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/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
+        }
+    }
+}