/// ## Notes when adding this resource for a new input type
+///
+/// When adding this resource for a new input type, you should:
+///
+/// * Call the [`Input::press`] method for each press event.
+/// * Call the [`Input::release`] method for each release event.
+/// * Call the [`Input::clear`] method at each frame start, before processing events.
 #[derive(Debug)]
 pub struct Input<T> {
     pressed: HashSet<T>,
@@ -23,6 +49,7 @@ impl<T> Input<T>
 where
     T: Copy + Eq + Hash,
 {
+    /// Register a press for input `input`.
     pub fn press(&mut self, input: T) {
         if !self.pressed(input) {
             self.just_pressed.insert(input);
@@ -31,42 +58,65 @@ where
         self.pressed.insert(input);
     }
 
+    /// Check if `input` has been pressed.
     pub fn pressed(&self, input: T) -> bool {
         self.pressed.contains(&input)
     }
 
+    /// Register a release for input `input`.
     pub fn release(&mut self, input: T) {
         self.pressed.remove(&input);
         self.just_released.insert(input);
     }
 
+    /// Check if `input` has been just pressed.
     pub fn just_pressed(&self, input: T) -> bool {
         self.just_pressed.contains(&input)
     }
 
+    /// Clear the "just pressed" state of `input`. Future calls to [`Input::just_pressed`] for the given
+    /// input will return false until a new press event occurs.
+    /// Returns true if `input` is currently "just pressed"
+    pub fn clear_just_pressed(&mut self, input: T) -> bool {
+        self.just_pressed.remove(&input)
+    }
+
+    /// Check if `input` has been just released.
     pub fn just_released(&self, input: T) -> bool {
         self.just_released.contains(&input)
     }
 
+    /// Clear the "just released" state of `input`. Future calls to [`Input::just_released`] for the given
+    /// input will return false until a new release event occurs.
+    /// Returns true if `input` is currently "just released"
+    pub fn clear_just_released(&mut self, input: T) -> bool {
+        self.just_released.remove(&input)
+    }
+
+    /// Reset all status for input `input`.
     pub fn reset(&mut self, input: T) {
         self.pressed.remove(&input);
         self.just_pressed.remove(&input);
         self.just_released.remove(&input);
     }
 
-    pub fn update(&mut self) {
+    /// Clear just pressed and just released information.
+    pub fn clear(&mut self) {
         self.just_pressed.clear();
         self.just_released.clear();
     }
 
+    /// List all inputs that are pressed.
     pub fn get_pressed(&self) -> impl ExactSizeIterator<Item = &T> {
         self.pressed.iter()
     }
 
+    /// List all inputs that are just pressed.
     pub fn get_just_pressed(&self) -> impl ExactSizeIterator<Item = &T> {
         self.just_pressed.iter()
     }
 
+    /// List all inputs that are just released.
     pub fn get_just_released(&self) -> impl ExactSizeIterator<Item = &T> {
         self.just_released.iter()
     }
@@ -100,8 +150,8 @@ mod test {
         assert!(input.pressed(DummyInput::Input1));
         assert!(input.pressed(DummyInput::Input2));
 
-        // Update the `Input` and check press state
-        input.update();
+        // Clear the `input`, removing just pressed and just released
+        input.clear();
 
         // Check if they're marked "just pressed"
         assert!(!input.just_pressed(DummyInput::Input1));
@@ -124,9 +174,8 @@ mod test {
         assert!(!input.pressed(DummyInput::Input1));
         assert!(!input.pressed(DummyInput::Input2));
 
-        // Update the `Input` and check for removal from `just_released`
-
-        input.update();
+        // Clear the `Input` and check for removal from `just_released`
+        input.clear();
 
         // Check that they're not incorrectly marked as just released
         assert!(!input.just_released(DummyInput::Input1));

crates/bevy_input/src/keyboard.rs

@@ -15,7 +15,7 @@ pub fn keyboard_input_system(
     mut keyboard_input: ResMut<Input<KeyCode>>,
     mut keyboard_input_events: EventReader<KeyboardInput>,
 ) {
-    keyboard_input.update();
+    keyboard_input.clear();
     for event in keyboard_input_events.iter() {
         if let KeyboardInput {
             key_code: Some(key_code),

crates/bevy_input/src/mouse.rs

@@ -47,7 +47,7 @@ pub fn mouse_button_input_system(
     mut mouse_button_input: ResMut<Input<MouseButton>>,
     mut mouse_button_input_events: EventReader<MouseButtonInput>,
 ) {
-    mouse_button_input.update();
+    mouse_button_input.clear();
     for event in mouse_button_input_events.iter() {
         match event.state {
             ElementState::Pressed => mouse_button_input.press(event.button),