only update Touches resource when needed

crates/bevy_input/src/touch.rs

@@ -400,23 +400,15 @@ impl Touches {
             }
         };
     }
-
-    /// Clears the `just_pressed`, `just_released`, and `just_canceled` collections.
-    ///
-    /// This is not clearing the `pressed` collection, because it could incorrectly mark
-    /// a touch input as not pressed even though it is pressed. This could happen if the
-    /// touch input is not moving for a single frame and would therefore be marked as
-    /// not pressed, because this function is called on every single frame no matter
-    /// if there was an event or not.
-    fn update(&mut self) {
-        self.just_pressed.clear();
-        self.just_released.clear();
-        self.just_canceled.clear();
-    }
 }
 
 /// Updates the [`Touches`] resource with the latest [`TouchInput`] events.
 ///
+/// This is not clearing the `pressed` collection, because it could incorrectly mark a touch input
+/// as not pressed even though it is pressed. This could happen if the touch input is not moving
+/// for a single frame and would therefore be marked as not pressed, because this function is
+/// called on every single frame no matter if there was an event or not.
+///
 /// ## Differences
 ///
 /// The main difference between the [`TouchInput`] event and the [`Touches`] resource is that
@@ -425,7 +417,15 @@ pub fn touch_screen_input_system(
     mut touch_state: ResMut<Touches>,
     mut touch_input_events: EventReader<TouchInput>,
 ) {
-    touch_state.update();
+    if !touch_state.just_pressed.is_empty() {
+        touch_state.just_pressed.clear();
+    }
+    if !touch_state.just_released.is_empty() {
+        touch_state.just_released.clear();
+    }
+    if !touch_state.just_canceled.is_empty() {
+        touch_state.just_canceled.clear();
+    }
 
     for event in touch_input_events.read() {
         touch_state.process_touch_event(event);