fix(engine): prevent dropped cursor motion input on Windows

4 files changed, 207 insertions, 76 deletions

diff --git a/engine/Cargo.toml b/engine/Cargo.toml
index 6187bb4..260bb56 100644
--- a/engine/Cargo.toml
+++ b/engine/Cargo.toml
@@ -40,6 +40,12 @@ features = ["derive"]
 git = "https://github.com/HampusMat/slang-rs"
 branch = "prebuilt-and-artifacts"
 
+[dependencies.portable-atomic]
+version = "=1.13.1"
+default-features = false # The "fallback" feature should not be enabled
+features = ["require-cas"]
+
+
 [build-dependencies]
 cfg_aliases = "0.2.1"
 build-rs = "0.3.4"
diff --git a/engine/src/data_types/vector.rs b/engine/src/data_types/vector.rs
index 933ca51..77173d6 100644
--- a/engine/src/data_types/vector.rs
+++ b/engine/src/data_types/vector.rs
@@ -113,6 +113,14 @@ impl<Value> From<[Value; 2]> for Vec2<Value>
     }
 }
 
+impl<Value> From<(Value, Value)> for Vec2<Value>
+{
+    fn from((x, y): (Value, Value)) -> Self
+    {
+        Self { x, y }
+    }
+}
+
 impl<Value> From<Vec2<Value>> for [Value; 2]
 {
     fn from(vec: Vec2<Value>) -> Self
diff --git a/engine/src/util.rs b/engine/src/util.rs
index 439fe9a..454a776 100644
--- a/engine/src/util.rs
+++ b/engine/src/util.rs
@@ -1,3 +1,9 @@
+use std::fmt::Debug;
+use std::mem::transmute;
+use std::sync::atomic::Ordering;
+
+use portable_atomic::AtomicU128;
+
 use crate::ecs::util::VecExt;
 
 #[derive(Debug)]
@@ -94,6 +100,96 @@ impl<T> OptionExt<T> for Option<T>
     }
 }
 
+pub struct AtomicTwoF64
+{
+    inner: AtomicU128,
+}
+
+impl AtomicTwoF64
+{
+    pub const fn new((first, second): (f64, f64)) -> Self
+    {
+        let mut bytes = [0u8; size_of::<u128>()];
+
+        bytes.copy_from_slice([first.to_ne_bytes(), second.to_ne_bytes()].as_flattened());
+
+        Self {
+            inner: AtomicU128::new(u128::from_ne_bytes(bytes)),
+        }
+    }
+
+    pub fn load(&self, order: Ordering) -> (f64, f64)
+    {
+        u128_to_two_f64(self.inner.load(order))
+    }
+
+    pub fn store(&self, values: (f64, f64), order: Ordering)
+    {
+        self.inner.store(two_f64_to_u128(values), order);
+    }
+
+    pub fn swap(&self, values: (f64, f64), order: Ordering) -> (f64, f64)
+    {
+        u128_to_two_f64(self.inner.swap(two_f64_to_u128(values), order))
+    }
+
+    pub fn compare_exchange(
+        &self,
+        current: (f64, f64),
+        new: (f64, f64),
+        success_order: Ordering,
+        failure_order: Ordering,
+    ) -> Result<(f64, f64), (f64, f64)>
+    {
+        self.inner
+            .compare_exchange(
+                two_f64_to_u128(current),
+                two_f64_to_u128(new),
+                success_order,
+                failure_order,
+            )
+            .map(|stored| u128_to_two_f64(stored))
+            .map_err(|stored| u128_to_two_f64(stored))
+    }
+}
+
+impl Debug for AtomicTwoF64
+{
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
+    {
+        let (first, second) = self.load(Ordering::Relaxed);
+
+        formatter
+            .debug_tuple("AtomicTwoF64")
+            .field(&first)
+            .field(&second)
+            .finish()
+    }
+}
+
+fn two_f64_to_u128((first, second): (f64, f64)) -> u128
+{
+    let mut bytes = [0u8; size_of::<u128>()];
+
+    bytes.copy_from_slice([first.to_ne_bytes(), second.to_ne_bytes()].as_flattened());
+
+    u128::from_ne_bytes(bytes)
+}
+
+fn u128_to_two_f64(src: u128) -> (f64, f64)
+{
+    let [first_bytes, second_bytes] = unsafe {
+        transmute::<[u8; size_of::<u128>()], [[u8; size_of::<f64>()]; 2]>(
+            src.to_ne_bytes(),
+        )
+    };
+
+    (
+        f64::from_ne_bytes(first_bytes),
+        f64::from_ne_bytes(second_bytes),
+    )
+}
+
 macro_rules! try_option {
     ($expr: expr) => {
         match $expr {
diff --git a/engine/src/windowing.rs b/engine/src/windowing.rs
index ea5a692..096a23f 100644
--- a/engine/src/windowing.rs
+++ b/engine/src/windowing.rs
@@ -1,3 +1,4 @@
+use std::hint::cold_path;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Weak};
 use std::thread::{Builder as ThreadBuilder, JoinHandle as ThreadJoinHandle};
@@ -33,8 +34,7 @@ use crate::ecs::sole::Single;
 use crate::ecs::system::observer::Observe;
 use crate::ecs::uid::Uid;
 use crate::ecs::{declare_entity, Query, Sole};
-use crate::util::MapVec;
-use crate::vector::Vec2;
+use crate::util::{AtomicTwoF64, MapVec};
 use crate::windowing::keyboard::{Key, KeyState, Keyboard, UnknownKeyCodeError};
 use crate::windowing::mouse::{
     Button as MouseButton,
@@ -130,7 +130,18 @@ fn update_stuff(
 {
     keyboard.make_key_states_previous();
     mouse_buttons.make_states_previous();
-    mouse.curr_tick_position_delta = Vec2::default();
+
+    mouse.curr_tick_position_delta = context
+        .shared_state
+        .relative_mouse_pos_delta
+        .swap((0.0, 0.0), Ordering::Relaxed)
+        .into();
+
+    mouse.position = context
+        .shared_state
+        .absolute_mouse_pos
+        .load(Ordering::Relaxed)
+        .into();
 
     let Context {
         ref message_from_app_receiver,
@@ -235,12 +246,6 @@ fn update_stuff(
             MessageFromApp::KeyboardKeyStateChanged(key, key_state) => {
                 keyboard.set_key_state(key, key_state);
             }
-            MessageFromApp::MouseMovedTo { position } => {
-                mouse.position = position;
-            }
-            MessageFromApp::MouseMoved { position_delta } => {
-                mouse.curr_tick_position_delta += position_delta;
-            }
             MessageFromApp::MouseButtonStateChanged(mouse_button, mouse_button_state) => {
                 mouse_buttons.set(mouse_button, mouse_button_state);
             }
@@ -300,9 +305,9 @@ fn handle_window_removed(
 pub struct Context
 {
     _thread: ThreadJoinHandle<()>,
-    is_dropped: Arc<AtomicBool>,
     message_from_app_receiver: ChannelReceiver<MessageFromApp>,
     message_to_app_sender: ChannelSender<MessageToApp>,
+    shared_state: Arc<SharedState>,
     display_handle: Option<OwnedDisplayHandle>,
     windows: MapVec<WindowId, (Arc<winit::window::Window>, Uid)>,
 }
@@ -362,10 +367,6 @@ impl Default for Context
 {
     fn default() -> Self
     {
-        let is_dropped = Arc::new(AtomicBool::new(false));
-
-        let is_dropped_b = is_dropped.clone();
-
         let (message_from_app_sender, message_from_app_receiver) =
             bounded_channel::<MessageFromApp>(MESSAGE_FROM_APP_CHANNEL_CAP);
 
@@ -374,6 +375,9 @@ impl Default for Context
         let (message_to_app_sender, message_to_app_receiver) =
             bounded_channel::<MessageToApp>(MESSAGE_TO_APP_CHANNEL_CAP);
 
+        let shared_state = Arc::new(SharedState::default());
+        let shared_state_b = shared_state.clone();
+
         Self {
             _thread: ThreadBuilder::new()
                 .name("windowing".to_string())
@@ -382,9 +386,8 @@ impl Default for Context
                         message_from_app_sender,
                         message_from_app_receiver: message_from_app_receiver_b,
                         message_to_app_receiver,
-                        is_dropped: is_dropped_b,
+                        shared_state: shared_state_b,
                         windows: MapVec::default(),
-                        focused_window_id: None,
                     };
 
                     let event_loop = match create_event_loop() {
@@ -402,9 +405,9 @@ impl Default for Context
                     }
                 })
                 .expect("Failed to create windowing thread"),
-            is_dropped,
             message_from_app_receiver,
             message_to_app_sender,
+            shared_state,
             display_handle: None,
             windows: MapVec::default(),
         }
@@ -415,7 +418,7 @@ impl Drop for Context
 {
     fn drop(&mut self)
     {
-        self.is_dropped.store(true, Ordering::Relaxed);
+        self.shared_state.is_dropped.store(true, Ordering::Relaxed);
     }
 }
 
@@ -450,14 +453,6 @@ enum MessageFromApp
     WindowCloseRequested(WindowId),
     WindowScaleFactorChanged(WindowId, f64),
     KeyboardKeyStateChanged(Key, KeyState),
-    MouseMovedTo
-    {
-        position: Vec2<f64>,
-    },
-    MouseMoved
-    {
-        position_delta: Vec2<f64>,
-    },
     MouseButtonStateChanged(MouseButton, MouseButtonState),
 }
 
@@ -469,14 +464,33 @@ enum MessageToApp
 }
 
 #[derive(Debug)]
+struct SharedState
+{
+    relative_mouse_pos_delta: AtomicTwoF64,
+    absolute_mouse_pos: AtomicTwoF64,
+    is_dropped: AtomicBool,
+}
+
+impl Default for SharedState
+{
+    fn default() -> Self
+    {
+        Self {
+            relative_mouse_pos_delta: AtomicTwoF64::new((0.0, 0.0)),
+            absolute_mouse_pos: AtomicTwoF64::new((0.0, 0.0)),
+            is_dropped: AtomicBool::new(false),
+        }
+    }
+}
+
+#[derive(Debug)]
 struct App
 {
     message_from_app_sender: ChannelSender<MessageFromApp>,
     message_from_app_receiver: ChannelReceiver<MessageFromApp>,
     message_to_app_receiver: ChannelReceiver<MessageToApp>,
-    is_dropped: Arc<AtomicBool>,
+    shared_state: Arc<SharedState>,
     windows: MapVec<WindowId, (Weak<WinitWindow>, WindowSettings)>,
-    focused_window_id: Option<WindowId>,
 }
 
 impl App
@@ -567,7 +581,7 @@ impl ApplicationHandler for App
                 ));
             }
             StartCause::Poll => {
-                if self.is_dropped.load(Ordering::Relaxed) {
+                if self.shared_state.is_dropped.load(Ordering::Relaxed) {
                     event_loop.exit();
                     return;
                 }
@@ -642,9 +656,38 @@ impl ApplicationHandler for App
                 ));
             }
             WindowEvent::CursorMoved { device_id: _, position } => {
-                self.send_message(MessageFromApp::MouseMovedTo {
-                    position: Vec2 { x: position.x, y: position.y },
-                });
+                self.shared_state
+                    .absolute_mouse_pos
+                    .store((position.x, position.y), Ordering::Relaxed);
+
+                let Some((window, window_settings)) =
+                    self.windows.get(&WindowId::from_inner(window_id))
+                else {
+                    cold_path();
+                    return;
+                };
+
+                if window_settings.cursor_grab_mode != CursorGrabMode::Locked {
+                    return;
+                }
+
+                let Some(window) = window.upgrade() else {
+                    cold_path();
+                    return;
+                };
+
+                let window_size = window.inner_size();
+
+                if let Err(err) = window.set_cursor_position(PhysicalPosition {
+                    x: window_size.width / 2,
+                    y: window_size.height / 2,
+                }) {
+                    cold_path();
+                    tracing::error!(
+                        window_id=?window_id,
+                        "Failed to lock cursor position: {err}"
+                    );
+                };
             }
             WindowEvent::MouseInput { device_id: _, state, button } => {
                 self.send_message(MessageFromApp::MouseButtonStateChanged(
@@ -652,13 +695,6 @@ impl ApplicationHandler for App
                     state.into(),
                 ));
             }
-            WindowEvent::Focused(is_focused) => {
-                if is_focused {
-                    self.focused_window_id = Some(WindowId::from_inner(window_id));
-                } else {
-                    self.focused_window_id = None;
-                }
-            }
             WindowEvent::ScaleFactorChanged { scale_factor, inner_size_writer: _ } => {
                 self.send_message(MessageFromApp::WindowScaleFactorChanged(
                     WindowId::from_inner(window_id),
@@ -679,44 +715,29 @@ impl ApplicationHandler for App
     {
         match device_event {
             DeviceEvent::MouseMotion { delta } => {
-                self.send_message(MessageFromApp::MouseMoved {
-                    position_delta: Vec2 { x: delta.0, y: delta.1 },
-                });
-
-                let Some(focused_window_id) = self.focused_window_id else {
-                    return;
-                };
-
-                let Some((focused_window, focused_window_settings)) =
-                    self.windows.get(&focused_window_id)
-                else {
-                    tracing::error!(
-                        window_id=?focused_window_id,
-                        "Focused window not found"
-                    );
-                    return;
-                };
-
-                if focused_window_settings.cursor_grab_mode != CursorGrabMode::Locked {
-                    return;
+                let curr_mouse_pos_delta = self
+                    .shared_state
+                    .relative_mouse_pos_delta
+                    .load(Ordering::Relaxed);
+
+                if self
+                    .shared_state
+                    .relative_mouse_pos_delta
+                    .compare_exchange(
+                        curr_mouse_pos_delta,
+                        (
+                            curr_mouse_pos_delta.0 + delta.0,
+                            curr_mouse_pos_delta.1 + delta.1,
+                        ),
+                        Ordering::Relaxed,
+                        Ordering::Relaxed,
+                    )
+                    .is_err()
+                {
+                    self.shared_state
+                        .relative_mouse_pos_delta
+                        .store(delta, Ordering::Relaxed);
                 }
-
-                // TODO: This might need to be optimized
-                let Some(focused_window) = focused_window.upgrade() else {
-                    return;
-                };
-
-                let focused_window_size = focused_window.inner_size();
-
-                if let Err(err) = focused_window.set_cursor_position(PhysicalPosition {
-                    x: focused_window_size.width / 2,
-                    y: focused_window_size.height / 2,
-                }) {
-                    tracing::error!(
-                        window_id=?focused_window_id,
-                        "Failed to set cursor position in focused window: {err}"
-                    );
-                };
             }
             _ => {}
         }