wayland: Reuse buffers and pools; check buffer release

Also updates `winit` example to redraw on resize, which seems to be
necessary.

With this resizing seems to be entirely smooth, without visual
corruption from it overwriting the buffer the server is displaying.

src/wayland/mod.rs

@@ -0,0 +1,125 @@
+use crate::{error::unwrap, GraphicsContextImpl, SwBufError};
+use raw_window_handle::{WaylandDisplayHandle, WaylandWindowHandle};
+use wayland_client::{
+    backend::{Backend, ObjectId},
+    globals::{registry_queue_init, GlobalListContents},
+    protocol::{wl_registry, wl_shm, wl_surface},
+    Connection, Dispatch, EventQueue, Proxy, QueueHandle,
+};
+
+mod buffer;
+use buffer::WaylandBuffer;
+
+struct State;
+
+pub struct WaylandImpl {
+    event_queue: EventQueue<State>,
+    qh: QueueHandle<State>,
+    surface: wl_surface::WlSurface,
+    shm: wl_shm::WlShm,
+    buffers: Vec<WaylandBuffer>,
+}
+
+impl WaylandImpl {
+    pub unsafe fn new(
+        window_handle: WaylandWindowHandle,
+        display_handle: WaylandDisplayHandle,
+    ) -> Result<Self, SwBufError> {
+        let conn = Connection::from_backend(Backend::from_foreign_display(
+            display_handle.display as *mut _,
+        ));
+        let (globals, event_queue) = unwrap(
+            registry_queue_init(&conn),
+            "Failed to make round trip to server",
+        )?;
+        let qh = event_queue.handle();
+        let shm: wl_shm::WlShm = unwrap(
+            globals.bind(&qh, 1..=1, ()),
+            "Failed to instantiate Wayland Shm",
+        )?;
+        let surface_id = unwrap(
+            ObjectId::from_ptr(
+                wl_surface::WlSurface::interface(),
+                window_handle.surface as _,
+            ),
+            "Failed to create proxy for surface ID.",
+        )?;
+        let surface = unwrap(
+            wl_surface::WlSurface::from_id(&conn, surface_id),
+            "Failed to create proxy for surface ID.",
+        )?;
+        Ok(Self {
+            event_queue: event_queue,
+            qh,
+            surface,
+            shm,
+            buffers: Vec::new(),
+        })
+    }
+
+    // Allocate or reuse a buffer of the given size
+    fn buffer(&mut self, width: i32, height: i32) -> &WaylandBuffer {
+        if let Some(idx) = self.buffers.iter().position(|i| i.released()) {
+            self.buffers[idx].resize(width, height);
+            &mut self.buffers[idx]
+        } else {
+            self.buffers
+                .push(WaylandBuffer::new(&self.shm, width, height, &self.qh));
+            self.buffers.last().unwrap()
+        }
+    }
+}
+
+impl GraphicsContextImpl for WaylandImpl {
+    unsafe fn set_buffer(&mut self, buffer: &[u32], width: u16, height: u16) {
+        let _ = self.event_queue.dispatch_pending(&mut State);
+
+        let surface = self.surface.clone();
+        let wayland_buffer = self.buffer(width.into(), height.into());
+        wayland_buffer.write(buffer);
+        wayland_buffer.attach(&surface);
+
+        // FIXME: Proper damaging mechanism.
+        //
+        // In order to propagate changes on compositors which track damage, for now damage the entire surface.
+        if self.surface.version() < 4 {
+            // FIXME: Accommodate scale factor since wl_surface::damage is in terms of surface coordinates while
+            // wl_surface::damage_buffer is in buffer coordinates.
+            //
+            // i32::MAX is a valid damage box (most compositors interpret the damage box as "the entire surface")
+            self.surface.damage(0, 0, i32::MAX, i32::MAX);
+        } else {
+            // Introduced in version 4, it is an error to use this request in version 3 or lower.
+            self.surface
+                .damage_buffer(0, 0, width as i32, height as i32);
+        }
+        self.surface.commit();
+
+        let _ = self.event_queue.flush();
+    }
+}
+
+impl Dispatch<wl_registry::WlRegistry, GlobalListContents> for State {
+    fn event(
+        _: &mut State,
+        _: &wl_registry::WlRegistry,
+        _: wl_registry::Event,
+        _: &GlobalListContents,
+        _: &Connection,
+        _: &QueueHandle<State>,
+    ) {
+        // Ignore globals added after initialization
+    }
+}
+
+impl Dispatch<wl_shm::WlShm, ()> for State {
+    fn event(
+        _: &mut State,
+        _: &wl_shm::WlShm,
+        _: wl_shm::Event,
+        _: &(),
+        _: &Connection,
+        _: &QueueHandle<State>,
+    ) {
+    }
+}