Event Loop 2.0 API and Windows implementation (#638)

* Rename EventsLoop and associated types to EventLoop

* Rename WindowEvent::Refresh to WindowEvent::Redraw

* Remove second thread from win32 backend

* Update run_forever to hijack thread

* Replace windows Mutex with parking_lot Mutex

* Implement new ControlFlow and associated events

* Add StartCause::Init support, timer example

* Add ability to send custom user events

* Fully invert windows control flow so win32 calls into winit's callback

* Add request_redraw

* Rename platform to platform_impl

* Rename os to platform, add Ext trait postfixes

* Add platform::desktop module with EventLoopExt::run_return

* Re-organize into module structure

* Improve documentation

* Small changes to examples

* Improve docs for run and run_return

* Change instances of "events_loop" to "event_loop"

* Rename MonitorId to MonitorHandle

* Add CHANGELOG entry

* Improve WaitUntil timer precision

* When SendEvent is called during event closure, buffer events

* Fix resize lag when waiting in some situations

* Update send test and errors that broke some examples/APIs

* Improve clarity/fix typos in docs

* Fix unreachable panic after setting ControlFlow to Poll during some RedrawRequested events.

* Fix crash when running in release mode

* Remove crossbeam dependency and make drop events work again

* Remove serde implementations from ControlFlow

* Fix 1.24.1 build

* Fix freeze when setting decorations

* Replace &EventLoop in callback with &EventLoopWindowTarget

* Document and implement Debug for EventLoopWindowTarget

* Fix some deadlocks that could occur when changing window state

* Fix thread executor not executing closure when called from non-loop thread

* Fix buffered events not getting dispatched

* Fix crash with runner refcell not getting dropped

* Address review feedback

* Fix CHANGELOG typo

* Catch panics in user callback

src/platform_impl/macos/event_loop.rs

@@ -0,0 +1,742 @@
+use {ControlFlow, EventLoopClosed};
+use cocoa::{self, appkit, foundation};
+use cocoa::appkit::{NSApplication, NSEvent, NSEventMask, NSEventModifierFlags, NSEventPhase, NSView, NSWindow};
+use events::{self, ElementState, Event, TouchPhase, WindowEvent, DeviceEvent, ModifiersState, KeyboardInput};
+use std::collections::VecDeque;
+use std::sync::{Arc, Mutex, Weak};
+use super::window::Window2;
+use std;
+use std::os::raw::*;
+use super::DeviceId;
+
+pub struct EventLoop {
+    modifiers: Modifiers,
+    pub shared: Arc<Shared>,
+}
+
+// State shared between the `EventLoop` and its registered windows.
+pub struct Shared {
+    pub windows: Mutex<Vec<Weak<Window2>>>,
+    pub pending_events: Mutex<VecDeque<Event>>,
+    // The user event callback given via either of the `poll_events` or `run_forever` methods.
+    //
+    // We store the user's callback here so that it may be accessed by each of the window delegate
+    // callbacks (e.g. resize, close, etc) for the duration of a call to either of the
+    // `poll_events` or `run_forever` methods.
+    //
+    // This is *only* `Some` for the duration of a call to either of these methods and will be
+    // `None` otherwise.
+    user_callback: UserCallback,
+}
+
+#[derive(Clone)]
+pub struct Proxy {}
+
+struct Modifiers {
+    shift_pressed: bool,
+    ctrl_pressed: bool,
+    win_pressed: bool,
+    alt_pressed: bool,
+}
+
+// Wrapping the user callback in a type allows us to:
+//
+// - ensure the callback pointer is never accidentally cloned
+// - ensure that only the `EventLoop` can `store` and `drop` the callback pointer
+// - Share access to the user callback with the NSWindow callbacks.
+pub struct UserCallback {
+    mutex: Mutex<Option<*mut FnMut(Event)>>,
+}
+
+
+impl Shared {
+
+    pub fn new() -> Self {
+        Shared {
+            windows: Mutex::new(Vec::new()),
+            pending_events: Mutex::new(VecDeque::new()),
+            user_callback: UserCallback { mutex: Mutex::new(None) },
+        }
+    }
+
+    fn call_user_callback_with_pending_events(&self) {
+        loop {
+            let event = match self.pending_events.lock().unwrap().pop_front() {
+                Some(event) => event,
+                None => return,
+            };
+            unsafe {
+                self.user_callback.call_with_event(event);
+            }
+        }
+    }
+
+    // Calls the user callback if one exists.
+    //
+    // Otherwise, stores the event in the `pending_events` queue.
+    //
+    // This is necessary for the case when `WindowDelegate` callbacks are triggered during a call
+    // to the user's callback.
+    pub fn call_user_callback_with_event_or_store_in_pending(&self, event: Event) {
+        if self.user_callback.mutex.lock().unwrap().is_some() {
+            unsafe {
+                self.user_callback.call_with_event(event);
+            }
+        } else {
+            self.pending_events.lock().unwrap().push_back(event);
+        }
+    }
+
+    // Removes the window with the given `Id` from the `windows` list.
+    //
+    // This is called in response to `windowWillClose`.
+    pub fn find_and_remove_window(&self, id: super::window::Id) {
+        if let Ok(mut windows) = self.windows.lock() {
+            windows.retain(|w| match w.upgrade() {
+                Some(w) => w.id() != id,
+                None => false,
+            });
+        }
+    }
+
+}
+
+
+impl Modifiers {
+    pub fn new() -> Self {
+        Modifiers {
+            shift_pressed: false,
+            ctrl_pressed: false,
+            win_pressed: false,
+            alt_pressed: false,
+        }
+    }
+}
+
+
+impl UserCallback {
+
+    // Here we store user's `callback` behind the mutex so that they may be safely shared between
+    // each of the window delegates.
+    //
+    // In order to make sure that the pointer is always valid, we must manually guarantee that it
+    // is dropped before the callback itself is dropped. Thus, this should *only* be called at the
+    // beginning of a call to `poll_events` and `run_forever`, both of which *must* drop the
+    // callback at the end of their scope using the `drop` method.
+    fn store<F>(&self, callback: &mut F)
+        where F: FnMut(Event)
+    {
+        let trait_object = callback as &mut FnMut(Event);
+        let trait_object_ptr = trait_object as *const FnMut(Event) as *mut FnMut(Event);
+        *self.mutex.lock().unwrap() = Some(trait_object_ptr);
+    }
+
+    // Emits the given event via the user-given callback.
+    //
+    // This is unsafe as it requires dereferencing the pointer to the user-given callback. We
+    // guarantee this is safe by ensuring the `UserCallback` never lives longer than the user-given
+    // callback.
+    //
+    // Note that the callback may not always be `Some`. This is because some `NSWindowDelegate`
+    // callbacks can be triggered by means other than `NSApp().sendEvent`. For example, if a window
+    // is destroyed or created during a call to the user's callback, the `WindowDelegate` methods
+    // may be called with `windowShouldClose` or `windowDidResignKey`.
+    unsafe fn call_with_event(&self, event: Event) {
+        let callback = match self.mutex.lock().unwrap().take() {
+            Some(callback) => callback,
+            None => return,
+        };
+        (*callback)(event);
+        *self.mutex.lock().unwrap() = Some(callback);
+    }
+
+    // Used to drop the user callback pointer at the end of the `poll_events` and `run_forever`
+    // methods. This is done to enforce our guarantee that the top callback will never live longer
+    // than the call to either `poll_events` or `run_forever` to which it was given.
+    fn drop(&self) {
+        self.mutex.lock().unwrap().take();
+    }
+
+}
+
+
+impl EventLoop {
+
+    pub fn new() -> Self {
+        // Mark this thread as the main thread of the Cocoa event system.
+        //
+        // This must be done before any worker threads get a chance to call it
+        // (e.g., via `EventLoopProxy::wakeup()`), causing a wrong thread to be
+        // marked as the main thread.
+        unsafe { appkit::NSApp(); }
+
+        EventLoop {
+            shared: Arc::new(Shared::new()),
+            modifiers: Modifiers::new(),
+        }
+    }
+
+    pub fn poll_events<F>(&mut self, mut callback: F)
+        where F: FnMut(Event),
+    {
+        unsafe {
+            if !msg_send![class!(NSThread), isMainThread] {
+                panic!("Events can only be polled from the main thread on macOS");
+            }
+        }
+
+        self.shared.user_callback.store(&mut callback);
+
+        // Loop as long as we have pending events to return.
+        loop {
+            unsafe {
+                // First, yield all pending events.
+                self.shared.call_user_callback_with_pending_events();
+
+                let pool = foundation::NSAutoreleasePool::new(cocoa::base::nil);
+
+                // Poll for the next event, returning `nil` if there are none.
+                let ns_event = appkit::NSApp().nextEventMatchingMask_untilDate_inMode_dequeue_(
+                    NSEventMask::NSAnyEventMask.bits() | NSEventMask::NSEventMaskPressure.bits(),
+                    foundation::NSDate::distantPast(cocoa::base::nil),
+                    foundation::NSDefaultRunLoopMode,
+                    cocoa::base::YES);
+
+                let event = self.ns_event_to_event(ns_event);
+
+                let _: () = msg_send![pool, release];
+
+                match event {
+                    // Call the user's callback.
+                    Some(event) => self.shared.user_callback.call_with_event(event),
+                    None => break,
+                }
+            }
+        }
+
+        self.shared.user_callback.drop();
+    }
+
+    pub fn run_forever<F>(&mut self, mut callback: F)
+        where F: FnMut(Event) -> ControlFlow
+    {
+        unsafe {
+            if !msg_send![class!(NSThread), isMainThread] {
+                panic!("Events can only be polled from the main thread on macOS");
+            }
+        }
+
+        // Track whether or not control flow has changed.
+        let control_flow = std::cell::Cell::new(ControlFlow::Continue);
+
+        let mut callback = |event| {
+            if let ControlFlow::Break = callback(event) {
+                control_flow.set(ControlFlow::Break);
+            }
+        };
+
+        self.shared.user_callback.store(&mut callback);
+
+        loop {
+            unsafe {
+                // First, yield all pending events.
+                self.shared.call_user_callback_with_pending_events();
+                if let ControlFlow::Break = control_flow.get() {
+                    break;
+                }
+
+                let pool = foundation::NSAutoreleasePool::new(cocoa::base::nil);
+
+                // Wait for the next event. Note that this function blocks during resize.
+                let ns_event = appkit::NSApp().nextEventMatchingMask_untilDate_inMode_dequeue_(
+                    NSEventMask::NSAnyEventMask.bits() | NSEventMask::NSEventMaskPressure.bits(),
+                    foundation::NSDate::distantFuture(cocoa::base::nil),
+                    foundation::NSDefaultRunLoopMode,
+                    cocoa::base::YES);
+
+                let maybe_event = self.ns_event_to_event(ns_event);
+
+                // Release the pool before calling the top callback in case the user calls either
+                // `run_forever` or `poll_events` within the callback.
+                let _: () = msg_send![pool, release];
+
+                if let Some(event) = maybe_event {
+                    self.shared.user_callback.call_with_event(event);
+                    if let ControlFlow::Break = control_flow.get() {
+                        break;
+                    }
+                }
+            }
+        }
+
+        self.shared.user_callback.drop();
+    }
+
+    // Convert some given `NSEvent` into a winit `Event`.
+    unsafe fn ns_event_to_event(&mut self, ns_event: cocoa::base::id) -> Option<Event> {
+        if ns_event == cocoa::base::nil {
+            return None;
+        }
+
+        // FIXME: Despite not being documented anywhere, an `NSEvent` is produced when a user opens
+        // Spotlight while the NSApplication is in focus. This `NSEvent` produces a `NSEventType`
+        // with value `21`. This causes a SEGFAULT as soon as we try to match on the `NSEventType`
+        // enum as there is no variant associated with the value. Thus, we return early if this
+        // sneaky event occurs. If someone does find some documentation on this, please fix this by
+        // adding an appropriate variant to the `NSEventType` enum in the cocoa-rs crate.
+        if ns_event.eventType() as u64 == 21 {
+            return None;
+        }
+
+        let event_type = ns_event.eventType();
+        let ns_window = ns_event.window();
+        let window_id = super::window::get_window_id(ns_window);
+
+        // FIXME: Document this. Why do we do this? Seems like it passes on events to window/app.
+        // If we don't do this, window does not become main for some reason.
+        appkit::NSApp().sendEvent_(ns_event);
+
+        let windows = self.shared.windows.lock().unwrap();
+        let maybe_window = windows.iter()
+            .filter_map(Weak::upgrade)
+            .find(|window| window_id == window.id());
+
+        let into_event = |window_event| Event::WindowEvent {
+            window_id: ::WindowId(window_id),
+            event: window_event,
+        };
+
+        // Returns `Some` window if one of our windows is the key window.
+        let maybe_key_window = || windows.iter()
+            .filter_map(Weak::upgrade)
+            .find(|window| {
+                let is_key_window: cocoa::base::BOOL = msg_send![*window.window, isKeyWindow];
+                is_key_window == cocoa::base::YES
+            });
+
+        match event_type {
+            // https://github.com/glfw/glfw/blob/50eccd298a2bbc272b4977bd162d3e4b55f15394/src/cocoa_window.m#L881
+            appkit::NSKeyUp  => {
+                if let Some(key_window) = maybe_key_window() {
+                    if event_mods(ns_event).logo {
+                        let _: () = msg_send![*key_window.window, sendEvent:ns_event];
+                    }
+                }
+                None
+            },
+            // similar to above, but for `<Cmd-.>`, the keyDown is suppressed instead of the
+            // KeyUp, and the above trick does not appear to work.
+            appkit::NSKeyDown => {
+                let modifiers = event_mods(ns_event);
+                let keycode = NSEvent::keyCode(ns_event);
+                if modifiers.logo && keycode == 47 {
+                    modifier_event(ns_event, NSEventModifierFlags::NSCommandKeyMask, false)
+                        .map(into_event)
+                } else {
+                    None
+                }
+            },
+            appkit::NSFlagsChanged => {
+                let mut events = std::collections::VecDeque::new();
+
+                if let Some(window_event) = modifier_event(
+                    ns_event,
+                    NSEventModifierFlags::NSShiftKeyMask,
+                    self.modifiers.shift_pressed,
+                ) {
+                    self.modifiers.shift_pressed = !self.modifiers.shift_pressed;
+                    events.push_back(into_event(window_event));
+                }
+
+                if let Some(window_event) = modifier_event(
+                    ns_event,
+                    NSEventModifierFlags::NSControlKeyMask,
+                    self.modifiers.ctrl_pressed,
+                ) {
+                    self.modifiers.ctrl_pressed = !self.modifiers.ctrl_pressed;
+                    events.push_back(into_event(window_event));
+                }
+
+                if let Some(window_event) = modifier_event(
+                    ns_event,
+                    NSEventModifierFlags::NSCommandKeyMask,
+                    self.modifiers.win_pressed,
+                ) {
+                    self.modifiers.win_pressed = !self.modifiers.win_pressed;
+                    events.push_back(into_event(window_event));
+                }
+
+                if let Some(window_event) = modifier_event(
+                    ns_event,
+                    NSEventModifierFlags::NSAlternateKeyMask,
+                    self.modifiers.alt_pressed,
+                ) {
+                    self.modifiers.alt_pressed = !self.modifiers.alt_pressed;
+                    events.push_back(into_event(window_event));
+                }
+
+                let event = events.pop_front();
+                self.shared.pending_events
+                    .lock()
+                    .unwrap()
+                    .extend(events.into_iter());
+                event
+            },
+
+            appkit::NSMouseEntered => {
+                let window = match maybe_window.or_else(maybe_key_window) {
+                    Some(window) => window,
+                    None => return None,
+                };
+
+                let window_point = ns_event.locationInWindow();
+                let view_point = if ns_window == cocoa::base::nil {
+                    let ns_size = foundation::NSSize::new(0.0, 0.0);
+                    let ns_rect = foundation::NSRect::new(window_point, ns_size);
+                    let window_rect = window.window.convertRectFromScreen_(ns_rect);
+                    window.view.convertPoint_fromView_(window_rect.origin, cocoa::base::nil)
+                } else {
+                    window.view.convertPoint_fromView_(window_point, cocoa::base::nil)
+                };
+
+                let view_rect = NSView::frame(*window.view);
+                let x = view_point.x as f64;
+                let y = (view_rect.size.height - view_point.y) as f64;
+                let window_event = WindowEvent::CursorMoved {
+                    device_id: DEVICE_ID,
+                    position: (x, y).into(),
+                    modifiers: event_mods(ns_event),
+                };
+                let event = Event::WindowEvent { window_id: ::WindowId(window.id()), event: window_event };
+                self.shared.pending_events.lock().unwrap().push_back(event);
+                Some(into_event(WindowEvent::CursorEntered { device_id: DEVICE_ID }))
+            },
+            appkit::NSMouseExited => { Some(into_event(WindowEvent::CursorLeft { device_id: DEVICE_ID })) },
+
+            appkit::NSMouseMoved |
+            appkit::NSLeftMouseDragged |
+            appkit::NSOtherMouseDragged |
+            appkit::NSRightMouseDragged => {
+                // If the mouse movement was on one of our windows, use it.
+                // Otherwise, if one of our windows is the key window (receiving input), use it.
+                // Otherwise, return `None`.
+                match maybe_window.or_else(maybe_key_window) {
+                    Some(_window) => (),
+                    None => return None,
+                }
+
+                let mut events = std::collections::VecDeque::with_capacity(3);
+
+                let delta_x = ns_event.deltaX() as f64;
+                if delta_x != 0.0 {
+                    let motion_event = DeviceEvent::Motion { axis: 0, value: delta_x };
+                    let event = Event::DeviceEvent { device_id: DEVICE_ID, event: motion_event };
+                    events.push_back(event);
+                }
+
+                let delta_y = ns_event.deltaY() as f64;
+                if delta_y != 0.0 {
+                    let motion_event = DeviceEvent::Motion { axis: 1, value: delta_y };
+                    let event = Event::DeviceEvent { device_id: DEVICE_ID, event: motion_event };
+                    events.push_back(event);
+                }
+
+                if delta_x != 0.0 || delta_y != 0.0 {
+                    let motion_event = DeviceEvent::MouseMotion { delta: (delta_x, delta_y) };
+                    let event = Event::DeviceEvent { device_id: DEVICE_ID, event: motion_event };
+                    events.push_back(event);
+                }
+
+                let event = events.pop_front();
+                self.shared.pending_events.lock().unwrap().extend(events.into_iter());
+                event
+            },
+
+            appkit::NSScrollWheel => {
+                // If none of the windows received the scroll, return `None`.
+                if maybe_window.is_none() {
+                    return None;
+                }
+
+                use events::MouseScrollDelta::{LineDelta, PixelDelta};
+                let delta = if ns_event.hasPreciseScrollingDeltas() == cocoa::base::YES {
+                    PixelDelta((
+                        ns_event.scrollingDeltaX() as f64,
+                        ns_event.scrollingDeltaY() as f64,
+                    ).into())
+                } else {
+                    // TODO: This is probably wrong
+                    LineDelta(
+                        ns_event.scrollingDeltaX() as f32,
+                        ns_event.scrollingDeltaY() as f32,
+                    )
+                };
+                let phase = match ns_event.phase() {
+                    NSEventPhase::NSEventPhaseMayBegin | NSEventPhase::NSEventPhaseBegan => TouchPhase::Started,
+                    NSEventPhase::NSEventPhaseEnded => TouchPhase::Ended,
+                    _ => TouchPhase::Moved,
+                };
+                self.shared.pending_events.lock().unwrap().push_back(Event::DeviceEvent {
+                    device_id: DEVICE_ID,
+                    event: DeviceEvent::MouseWheel {
+                        delta: if ns_event.hasPreciseScrollingDeltas() == cocoa::base::YES {
+                            PixelDelta((
+                                ns_event.scrollingDeltaX() as f64,
+                                ns_event.scrollingDeltaY() as f64,
+                            ).into())
+                        } else {
+                            LineDelta(
+                                ns_event.scrollingDeltaX() as f32,
+                                ns_event.scrollingDeltaY() as f32,
+                            )
+                        },
+                    }
+                });
+                let window_event = WindowEvent::MouseWheel { device_id: DEVICE_ID, delta: delta, phase: phase, modifiers: event_mods(ns_event) };
+                Some(into_event(window_event))
+            },
+
+            appkit::NSEventTypePressure => {
+                let pressure = ns_event.pressure();
+                let stage = ns_event.stage();
+                let window_event = WindowEvent::TouchpadPressure { device_id: DEVICE_ID, pressure: pressure, stage: stage };
+                Some(into_event(window_event))
+            },
+
+            appkit::NSApplicationDefined => match ns_event.subtype() {
+                appkit::NSEventSubtype::NSApplicationActivatedEventType => {
+                    Some(Event::Awakened)
+                },
+                _ => None,
+            },
+
+            _  => None,
+        }
+    }
+
+    pub fn create_proxy(&self) -> Proxy {
+        Proxy {}
+    }
+
+}
+
+impl Proxy {
+    pub fn wakeup(&self) -> Result<(), EventLoopClosed> {
+        // Awaken the event loop by triggering `NSApplicationActivatedEventType`.
+        unsafe {
+            let pool = foundation::NSAutoreleasePool::new(cocoa::base::nil);
+            let event =
+                NSEvent::otherEventWithType_location_modifierFlags_timestamp_windowNumber_context_subtype_data1_data2_(
+                    cocoa::base::nil,
+                    appkit::NSApplicationDefined,
+                    foundation::NSPoint::new(0.0, 0.0),
+                    appkit::NSEventModifierFlags::empty(),
+                    0.0,
+                    0,
+                    cocoa::base::nil,
+                    appkit::NSEventSubtype::NSApplicationActivatedEventType,
+                    0,
+                    0);
+            appkit::NSApp().postEvent_atStart_(event, cocoa::base::NO);
+            foundation::NSAutoreleasePool::drain(pool);
+        }
+        Ok(())
+    }
+}
+
+pub fn to_virtual_key_code(code: c_ushort) -> Option<events::VirtualKeyCode> {
+    Some(match code {
+        0x00 => events::VirtualKeyCode::A,
+        0x01 => events::VirtualKeyCode::S,
+        0x02 => events::VirtualKeyCode::D,
+        0x03 => events::VirtualKeyCode::F,
+        0x04 => events::VirtualKeyCode::H,
+        0x05 => events::VirtualKeyCode::G,
+        0x06 => events::VirtualKeyCode::Z,
+        0x07 => events::VirtualKeyCode::X,
+        0x08 => events::VirtualKeyCode::C,
+        0x09 => events::VirtualKeyCode::V,
+        //0x0a => World 1,
+        0x0b => events::VirtualKeyCode::B,
+        0x0c => events::VirtualKeyCode::Q,
+        0x0d => events::VirtualKeyCode::W,
+        0x0e => events::VirtualKeyCode::E,
+        0x0f => events::VirtualKeyCode::R,
+        0x10 => events::VirtualKeyCode::Y,
+        0x11 => events::VirtualKeyCode::T,
+        0x12 => events::VirtualKeyCode::Key1,
+        0x13 => events::VirtualKeyCode::Key2,
+        0x14 => events::VirtualKeyCode::Key3,
+        0x15 => events::VirtualKeyCode::Key4,
+        0x16 => events::VirtualKeyCode::Key6,
+        0x17 => events::VirtualKeyCode::Key5,
+        0x18 => events::VirtualKeyCode::Equals,
+        0x19 => events::VirtualKeyCode::Key9,
+        0x1a => events::VirtualKeyCode::Key7,
+        0x1b => events::VirtualKeyCode::Minus,
+        0x1c => events::VirtualKeyCode::Key8,
+        0x1d => events::VirtualKeyCode::Key0,
+        0x1e => events::VirtualKeyCode::RBracket,
+        0x1f => events::VirtualKeyCode::O,
+        0x20 => events::VirtualKeyCode::U,
+        0x21 => events::VirtualKeyCode::LBracket,
+        0x22 => events::VirtualKeyCode::I,
+        0x23 => events::VirtualKeyCode::P,
+        0x24 => events::VirtualKeyCode::Return,
+        0x25 => events::VirtualKeyCode::L,
+        0x26 => events::VirtualKeyCode::J,
+        0x27 => events::VirtualKeyCode::Apostrophe,
+        0x28 => events::VirtualKeyCode::K,
+        0x29 => events::VirtualKeyCode::Semicolon,
+        0x2a => events::VirtualKeyCode::Backslash,
+        0x2b => events::VirtualKeyCode::Comma,
+        0x2c => events::VirtualKeyCode::Slash,
+        0x2d => events::VirtualKeyCode::N,
+        0x2e => events::VirtualKeyCode::M,
+        0x2f => events::VirtualKeyCode::Period,
+        0x30 => events::VirtualKeyCode::Tab,
+        0x31 => events::VirtualKeyCode::Space,
+        0x32 => events::VirtualKeyCode::Grave,
+        0x33 => events::VirtualKeyCode::Back,
+        //0x34 => unkown,
+        0x35 => events::VirtualKeyCode::Escape,
+        0x36 => events::VirtualKeyCode::LWin,
+        0x37 => events::VirtualKeyCode::RWin,
+        0x38 => events::VirtualKeyCode::LShift,
+        //0x39 => Caps lock,
+        0x3a => events::VirtualKeyCode::LAlt,
+        0x3b => events::VirtualKeyCode::LControl,
+        0x3c => events::VirtualKeyCode::RShift,
+        0x3d => events::VirtualKeyCode::RAlt,
+        0x3e => events::VirtualKeyCode::RControl,
+        //0x3f => Fn key,
+        0x40 => events::VirtualKeyCode::F17,
+        0x41 => events::VirtualKeyCode::Decimal,
+        //0x42 -> unkown,
+        0x43 => events::VirtualKeyCode::Multiply,
+        //0x44 => unkown,
+        0x45 => events::VirtualKeyCode::Add,
+        //0x46 => unkown,
+        0x47 => events::VirtualKeyCode::Numlock,
+        //0x48 => KeypadClear,
+        0x49 => events::VirtualKeyCode::VolumeUp,
+        0x4a => events::VirtualKeyCode::VolumeDown,
+        0x4b => events::VirtualKeyCode::Divide,
+        0x4c => events::VirtualKeyCode::NumpadEnter,
+        //0x4d => unkown,
+        0x4e => events::VirtualKeyCode::Subtract,
+        0x4f => events::VirtualKeyCode::F18,
+        0x50 => events::VirtualKeyCode::F19,
+        0x51 => events::VirtualKeyCode::NumpadEquals,
+        0x52 => events::VirtualKeyCode::Numpad0,
+        0x53 => events::VirtualKeyCode::Numpad1,
+        0x54 => events::VirtualKeyCode::Numpad2,
+        0x55 => events::VirtualKeyCode::Numpad3,
+        0x56 => events::VirtualKeyCode::Numpad4,
+        0x57 => events::VirtualKeyCode::Numpad5,
+        0x58 => events::VirtualKeyCode::Numpad6,
+        0x59 => events::VirtualKeyCode::Numpad7,
+        0x5a => events::VirtualKeyCode::F20,
+        0x5b => events::VirtualKeyCode::Numpad8,
+        0x5c => events::VirtualKeyCode::Numpad9,
+        0x5d => events::VirtualKeyCode::Yen,
+        //0x5e => JIS Ro,
+        //0x5f => unkown,
+        0x60 => events::VirtualKeyCode::F5,
+        0x61 => events::VirtualKeyCode::F6,
+        0x62 => events::VirtualKeyCode::F7,
+        0x63 => events::VirtualKeyCode::F3,
+        0x64 => events::VirtualKeyCode::F8,
+        0x65 => events::VirtualKeyCode::F9,
+        //0x66 => JIS Eisuu (macOS),
+        0x67 => events::VirtualKeyCode::F11,
+        //0x68 => JIS Kana (macOS),
+        0x69 => events::VirtualKeyCode::F13,
+        0x6a => events::VirtualKeyCode::F16,
+        0x6b => events::VirtualKeyCode::F14,
+        //0x6c => unkown,
+        0x6d => events::VirtualKeyCode::F10,
+        //0x6e => unkown,
+        0x6f => events::VirtualKeyCode::F12,
+        //0x70 => unkown,
+        0x71 => events::VirtualKeyCode::F15,
+        0x72 => events::VirtualKeyCode::Insert,
+        0x73 => events::VirtualKeyCode::Home,
+        0x74 => events::VirtualKeyCode::PageUp,
+        0x75 => events::VirtualKeyCode::Delete,
+        0x76 => events::VirtualKeyCode::F4,
+        0x77 => events::VirtualKeyCode::End,
+        0x78 => events::VirtualKeyCode::F2,
+        0x79 => events::VirtualKeyCode::PageDown,
+        0x7a => events::VirtualKeyCode::F1,
+        0x7b => events::VirtualKeyCode::Left,
+        0x7c => events::VirtualKeyCode::Right,
+        0x7d => events::VirtualKeyCode::Down,
+        0x7e => events::VirtualKeyCode::Up,
+        //0x7f =>  unkown,
+
+        0xa => events::VirtualKeyCode::Caret,
+        _ => return None,
+    })
+}
+
+pub fn check_additional_virtual_key_codes(
+    s: &Option<String>
+) -> Option<events::VirtualKeyCode> {
+    if let &Some(ref s) = s {
+        if let Some(ch) = s.encode_utf16().next() {
+            return Some(match ch {
+                0xf718 => events::VirtualKeyCode::F21,
+                0xf719 => events::VirtualKeyCode::F22,
+                0xf71a => events::VirtualKeyCode::F23,
+                0xf71b => events::VirtualKeyCode::F24,
+                _ => return None,
+            })
+        }
+    }
+    None
+}
+
+pub fn event_mods(event: cocoa::base::id) -> ModifiersState {
+    let flags = unsafe {
+        NSEvent::modifierFlags(event)
+    };
+    ModifiersState {
+        shift: flags.contains(NSEventModifierFlags::NSShiftKeyMask),
+        ctrl: flags.contains(NSEventModifierFlags::NSControlKeyMask),
+        alt: flags.contains(NSEventModifierFlags::NSAlternateKeyMask),
+        logo: flags.contains(NSEventModifierFlags::NSCommandKeyMask),
+    }
+}
+
+unsafe fn modifier_event(
+    ns_event: cocoa::base::id,
+    keymask: NSEventModifierFlags,
+    was_key_pressed: bool,
+) -> Option<WindowEvent> {
+    if !was_key_pressed && NSEvent::modifierFlags(ns_event).contains(keymask)
+    || was_key_pressed && !NSEvent::modifierFlags(ns_event).contains(keymask) {
+        let state = if was_key_pressed {
+            ElementState::Released
+        } else {
+            ElementState::Pressed
+        };
+        let keycode = NSEvent::keyCode(ns_event);
+        let scancode = keycode as u32;
+        let virtual_keycode = to_virtual_key_code(keycode);
+        Some(WindowEvent::KeyboardInput {
+            device_id: DEVICE_ID,
+            input: KeyboardInput {
+                state,
+                scancode,
+                virtual_keycode,
+                modifiers: event_mods(ns_event),
+            },
+        })
+    } else {
+        None
+    }
+}
+
+// Constant device ID, to be removed when this backend is updated to report real device IDs.
+pub const DEVICE_ID: ::DeviceId = ::DeviceId(DeviceId);

src/platform_impl/macos/ffi.rs

@@ -0,0 +1,107 @@
+// TODO: Upstream these
+
+#![allow(dead_code, non_snake_case, non_upper_case_globals)]
+
+use cocoa::base::id;
+use cocoa::foundation::{NSInteger, NSUInteger};
+use objc;
+
+pub const NSNotFound: NSInteger = NSInteger::max_value();
+
+#[repr(C)]
+pub struct NSRange {
+    pub location: NSUInteger,
+    pub length: NSUInteger,
+}
+
+impl NSRange {
+    #[inline]
+    pub fn new(location: NSUInteger, length: NSUInteger) -> NSRange {
+        NSRange { location, length }
+    }
+}
+
+unsafe impl objc::Encode for NSRange {
+    fn encode() -> objc::Encoding {
+        let encoding = format!(
+            // TODO: Verify that this is correct
+            "{{NSRange={}{}}}",
+            NSUInteger::encode().as_str(),
+            NSUInteger::encode().as_str(),
+        );
+        unsafe { objc::Encoding::from_str(&encoding) }
+    }
+}
+
+pub trait NSMutableAttributedString: Sized {
+    unsafe fn alloc(_: Self) -> id {
+        msg_send![class!(NSMutableAttributedString), alloc]
+    }
+
+    unsafe fn init(self) -> id; // *mut NSMutableAttributedString
+    unsafe fn initWithString(self, string: id) -> id;
+    unsafe fn initWithAttributedString(self, string: id) -> id;
+
+    unsafe fn string(self) -> id; // *mut NSString
+    unsafe fn mutableString(self) -> id; // *mut NSMutableString
+    unsafe fn length(self) -> NSUInteger;
+}
+
+impl NSMutableAttributedString for id {
+    unsafe fn init(self) -> id {
+        msg_send![self, init]
+    }
+
+    unsafe fn initWithString(self, string: id) -> id {
+        msg_send![self, initWithString:string]
+    }
+
+    unsafe fn initWithAttributedString(self, string: id) -> id {
+        msg_send![self, initWithAttributedString:string]
+    }
+
+    unsafe fn string(self) -> id {
+        msg_send![self, string]
+    }
+
+    unsafe fn mutableString(self) -> id {
+        msg_send![self, mutableString]
+    }
+
+    unsafe fn length(self) -> NSUInteger {
+        msg_send![self, length]
+    }
+}
+
+pub const kCGBaseWindowLevelKey: NSInteger = 0;
+pub const kCGMinimumWindowLevelKey: NSInteger = 1;
+pub const kCGDesktopWindowLevelKey: NSInteger = 2;
+pub const kCGBackstopMenuLevelKey: NSInteger = 3;
+pub const kCGNormalWindowLevelKey: NSInteger = 4;
+pub const kCGFloatingWindowLevelKey: NSInteger = 5;
+pub const kCGTornOffMenuWindowLevelKey: NSInteger = 6;
+pub const kCGDockWindowLevelKey: NSInteger = 7;
+pub const kCGMainMenuWindowLevelKey: NSInteger = 8;
+pub const kCGStatusWindowLevelKey: NSInteger = 9;
+pub const kCGModalPanelWindowLevelKey: NSInteger = 10;
+pub const kCGPopUpMenuWindowLevelKey: NSInteger = 11;
+pub const kCGDraggingWindowLevelKey: NSInteger = 12;
+pub const kCGScreenSaverWindowLevelKey: NSInteger = 13;
+pub const kCGMaximumWindowLevelKey: NSInteger = 14;
+pub const kCGOverlayWindowLevelKey: NSInteger = 15;
+pub const kCGHelpWindowLevelKey: NSInteger = 16;
+pub const kCGUtilityWindowLevelKey: NSInteger = 17;
+pub const kCGDesktopIconWindowLevelKey: NSInteger = 18;
+pub const kCGCursorWindowLevelKey: NSInteger = 19;
+pub const kCGNumberOfWindowLevelKeys: NSInteger = 20;
+
+pub enum NSWindowLevel {
+    NSNormalWindowLevel = kCGBaseWindowLevelKey as _,
+    NSFloatingWindowLevel = kCGFloatingWindowLevelKey as _,
+    NSTornOffMenuWindowLevel = kCGTornOffMenuWindowLevelKey as _,
+    NSModalPanelWindowLevel = kCGModalPanelWindowLevelKey as _,
+    NSMainMenuWindowLevel = kCGMainMenuWindowLevelKey as _,
+    NSStatusWindowLevel = kCGStatusWindowLevelKey as _,
+    NSPopUpMenuWindowLevel = kCGPopUpMenuWindowLevelKey as _,
+    NSScreenSaverWindowLevel = kCGScreenSaverWindowLevelKey as _,
+}

src/platform_impl/macos/mod.rs

@@ -0,0 +1,51 @@
+#![cfg(target_os = "macos")]
+
+pub use self::event_loop::{EventLoop, Proxy as EventLoopProxy};
+pub use self::monitor::MonitorHandle;
+pub use self::window::{Id as WindowId, PlatformSpecificWindowBuilderAttributes, Window2};
+use std::sync::Arc;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct DeviceId;
+
+impl DeviceId {
+    pub unsafe fn dummy() -> Self {
+        DeviceId
+    }
+}
+
+use {CreationError};
+
+pub struct Window {
+    pub window: Arc<Window2>,
+}
+
+impl ::std::ops::Deref for Window {
+    type Target = Window2;
+    #[inline]
+    fn deref(&self) -> &Window2 {
+        &*self.window
+    }
+}
+
+impl Window {
+
+    pub fn new(event_loop: &EventLoop,
+               attributes: ::WindowAttributes,
+               pl_attribs: PlatformSpecificWindowBuilderAttributes) -> Result<Self, CreationError>
+    {
+        let weak_shared = Arc::downgrade(&event_loop.shared);
+        let window = Arc::new(try!(Window2::new(weak_shared, attributes, pl_attribs)));
+        let weak_window = Arc::downgrade(&window);
+        event_loop.shared.windows.lock().unwrap().push(weak_window);
+        Ok(Window { window: window })
+    }
+
+}
+
+mod event_loop;
+mod ffi;
+mod monitor;
+mod util;
+mod view;
+mod window;

src/platform_impl/macos/monitor.rs

@@ -0,0 +1,147 @@
+use std::collections::VecDeque;
+use std::fmt;
+
+use cocoa::appkit::NSScreen;
+use cocoa::base::{id, nil};
+use cocoa::foundation::{NSString, NSUInteger};
+use core_graphics::display::{CGDirectDisplayID, CGDisplay, CGDisplayBounds};
+
+use {PhysicalPosition, PhysicalSize};
+use super::EventLoop;
+use super::window::{IdRef, Window2};
+
+#[derive(Clone, PartialEq)]
+pub struct MonitorHandle(CGDirectDisplayID);
+
+fn get_available_monitors() -> VecDeque<MonitorHandle> {
+    if let Ok(displays) = CGDisplay::active_displays() {
+        let mut monitors = VecDeque::with_capacity(displays.len());
+        for d in displays {
+            monitors.push_back(MonitorHandle(d));
+        }
+        monitors
+    } else {
+        VecDeque::with_capacity(0)
+    }
+}
+
+pub fn get_primary_monitor() -> MonitorHandle {
+    let id = MonitorHandle(CGDisplay::main().id);
+    id
+}
+
+impl EventLoop {
+    #[inline]
+    pub fn get_available_monitors(&self) -> VecDeque<MonitorHandle> {
+        get_available_monitors()
+    }
+
+    #[inline]
+    pub fn get_primary_monitor(&self) -> MonitorHandle {
+        get_primary_monitor()
+    }
+
+    pub fn make_monitor_from_display(id: CGDirectDisplayID) -> MonitorHandle {
+        let id = MonitorHandle(id);
+        id
+    }
+}
+
+impl Window2 {
+    #[inline]
+    pub fn get_available_monitors(&self) -> VecDeque<MonitorHandle> {
+        get_available_monitors()
+    }
+
+    #[inline]
+    pub fn get_primary_monitor(&self) -> MonitorHandle {
+        get_primary_monitor()
+    }
+}
+
+impl fmt::Debug for MonitorHandle {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        #[derive(Debug)]
+        struct MonitorHandle {
+            name: Option<String>,
+            native_identifier: u32,
+            dimensions: PhysicalSize,
+            position: PhysicalPosition,
+            hidpi_factor: f64,
+        }
+
+        let monitor_id_proxy = MonitorHandle {
+            name: self.get_name(),
+            native_identifier: self.get_native_identifier(),
+            dimensions: self.get_dimensions(),
+            position: self.get_position(),
+            hidpi_factor: self.get_hidpi_factor(),
+        };
+
+        monitor_id_proxy.fmt(f)
+    }
+}
+
+impl MonitorHandle {
+    pub fn get_name(&self) -> Option<String> {
+        let MonitorHandle(display_id) = *self;
+        let screen_num = CGDisplay::new(display_id).model_number();
+        Some(format!("Monitor #{}", screen_num))
+    }
+
+    #[inline]
+    pub fn get_native_identifier(&self) -> u32 {
+        self.0
+    }
+
+    pub fn get_dimensions(&self) -> PhysicalSize {
+        let MonitorHandle(display_id) = *self;
+        let display = CGDisplay::new(display_id);
+        let height = display.pixels_high();
+        let width = display.pixels_wide();
+        PhysicalSize::from_logical(
+            (width as f64, height as f64),
+            self.get_hidpi_factor(),
+        )
+    }
+
+    #[inline]
+    pub fn get_position(&self) -> PhysicalPosition {
+        let bounds = unsafe { CGDisplayBounds(self.get_native_identifier()) };
+        PhysicalPosition::from_logical(
+            (bounds.origin.x as f64, bounds.origin.y as f64),
+            self.get_hidpi_factor(),
+        )
+    }
+
+    pub fn get_hidpi_factor(&self) -> f64 {
+        let screen = match self.get_nsscreen() {
+            Some(screen) => screen,
+            None => return 1.0, // default to 1.0 when we can't find the screen
+        };
+        unsafe { NSScreen::backingScaleFactor(screen) as f64 }
+    }
+
+    pub(crate) fn get_nsscreen(&self) -> Option<id> {
+        unsafe {
+            let native_id = self.get_native_identifier();
+            let screens = NSScreen::screens(nil);
+            let count: NSUInteger = msg_send![screens, count];
+            let key = IdRef::new(NSString::alloc(nil).init_str("NSScreenNumber"));
+            let mut matching_screen: Option<id> = None;
+            for i in 0..count {
+                let screen = msg_send![screens, objectAtIndex: i as NSUInteger];
+                let device_description = NSScreen::deviceDescription(screen);
+                let value: id = msg_send![device_description, objectForKey:*key];
+                if value != nil {
+                    let screen_number: NSUInteger = msg_send![value, unsignedIntegerValue];
+                    if screen_number as u32 == native_id {
+                        matching_screen = Some(screen);
+                        break;
+                    }
+                }
+            }
+            matching_screen
+        }
+    }
+}

src/platform_impl/macos/util.rs

@@ -0,0 +1,38 @@
+use cocoa::appkit::NSWindowStyleMask;
+use cocoa::base::{id, nil};
+use cocoa::foundation::{NSRect, NSUInteger};
+use core_graphics::display::CGDisplay;
+
+use platform_impl::platform::ffi;
+use platform_impl::platform::window::IdRef;
+
+pub const EMPTY_RANGE: ffi::NSRange = ffi::NSRange {
+    location: ffi::NSNotFound as NSUInteger,
+    length: 0,
+};
+
+// For consistency with other platforms, this will...
+// 1. translate the bottom-left window corner into the top-left window corner
+// 2. translate the coordinate from a bottom-left origin coordinate system to a top-left one
+pub fn bottom_left_to_top_left(rect: NSRect) -> f64 {
+    CGDisplay::main().pixels_high() as f64 - (rect.origin.y + rect.size.height)
+}
+
+pub unsafe fn set_style_mask(window: id, view: id, mask: NSWindowStyleMask) {
+    use cocoa::appkit::NSWindow;
+    window.setStyleMask_(mask);
+    // If we don't do this, key handling will break. Therefore, never call `setStyleMask` directly!
+    window.makeFirstResponder_(view);
+}
+
+pub unsafe fn create_input_context(view: id) -> IdRef {
+    let input_context: id = msg_send![class!(NSTextInputContext), alloc];
+    let input_context: id = msg_send![input_context, initWithClient:view];
+    IdRef::new(input_context)
+}
+
+#[allow(dead_code)]
+pub unsafe fn open_emoji_picker() {
+    let app: id = msg_send![class!(NSApplication), sharedApplication];
+    let _: () = msg_send![app, orderFrontCharacterPalette:nil];
+}

src/platform_impl/macos/view.rs

@@ -0,0 +1,648 @@
+// This is a pretty close port of the implementation in GLFW:
+// https://github.com/glfw/glfw/blob/7ef34eb06de54dd9186d3d21a401b2ef819b59e7/src/cocoa_window.m
+
+use std::{slice, str};
+use std::boxed::Box;
+use std::collections::VecDeque;
+use std::os::raw::*;
+use std::sync::{Arc, Mutex, Weak};
+
+use cocoa::base::{id, nil};
+use cocoa::appkit::{NSEvent, NSView, NSWindow};
+use cocoa::foundation::{NSPoint, NSRect, NSSize, NSString, NSUInteger};
+use objc::declare::ClassDecl;
+use objc::runtime::{Class, Object, Protocol, Sel, BOOL, YES};
+
+use {ElementState, Event, KeyboardInput, MouseButton, WindowEvent, WindowId};
+use platform_impl::platform::event_loop::{DEVICE_ID, event_mods, Shared, to_virtual_key_code, check_additional_virtual_key_codes};
+use platform_impl::platform::util;
+use platform_impl::platform::ffi::*;
+use platform_impl::platform::window::{get_window_id, IdRef};
+
+struct ViewState {
+    window: id,
+    shared: Weak<Shared>,
+    cursor: Arc<Mutex<util::Cursor>>,
+    ime_spot: Option<(f64, f64)>,
+    raw_characters: Option<String>,
+    is_key_down: bool,
+}
+
+pub fn new_view(window: id, shared: Weak<Shared>) -> (IdRef, Weak<Mutex<util::Cursor>>) {
+    let cursor = Default::default();
+    let cursor_access = Arc::downgrade(&cursor);
+    let state = ViewState {
+        window,
+        shared,
+        cursor,
+        ime_spot: None,
+        raw_characters: None,
+        is_key_down: false,
+    };
+    unsafe {
+        // This is free'd in `dealloc`
+        let state_ptr = Box::into_raw(Box::new(state)) as *mut c_void;
+        let view: id = msg_send![VIEW_CLASS.0, alloc];
+        (IdRef::new(msg_send![view, initWithWinit:state_ptr]), cursor_access)
+    }
+}
+
+pub fn set_ime_spot(view: id, input_context: id, x: f64, y: f64) {
+    unsafe {
+        let state_ptr: *mut c_void = *(*view).get_mut_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+        let content_rect = NSWindow::contentRectForFrameRect_(
+            state.window,
+            NSWindow::frame(state.window),
+        );
+        let base_x = content_rect.origin.x as f64;
+        let base_y = (content_rect.origin.y + content_rect.size.height) as f64;
+        state.ime_spot = Some((base_x + x, base_y - y));
+        let _: () = msg_send![input_context, invalidateCharacterCoordinates];
+    }
+}
+
+struct ViewClass(*const Class);
+unsafe impl Send for ViewClass {}
+unsafe impl Sync for ViewClass {}
+
+lazy_static! {
+    static ref VIEW_CLASS: ViewClass = unsafe {
+        let superclass = class!(NSView);
+        let mut decl = ClassDecl::new("WinitView", superclass).unwrap();
+        decl.add_method(sel!(dealloc), dealloc as extern fn(&Object, Sel));
+        decl.add_method(
+            sel!(initWithWinit:),
+            init_with_winit as extern fn(&Object, Sel, *mut c_void) -> id,
+        );
+        decl.add_method(
+            sel!(drawRect:),
+            draw_rect as extern fn(&Object, Sel, NSRect),
+        );
+        decl.add_method(
+            sel!(resetCursorRects),
+            reset_cursor_rects as extern fn(&Object, Sel),
+        );
+        decl.add_method(sel!(hasMarkedText), has_marked_text as extern fn(&Object, Sel) -> BOOL);
+        decl.add_method(
+            sel!(markedRange),
+            marked_range as extern fn(&Object, Sel) -> NSRange,
+        );
+        decl.add_method(sel!(selectedRange), selected_range as extern fn(&Object, Sel) -> NSRange);
+        decl.add_method(
+            sel!(setMarkedText:selectedRange:replacementRange:),
+            set_marked_text as extern fn(&mut Object, Sel, id, NSRange, NSRange),
+        );
+        decl.add_method(sel!(unmarkText), unmark_text as extern fn(&Object, Sel));
+        decl.add_method(
+            sel!(validAttributesForMarkedText),
+            valid_attributes_for_marked_text as extern fn(&Object, Sel) -> id,
+        );
+        decl.add_method(
+            sel!(attributedSubstringForProposedRange:actualRange:),
+            attributed_substring_for_proposed_range
+                as extern fn(&Object, Sel, NSRange, *mut c_void) -> id,
+        );
+        decl.add_method(
+            sel!(insertText:replacementRange:),
+            insert_text as extern fn(&Object, Sel, id, NSRange),
+        );
+        decl.add_method(
+            sel!(characterIndexForPoint:),
+            character_index_for_point as extern fn(&Object, Sel, NSPoint) -> NSUInteger,
+        );
+        decl.add_method(
+            sel!(firstRectForCharacterRange:actualRange:),
+            first_rect_for_character_range
+                as extern fn(&Object, Sel, NSRange, *mut c_void) -> NSRect,
+        );
+        decl.add_method(
+            sel!(doCommandBySelector:),
+            do_command_by_selector as extern fn(&Object, Sel, Sel),
+        );
+        decl.add_method(sel!(keyDown:), key_down as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(keyUp:), key_up as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(insertTab:), insert_tab as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(insertBackTab:), insert_back_tab as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(mouseDown:), mouse_down as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(mouseUp:), mouse_up as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(rightMouseDown:), right_mouse_down as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(rightMouseUp:), right_mouse_up as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(otherMouseDown:), other_mouse_down as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(otherMouseUp:), other_mouse_up as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(mouseMoved:), mouse_moved as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(mouseDragged:), mouse_dragged as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(rightMouseDragged:), right_mouse_dragged as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(otherMouseDragged:), other_mouse_dragged as extern fn(&Object, Sel, id));
+        decl.add_method(sel!(_wantsKeyDownForEvent:), wants_key_down_for_event as extern fn(&Object, Sel, id) -> BOOL);
+        decl.add_ivar::<*mut c_void>("winitState");
+        decl.add_ivar::<id>("markedText");
+        let protocol = Protocol::get("NSTextInputClient").unwrap();
+        decl.add_protocol(&protocol);
+        ViewClass(decl.register())
+    };
+}
+
+extern fn dealloc(this: &Object, _sel: Sel) {
+    unsafe {
+        let state: *mut c_void = *this.get_ivar("winitState");
+        let marked_text: id = *this.get_ivar("markedText");
+        let _: () = msg_send![marked_text, release];
+        Box::from_raw(state as *mut ViewState);
+    }
+}
+
+extern fn init_with_winit(this: &Object, _sel: Sel, state: *mut c_void) -> id {
+    unsafe {
+        let this: id = msg_send![this, init];
+        if this != nil {
+            (*this).set_ivar("winitState", state);
+            let marked_text = <id as NSMutableAttributedString>::init(
+                NSMutableAttributedString::alloc(nil),
+            );
+            (*this).set_ivar("markedText", marked_text);
+        }
+        this
+    }
+}
+
+extern fn draw_rect(this: &Object, _sel: Sel, rect: NSRect) {
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        if let Some(shared) = state.shared.upgrade() {
+            let window_event = Event::WindowEvent {
+                window_id: WindowId(get_window_id(state.window)),
+                event: WindowEvent::Refresh,
+            };
+            shared.pending_events
+                .lock()
+                .unwrap()
+                .push_back(window_event);
+        }
+
+        let superclass = util::superclass(this);
+        let () = msg_send![super(this, superclass), drawRect:rect];
+    }
+}
+
+extern fn reset_cursor_rects(this: &Object, _sel: Sel) {
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        let bounds: NSRect = msg_send![this, bounds];
+        let cursor = state.cursor.lock().unwrap().load();
+        let _: () = msg_send![this,
+            addCursorRect:bounds
+            cursor:cursor
+        ];
+    }
+}
+
+extern fn has_marked_text(this: &Object, _sel: Sel) -> BOOL {
+    //println!("hasMarkedText");
+    unsafe {
+        let marked_text: id = *this.get_ivar("markedText");
+        (marked_text.length() > 0) as i8
+    }
+}
+
+extern fn marked_range(this: &Object, _sel: Sel) -> NSRange {
+    //println!("markedRange");
+    unsafe {
+        let marked_text: id = *this.get_ivar("markedText");
+        let length = marked_text.length();
+        if length > 0 {
+            NSRange::new(0, length - 1)
+        } else {
+            util::EMPTY_RANGE
+        }
+    }
+}
+
+extern fn selected_range(_this: &Object, _sel: Sel) -> NSRange {
+    //println!("selectedRange");
+    util::EMPTY_RANGE
+}
+
+extern fn set_marked_text(
+    this: &mut Object,
+    _sel: Sel,
+    string: id,
+    _selected_range: NSRange,
+    _replacement_range: NSRange,
+) {
+    //println!("setMarkedText");
+    unsafe {
+        let marked_text_ref: &mut id = this.get_mut_ivar("markedText");
+        let _: () = msg_send![(*marked_text_ref), release];
+        let marked_text = NSMutableAttributedString::alloc(nil);
+        let has_attr = msg_send![string, isKindOfClass:class!(NSAttributedString)];
+        if has_attr {
+            marked_text.initWithAttributedString(string);
+        } else {
+            marked_text.initWithString(string);
+        };
+        *marked_text_ref = marked_text;
+    }
+}
+
+extern fn unmark_text(this: &Object, _sel: Sel) {
+    //println!("unmarkText");
+    unsafe {
+        let marked_text: id = *this.get_ivar("markedText");
+        let mutable_string = marked_text.mutableString();
+        let _: () = msg_send![mutable_string, setString:""];
+        let input_context: id = msg_send![this, inputContext];
+        let _: () = msg_send![input_context, discardMarkedText];
+    }
+}
+
+extern fn valid_attributes_for_marked_text(_this: &Object, _sel: Sel) -> id {
+    //println!("validAttributesForMarkedText");
+    unsafe { msg_send![class!(NSArray), array] }
+}
+
+extern fn attributed_substring_for_proposed_range(
+    _this: &Object,
+    _sel: Sel,
+    _range: NSRange,
+    _actual_range: *mut c_void, // *mut NSRange
+) -> id {
+    //println!("attributedSubstringForProposedRange");
+    nil
+}
+
+extern fn character_index_for_point(_this: &Object, _sel: Sel, _point: NSPoint) -> NSUInteger {
+    //println!("characterIndexForPoint");
+    0
+}
+
+extern fn first_rect_for_character_range(
+    this: &Object,
+    _sel: Sel,
+    _range: NSRange,
+    _actual_range: *mut c_void, // *mut NSRange
+) -> NSRect {
+    //println!("firstRectForCharacterRange");
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+        let (x, y) = state.ime_spot.unwrap_or_else(|| {
+            let content_rect = NSWindow::contentRectForFrameRect_(
+                state.window,
+                NSWindow::frame(state.window),
+            );
+            let x = content_rect.origin.x;
+            let y = util::bottom_left_to_top_left(content_rect);
+            (x, y)
+        });
+
+        NSRect::new(
+            NSPoint::new(x as _, y as _),
+            NSSize::new(0.0, 0.0),
+        )
+    }
+}
+
+extern fn insert_text(this: &Object, _sel: Sel, string: id, _replacement_range: NSRange) {
+    //println!("insertText");
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        let has_attr = msg_send![string, isKindOfClass:class!(NSAttributedString)];
+        let characters = if has_attr {
+            // This is a *mut NSAttributedString
+            msg_send![string, string]
+        } else {
+            // This is already a *mut NSString
+            string
+        };
+
+        let slice = slice::from_raw_parts(
+            characters.UTF8String() as *const c_uchar,
+            characters.len(),
+        );
+        let string = str::from_utf8_unchecked(slice);
+        state.is_key_down = true;
+
+        // We don't need this now, but it's here if that changes.
+        //let event: id = msg_send![class!(NSApp), currentEvent];
+
+        let mut events = VecDeque::with_capacity(characters.len());
+        for character in string.chars() {
+            events.push_back(Event::WindowEvent {
+                window_id: WindowId(get_window_id(state.window)),
+                event: WindowEvent::ReceivedCharacter(character),
+            });
+        }
+
+        if let Some(shared) = state.shared.upgrade() {
+            shared.pending_events
+                .lock()
+                .unwrap()
+                .append(&mut events);
+        }
+    }
+}
+
+extern fn do_command_by_selector(this: &Object, _sel: Sel, command: Sel) {
+    //println!("doCommandBySelector");
+    // Basically, we're sent this message whenever a keyboard event that doesn't generate a "human readable" character
+    // happens, i.e. newlines, tabs, and Ctrl+C.
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        let shared = if let Some(shared) = state.shared.upgrade() {
+            shared
+        } else {
+            return;
+        };
+
+        let mut events = VecDeque::with_capacity(1);
+        if command == sel!(insertNewline:) {
+            // The `else` condition would emit the same character, but I'm keeping this here both...
+            // 1) as a reminder for how `doCommandBySelector` works
+            // 2) to make our use of carriage return explicit
+            events.push_back(Event::WindowEvent {
+                window_id: WindowId(get_window_id(state.window)),
+                event: WindowEvent::ReceivedCharacter('\r'),
+            });
+        } else {
+            let raw_characters = state.raw_characters.take();
+            if let Some(raw_characters) = raw_characters {
+                for character in raw_characters.chars() {
+                    events.push_back(Event::WindowEvent {
+                        window_id: WindowId(get_window_id(state.window)),
+                        event: WindowEvent::ReceivedCharacter(character),
+                    });
+                }
+            }
+        };
+
+        shared.pending_events
+            .lock()
+            .unwrap()
+            .append(&mut events);
+    }
+}
+
+fn get_characters(event: id) -> Option<String> {
+    unsafe {
+        let characters: id = msg_send![event, characters];
+        let slice = slice::from_raw_parts(
+            characters.UTF8String() as *const c_uchar,
+            characters.len(),
+        );
+        let string = str::from_utf8_unchecked(slice);
+        Some(string.to_owned())
+    }
+}
+
+extern fn key_down(this: &Object, _sel: Sel, event: id) {
+    //println!("keyDown");
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+        let window_id = WindowId(get_window_id(state.window));
+
+        state.raw_characters = get_characters(event);
+
+        let keycode: c_ushort = msg_send![event, keyCode];
+        // We are checking here for F21-F24 keys, since their keycode
+        // can vary, but we know that they are encoded
+        // in characters property.
+        let virtual_keycode = to_virtual_key_code(keycode)
+            .or_else(|| {
+                check_additional_virtual_key_codes(&state.raw_characters)
+            });
+        let scancode = keycode as u32;
+        let is_repeat = msg_send![event, isARepeat];
+
+        let window_event = Event::WindowEvent {
+            window_id,
+            event: WindowEvent::KeyboardInput {
+                device_id: DEVICE_ID,
+                input: KeyboardInput {
+                    state: ElementState::Pressed,
+                    scancode,
+                    virtual_keycode,
+                    modifiers: event_mods(event),
+                },
+            },
+        };
+
+        let characters: id = msg_send![event, characters];
+        let slice = slice::from_raw_parts(
+            characters.UTF8String() as *const c_uchar,
+            characters.len(),
+            );
+        let string = str::from_utf8_unchecked(slice);
+
+        state.raw_characters = {
+            Some(string.to_owned())
+        };
+
+        if let Some(shared) = state.shared.upgrade() {
+            shared.pending_events
+                .lock()
+                .unwrap()
+                .push_back(window_event);
+            // Emit `ReceivedCharacter` for key repeats
+            if is_repeat && state.is_key_down{
+                for character in string.chars() {
+                    let window_event = Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ReceivedCharacter(character),
+                    };
+                    shared.pending_events
+                        .lock()
+                        .unwrap()
+                        .push_back(window_event);
+                }
+            } else {
+                // Some keys (and only *some*, with no known reason) don't trigger `insertText`, while others do...
+                // So, we don't give repeats the opportunity to trigger that, since otherwise our hack will cause some
+                // keys to generate twice as many characters.
+                let array: id = msg_send![class!(NSArray), arrayWithObject:event];
+                let (): _ = msg_send![this, interpretKeyEvents:array];
+            }
+        }
+    }
+}
+
+extern fn key_up(this: &Object, _sel: Sel, event: id) {
+    //println!("keyUp");
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        state.is_key_down = false;
+
+        // We need characters here to check for additional keys such as
+        // F21-F24.
+        let characters = get_characters(event);
+
+        let keycode: c_ushort = msg_send![event, keyCode];
+        let virtual_keycode = to_virtual_key_code(keycode)
+            .or_else(|| {
+                check_additional_virtual_key_codes(&characters)
+            });
+        let scancode = keycode as u32;
+        let window_event = Event::WindowEvent {
+            window_id: WindowId(get_window_id(state.window)),
+            event: WindowEvent::KeyboardInput {
+                device_id: DEVICE_ID,
+                input: KeyboardInput {
+                    state: ElementState::Released,
+                    scancode,
+                    virtual_keycode,
+                    modifiers: event_mods(event),
+                },
+            },
+        };
+
+        if let Some(shared) = state.shared.upgrade() {
+            shared.pending_events
+                .lock()
+                .unwrap()
+                .push_back(window_event);
+        }
+    }
+}
+
+extern fn insert_tab(this: &Object, _sel: Sel, _sender: id) {
+    unsafe {
+        let window: id = msg_send![this, window];
+        let first_responder: id = msg_send![window, firstResponder];
+        let this_ptr = this as *const _ as *mut _;
+        if first_responder == this_ptr {
+            let (): _ = msg_send![window, selectNextKeyView:this];
+        }
+    }
+}
+
+extern fn insert_back_tab(this: &Object, _sel: Sel, _sender: id) {
+    unsafe {
+        let window: id = msg_send![this, window];
+        let first_responder: id = msg_send![window, firstResponder];
+        let this_ptr = this as *const _ as *mut _;
+        if first_responder == this_ptr {
+            let (): _ = msg_send![window, selectPreviousKeyView:this];
+        }
+    }
+}
+
+fn mouse_click(this: &Object, event: id, button: MouseButton, button_state: ElementState) {
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        let window_event = Event::WindowEvent {
+            window_id: WindowId(get_window_id(state.window)),
+            event: WindowEvent::MouseInput {
+                device_id: DEVICE_ID,
+                state: button_state,
+                button,
+                modifiers: event_mods(event),
+            },
+        };
+
+        if let Some(shared) = state.shared.upgrade() {
+            shared.pending_events
+                .lock()
+                .unwrap()
+                .push_back(window_event);
+        }
+    }
+}
+
+extern fn mouse_down(this: &Object, _sel: Sel, event: id) {
+    mouse_click(this, event, MouseButton::Left, ElementState::Pressed);
+}
+
+extern fn mouse_up(this: &Object, _sel: Sel, event: id) {
+    mouse_click(this, event, MouseButton::Left, ElementState::Released);
+}
+
+extern fn right_mouse_down(this: &Object, _sel: Sel, event: id) {
+    mouse_click(this, event, MouseButton::Right, ElementState::Pressed);
+}
+
+extern fn right_mouse_up(this: &Object, _sel: Sel, event: id) {
+    mouse_click(this, event, MouseButton::Right, ElementState::Released);
+}
+
+extern fn other_mouse_down(this: &Object, _sel: Sel, event: id) {
+    mouse_click(this, event, MouseButton::Middle, ElementState::Pressed);
+}
+
+extern fn other_mouse_up(this: &Object, _sel: Sel, event: id) {
+    mouse_click(this, event, MouseButton::Middle, ElementState::Released);
+}
+
+fn mouse_motion(this: &Object, event: id) {
+    unsafe {
+        let state_ptr: *mut c_void = *this.get_ivar("winitState");
+        let state = &mut *(state_ptr as *mut ViewState);
+
+        // We have to do this to have access to the `NSView` trait...
+        let view: id = this as *const _ as *mut _;
+
+        let window_point = event.locationInWindow();
+        let view_point = view.convertPoint_fromView_(window_point, nil);
+        let view_rect = NSView::frame(view);
+
+        if view_point.x.is_sign_negative()
+        || view_point.y.is_sign_negative()
+        || view_point.x > view_rect.size.width
+        || view_point.y > view_rect.size.height {
+            // Point is outside of the client area (view)
+            return;
+        }
+
+        let x = view_point.x as f64;
+        let y = view_rect.size.height as f64 - view_point.y as f64;
+
+        let window_event = Event::WindowEvent {
+            window_id: WindowId(get_window_id(state.window)),
+            event: WindowEvent::CursorMoved {
+                device_id: DEVICE_ID,
+                position: (x, y).into(),
+                modifiers: event_mods(event),
+            },
+        };
+
+        if let Some(shared) = state.shared.upgrade() {
+            shared.pending_events
+                .lock()
+                .unwrap()
+                .push_back(window_event);
+        }
+    }
+}
+
+extern fn mouse_moved(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
+}
+
+extern fn mouse_dragged(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
+}
+
+extern fn right_mouse_dragged(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
+}
+
+extern fn other_mouse_dragged(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
+}
+
+// https://github.com/chromium/chromium/blob/a86a8a6bcfa438fa3ac2eba6f02b3ad1f8e0756f/ui/views/cocoa/bridged_content_view.mm#L816
+extern fn wants_key_down_for_event(_this: &Object, _se: Sel, _event: id) -> BOOL {
+    YES
+}