Owned pixel buffer for no-copy presentation

Cargo.toml

@@ -14,7 +14,7 @@ rust-version = "1.60.0"
 
 [features]
 default = ["x11", "wayland", "wayland-dlopen"]
-wayland = ["wayland-backend", "wayland-client", "nix", "fastrand"]
+wayland = ["wayland-backend", "wayland-client", "memmap2", "nix", "fastrand"]
 wayland-dlopen = ["wayland-sys/dlopen"]
 x11 = ["bytemuck", "nix", "x11rb", "x11-dl"]
 
@@ -25,6 +25,7 @@ thiserror = "1.0.30"
 
 [target.'cfg(all(unix, not(any(target_vendor = "apple", target_os = "android", target_os = "redox"))))'.dependencies]
 bytemuck = { version = "1.12.3", optional = true }
+memmap2 = { version = "0.5.8", optional = true }
 nix = { version = "0.26.1", optional = true }
 wayland-backend = { version = "0.1.0", features = ["client_system"], optional = true }
 wayland-client = { version = "0.30.0", optional = true }

examples/winit.rs

@@ -32,21 +32,21 @@ fn main() {
                     let size = window.inner_size();
                     (size.width, size.height)
                 };
-                let buffer = (0..((width * height) as usize))
-                    .map(|index| {
-                        let y = index / (width as usize);
-                        let x = index % (width as usize);
-                        let red = x % 255;
-                        let green = y % 255;
-                        let blue = (x * y) % 255;
 
-                        let color = blue | (green << 8) | (red << 16);
+                surface.resize(width, height);
 
-                        color as u32
-                    })
-                    .collect::<Vec<_>>();
+                let buffer = surface.buffer_mut();
+                for index in 0..(width * height) {
+                    let y = index as u32 / width;
+                    let x = index as u32 % width;
+                    let red = x % 255;
+                    let green = y % 255;
+                    let blue = (x * y) % 255;
 
-                surface.set_buffer(&buffer, width as u16, height as u16);
+                    buffer[index as usize] = blue | (green << 8) | (red << 16);
+                }
+
+                surface.present();
             }
             Event::WindowEvent {
                 event: WindowEvent::CloseRequested,

src/lib.rs

@@ -71,6 +71,33 @@ macro_rules! make_dispatch {
         }
 
         impl SurfaceDispatch {
+            pub fn resize(&mut self, width: u32, height: u32) {
+                match self {
+                    $(
+                        $(#[$attr])*
+                        Self::$name(inner) => inner.resize(width, height),
+                    )*
+                }
+            }
+
+            pub fn buffer_mut(&mut self) -> &mut [u32] {
+                match self {
+                    $(
+                        $(#[$attr])*
+                        Self::$name(inner) => inner.buffer_mut(),
+                    )*
+                }
+            }
+
+            pub fn present(&mut self) {
+                match self {
+                    $(
+                        $(#[$attr])*
+                        Self::$name(inner) => inner.present(),
+                    )*
+                }
+            }
+
             unsafe fn set_buffer(&mut self, buffer: &[u32], width: u16, height: u16) {
                 match self {
                     $(
@@ -235,6 +262,18 @@ impl Surface {
         })
     }
 
+    pub fn resize(&mut self, width: u32, height: u32) {
+        self.surface_impl.resize(width, height);
+    }
+
+    pub fn buffer_mut(&mut self) -> &mut [u32] {
+        self.surface_impl.buffer_mut()
+    }
+
+    pub fn present(&mut self) {
+        self.surface_impl.present();
+    }
+
     /// Shows the given buffer with the given width and height on the window corresponding to this
     /// graphics context. Panics if buffer.len() ≠ width*height. If the size of the buffer does
     /// not match the size of the window, the buffer is drawn in the upper-left corner of the window.

src/wayland/buffer.rs

@@ -1,7 +1,9 @@
+use memmap2::MmapMut;
 use std::{
     ffi::CStr,
     fs::File,
-    os::unix::prelude::{AsRawFd, FileExt, FromRawFd},
+    os::unix::prelude::{AsRawFd, FromRawFd},
+    slice,
     sync::{
         atomic::{AtomicBool, Ordering},
         Arc,
@@ -69,9 +71,19 @@ fn create_memfile() -> File {
     panic!("Failed to generate non-existant shm name")
 }
 
+// Round size to use for pool for given dimentions, rounding up to power of 2
+fn get_pool_size(width: i32, height: i32) -> i32 {
+    ((width * height * 4) as u32).next_power_of_two() as i32
+}
+
+unsafe fn map_file(file: &File) -> MmapMut {
+    unsafe { MmapMut::map_mut(file.as_raw_fd()).expect("Failed to map shared memory") }
+}
+
 pub(super) struct WaylandBuffer {
     qh: QueueHandle<State>,
     tempfile: File,
+    map: MmapMut,
     pool: wl_shm_pool::WlShmPool,
     pool_size: i32,
     buffer: wl_buffer::WlBuffer,
@@ -82,8 +94,15 @@ pub(super) struct WaylandBuffer {
 
 impl WaylandBuffer {
     pub fn new(shm: &wl_shm::WlShm, width: i32, height: i32, qh: &QueueHandle<State>) -> Self {
+        // Calculate size to use for shm pool
+        let pool_size = get_pool_size(width, height);
+
+        // Create an `mmap` shared memory
         let tempfile = create_memfile();
-        let pool_size = width * height * 4;
+        let _ = tempfile.set_len(pool_size as u64);
+        let map = unsafe { map_file(&tempfile) };
+
+        // Create wayland shm pool and buffer
         let pool = shm.create_pool(tempfile.as_raw_fd(), pool_size, qh, ());
         let released = Arc::new(AtomicBool::new(true));
         let buffer = pool.create_buffer(
@@ -95,8 +114,10 @@ impl WaylandBuffer {
             qh,
             released.clone(),
         );
+
         Self {
             qh: qh.clone(),
+            map,
             tempfile,
             pool,
             pool_size,
@@ -119,6 +140,7 @@ impl WaylandBuffer {
                 let _ = self.tempfile.set_len(size as u64);
                 self.pool.resize(size);
                 self.pool_size = size;
+                self.map = unsafe { map_file(&self.tempfile) };
             }
 
             // Create buffer with correct size
@@ -131,15 +153,10 @@ impl WaylandBuffer {
                 &self.qh,
                 self.released.clone(),
             );
-        }
-    }
 
-    pub fn write(&self, buffer: &[u32]) {
-        let buffer =
-            unsafe { std::slice::from_raw_parts(buffer.as_ptr() as *const u8, buffer.len() * 4) };
-        self.tempfile
-            .write_all_at(buffer, 0)
-            .expect("Failed to write buffer to temporary file.");
+            self.width = width;
+            self.height = height;
+        }
     }
 
     pub fn attach(&self, surface: &wl_surface::WlSurface) {
@@ -150,6 +167,14 @@ impl WaylandBuffer {
     pub fn released(&self) -> bool {
         self.released.load(Ordering::SeqCst)
     }
+
+    fn len(&self) -> usize {
+        self.width as usize * self.height as usize
+    }
+
+    pub unsafe fn mapped_mut(&mut self) -> &mut [u32] {
+        unsafe { slice::from_raw_parts_mut(self.map.as_mut_ptr() as *mut u32, self.len()) }
+    }
 }
 
 impl Drop for WaylandBuffer {

src/wayland/mod.rs

@@ -47,6 +47,8 @@ pub struct WaylandImpl {
     display: Arc<WaylandDisplayImpl>,
     surface: wl_surface::WlSurface,
     buffers: Option<(WaylandBuffer, WaylandBuffer)>,
+    width: i32,
+    height: i32,
 }
 
 impl WaylandImpl {
@@ -72,61 +74,82 @@ impl WaylandImpl {
             display,
             surface,
             buffers: Default::default(),
+            width: 0,
+            height: 0,
         })
     }
 
-    fn buffer(&mut self, width: i32, height: i32) -> &WaylandBuffer {
-        self.buffers = Some(if let Some((front, mut back)) = self.buffers.take() {
-            // Swap buffers; block if back buffer not released yet
+    // Allocate front and back buffer
+    fn alloc_buffers(&mut self) {
+        self.buffers = Some((
+            WaylandBuffer::new(&self.display.shm, self.width, self.height, &self.display.qh),
+            WaylandBuffer::new(&self.display.shm, self.width, self.height, &self.display.qh),
+        ));
+    }
+
+    pub fn resize(&mut self, width: u32, height: u32) {
+        self.width = width as i32;
+        self.height = height as i32;
+    }
+
+    pub fn buffer_mut(&mut self) -> &mut [u32] {
+        if let Some((_front, back)) = &mut self.buffers {
+            // Block if back buffer not released yet
             if !back.released() {
                 let mut event_queue = self.display.event_queue.lock().unwrap();
                 while !back.released() {
                     event_queue.blocking_dispatch(&mut State).unwrap();
                 }
             }
-            back.resize(width, height);
-            (back, front)
+
+            // Resize, if buffer isn't large enough
+            back.resize(self.width, self.height);
         } else {
-            // Allocate front and back buffer
-            (
-                WaylandBuffer::new(&self.display.shm, width, height, &self.display.qh),
-                WaylandBuffer::new(&self.display.shm, width, height, &self.display.qh),
-            )
-        });
-        &self.buffers.as_ref().unwrap().0
+            self.alloc_buffers();
+        };
+
+        unsafe { self.buffers.as_mut().unwrap().1.mapped_mut() }
     }
 
-    pub(super) unsafe fn set_buffer(&mut self, buffer: &[u32], width: u16, height: u16) {
+    pub fn present(&mut self) {
         let _ = self
             .display
             .event_queue
             .lock()
             .unwrap()
             .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.
+        if let Some((front, back)) = &mut self.buffers {
+            // Swap front and back buffer
+            std::mem::swap(front, back);
+
+            front.attach(&self.surface);
+
+            // FIXME: Proper damaging mechanism.
             //
-            // 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);
+            // 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, self.width, self.height);
+            }
+
+            self.surface.commit();
         }
-        self.surface.commit();
 
         let _ = self.display.event_queue.lock().unwrap().flush();
     }
+
+    pub unsafe fn set_buffer(&mut self, buffer: &[u32], width: u16, height: u16) {
+        self.resize(width.into(), height.into());
+        self.buffer_mut().copy_from_slice(buffer);
+        self.present();
+    }
 }
 
 impl Dispatch<wl_registry::WlRegistry, GlobalListContents> for State {