Add EventLoopBuilder

This commit adds an `EventLoopBuilder` struct to simplify event loop
customization and providing options to it upon creation. It also
deprecates the use of `EventLoop::with_user_event` in favor of the same
method on new builder, and replaces old platforms specific extension
traits with the new ones on the `EventLoopBuilder`.

CHANGELOG.md

@@ -13,6 +13,11 @@ And please only add new entries to the top of this list, right below the `# Unre
 - **Breaking:** Bump `ndk` version to 0.6, ndk-sys to `v0.3`, `ndk-glue` to `0.6`.
 - Remove no longer needed `WINIT_LINK_COLORSYNC` environment variable.
 - **Breaking:** Rename the `Exit` variant of `ControlFlow` to `ExitWithCode`, which holds a value to control the exit code after running. Add an `Exit` constant which aliases to `ExitWithCode(0)` instead to avoid major breakage. This shouldn't affect most existing programs.
+- Add `EventLoopBuilder`, which allows you to create and tweak the settings of an event loop before creating it.
+- Deprecated `EventLoop::with_user_event`; use `EventLoopBuilder::with_user_event` instead.
+- **Breaking:** Replaced `EventLoopExtMacOS` with `EventLoopBuilderExtMacOS` (which also has renamed methods).
+- **Breaking:** Replaced `EventLoopExtWindows` with `EventLoopBuilderExtWindows` (which also has renamed methods).
+- **Breaking:** Replaced `EventLoopExtUnix` with `EventLoopBuilderExtUnix` (which also has renamed methods).
 
 # 0.26.1 (2022-01-05)
 

examples/custom_events.rs

@@ -3,7 +3,7 @@ fn main() {
     use simple_logger::SimpleLogger;
     use winit::{
         event::{Event, WindowEvent},
-        event_loop::{ControlFlow, EventLoop},
+        event_loop::{ControlFlow, EventLoopBuilder},
         window::WindowBuilder,
     };
 
@@ -13,7 +13,7 @@ fn main() {
     }
 
     SimpleLogger::new().init().unwrap();
-    let event_loop = EventLoop::<CustomEvent>::with_user_event();
+    let event_loop = EventLoopBuilder::<CustomEvent>::with_user_event().build();
 
     let _window = WindowBuilder::new()
         .with_title("A fantastic window!")

src/event_loop.rs

@@ -10,6 +10,7 @@
 //! [event_loop_proxy]: crate::event_loop::EventLoopProxy
 //! [send_event]: crate::event_loop::EventLoopProxy::send_event
 use instant::Instant;
+use std::marker::PhantomData;
 use std::ops::Deref;
 use std::{error, fmt};
 
@@ -31,7 +32,7 @@ use crate::{event::Event, monitor::MonitorHandle, platform_impl};
 ///
 pub struct EventLoop<T: 'static> {
     pub(crate) event_loop: platform_impl::EventLoop<T>,
-    pub(crate) _marker: ::std::marker::PhantomData<*mut ()>, // Not Send nor Sync
+    pub(crate) _marker: PhantomData<*mut ()>, // Not Send nor Sync
 }
 
 /// Target that associates windows with an `EventLoop`.
@@ -42,7 +43,62 @@ pub struct EventLoop<T: 'static> {
 /// `&EventLoop`.
 pub struct EventLoopWindowTarget<T: 'static> {
     pub(crate) p: platform_impl::EventLoopWindowTarget<T>,
-    pub(crate) _marker: ::std::marker::PhantomData<*mut ()>, // Not Send nor Sync
+    pub(crate) _marker: PhantomData<*mut ()>, // Not Send nor Sync
+}
+
+/// Object that allows building the event loop.
+///
+/// This is used to make specifying options that affect the whole application
+/// easier. But note that constructing multiple event loops is not supported.
+#[derive(Debug, Clone, Default)]
+pub struct EventLoopBuilder<T: 'static> {
+    pub(crate) platform_specific: platform_impl::PlatformSpecificEventLoopAttributes,
+    _p: PhantomData<T>,
+}
+
+impl EventLoopBuilder<()> {
+    /// Start building a new event loop.
+    #[inline]
+    pub fn new() -> Self {
+        Self::with_user_event()
+    }
+}
+
+impl<T> EventLoopBuilder<T> {
+    /// Start building a new event loop, with the given type as the user event
+    /// type.
+    #[inline]
+    pub fn with_user_event() -> Self {
+        Self {
+            platform_specific: Default::default(),
+            _p: PhantomData,
+        }
+    }
+
+    /// Builds a new event loop.
+    ///
+    /// ***For cross-platform compatibility, the `EventLoop` must be created on the main thread.***
+    /// Attempting to create the event loop on a different thread will panic. This restriction isn't
+    /// strictly necessary on all platforms, but is imposed to eliminate any nasty surprises when
+    /// porting to platforms that require it. `EventLoopBuilderExt::any_thread` functions are exposed
+    /// in the relevant `platform` module if the target platform supports creating an event loop on
+    /// any thread.
+    ///
+    /// Usage will result in display backend initialisation, this can be controlled on linux
+    /// using an environment variable `WINIT_UNIX_BACKEND`. Legal values are `x11` and `wayland`.
+    /// If it is not set, winit will try to connect to a wayland connection, and if it fails will
+    /// fallback on x11. If this variable is set with any other value, winit will panic.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **iOS:** Can only be called on the main thread.
+    #[inline]
+    pub fn build(&mut self) -> EventLoop<T> {
+        EventLoop {
+            event_loop: platform_impl::EventLoop::new(&self.platform_specific),
+            _marker: PhantomData,
+        }
+    }
 }
 
 impl<T> fmt::Debug for EventLoop<T> {
@@ -119,41 +175,17 @@ impl Default for ControlFlow {
 }
 
 impl EventLoop<()> {
-    /// Builds a new event loop with a `()` as the user event type.
+    /// Alias for `EventLoopBuilder::new().build()`.
-    ///
+    #[inline]
-    /// ***For cross-platform compatibility, the `EventLoop` must be created on the main thread.***
-    /// Attempting to create the event loop on a different thread will panic. This restriction isn't
-    /// strictly necessary on all platforms, but is imposed to eliminate any nasty surprises when
-    /// porting to platforms that require it. `EventLoopExt::new_any_thread` functions are exposed
-    /// in the relevant `platform` module if the target platform supports creating an event loop on
-    /// any thread.
-    ///
-    /// Usage will result in display backend initialisation, this can be controlled on linux
-    /// using an environment variable `WINIT_UNIX_BACKEND`. Legal values are `x11` and `wayland`.
-    /// If it is not set, winit will try to connect to a wayland connection, and if it fails will
-    /// fallback on x11. If this variable is set with any other value, winit will panic.
-    ///
-    /// ## Platform-specific
-    ///
-    /// - **iOS:** Can only be called on the main thread.
     pub fn new() -> EventLoop<()> {
-        EventLoop::<()>::with_user_event()
+        EventLoopBuilder::new().build()
     }
 }
 
 impl<T> EventLoop<T> {
-    /// Builds a new event loop.
+    #[deprecated = "Use `EventLoopBuiler::<T>::with_user_event().build()` instead."]
-    ///
-    /// All caveats documented in [`EventLoop::new`] apply to this function.
-    ///
-    /// ## Platform-specific
-    ///
-    /// - **iOS:** Can only be called on the main thread.
     pub fn with_user_event() -> EventLoop<T> {
-        EventLoop {
+        EventLoopBuilder::<T>::with_user_event().build()
-            event_loop: platform_impl::EventLoop::new(),
-            _marker: ::std::marker::PhantomData,
-        }
     }
 
     /// Hijacks the calling thread and initializes the winit event loop with the provided

src/platform/macos.rs

@@ -4,9 +4,8 @@ use std::os::raw::c_void;
 
 use crate::{
     dpi::LogicalSize,
-    event_loop::{EventLoop, EventLoopWindowTarget},
+    event_loop::{EventLoopBuilder, EventLoopWindowTarget},
     monitor::MonitorHandle,
-    platform_impl::get_aux_state_mut,
     window::{Window, WindowBuilder},
 };
 
@@ -74,7 +73,7 @@ impl WindowExtMacOS for Window {
 }
 
 /// Corresponds to `NSApplicationActivationPolicy`.
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum ActivationPolicy {
     /// Corresponds to `NSApplicationActivationPolicyRegular`.
     Regular,
@@ -179,36 +178,63 @@ impl WindowBuilderExtMacOS for WindowBuilder {
     }
 }
 
-pub trait EventLoopExtMacOS {
+pub trait EventLoopBuilderExtMacOS {
-    /// Sets the activation policy for the application. It is set to
+    /// Sets the activation policy for the application.
-    /// `NSApplicationActivationPolicyRegular` by default.
     ///
-    /// This function only takes effect if it's called before calling [`run`](crate::event_loop::EventLoop::run) or
+    /// It is set to [`ActivationPolicy::Regular`] by default.
-    /// [`run_return`](crate::platform::run_return::EventLoopExtRunReturn::run_return)
+    ///
-    fn set_activation_policy(&mut self, activation_policy: ActivationPolicy);
+    /// # Example
+    ///
+    /// Set the activation policy to "accessory".
+    ///
+    /// ```
+    /// use winit::event_loop::EventLoopBuilder;
+    /// #[cfg(target_os = "macos")]
+    /// use winit::platform::macos::{EventLoopBuilderExtMacOS, ActivationPolicy};
+    ///
+    /// let mut builder = EventLoopBuilder::new();
+    /// #[cfg(target_os = "macos")]
+    /// builder.with_activation_policy(ActivationPolicy::Accessory);
+    /// # if false { // We can't test this part
+    /// let event_loop = builder.build();
+    /// # }
+    /// ```
+    fn with_activation_policy(&mut self, activation_policy: ActivationPolicy) -> &mut Self;
 
-    /// Used to prevent a default menubar menu from getting created
+    /// Used to control whether a default menubar menu is created.
     ///
-    /// The default menu creation is enabled by default.
+    /// Menu creation is enabled by default.
     ///
-    /// This function only takes effect if it's called before calling
+    /// # Example
-    /// [`run`](crate::event_loop::EventLoop::run) or
+    ///
-    /// [`run_return`](crate::platform::run_return::EventLoopExtRunReturn::run_return)
+    /// Disable creating a default menubar.
-    fn enable_default_menu_creation(&mut self, enable: bool);
+    ///
+    /// ```
+    /// use winit::event_loop::EventLoopBuilder;
+    /// #[cfg(target_os = "macos")]
+    /// use winit::platform::macos::EventLoopBuilderExtMacOS;
+    ///
+    /// let mut builder = EventLoopBuilder::new();
+    /// #[cfg(target_os = "macos")]
+    /// builder.with_default_menu(false);
+    /// # if false { // We can't test this part
+    /// let event_loop = builder.build();
+    /// # }
+    /// ```
+    fn with_default_menu(&mut self, enable: bool) -> &mut Self;
 }
-impl<T> EventLoopExtMacOS for EventLoop<T> {
+
+impl<T> EventLoopBuilderExtMacOS for EventLoopBuilder<T> {
     #[inline]
-    fn set_activation_policy(&mut self, activation_policy: ActivationPolicy) {
+    fn with_activation_policy(&mut self, activation_policy: ActivationPolicy) -> &mut Self {
-        unsafe {
+        self.platform_specific.activation_policy = activation_policy;
-            get_aux_state_mut(&**self.event_loop.delegate).activation_policy = activation_policy;
+        self
-        }
     }
 
     #[inline]
-    fn enable_default_menu_creation(&mut self, enable: bool) {
+    fn with_default_menu(&mut self, enable: bool) -> &mut Self {
-        unsafe {
+        self.platform_specific.default_menu = enable;
-            get_aux_state_mut(&**self.event_loop.delegate).create_default_menu = enable;
+        self
-        }
     }
 }
 

src/platform/unix.rs

@@ -11,7 +11,7 @@ use std::os::raw;
 use std::{ptr, sync::Arc};
 
 use crate::{
-    event_loop::{EventLoop, EventLoopWindowTarget},
+    event_loop::{EventLoopBuilder, EventLoopWindowTarget},
     monitor::MonitorHandle,
     window::{Window, WindowBuilder},
 };
@@ -21,8 +21,7 @@ use crate::dpi::Size;
 #[cfg(feature = "x11")]
 use crate::platform_impl::x11::{ffi::XVisualInfo, XConnection};
 use crate::platform_impl::{
-    EventLoop as LinuxEventLoop, EventLoopWindowTarget as LinuxEventLoopWindowTarget,
+    Backend, EventLoopWindowTarget as LinuxEventLoopWindowTarget, Window as LinuxWindow,
-    Window as LinuxWindow,
 };
 
 // TODO: stupid hack so that glutin can do its work
@@ -93,100 +92,42 @@ impl<T> EventLoopWindowTargetExtUnix for EventLoopWindowTarget<T> {
     }
 }
 
-/// Additional methods on `EventLoop` that are specific to Unix.
+/// Additional methods on [`EventLoopBuilder`] that are specific to Unix.
-pub trait EventLoopExtUnix {
+pub trait EventLoopBuilderExtUnix {
-    /// Builds a new `EventLoop` that is forced to use X11.
+    /// Force using X11.
-    ///
-    /// # Panics
-    ///
-    /// If called outside the main thread. To initialize an X11 event loop outside
-    /// the main thread, use [`new_x11_any_thread`](#tymethod.new_x11_any_thread).
     #[cfg(feature = "x11")]
-    fn new_x11() -> Result<Self, XNotSupported>
+    fn with_x11(&mut self) -> &mut Self;
-    where
-        Self: Sized;
 
-    /// Builds a new `EventLoop` that is forced to use Wayland.
+    /// Force using Wayland.
-    ///
-    /// # Panics
-    ///
-    /// If called outside the main thread. To initialize a Wayland event loop outside
-    /// the main thread, use [`new_wayland_any_thread`](#tymethod.new_wayland_any_thread).
     #[cfg(feature = "wayland")]
-    fn new_wayland() -> Self
+    fn with_wayland(&mut self) -> &mut Self;
-    where
-        Self: Sized;
 
-    /// Builds a new `EventLoop` on any thread.
+    /// Whether to allow the event loop to be created off of the main thread.
     ///
-    /// This method bypasses the cross-platform compatibility requirement
+    /// By default, the window is only allowed to be created on the main
-    /// that `EventLoop` be created on the main thread.
+    /// thread, to make platform compatibility easier.
-    fn new_any_thread() -> Self
+    fn with_any_thread(&mut self, any_thread: bool) -> &mut Self;
-    where
-        Self: Sized;
-
-    /// Builds a new X11 `EventLoop` on any thread.
-    ///
-    /// This method bypasses the cross-platform compatibility requirement
-    /// that `EventLoop` be created on the main thread.
-    #[cfg(feature = "x11")]
-    fn new_x11_any_thread() -> Result<Self, XNotSupported>
-    where
-        Self: Sized;
-
-    /// Builds a new Wayland `EventLoop` on any thread.
-    ///
-    /// This method bypasses the cross-platform compatibility requirement
-    /// that `EventLoop` be created on the main thread.
-    #[cfg(feature = "wayland")]
-    fn new_wayland_any_thread() -> Self
-    where
-        Self: Sized;
 }
 
-fn wrap_ev<T>(event_loop: LinuxEventLoop<T>) -> EventLoop<T> {
+impl<T> EventLoopBuilderExtUnix for EventLoopBuilder<T> {
-    EventLoop {
-        event_loop,
-        _marker: std::marker::PhantomData,
-    }
-}
-
-impl<T> EventLoopExtUnix for EventLoop<T> {
-    #[inline]
-    fn new_any_thread() -> Self {
-        wrap_ev(LinuxEventLoop::new_any_thread())
-    }
-
     #[inline]
     #[cfg(feature = "x11")]
-    fn new_x11_any_thread() -> Result<Self, XNotSupported> {
+    fn with_x11(&mut self) -> &mut Self {
-        LinuxEventLoop::new_x11_any_thread().map(wrap_ev)
+        self.platform_specific.forced_backend = Some(Backend::X);
+        self
     }
 
     #[inline]
     #[cfg(feature = "wayland")]
-    fn new_wayland_any_thread() -> Self {
+    fn with_wayland(&mut self) -> &mut Self {
-        wrap_ev(
+        self.platform_specific.forced_backend = Some(Backend::Wayland);
-            LinuxEventLoop::new_wayland_any_thread()
+        self
-                // TODO: propagate
-                .expect("failed to open Wayland connection"),
-        )
     }
 
     #[inline]
-    #[cfg(feature = "x11")]
+    fn with_any_thread(&mut self, any_thread: bool) -> &mut Self {
-    fn new_x11() -> Result<Self, XNotSupported> {
+        self.platform_specific.any_thread = any_thread;
-        LinuxEventLoop::new_x11().map(wrap_ev)
+        self
-    }
-
-    #[inline]
-    #[cfg(feature = "wayland")]
-    fn new_wayland() -> Self {
-        wrap_ev(
-            LinuxEventLoop::new_wayland()
-                // TODO: propagate
-                .expect("failed to open Wayland connection"),
-        )
     }
 }
 

src/platform/windows.rs

@@ -9,62 +9,61 @@ use winapi::shared::windef::{HMENU, HWND};
 use crate::{
     dpi::PhysicalSize,
     event::DeviceId,
-    event_loop::EventLoop,
+    event_loop::EventLoopBuilder,
     monitor::MonitorHandle,
-    platform_impl::{EventLoop as WindowsEventLoop, Parent, WinIcon},
+    platform_impl::{Parent, WinIcon},
     window::{BadIcon, Icon, Theme, Window, WindowBuilder},
 };
 
 /// Additional methods on `EventLoop` that are specific to Windows.
-pub trait EventLoopExtWindows {
+pub trait EventLoopBuilderExtWindows {
-    /// Creates an event loop off of the main thread.
+    /// Whether to allow the event loop to be created off of the main thread.
+    ///
+    /// By default, the window is only allowed to be created on the main
+    /// thread, to make platform compatibility easier.
     ///
     /// # `Window` caveats
     ///
     /// Note that any `Window` created on the new thread will be destroyed when the thread
     /// terminates. Attempting to use a `Window` after its parent thread terminates has
     /// unspecified, although explicitly not undefined, behavior.
-    fn new_any_thread() -> Self
+    fn with_any_thread(&mut self, any_thread: bool) -> &mut Self;
-    where
-        Self: Sized;
 
-    /// By default, winit on Windows will attempt to enable process-wide DPI awareness. If that's
+    /// Whether to enable process-wide DPI awareness.
-    /// undesirable, you can create an `EventLoop` using this function instead.
-    fn new_dpi_unaware() -> Self
-    where
-        Self: Sized;
-
-    /// Creates a DPI-unaware event loop off of the main thread.
     ///
-    /// The `Window` caveats in [`new_any_thread`](EventLoopExtWindows::new_any_thread) also apply here.
+    /// By default, `winit` will attempt to enable process-wide DPI awareness. If
-    fn new_dpi_unaware_any_thread() -> Self
+    /// that's undesirable, you can disable it with this function.
-    where
+    ///
-        Self: Sized;
+    /// # Example
+    ///
+    /// Disable process-wide DPI awareness.
+    ///
+    /// ```
+    /// use winit::event_loop::EventLoopBuilder;
+    /// #[cfg(target_os = "windows")]
+    /// use winit::platform::windows::EventLoopBuilderExtWindows;
+    ///
+    /// let mut builder = EventLoopBuilder::new();
+    /// #[cfg(target_os = "windows")]
+    /// builder.with_dpi_aware(false);
+    /// # if false { // We can't test this part
+    /// let event_loop = builder.build();
+    /// # }
+    /// ```
+    fn with_dpi_aware(&mut self, dpi_aware: bool) -> &mut Self;
 }
 
-impl<T> EventLoopExtWindows for EventLoop<T> {
+impl<T> EventLoopBuilderExtWindows for EventLoopBuilder<T> {
     #[inline]
-    fn new_any_thread() -> Self {
+    fn with_any_thread(&mut self, any_thread: bool) -> &mut Self {
-        EventLoop {
+        self.platform_specific.any_thread = any_thread;
-            event_loop: WindowsEventLoop::new_any_thread(),
+        self
-            _marker: ::std::marker::PhantomData,
-        }
     }
 
     #[inline]
-    fn new_dpi_unaware() -> Self {
+    fn with_dpi_aware(&mut self, dpi_aware: bool) -> &mut Self {
-        EventLoop {
+        self.platform_specific.dpi_aware = dpi_aware;
-            event_loop: WindowsEventLoop::new_dpi_unaware(),
+        self
-            _marker: ::std::marker::PhantomData,
-        }
-    }
-
-    #[inline]
-    fn new_dpi_unaware_any_thread() -> Self {
-        EventLoop {
-            event_loop: WindowsEventLoop::new_dpi_unaware_any_thread(),
-            _marker: ::std::marker::PhantomData,
-        }
     }
 }
 

src/platform_impl/android/mod.rs

@@ -71,6 +71,9 @@ pub struct EventLoop<T: 'static> {
     running: bool,
 }
 
+#[derive(Default, Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) struct PlatformSpecificEventLoopAttributes {}
+
 macro_rules! call_event_handler {
     ( $event_handler:expr, $window_target:expr, $cf:expr, $event:expr ) => {{
         if let ControlFlow::ExitWithCode(code) = $cf {
@@ -82,7 +85,7 @@ macro_rules! call_event_handler {
 }
 
 impl<T: 'static> EventLoop<T> {
-    pub fn new() -> Self {
+    pub(crate) fn new(_: &PlatformSpecificEventLoopAttributes) -> Self {
         Self {
             window_target: event_loop::EventLoopWindowTarget {
                 p: EventLoopWindowTarget {

src/platform_impl/ios/event_loop.rs

@@ -69,8 +69,11 @@ pub struct EventLoop<T: 'static> {
     window_target: RootEventLoopWindowTarget<T>,
 }
 
+#[derive(Default, Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) struct PlatformSpecificEventLoopAttributes {}
+
 impl<T: 'static> EventLoop<T> {
-    pub fn new() -> EventLoop<T> {
+    pub(crate) fn new(_: &PlatformSpecificEventLoopAttributes) -> EventLoop<T> {
         static mut SINGLETON_INIT: bool = false;
         unsafe {
             assert_main_thread!("`EventLoop` can only be created on the main thread on iOS");

src/platform_impl/ios/mod.rs

@@ -78,8 +78,10 @@ mod window;
 
 use std::fmt;
 
-pub use self::{
+pub(crate) use self::{
-    event_loop::{EventLoop, EventLoopProxy, EventLoopWindowTarget},
+    event_loop::{
+        EventLoop, EventLoopProxy, EventLoopWindowTarget, PlatformSpecificEventLoopAttributes,
+    },
     monitor::{MonitorHandle, VideoMode},
     window::{PlatformSpecificWindowBuilderAttributes, Window, WindowId},
 };

src/platform_impl/linux/mod.rs

@@ -49,6 +49,29 @@ pub mod x11;
 /// If this variable is set with any other value, winit will panic.
 const BACKEND_PREFERENCE_ENV_VAR: &str = "WINIT_UNIX_BACKEND";
 
+#[derive(Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) enum Backend {
+    #[cfg(feature = "x11")]
+    X,
+    #[cfg(feature = "wayland")]
+    Wayland,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) struct PlatformSpecificEventLoopAttributes {
+    pub(crate) forced_backend: Option<Backend>,
+    pub(crate) any_thread: bool,
+}
+
+impl Default for PlatformSpecificEventLoopAttributes {
+    fn default() -> Self {
+        Self {
+            forced_backend: None,
+            any_thread: false,
+        }
+    }
+}
+
 #[derive(Clone)]
 pub struct PlatformSpecificWindowBuilderAttributes {
     #[cfg(feature = "x11")]
@@ -568,13 +591,28 @@ impl<T: 'static> Clone for EventLoopProxy<T> {
 }
 
 impl<T: 'static> EventLoop<T> {
-    pub fn new() -> EventLoop<T> {
+    pub(crate) fn new(attributes: &PlatformSpecificEventLoopAttributes) -> Self {
-        assert_is_main_thread("new_any_thread");
+        if !attributes.any_thread && !is_main_thread() {
-
+            panic!(
-        EventLoop::new_any_thread()
+                "Initializing the event loop outside of the main thread is a significant \
+                 cross-platform compatibility hazard. If you absolutely need to create an \
+                 EventLoop on a different thread, you can use the \
+                 `EventLoopBuilderExtUnix::any_thread` function."
+            );
+        }
+
+        #[cfg(feature = "x11")]
+        if attributes.forced_backend == Some(Backend::X) {
+            // TODO: Propagate
+            return EventLoop::new_x11_any_thread().unwrap();
+        }
+
+        #[cfg(feature = "wayland")]
+        if attributes.forced_backend == Some(Backend::Wayland) {
+            // TODO: Propagate
+            return EventLoop::new_wayland_any_thread().expect("failed to open Wayland connection");
         }
 
-    pub fn new_any_thread() -> EventLoop<T> {
         if let Ok(env_var) = env::var(BACKEND_PREFERENCE_ENV_VAR) {
             match env_var.as_str() {
                 "x11" => {
@@ -623,26 +661,12 @@ impl<T: 'static> EventLoop<T> {
     }
 
     #[cfg(feature = "wayland")]
-    pub fn new_wayland() -> Result<EventLoop<T>, Box<dyn Error>> {
+    fn new_wayland_any_thread() -> Result<EventLoop<T>, Box<dyn Error>> {
-        assert_is_main_thread("new_wayland_any_thread");
-
-        EventLoop::new_wayland_any_thread()
-    }
-
-    #[cfg(feature = "wayland")]
-    pub fn new_wayland_any_thread() -> Result<EventLoop<T>, Box<dyn Error>> {
         wayland::EventLoop::new().map(EventLoop::Wayland)
     }
 
     #[cfg(feature = "x11")]
-    pub fn new_x11() -> Result<EventLoop<T>, XNotSupported> {
+    fn new_x11_any_thread() -> Result<EventLoop<T>, XNotSupported> {
-        assert_is_main_thread("new_x11_any_thread");
-
-        EventLoop::new_x11_any_thread()
-    }
-
-    #[cfg(feature = "x11")]
-    pub fn new_x11_any_thread() -> Result<EventLoop<T>, XNotSupported> {
         let xconn = match X11_BACKEND.lock().as_ref() {
             Ok(xconn) => xconn.clone(),
             Err(err) => return Err(err.clone()),
@@ -750,17 +774,6 @@ fn sticky_exit_callback<T, F>(
     }
 }
 
-fn assert_is_main_thread(suggested_method: &str) {
-    if !is_main_thread() {
-        panic!(
-            "Initializing the event loop outside of the main thread is a significant \
-             cross-platform compatibility hazard. If you really, absolutely need to create an \
-             EventLoop on a different thread, please use the `EventLoopExtUnix::{}` function.",
-            suggested_method
-        );
-    }
-}
-
 #[cfg(target_os = "linux")]
 fn is_main_thread() -> bool {
     use libc::{c_long, getpid, syscall, SYS_gettid};

src/platform_impl/macos/app_delegate.rs

@@ -13,12 +13,8 @@ use std::{
 static AUX_DELEGATE_STATE_NAME: &str = "auxState";
 
 pub struct AuxDelegateState {
-    /// We store this value in order to be able to defer setting the activation policy until
-    /// after the app has finished launching. If the activation policy is set earlier, the
-    /// menubar is initially unresponsive on macOS 10.15 for example.
     pub activation_policy: ActivationPolicy,
-
+    pub default_menu: bool,
-    pub create_default_menu: bool,
 }
 
 pub struct AppDelegateClass(pub *const Class);
@@ -54,11 +50,12 @@ extern "C" fn new(class: &Class, _: Sel) -> id {
     unsafe {
         let this: id = msg_send![class, alloc];
         let this: id = msg_send![this, init];
+        // TODO: Remove the need for this initialization here
         (*this).set_ivar(
             AUX_DELEGATE_STATE_NAME,
             Box::into_raw(Box::new(RefCell::new(AuxDelegateState {
                 activation_policy: ActivationPolicy::Regular,
-                create_default_menu: true,
+                default_menu: true,
             }))) as *mut c_void,
         );
         this

src/platform_impl/macos/app_state.rs

@@ -296,7 +296,7 @@ impl AppState {
         };
         HANDLER.set_ready();
         HANDLER.waker().start();
-        let create_default_menu = unsafe { get_aux_state_mut(app_delegate).create_default_menu };
+        let create_default_menu = unsafe { get_aux_state_mut(app_delegate).default_menu };
         if create_default_menu {
             // The menubar initialization should be before the `NewEvents` event, to allow
             // overriding of the default menu even if it's created
@@ -486,7 +486,7 @@ fn apply_activation_policy(app_delegate: &Object) {
         let ns_app = NSApp();
         // We need to delay setting the activation policy and activating the app
         // until `applicationDidFinishLaunching` has been called. Otherwise the
-        // menu bar won't be interactable.
+        // menu bar is initially unresponsive on macOS 10.15.
         let act_pol = get_aux_state_mut(app_delegate).activation_policy;
         ns_app.setActivationPolicy_(match act_pol {
             ActivationPolicy::Regular => NSApplicationActivationPolicyRegular,

src/platform_impl/macos/event_loop.rs

@@ -22,7 +22,10 @@ use crate::{
     event::Event,
     event_loop::{ControlFlow, EventLoopClosed, EventLoopWindowTarget as RootWindowTarget},
     monitor::MonitorHandle as RootMonitorHandle,
-    platform_impl::platform::{
+    platform::macos::ActivationPolicy,
+    platform_impl::{
+        get_aux_state_mut,
+        platform::{
             app::APP_CLASS,
             app_delegate::APP_DELEGATE_CLASS,
             app_state::{AppState, Callback},
@@ -30,6 +33,7 @@ use crate::{
             observer::*,
             util::IdRef,
         },
+    },
 };
 
 #[derive(Default)]
@@ -100,7 +104,9 @@ impl<T> EventLoopWindowTarget<T> {
 }
 
 pub struct EventLoop<T: 'static> {
-    pub(crate) delegate: IdRef,
+    /// The delegate is only weakly referenced by NSApplication, so we keep
+    /// it around here as well.
+    _delegate: IdRef,
 
     window_target: Rc<RootWindowTarget<T>>,
     panic_info: Rc<PanicInfo>,
@@ -114,8 +120,23 @@ pub struct EventLoop<T: 'static> {
     _callback: Option<Rc<Callback<T>>>,
 }
 
+#[derive(Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) struct PlatformSpecificEventLoopAttributes {
+    pub(crate) activation_policy: ActivationPolicy,
+    pub(crate) default_menu: bool,
+}
+
+impl Default for PlatformSpecificEventLoopAttributes {
+    fn default() -> Self {
+        Self {
+            activation_policy: Default::default(), // Regular
+            default_menu: true,
+        }
+    }
+}
+
 impl<T> EventLoop<T> {
-    pub fn new() -> Self {
+    pub(crate) fn new(attributes: &PlatformSpecificEventLoopAttributes) -> Self {
         let delegate = unsafe {
             let is_main_thread: BOOL = msg_send!(class!(NSThread), isMainThread);
             if is_main_thread == NO {
@@ -129,15 +150,21 @@ impl<T> EventLoop<T> {
             let app: id = msg_send![APP_CLASS.0, sharedApplication];
 
             let delegate = IdRef::new(msg_send![APP_DELEGATE_CLASS.0, new]);
+
+            let mut aux_state = get_aux_state_mut(&**delegate);
+            aux_state.activation_policy = attributes.activation_policy;
+            aux_state.default_menu = attributes.default_menu;
+
             autoreleasepool(|| {
                 let _: () = msg_send![app, setDelegate:*delegate];
             });
+
             delegate
         };
         let panic_info: Rc<PanicInfo> = Default::default();
         setup_control_flow_observers(Rc::downgrade(&panic_info));
         EventLoop {
-            delegate,
+            _delegate: delegate,
             window_target: Rc::new(RootWindowTarget {
                 p: Default::default(),
                 _marker: PhantomData,

src/platform_impl/macos/mod.rs

@@ -18,9 +18,12 @@ mod window_delegate;
 
 use std::{fmt, ops::Deref, sync::Arc};
 
-pub use self::{
+pub(crate) use self::{
-    app_delegate::{get_aux_state_mut, AuxDelegateState},
+    app_delegate::get_aux_state_mut,
-    event_loop::{EventLoop, EventLoopWindowTarget, Proxy as EventLoopProxy},
+    event_loop::{
+        EventLoop, EventLoopWindowTarget, PlatformSpecificEventLoopAttributes,
+        Proxy as EventLoopProxy,
+    },
     monitor::{MonitorHandle, VideoMode},
     window::{Id as WindowId, PlatformSpecificWindowBuilderAttributes, UnownedWindow},
 };

src/platform_impl/web/event_loop/mod.rs

@@ -16,8 +16,11 @@ pub struct EventLoop<T: 'static> {
     elw: root::EventLoopWindowTarget<T>,
 }
 
+#[derive(Default, Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) struct PlatformSpecificEventLoopAttributes {}
+
 impl<T> EventLoop<T> {
-    pub fn new() -> Self {
+    pub(crate) fn new(_: &PlatformSpecificEventLoopAttributes) -> Self {
         EventLoop {
             elw: root::EventLoopWindowTarget {
                 p: WindowTarget::new(),

src/platform_impl/web/mod.rs

@@ -28,8 +28,9 @@ mod backend;
 
 pub use self::device::Id as DeviceId;
 pub use self::error::OsError;
-pub use self::event_loop::{
+pub(crate) use self::event_loop::{
-    EventLoop, Proxy as EventLoopProxy, WindowTarget as EventLoopWindowTarget,
+    EventLoop, PlatformSpecificEventLoopAttributes, Proxy as EventLoopProxy,
+    WindowTarget as EventLoopWindowTarget,
 };
 pub use self::monitor::{Handle as MonitorHandle, Mode as VideoMode};
 pub use self::window::{

src/platform_impl/windows/event_loop.rs

@@ -113,48 +113,44 @@ pub struct EventLoop<T: 'static> {
     window_target: RootELW<T>,
 }
 
+#[derive(Debug, Copy, Clone, PartialEq, Hash)]
+pub(crate) struct PlatformSpecificEventLoopAttributes {
+    pub(crate) any_thread: bool,
+    pub(crate) dpi_aware: bool,
+}
+
+impl Default for PlatformSpecificEventLoopAttributes {
+    fn default() -> Self {
+        Self {
+            any_thread: false,
+            dpi_aware: true,
+        }
+    }
+}
+
 pub struct EventLoopWindowTarget<T: 'static> {
     thread_id: DWORD,
     thread_msg_target: HWND,
     pub(crate) runner_shared: EventLoopRunnerShared<T>,
 }
 
-macro_rules! main_thread_check {
-    ($fn_name:literal) => {{
-        let thread_id = unsafe { processthreadsapi::GetCurrentThreadId() };
-        if thread_id != main_thread_id() {
-            panic!(concat!(
-                "Initializing the event loop outside of the main thread is a significant \
-                 cross-platform compatibility hazard. If you really, absolutely need to create an \
-                 EventLoop on a different thread, please use the `EventLoopExtWindows::",
-                $fn_name,
-                "` function."
-            ));
-        }
-    }};
-}
-
 impl<T: 'static> EventLoop<T> {
-    pub fn new() -> EventLoop<T> {
+    pub(crate) fn new(attributes: &PlatformSpecificEventLoopAttributes) -> Self {
-        main_thread_check!("new_any_thread");
-
-        Self::new_any_thread()
-    }
-
-    pub fn new_any_thread() -> EventLoop<T> {
-        become_dpi_aware();
-        Self::new_dpi_unaware_any_thread()
-    }
-
-    pub fn new_dpi_unaware() -> EventLoop<T> {
-        main_thread_check!("new_dpi_unaware_any_thread");
-
-        Self::new_dpi_unaware_any_thread()
-    }
-
-    pub fn new_dpi_unaware_any_thread() -> EventLoop<T> {
         let thread_id = unsafe { processthreadsapi::GetCurrentThreadId() };
 
+        if !attributes.any_thread && thread_id != main_thread_id() {
+            panic!(
+                "Initializing the event loop outside of the main thread is a significant \
+                 cross-platform compatibility hazard. If you absolutely need to create an \
+                 EventLoop on a different thread, you can use the \
+                 `EventLoopBuilderExtWindows::any_thread` function."
+            );
+        }
+
+        if attributes.dpi_aware {
+            become_dpi_aware();
+        }
+
         let thread_msg_target = create_event_target_window::<T>();
 
         let send_thread_msg_target = thread_msg_target as usize;

src/platform_impl/windows/mod.rs

@@ -2,8 +2,10 @@
 
 use winapi::{self, shared::windef::HMENU, shared::windef::HWND};
 
-pub use self::{
+pub(crate) use self::{
-    event_loop::{EventLoop, EventLoopProxy, EventLoopWindowTarget},
+    event_loop::{
+        EventLoop, EventLoopProxy, EventLoopWindowTarget, PlatformSpecificEventLoopAttributes,
+    },
     icon::WinIcon,
     monitor::{MonitorHandle, VideoMode},
     window::Window,

src/window.rs

@@ -83,7 +83,7 @@ impl WindowId {
     }
 }
 
-/// Object that allows you to build windows.
+/// Object that allows building windows.
 #[derive(Clone, Default)]
 pub struct WindowBuilder {
     /// The attributes to use to create the window.