api: make surfaceSend

CHANGELOG.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+- Change `Surface` to be `Send`. This makes it consistent with the context, so now they are both `Send` but not `Sync`.
+
 # Version 0.31.2
 
 - Fixed EGL not setting context version with EGL versions before 1.5 and missing context ext.

glutin/src/api/cgl/surface.rs

@@ -81,7 +81,7 @@ impl Display {
             config: config.clone(),
             ns_view,
             ns_window,
-            _nosendsync: PhantomData,
+            _nosync: PhantomData,
             _ty: PhantomData,
         };
         Ok(surface)
@@ -94,10 +94,13 @@ pub struct Surface<T: SurfaceTypeTrait> {
     config: Config,
     pub(crate) ns_view: MainThreadBound<Id<NSView>>,
     ns_window: MainThreadBound<Id<NSWindow>>,
-    _nosendsync: PhantomData<*const std::ffi::c_void>,
+    _nosync: PhantomData<*const std::ffi::c_void>,
     _ty: PhantomData<T>,
 }
 
+// Impl only `Send` for Surface.
+unsafe impl<T: SurfaceTypeTrait> Send for Surface<T> {}
+
 impl<T: SurfaceTypeTrait> GlSurface<T> for Surface<T> {
     type Context = PossiblyCurrentContext;
     type SurfaceType = T;

glutin/src/api/egl/surface.rs

@@ -252,6 +252,9 @@ pub struct Surface<T: SurfaceTypeTrait> {
     _ty: PhantomData<T>,
 }
 
+// Impl only `Send` for Surface.
+unsafe impl<T: SurfaceTypeTrait> Send for Surface<T> {}
+
 impl<T: SurfaceTypeTrait> Surface<T> {
     /// Swaps the underlying back buffers when the surface is not single
     /// buffered and pass the [`Rect`] information to the system

glutin/src/api/glx/surface.rs

@@ -159,6 +159,9 @@ pub struct Surface<T: SurfaceTypeTrait> {
     _ty: PhantomData<T>,
 }
 
+// Impl only `Send` for Surface.
+unsafe impl<T: SurfaceTypeTrait> Send for Surface<T> {}
+
 impl<T: SurfaceTypeTrait> Surface<T> {
     /// # Safety
     ///

glutin/src/api/wgl/surface.rs

@@ -81,6 +81,9 @@ pub struct Surface<T: SurfaceTypeTrait> {
     _ty: PhantomData<T>,
 }
 
+// Impl only `Send` for Surface.
+unsafe impl<T: SurfaceTypeTrait> Send for Surface<T> {}
+
 impl<T: SurfaceTypeTrait> Drop for Surface<T> {
     fn drop(&mut self) {
         unsafe {

glutin/src/surface.rs

@@ -262,10 +262,11 @@ pub enum SurfaceType {
 
 /// The GL surface that is used for rendering.
 ///
-/// The GL surface is not thread safe, it can neither be [`Send`] nor [`Sync`],
-/// so it should be created on the thread it'll be used to render.
+/// Similar to the context, the GL surface is [`Send`] but not [`Sync`]. This
+/// means it could be sent to a different thread as long as it is not current on
+/// another thread.
 ///
-/// ```compile_fail
+/// ```no_run
 /// fn test_send<T: Send>() {}
 /// test_send::<glutin::surface::Surface<glutin::surface::WindowSurface>>();
 /// ```

glutin_examples/examples/switch_render_thread.rs

@@ -0,0 +1,316 @@
+use std::error::Error;
+use std::num::NonZeroU32;
+use std::sync::mpsc::{self, Sender};
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+use glutin::config::ConfigTemplateBuilder;
+use glutin::context::{ContextAttributesBuilder, PossiblyCurrentContext};
+use glutin::display::GetGlDisplay;
+use glutin::error::{Error as GlutinError, ErrorKind};
+use glutin::prelude::{NotCurrentGlContext, PossiblyCurrentGlContext, *};
+use glutin::surface::{GlSurface, Surface, WindowSurface};
+use glutin_examples::gl::types::GLfloat;
+use glutin_examples::{gl_config_picker, Renderer};
+use glutin_winit::{self, DisplayBuilder, GlWindow};
+use raw_window_handle::HasRawWindowHandle;
+use winit::dpi::PhysicalSize;
+use winit::event::{ElementState, Event, WindowEvent};
+use winit::event_loop::{EventLoopBuilder, EventLoopProxy};
+use winit::window::{Window, WindowBuilder};
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let event_loop = EventLoopBuilder::<PlatformThreadEvent>::with_user_event().build().unwrap();
+
+    let (_window, render_context) = create_window_with_render_context(&event_loop)?;
+    let render_context = Arc::new(Mutex::new(render_context));
+
+    // `EventLoopProxy` allows you to dispatch custom events to the main Winit event
+    // loop from any thread.
+    let event_loop_proxy = event_loop.create_proxy();
+
+    let (_render_threads, render_thread_senders) =
+        spawn_render_threads(render_context, event_loop_proxy);
+
+    let mut app_state = AppState {
+        render_thread_senders,
+        render_thread_index: 0,
+        thread_switch_in_progress: false,
+    };
+    app_state.send_event_to_current_render_thread(RenderThreadEvent::MakeCurrent);
+
+    event_loop.run(move |event, elwt| match event {
+        Event::WindowEvent { event: WindowEvent::CloseRequested, .. } => elwt.exit(),
+        Event::WindowEvent { event: WindowEvent::Resized(size), .. } => {
+            if size.width != 0 && size.height != 0 {
+                app_state.send_event_to_current_render_thread(RenderThreadEvent::Resize(
+                    PhysicalSize {
+                        width: NonZeroU32::new(size.width).unwrap(),
+                        height: NonZeroU32::new(size.height).unwrap(),
+                    },
+                ));
+            }
+        },
+        Event::WindowEvent { event: WindowEvent::RedrawRequested, .. } => {
+            app_state.send_event_to_current_render_thread(RenderThreadEvent::Draw);
+        },
+        Event::WindowEvent {
+            event: WindowEvent::MouseInput { state: ElementState::Pressed, .. },
+            ..
+        } => {
+            app_state.start_render_thread_switch();
+        },
+        Event::UserEvent(event) => match event {
+            PlatformThreadEvent::ContextNotCurrent => {
+                app_state.complete_render_thread_switch();
+            },
+        },
+        _ => (),
+    })?;
+
+    Ok(())
+}
+
+struct AppState {
+    render_thread_senders: Vec<Sender<RenderThreadEvent>>,
+    render_thread_index: usize,
+    thread_switch_in_progress: bool,
+}
+
+impl AppState {
+    fn send_event_to_current_render_thread(&self, event: RenderThreadEvent) {
+        if self.thread_switch_in_progress {
+            return;
+        }
+
+        if let Some(tx) = self.render_thread_senders.get(self.render_thread_index) {
+            tx.send(event).expect("sending event to current render thread failed");
+        }
+    }
+
+    fn start_render_thread_switch(&mut self) {
+        self.send_event_to_current_render_thread(RenderThreadEvent::MakeNotCurrent);
+
+        self.thread_switch_in_progress = true;
+    }
+
+    fn complete_render_thread_switch(&mut self) {
+        self.thread_switch_in_progress = false;
+
+        self.render_thread_index += 1;
+        if self.render_thread_index == self.render_thread_senders.len() {
+            self.render_thread_index = 0;
+        }
+
+        self.send_event_to_current_render_thread(RenderThreadEvent::MakeCurrent);
+        self.send_event_to_current_render_thread(RenderThreadEvent::Draw);
+    }
+}
+
+/// A rendering context that can be shared between tasks.
+struct RenderContext {
+    context: Option<PossiblyCurrentContext>,
+    surface: Surface<WindowSurface>,
+    renderer: Renderer,
+}
+
+unsafe impl Send for RenderContext {}
+
+impl RenderContext {
+    fn new(
+        context: PossiblyCurrentContext,
+        surface: Surface<WindowSurface>,
+        renderer: Renderer,
+    ) -> Self {
+        Self { context: Some(context), surface, renderer }
+    }
+
+    fn make_current(&mut self) -> Result<(), impl Error> {
+        let ctx =
+            self.context.take().ok_or_else(|| GlutinError::from(ErrorKind::BadContextState))?;
+        let result = ctx.make_current(&self.surface);
+        self.context = Some(ctx);
+        result
+    }
+
+    fn make_not_current(&mut self) -> Result<(), impl Error> {
+        let ctx =
+            self.context.take().ok_or_else(|| GlutinError::from(ErrorKind::BadContextState))?;
+        let not_current_ctx = ctx.make_not_current()?;
+        self.context = Some(not_current_ctx.treat_as_possibly_current());
+        Ok::<(), GlutinError>(())
+    }
+
+    fn swap_buffers(&mut self) -> Result<(), impl Error> {
+        let ctx =
+            self.context.take().ok_or_else(|| GlutinError::from(ErrorKind::BadContextState))?;
+        let result = self.surface.swap_buffers(&ctx);
+        self.context = Some(ctx);
+        result
+    }
+
+    fn draw_with_clear_color(&self, red: GLfloat, green: GLfloat, blue: GLfloat, alpha: GLfloat) {
+        self.renderer.draw_with_clear_color(red, green, blue, alpha)
+    }
+
+    fn resize(&mut self, size: PhysicalSize<NonZeroU32>) {
+        let Some(ctx) = self.context.take() else {
+            return;
+        };
+        self.surface.resize(&ctx, size.width, size.height);
+        self.context = Some(ctx);
+
+        self.renderer.resize(size.width.get() as i32, size.height.get() as i32);
+    }
+}
+
+fn create_window_with_render_context(
+    event_loop: &winit::event_loop::EventLoop<PlatformThreadEvent>,
+) -> Result<(Window, RenderContext), Box<dyn Error>> {
+    let window_builder = WindowBuilder::new().with_transparent(true);
+
+    let template = ConfigTemplateBuilder::new().with_alpha_size(8);
+
+    let display_builder = DisplayBuilder::new().with_window_builder(Some(window_builder));
+
+    let (mut window, gl_config) = display_builder.build(event_loop, template, gl_config_picker)?;
+
+    println!("Picked a config with {} samples", gl_config.num_samples());
+
+    let raw_window_handle = window.as_ref().map(|window| window.raw_window_handle());
+
+    let window = window.take().unwrap();
+
+    let gl_display = gl_config.display();
+
+    let context_attributes = ContextAttributesBuilder::new().build(raw_window_handle);
+
+    let not_current_gl_context = unsafe {
+        gl_display
+            .create_context(&gl_config, &context_attributes)
+            .expect("failed to create context")
+    };
+
+    let attrs = window.build_surface_attributes(<_>::default());
+    let gl_surface =
+        unsafe { gl_config.display().create_window_surface(&gl_config, &attrs).unwrap() };
+
+    // Make it current.
+    let gl_context = not_current_gl_context.make_current(&gl_surface).unwrap();
+
+    // The context needs to be current for the Renderer to set up shaders and
+    // buffers. It also performs function loading, which needs a current context on
+    // WGL.
+    let renderer = Renderer::new(&gl_display);
+
+    let gl_context = gl_context.make_not_current().unwrap().treat_as_possibly_current();
+
+    Ok((window, RenderContext::new(gl_context, gl_surface, renderer)))
+}
+
+fn spawn_render_threads(
+    render_context: Arc<Mutex<RenderContext>>,
+    event_loop_proxy: EventLoopProxy<PlatformThreadEvent>,
+) -> (Vec<RenderThread>, Vec<Sender<RenderThreadEvent>>) {
+    let mut senders = Vec::new();
+    let mut render_threads = Vec::new();
+
+    for id in 0..3 {
+        let render_thread = RenderThread::new(id, render_context.clone());
+        let tx = render_thread.spawn(event_loop_proxy.clone());
+
+        render_threads.push(render_thread);
+        senders.push(tx);
+    }
+
+    (render_threads, senders)
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+struct Color {
+    r: GLfloat,
+    g: GLfloat,
+    b: GLfloat,
+    a: GLfloat,
+}
+
+impl Color {
+    fn new(r: GLfloat, g: GLfloat, b: GLfloat, a: GLfloat) -> Self {
+        Self { r, g, b, a }
+    }
+
+    fn new_from_index(color_index: i32) -> Self {
+        match color_index {
+            0 => Color::new(1.0, 0.0, 0.0, 0.9),
+            1 => Color::new(0.0, 1.0, 0.0, 0.9),
+            2 => Color::new(0.0, 0.0, 1.0, 0.9),
+            _ => Default::default(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum RenderThreadEvent {
+    Draw,
+    MakeCurrent,
+    MakeNotCurrent,
+    Resize(PhysicalSize<NonZeroU32>),
+}
+
+#[derive(Debug, Clone, Copy)]
+enum PlatformThreadEvent {
+    ContextNotCurrent,
+}
+
+struct RenderThread {
+    id: i32,
+    color: Color,
+    render_context: Arc<Mutex<RenderContext>>,
+}
+
+impl RenderThread {
+    fn new(id: i32, render_context: Arc<Mutex<RenderContext>>) -> Self {
+        let color = Color::new_from_index(id);
+        Self { id, color, render_context }
+    }
+
+    fn spawn(
+        &self,
+        event_loop_proxy: EventLoopProxy<PlatformThreadEvent>,
+    ) -> Sender<RenderThreadEvent> {
+        let (tx, rx) = mpsc::channel();
+
+        let (id, color, render_context) = (self.id, self.color, self.render_context.clone());
+
+        thread::spawn(move || {
+            for event in rx {
+                let mut render_context_guard = render_context.lock().unwrap();
+
+                match event {
+                    RenderThreadEvent::Draw => {
+                        println!("thread {}: drawing", id);
+                        render_context_guard
+                            .draw_with_clear_color(color.r, color.g, color.b, color.a);
+                        render_context_guard.swap_buffers().expect("swap buffers failed");
+                    },
+                    RenderThreadEvent::MakeCurrent => {
+                        println!("thread {}: make current", id);
+                        render_context_guard.make_current().expect("make current failed");
+                    },
+                    RenderThreadEvent::MakeNotCurrent => {
+                        println!("thread {}: make not current", id);
+                        render_context_guard.make_not_current().expect("make not current failed");
+                        event_loop_proxy
+                            .send_event(PlatformThreadEvent::ContextNotCurrent)
+                            .expect("sending context-not-current event failed");
+                    },
+                    RenderThreadEvent::Resize(size) => {
+                        render_context_guard.resize(size);
+                    },
+                }
+            }
+        });
+
+        tx
+    }
+}