feat: optimize input system, avoid heap allocations, disable as many events as possible

src/game.rs

@@ -31,6 +31,7 @@ use bevy_ecs::schedule::common_conditions::resource_changed;
 use bevy_ecs::schedule::{Condition, IntoScheduleConfigs, Schedule, SystemSet};
 use bevy_ecs::system::ResMut;
 use bevy_ecs::world::World;
+use sdl2::event::EventType;
 use sdl2::image::LoadTexture;
 use sdl2::render::{BlendMode, Canvas, ScaleMode, TextureCreator};
 use sdl2::rwops::RWops;
@@ -83,8 +84,63 @@ impl Game {
     pub fn new(
         mut canvas: Canvas<Window>,
         texture_creator: TextureCreator<WindowContext>,
-        event_pump: EventPump,
+        mut event_pump: EventPump,
     ) -> GameResult<Game> {
+        // Disable uninteresting events
+        for event_type in [
+            EventType::JoyAxisMotion,
+            EventType::JoyBallMotion,
+            EventType::JoyHatMotion,
+            EventType::JoyButtonDown,
+            EventType::JoyButtonUp,
+            EventType::JoyDeviceAdded,
+            EventType::JoyDeviceRemoved,
+            EventType::ControllerAxisMotion,
+            EventType::ControllerButtonDown,
+            EventType::ControllerButtonUp,
+            EventType::ControllerDeviceAdded,
+            EventType::ControllerDeviceRemoved,
+            EventType::ControllerDeviceRemapped,
+            EventType::ControllerTouchpadDown,
+            EventType::ControllerTouchpadMotion,
+            EventType::ControllerTouchpadUp,
+            EventType::FingerDown,
+            EventType::FingerUp,
+            EventType::FingerMotion,
+            EventType::DollarGesture,
+            EventType::DollarRecord,
+            EventType::MultiGesture,
+            EventType::ClipboardUpdate,
+            EventType::DropFile,
+            EventType::DropText,
+            EventType::DropBegin,
+            EventType::DropComplete,
+            EventType::AudioDeviceAdded,
+            EventType::AudioDeviceRemoved,
+            EventType::RenderTargetsReset,
+            EventType::RenderDeviceReset,
+            EventType::LocaleChanged,
+            EventType::TextInput,
+            EventType::TextEditing,
+            EventType::Display,
+            EventType::Window,
+            EventType::MouseWheel,
+            EventType::MouseMotion,
+            EventType::MouseButtonDown,
+            EventType::MouseButtonUp,
+            EventType::MouseButtonDown,
+            EventType::AppDidEnterBackground,
+            EventType::AppWillEnterForeground,
+            EventType::AppWillEnterBackground,
+            EventType::AppDidEnterForeground,
+            EventType::AppLowMemory,
+            EventType::AppTerminating,
+            EventType::User,
+            EventType::Last,
+        ] {
+            event_pump.disable_event(event_type);
+        }
+
         let ttf_context = Box::leak(Box::new(sdl2::ttf::init().map_err(|e| GameError::Sdl(e.to_string()))?));
         let mut backbuffer = texture_creator
             .create_texture_target(None, CANVAS_SIZE.x, CANVAS_SIZE.y)

src/systems/input.rs

@@ -7,6 +7,7 @@ use bevy_ecs::{
 };
 use glam::Vec2;
 use sdl2::{event::Event, keyboard::Keycode, EventPump};
+use smallvec::{smallvec, SmallVec};
 
 use crate::systems::components::DeltaTime;
 use crate::{
@@ -133,10 +134,22 @@ pub fn input_system(
 ) {
     let mut cursor_seen = false;
     // Collect all events for this frame.
-    let frame_events: Vec<Event> = pump.poll_iter().collect();
+    let frame_events: SmallVec<[Event; 3]> = pump.poll_iter().collect();
+
+    // Warn if the smallvec was heap allocated due to exceeding stack capacity
+    #[cfg(debug_assertions)]
+    {
+        if frame_events.len() > frame_events.capacity() {
+            tracing::warn!(
+                "More than {} events in a frame, consider adjusting stack capacity: {:?}",
+                frame_events.capacity(),
+                frame_events
+            );
+        }
+    }
 
     // Handle non-keyboard events inline and build a simplified keyboard event stream.
-    let mut simple_key_events = Vec::new();
+    let mut simple_key_events: SmallVec<[SimpleKeyEvent; 3]> = smallvec![];
     for event in &frame_events {
         match *event {
             Event::Quit { .. } => {
@@ -149,21 +162,25 @@ pub fn input_system(
                 };
                 cursor_seen = true;
             }
-            Event::KeyDown {
+            Event::KeyDown { keycode, repeat, .. } => {
-                keycode: Some(key),
+                if let Some(key) = keycode {
-                repeat: false,
+                    if repeat {
-                ..
+                        continue;
-            } => {
+                    }
-                simple_key_events.push(SimpleKeyEvent::KeyDown(key));
+                    simple_key_events.push(SimpleKeyEvent::KeyDown(key));
+                }
             }
-            Event::KeyUp {
+            Event::KeyUp { keycode, repeat, .. } => {
-                keycode: Some(key),
+                if let Some(key) = keycode {
-                repeat: false,
+                    if repeat {
-                ..
+                        continue;
-            } => {
+                    }
-                simple_key_events.push(SimpleKeyEvent::KeyUp(key));
+                    simple_key_events.push(SimpleKeyEvent::KeyUp(key));
+                }
+            }
+            _ => {
+                tracing::warn!("Unhandled event, consider disabling: {:?}", event);
             }
-            _ => {}
         }
     }