Implement downcasting function from Surface to Window et al.

Author: jgcodes2020

winit-core/src/lib.rs

@@ -18,6 +18,7 @@ pub mod event_loop;
 pub mod icon;
 pub mod keyboard;
 pub mod monitor;
+#[macro_use]
 pub mod window;
 
 // `Instant` is not actually available on `wasm32-unknown-unknown`, the `std` implementation there

winit-core/src/window.rs

@@ -461,6 +461,12 @@ impl_dyn_casting!(PlatformWindowAttributes);
 /// 
 /// The surface is closed when dropped.
 pub trait Surface: AsAny + Send + Sync + fmt::Debug {
+    /// Attempts to downcast this surface to a core surface type, e.g. [`Window`].
+    fn try_downcast(&self) -> Option<SurfaceDowncastRef<'_>>;
+
+    /// Attempts to downcast this surface mutably to a core surface type, e.g. [`Window`].
+    fn try_downcast_mut(&mut self) -> Option<SurfaceDowncastMut<'_>>;
+
     /// Returns an identifier unique to the window.
     fn id(&self) -> SurfaceId;
 
@@ -1965,3 +1971,47 @@ mod tests {
         .is_some());
     }
 }
+/// Dynamic reference to one of the common surface traits.
+pub enum SurfaceDowncastRef<'a> {
+    /// A toplevel window, see [`Window`] for details.
+    Window(&'a dyn Window),
+}
+
+/// Dynamic mutable reference to one of the common surface traits.
+pub enum SurfaceDowncastMut<'a> {
+    /// A toplevel window, see [`Window`] for details.
+    Window(&'a mut dyn Window),
+}
+
+/// Helper macro for implementing [`Surface::try_downcast`] and [`Surface::try_downcast_mut`].
+/// ## Syntax
+/// Use the names of variants of [`SurfaceDowncastRef`] or [`SurfaceDowncastMut`] to return that type:
+/// ```ignore
+/// impl_surface_downcast!(Window);
+/// ```
+/// You may also use the special identifier `None` to cause the downcast to fail.
+/// ```ignore
+/// impl_surface_downcast!(None);
+/// ```
+#[macro_export]
+macro_rules! impl_surface_downcast {
+    (None) => {
+        fn try_downcast(&self) -> Option<$crate::window::SurfaceDowncastRef<'_>> {
+            None
+        }
+
+        fn try_downcast_mut(&mut self) -> Option<$crate::window::SurfaceDowncastMut<'_>> {
+            None
+        }
+    };
+    ($variant:ident) => {
+        fn try_downcast(&self) -> Option<$crate::window::SurfaceDowncastRef<'_>> {
+            Some($crate::window::SurfaceDowncastRef::$variant(self))
+        }
+
+        fn try_downcast_mut(&mut self) -> Option<$crate::window::SurfaceDowncastMut<'_>> {
+            Some($crate::window::SurfaceDowncastMut::$variant(self))
+            
+        }
+    };
+}

winit-orbital/src/window.rs

@@ -5,6 +5,7 @@ use std::sync::{Arc, Mutex};
 use dpi::{PhysicalInsets, PhysicalPosition, PhysicalSize, Position, Size};
 use winit_core::cursor::Cursor;
 use winit_core::error::{NotSupportedError, RequestError};
+use winit_core::impl_surface_downcast;
 use winit_core::monitor::{Fullscreen, MonitorHandle as CoreMonitorHandle};
 use winit_core::window::{self, Window as CoreWindow, Surface as CoreSurface, SurfaceId};
 
@@ -157,6 +158,8 @@ impl Window {
 }
 
 impl CoreSurface for Window {
+    impl_surface_downcast!(Window);
+    
     fn id(&self) -> SurfaceId {
         SurfaceId::from_raw(self.window_socket.fd)
     }

winit-wayland/src/window/mod.rs

@@ -18,6 +18,7 @@ use winit_core::cursor::Cursor;
 use winit_core::error::{NotSupportedError, RequestError};
 use winit_core::event::{Ime, WindowEvent};
 use winit_core::event_loop::AsyncRequestSerial;
+use winit_core::impl_surface_downcast;
 use winit_core::monitor::{Fullscreen, MonitorHandle as CoreMonitorHandle};
 use winit_core::window::{
     CursorGrabMode, ImeCapabilities, ImeRequest, ImeRequestError, ResizeDirection, Theme,
@@ -283,6 +284,8 @@ impl rwh_06::HasDisplayHandle for Window {
 }
 
 impl CoreSurface for Window {
+    impl_surface_downcast!(Window);
+
     fn id(&self) -> SurfaceId {
         self.window_id
     }

winit-web/src/window.rs

@@ -10,6 +10,7 @@ use web_sys::HtmlCanvasElement;
 use winit_core::cursor::Cursor;
 use winit_core::error::{NotSupportedError, RequestError};
 use winit_core::icon::Icon;
+use winit_core::impl_surface_downcast;
 use winit_core::monitor::{Fullscreen, MonitorHandle as CoremMonitorHandle};
 use winit_core::window::{
     CursorGrabMode, ImeRequestError, ResizeDirection, Surface as RootSurface, SurfaceId, Theme,
@@ -103,6 +104,8 @@ impl Window {
 }
 
 impl RootSurface for Window {
+    impl_surface_downcast!(Window);
+    
     fn id(&self) -> SurfaceId {
         self.inner.queue(|inner| inner.id)
     }

winit-x11/src/window.rs

@@ -16,6 +16,7 @@ use winit_core::error::{NotSupportedError, RequestError};
 use winit_core::event::{SurfaceSizeWriter, WindowEvent};
 use winit_core::event_loop::AsyncRequestSerial;
 use winit_core::icon::RgbaIcon;
+use winit_core::impl_surface_downcast;
 use winit_core::monitor::{
     Fullscreen, MonitorHandle as CoreMonitorHandle, MonitorHandleProvider, VideoMode,
 };
@@ -67,6 +68,8 @@ impl Window {
 }
 
 impl CoreSurface for Window {
+    impl_surface_downcast!(Window);
+
     fn id(&self) -> SurfaceId {
         self.0.id()
     }