Merge pull request #99 from rust-windowing/damage

Add `Buffer::present_with_damage()` and `Buffer::age()`

src/cg.rs

@@ -1,4 +1,4 @@
-use crate::SoftBufferError;
+use crate::{Rect, SoftBufferError};
 use core_graphics::base::{
     kCGBitmapByteOrder32Little, kCGImageAlphaNoneSkipFirst, kCGRenderingIntentDefault,
 };
@@ -92,6 +92,10 @@ impl<'a> BufferImpl<'a> {
         &mut self.buffer
     }
 
+    pub fn age(&self) -> u8 {
+        0
+    }
+
     pub fn present(self) -> Result<(), SoftBufferError> {
         let data_provider = CGDataProvider::from_buffer(Arc::new(Buffer(self.buffer)));
         let image = CGImage::new(
@@ -124,6 +128,10 @@ impl<'a> BufferImpl<'a> {
 
         Ok(())
     }
+
+    pub fn present_with_damage(self, _damage: &[Rect]) -> Result<(), SoftBufferError> {
+        self.present()
+    }
 }
 
 impl Drop for CGImpl {

src/error.rs

@@ -36,6 +36,11 @@ pub enum SoftBufferError {
         height: NonZeroU32,
     },
 
+    #[error(
+        "Damage rect {}x{} at ({}, {}) out of range for backend.", .rect.width, .rect.height, .rect.x, .rect.y,
+    )]
+    DamageOutOfRange { rect: crate::Rect },
+
     #[error("Platform error")]
     PlatformError(Option<String>, Option<Box<dyn Error>>),
 

src/lib.rs

@@ -137,6 +137,15 @@ macro_rules! make_dispatch {
                 }
             }
 
+            pub fn age(&self) -> u8 {
+                match self {
+                    $(
+                        $(#[$attr])*
+                        Self::$name(inner) => inner.age(),
+                    )*
+                }
+            }
+
             pub fn present(self) -> Result<(), SoftBufferError> {
                 match self {
                     $(
@@ -145,6 +154,15 @@ macro_rules! make_dispatch {
                     )*
                 }
             }
+
+            pub fn present_with_damage(self, damage: &[Rect]) -> Result<(), SoftBufferError> {
+                match self {
+                    $(
+                        $(#[$attr])*
+                        Self::$name(inner) => inner.present_with_damage(damage),
+                    )*
+                }
+            }
         }
     };
 }
@@ -220,6 +238,19 @@ impl Context {
     }
 }
 
+/// A rectangular region of the buffer coordinate space.
+#[derive(Clone, Copy, Debug)]
+pub struct Rect {
+    /// x coordinate of top left corner
+    pub x: u32,
+    /// y coordinate of top left corner
+    pub y: u32,
+    /// width
+    pub width: NonZeroU32,
+    /// height
+    pub height: NonZeroU32,
+}
+
 /// A surface for drawing to a window with software buffers.
 pub struct Surface {
     /// This is boxed so that `Surface` is the same size on every platform.
@@ -329,7 +360,7 @@ impl Surface {
 
     /// Return a [`Buffer`] that the next frame should be rendered into. The size must
     /// be set with [`Surface::resize`] first. The initial contents of the buffer may be zeroed, or
-    /// may contain a previous frame.
+    /// may contain a previous frame. Call [`Buffer::age`] to determine this.
     pub fn buffer_mut(&mut self) -> Result<Buffer, SoftBufferError> {
         Ok(Buffer {
             buffer_impl: self.surface_impl.buffer_mut()?,
@@ -380,6 +411,16 @@ pub struct Buffer<'a> {
 }
 
 impl<'a> Buffer<'a> {
+    /// Is age is the number of frames ago this buffer was last presented. So if the value is
+    /// `1`, it is the same as the last frame, and if it is `2`, it is the same as the frame
+    /// before that (for backends using double buffering). If the value is `0`, it is a new
+    /// buffer that has unspecified contents.
+    ///
+    /// This can be used to update only a portion of the buffer.
+    pub fn age(&self) -> u8 {
+        self.buffer_impl.age()
+    }
+
     /// Presents buffer to the window.
     ///
     /// # Platform dependent behavior
@@ -395,6 +436,20 @@ impl<'a> Buffer<'a> {
     pub fn present(self) -> Result<(), SoftBufferError> {
         self.buffer_impl.present()
     }
+
+    /// Presents buffer to the window, with damage regions.
+    ///
+    /// # Platform dependent behavior
+    ///
+    /// Supported on:
+    /// - Wayland
+    /// - X, when XShm is available
+    /// - Win32
+    ///
+    /// Otherwise this is equivalent to [`Self::present`].
+    pub fn present_with_damage(self, damage: &[Rect]) -> Result<(), SoftBufferError> {
+        self.buffer_impl.present_with_damage(damage)
+    }
 }
 
 impl<'a> ops::Deref for Buffer<'a> {

src/orbital.rs

@@ -1,7 +1,7 @@
 use raw_window_handle::OrbitalWindowHandle;
 use std::{cmp, num::NonZeroU32, slice, str};
 
-use crate::SoftBufferError;
+use crate::{Rect, SoftBufferError};
 
 struct OrbitalMap {
     address: usize,
@@ -57,6 +57,7 @@ pub struct OrbitalImpl {
     handle: OrbitalWindowHandle,
     width: u32,
     height: u32,
+    presented: bool,
 }
 
 impl OrbitalImpl {
@@ -65,12 +66,18 @@ impl OrbitalImpl {
             handle,
             width: 0,
             height: 0,
+            presented: false,
         })
     }
 
     pub fn resize(&mut self, width: NonZeroU32, height: NonZeroU32) -> Result<(), SoftBufferError> {
-        self.width = width.get();
+        let width = width.get();
-        self.height = height.get();
+        let height = height.get();
+        if width != self.width && height != self.height {
+            self.presented = false;
+            self.width = width;
+            self.height = height;
+        }
         Ok(())
     }
 
@@ -177,11 +184,19 @@ impl<'a> BufferImpl<'a> {
         }
     }
 
+    pub fn age(&self) -> u8 {
+        match self.pixels {
+            Pixels::Mapping(_) if self.imp.presented => 1,
+            _ => 0,
+        }
+    }
+
     pub fn present(self) -> Result<(), SoftBufferError> {
         match self.pixels {
             Pixels::Mapping(mapping) => {
                 drop(mapping);
                 syscall::fsync(self.imp.window_fd()).expect("failed to sync orbital window");
+                self.imp.presented = true;
             }
             Pixels::Buffer(buffer) => {
                 self.imp
@@ -191,4 +206,8 @@ impl<'a> BufferImpl<'a> {
 
         Ok(())
     }
+
+    pub fn present_with_damage(self, _damage: &[Rect]) -> Result<(), SoftBufferError> {
+        self.present()
+    }
 }

src/wayland/buffer.rs

@@ -90,6 +90,7 @@ pub(super) struct WaylandBuffer {
     width: i32,
     height: i32,
     released: Arc<AtomicBool>,
+    pub age: u8,
 }
 
 impl WaylandBuffer {
@@ -125,6 +126,7 @@ impl WaylandBuffer {
             width,
             height,
             released,
+            age: 0,
         }
     }
 

src/wayland/mod.rs

@@ -1,4 +1,4 @@
-use crate::{error::SwResultExt, util, SoftBufferError};
+use crate::{error::SwResultExt, util, Rect, SoftBufferError};
 use raw_window_handle::{WaylandDisplayHandle, WaylandWindowHandle};
 use std::{
     cell::RefCell,
@@ -125,72 +125,107 @@ impl WaylandImpl {
             ));
         };
 
-        Ok(BufferImpl(util::BorrowStack::new(self, |buffer| {
+        let age = self.buffers.as_mut().unwrap().1.age;
-            Ok(unsafe { buffer.buffers.as_mut().unwrap().1.mapped_mut() })
+        Ok(BufferImpl {
-        })?))
+            stack: util::BorrowStack::new(self, |buffer| {
+                Ok(unsafe { buffer.buffers.as_mut().unwrap().1.mapped_mut() })
+            })?,
+            age,
+        })
     }
 
     /// Fetch the buffer from the window.
     pub fn fetch(&mut self) -> Result<Vec<u32>, SoftBufferError> {
         Err(SoftBufferError::Unimplemented)
     }
-}
 
-pub struct BufferImpl<'a>(util::BorrowStack<'a, WaylandImpl, [u32]>);
+    fn present_with_damage(&mut self, damage: &[Rect]) -> Result<(), SoftBufferError> {
-
+        let _ = self
-impl<'a> BufferImpl<'a> {
-    #[inline]
-    pub fn pixels(&self) -> &[u32] {
-        self.0.member()
-    }
-
-    #[inline]
-    pub fn pixels_mut(&mut self) -> &mut [u32] {
-        self.0.member_mut()
-    }
-
-    pub fn present(self) -> Result<(), SoftBufferError> {
-        let imp = self.0.into_container();
-
-        let (width, height) = imp
-            .size
-            .expect("Must set size of surface before calling `present()`");
-
-        let _ = imp
             .display
             .event_queue
             .borrow_mut()
             .dispatch_pending(&mut State);
 
-        if let Some((front, back)) = &mut imp.buffers {
+        if let Some((front, back)) = &mut self.buffers {
+            front.age = 1;
+            if back.age != 0 {
+                back.age += 1;
+            }
+
             // Swap front and back buffer
             std::mem::swap(front, back);
 
-            front.attach(&imp.surface);
+            front.attach(&self.surface);
 
-            // FIXME: Proper damaging mechanism.
+            // Like Mesa's EGL/WSI implementation, we damage the whole buffer with `i32::MAX` if
-            //
+            // the compositor doesn't support `damage_buffer`.
-            // In order to propagate changes on compositors which track damage, for now damage the entire surface.
+            // https://bugs.freedesktop.org/show_bug.cgi?id=78190
-            if imp.surface.version() < 4 {
+            if self.surface.version() < 4 {
-                // FIXME: Accommodate scale factor since wl_surface::damage is in terms of surface coordinates while
+                self.surface.damage(0, 0, i32::MAX, i32::MAX);
-                // 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")
-                imp.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.
+                for rect in damage {
-                imp.surface.damage_buffer(0, 0, width.get(), height.get());
+                    // Introduced in version 4, it is an error to use this request in version 3 or lower.
+                    let (x, y, width, height) = (|| {
+                        Some((
+                            i32::try_from(rect.x).ok()?,
+                            i32::try_from(rect.y).ok()?,
+                            i32::try_from(rect.width.get()).ok()?,
+                            i32::try_from(rect.height.get()).ok()?,
+                        ))
+                    })()
+                    .ok_or(SoftBufferError::DamageOutOfRange { rect: *rect })?;
+                    self.surface.damage_buffer(x, y, width, height);
+                }
             }
 
-            imp.surface.commit();
+            self.surface.commit();
         }
 
-        let _ = imp.display.event_queue.borrow_mut().flush();
+        let _ = self.display.event_queue.borrow_mut().flush();
 
         Ok(())
     }
 }
 
+pub struct BufferImpl<'a> {
+    stack: util::BorrowStack<'a, WaylandImpl, [u32]>,
+    age: u8,
+}
+
+impl<'a> BufferImpl<'a> {
+    #[inline]
+    pub fn pixels(&self) -> &[u32] {
+        self.stack.member()
+    }
+
+    #[inline]
+    pub fn pixels_mut(&mut self) -> &mut [u32] {
+        self.stack.member_mut()
+    }
+
+    pub fn age(&self) -> u8 {
+        self.age
+    }
+
+    pub fn present_with_damage(self, damage: &[Rect]) -> Result<(), SoftBufferError> {
+        self.stack.into_container().present_with_damage(damage)
+    }
+
+    pub fn present(self) -> Result<(), SoftBufferError> {
+        let imp = self.stack.into_container();
+        let (width, height) = imp
+            .size
+            .expect("Must set size of surface before calling `present()`");
+        imp.present_with_damage(&[Rect {
+            x: 0,
+            y: 0,
+            // We know width/height will be non-negative
+            width: width.try_into().unwrap(),
+            height: height.try_into().unwrap(),
+        }])
+    }
+}
+
 impl Dispatch<wl_registry::WlRegistry, GlobalListContents> for State {
     fn event(
         _: &mut State,

src/web.rs

@@ -9,7 +9,7 @@ use web_sys::HtmlCanvasElement;
 use web_sys::ImageData;
 
 use crate::error::SwResultExt;
-use crate::SoftBufferError;
+use crate::{Rect, SoftBufferError};
 use std::convert::TryInto;
 use std::marker::PhantomData;
 use std::num::NonZeroU32;
@@ -42,11 +42,11 @@ pub struct WebImpl {
     /// The buffer that we're drawing to.
     buffer: Vec<u32>,
 
-    /// The current width of the canvas.
+    /// Buffer has been presented.
-    width: u32,
+    buffer_presented: bool,
 
-    /// The current height of the canvas.
+    /// The current canvas width/height.
-    height: u32,
+    size: Option<(NonZeroU32, NonZeroU32)>,
 }
 
 impl WebImpl {
@@ -78,8 +78,8 @@ impl WebImpl {
             canvas,
             ctx,
             buffer: Vec::new(),
-            width: 0,
+            buffer_presented: false,
-            height: 0,
+            size: None,
         })
     }
 
@@ -89,14 +89,14 @@ impl WebImpl {
         width: NonZeroU32,
         height: NonZeroU32,
     ) -> Result<(), SoftBufferError> {
-        let width = width.get();
+        if self.size != Some((width, height)) {
-        let height = height.get();
+            self.buffer_presented = false;
+            self.buffer.resize(total_len(width.get(), height.get()), 0);
+            self.canvas.set_width(width.get());
+            self.canvas.set_height(height.get());
+            self.size = Some((width, height));
+        }
 
-        self.buffer.resize(total_len(width, height), 0);
-        self.canvas.set_width(width);
-        self.canvas.set_height(height);
-        self.width = width;
-        self.height = height;
         Ok(())
     }
 
@@ -105,11 +105,75 @@ impl WebImpl {
         Ok(BufferImpl { imp: self })
     }
 
+    fn present_with_damage(&mut self, damage: &[Rect]) -> Result<(), SoftBufferError> {
+        let (width, _height) = self
+            .size
+            .expect("Must set size of surface before calling `present_with_damage()`");
+        // Create a bitmap from the buffer.
+        let bitmap: Vec<_> = self
+            .buffer
+            .iter()
+            .copied()
+            .flat_map(|pixel| [(pixel >> 16) as u8, (pixel >> 8) as u8, pixel as u8, 255])
+            .collect();
+
+        #[cfg(target_feature = "atomics")]
+        let result = {
+            use js_sys::{Uint8Array, Uint8ClampedArray};
+            use wasm_bindgen::prelude::wasm_bindgen;
+            use wasm_bindgen::JsValue;
+
+            #[wasm_bindgen]
+            extern "C" {
+                #[wasm_bindgen(js_name = ImageData)]
+                type ImageDataExt;
+
+                #[wasm_bindgen(catch, constructor, js_class = ImageData)]
+                fn new(array: Uint8ClampedArray, sw: u32) -> Result<ImageDataExt, JsValue>;
+            }
+
+            let array = Uint8Array::new_with_length(bitmap.len() as u32);
+            array.copy_from(&bitmap);
+            let array = Uint8ClampedArray::new(&array);
+            ImageDataExt::new(array, width.get())
+                .map(JsValue::from)
+                .map(ImageData::unchecked_from_js)
+        };
+        #[cfg(not(target_feature = "atomics"))]
+        let result =
+            ImageData::new_with_u8_clamped_array(wasm_bindgen::Clamped(&bitmap), width.get());
+        // This should only throw an error if the buffer we pass's size is incorrect.
+        let image_data = result.unwrap();
+
+        for rect in damage {
+            // This can only throw an error if `data` is detached, which is impossible.
+            self.ctx
+                .put_image_data_with_dirty_x_and_dirty_y_and_dirty_width_and_dirty_height(
+                    &image_data,
+                    rect.x.into(),
+                    rect.y.into(),
+                    rect.x.into(),
+                    rect.y.into(),
+                    rect.width.get().into(),
+                    rect.height.get().into(),
+                )
+                .unwrap();
+        }
+
+        self.buffer_presented = true;
+
+        Ok(())
+    }
+
     /// Fetch the buffer from the window.
     pub fn fetch(&mut self) -> Result<Vec<u32>, SoftBufferError> {
+        let (width, height) = self
+            .size
+            .expect("Must set size of surface before calling `fetch()`");
+
         let image_data = self
             .ctx
-            .get_image_data(0., 0., self.width.into(), self.height.into())
+            .get_image_data(0., 0., width.get().into(), height.get().into())
             .ok()
             // TODO: Can also error if width or height are 0.
             .swbuf_err("`Canvas` contains pixels from a different origin")?;
@@ -157,49 +221,30 @@ impl<'a> BufferImpl<'a> {
         &mut self.imp.buffer
     }
 
+    pub fn age(&self) -> u8 {
+        if self.imp.buffer_presented {
+            1
+        } else {
+            0
+        }
+    }
+
     /// Push the buffer to the canvas.
     pub fn present(self) -> Result<(), SoftBufferError> {
-        // Create a bitmap from the buffer.
+        let (width, height) = self
-        let bitmap: Vec<_> = self
             .imp
-            .buffer
+            .size
-            .iter()
+            .expect("Must set size of surface before calling `present()`");
-            .copied()
+        self.imp.present_with_damage(&[Rect {
-            .flat_map(|pixel| [(pixel >> 16) as u8, (pixel >> 8) as u8, pixel as u8, 255])
+            x: 0,
-            .collect();
+            y: 0,
+            width,
+            height,
+        }])
+    }
 
-        #[cfg(target_feature = "atomics")]
+    pub fn present_with_damage(self, damage: &[Rect]) -> Result<(), SoftBufferError> {
-        let result = {
+        self.imp.present_with_damage(damage)
-            use js_sys::{Uint8Array, Uint8ClampedArray};
-            use wasm_bindgen::prelude::wasm_bindgen;
-            use wasm_bindgen::JsValue;
-
-            #[wasm_bindgen]
-            extern "C" {
-                #[wasm_bindgen(js_name = ImageData)]
-                type ImageDataExt;
-
-                #[wasm_bindgen(catch, constructor, js_class = ImageData)]
-                fn new(array: Uint8ClampedArray, sw: u32) -> Result<ImageDataExt, JsValue>;
-            }
-
-            let array = Uint8Array::new_with_length(bitmap.len() as u32);
-            array.copy_from(&bitmap);
-            let array = Uint8ClampedArray::new(&array);
-            ImageDataExt::new(array, self.imp.width)
-                .map(JsValue::from)
-                .map(ImageData::unchecked_from_js)
-        };
-        #[cfg(not(target_feature = "atomics"))]
-        let result =
-            ImageData::new_with_u8_clamped_array(wasm_bindgen::Clamped(&bitmap), self.imp.width);
-        // This should only throw an error if the buffer we pass's size is incorrect.
-        let image_data = result.unwrap();
-
-        // This can only throw an error if `data` is detached, which is impossible.
-        self.imp.ctx.put_image_data(&image_data, 0., 0.).unwrap();
-
-        Ok(())
     }
 }
 

src/win32.rs

@@ -2,7 +2,7 @@
 //!
 //! This module converts the input buffer into a bitmap and then stretches it to the window.
 
-use crate::SoftBufferError;
+use crate::{Rect, SoftBufferError};
 use raw_window_handle::Win32WindowHandle;
 
 use std::io;
@@ -27,6 +27,7 @@ struct Buffer {
     pixels: NonNull<u32>,
     width: NonZeroI32,
     height: NonZeroI32,
+    presented: bool,
 }
 
 impl Drop for Buffer {
@@ -101,6 +102,7 @@ impl Buffer {
             width,
             height,
             pixels,
+            presented: false,
         }
     }
 
@@ -203,6 +205,30 @@ impl Win32Impl {
         Ok(BufferImpl(self))
     }
 
+    fn present_with_damage(&mut self, damage: &[Rect]) -> Result<(), SoftBufferError> {
+        let buffer = self.buffer.as_mut().unwrap();
+        unsafe {
+            for rect in damage.iter().copied() {
+                let (x, y, width, height) = (|| {
+                    Some((
+                        i32::try_from(rect.x).ok()?,
+                        i32::try_from(rect.y).ok()?,
+                        i32::try_from(rect.width.get()).ok()?,
+                        i32::try_from(rect.height.get()).ok()?,
+                    ))
+                })()
+                .ok_or(SoftBufferError::DamageOutOfRange { rect })?;
+                Gdi::BitBlt(self.dc, x, y, width, height, buffer.dc, x, y, Gdi::SRCCOPY);
+            }
+
+            // Validate the window.
+            Gdi::ValidateRect(self.window, ptr::null_mut());
+        }
+        buffer.presented = true;
+
+        Ok(())
+    }
+
     /// Fetch the buffer from the window.
     pub fn fetch(&mut self) -> Result<Vec<u32>, SoftBufferError> {
         let buffer = self.buffer.as_ref().unwrap();
@@ -245,26 +271,27 @@ impl<'a> BufferImpl<'a> {
         self.0.buffer.as_mut().unwrap().pixels_mut()
     }
 
+    pub fn age(&self) -> u8 {
+        match self.0.buffer.as_ref() {
+            Some(buffer) if buffer.presented => 1,
+            _ => 0,
+        }
+    }
+
     pub fn present(self) -> Result<(), SoftBufferError> {
         let imp = self.0;
         let buffer = imp.buffer.as_ref().unwrap();
-        unsafe {
+        imp.present_with_damage(&[Rect {
-            Gdi::BitBlt(
+            x: 0,
-                imp.dc,
+            y: 0,
-                0,
+            // We know width/height will be non-negative
-                0,
+            width: buffer.width.try_into().unwrap(),
-                buffer.width.get(),
+            height: buffer.height.try_into().unwrap(),
-                buffer.height.get(),
+        }])
-                buffer.dc,
+    }
-                0,
-                0,
-                Gdi::SRCCOPY,
-            );
 
-            // Validate the window.
+    pub fn present_with_damage(self, damage: &[Rect]) -> Result<(), SoftBufferError> {
-            Gdi::ValidateRect(imp.window, ptr::null_mut());
+        let imp = self.0;
-        }
+        imp.present_with_damage(damage)
-
-        Ok(())
     }
 }

src/x11.rs

@@ -6,11 +6,16 @@
 #![allow(clippy::uninlined_format_args)]
 
 use crate::error::SwResultExt;
-use crate::SoftBufferError;
+use crate::{Rect, SoftBufferError};
 use nix::libc::{shmat, shmctl, shmdt, shmget, IPC_PRIVATE, IPC_RMID};
 use raw_window_handle::{XcbDisplayHandle, XcbWindowHandle, XlibDisplayHandle, XlibWindowHandle};
 use std::ptr::{null_mut, NonNull};
-use std::{fmt, io, mem, num::NonZeroU32, rc::Rc, slice};
+use std::{
+    fmt, io, mem,
+    num::{NonZeroU16, NonZeroU32},
+    rc::Rc,
+    slice,
+};
 
 use x11_dl::xlib::Display;
 use x11_dl::xlib_xcb::Xlib_xcb;
@@ -110,11 +115,11 @@ pub struct X11Impl {
     /// The buffer we draw to.
     buffer: Buffer,
 
-    /// The current buffer width.
+    /// Buffer has been presented.
-    width: u16,
+    buffer_presented: bool,
 
-    /// The current buffer height.
+    /// The current buffer width/height.
-    height: u16,
+    size: Option<(NonZeroU16, NonZeroU16)>,
 }
 
 /// The buffer that is being drawn to.
@@ -256,8 +261,8 @@ impl X11Impl {
             depth: geometry_reply.depth,
             visual_id,
             buffer,
-            width: 0,
+            buffer_presented: false,
-            height: 0,
+            size: None,
         })
     }
 
@@ -275,26 +280,22 @@ impl X11Impl {
         );
 
         // Width and height should fit in u16.
-        let width: u16 = width
+        let width: NonZeroU16 = width
-            .get()
             .try_into()
             .or(Err(SoftBufferError::SizeOutOfRange { width, height }))?;
-        let height: u16 = height
+        let height: NonZeroU16 = height.try_into().or(Err(SoftBufferError::SizeOutOfRange {
-            .get()
+            width: width.into(),
-            .try_into()
+            height,
-            .or(Err(SoftBufferError::SizeOutOfRange {
+        }))?;
-                width: NonZeroU32::new(width.into()).unwrap(),
-                height,
-            }))?;
 
-        if width != self.width || height != self.height {
+        if self.size != Some((width, height)) {
+            self.buffer_presented = false;
             self.buffer
-                .resize(&self.display.connection, width, height)
+                .resize(&self.display.connection, width.get(), height.get())
                 .swbuf_err("Failed to resize X11 buffer")?;
 
             // We successfully resized the buffer.
-            self.width = width;
+            self.size = Some((width, height));
-            self.height = height;
         }
 
         Ok(())
@@ -315,6 +316,10 @@ impl X11Impl {
     pub fn fetch(&mut self) -> Result<Vec<u32>, SoftBufferError> {
         log::trace!("fetch: window={:X}", self.window);
 
+        let (width, height) = self
+            .size
+            .expect("Must set size of surface before calling `fetch()`");
+
         // TODO: Is it worth it to do SHM here? Probably not.
         let reply = self
             .display
@@ -324,8 +329,8 @@ impl X11Impl {
                 self.window,
                 0,
                 0,
-                self.width,
+                width.get(),
-                self.height,
+                height.get(),
                 u32::MAX,
             )
             .swbuf_err("Failed to send image fetching request")?
@@ -360,13 +365,25 @@ impl<'a> BufferImpl<'a> {
         unsafe { self.0.buffer.buffer_mut() }
     }
 
+    pub fn age(&self) -> u8 {
+        if self.0.buffer_presented {
+            1
+        } else {
+            0
+        }
+    }
+
     /// Push the buffer to the window.
-    pub fn present(self) -> Result<(), SoftBufferError> {
+    pub fn present_with_damage(self, damage: &[Rect]) -> Result<(), SoftBufferError> {
         let imp = self.0;
 
+        let (surface_width, surface_height) = imp
+            .size
+            .expect("Must set size of surface before calling `present_with_damage()`");
+
         log::trace!("present: window={:X}", imp.window);
 
-        let result = match imp.buffer {
+        match imp.buffer {
             Buffer::Wire(ref wire) => {
                 // This is a suboptimal strategy, raise a stink in the debug logs.
                 log::debug!("Falling back to non-SHM method for window drawing.");
@@ -377,8 +394,8 @@ impl<'a> BufferImpl<'a> {
                         xproto::ImageFormat::Z_PIXMAP,
                         imp.window,
                         imp.gc,
-                        imp.width,
+                        surface_width.get(),
-                        imp.height,
+                        surface_height.get(),
                         0,
                         0,
                         0,
@@ -387,6 +404,7 @@ impl<'a> BufferImpl<'a> {
                     )
                     .map(|c| c.ignore_error())
                     .push_err()
+                    .swbuf_err("Failed to draw image to window")?;
             }
 
             Buffer::Shm(ref mut shm) => {
@@ -394,38 +412,69 @@ impl<'a> BufferImpl<'a> {
                 // SAFETY: We know that we called finish_wait() before this.
                 // Put the image into the window.
                 if let Some((_, segment_id)) = shm.seg {
-                    imp.display
+                    damage
-                        .connection
+                        .iter()
-                        .shm_put_image(
+                        .try_for_each(|rect| {
-                            imp.window,
+                            let (src_x, src_y, dst_x, dst_y, width, height) = (|| {
-                            imp.gc,
+                                Some((
-                            imp.width,
+                                    u16::try_from(rect.x).ok()?,
-                            imp.height,
+                                    u16::try_from(rect.y).ok()?,
-                            0,
+                                    i16::try_from(rect.x).ok()?,
-                            0,
+                                    i16::try_from(rect.y).ok()?,
-                            imp.width,
+                                    u16::try_from(rect.width.get()).ok()?,
-                            imp.height,
+                                    u16::try_from(rect.height.get()).ok()?,
-                            0,
+                                ))
-                            0,
+                            })(
-                            imp.depth,
+                            )
-                            xproto::ImageFormat::Z_PIXMAP.into(),
+                            .ok_or(SoftBufferError::DamageOutOfRange { rect: *rect })?;
-                            false,
+                            imp.display
-                            segment_id,
+                                .connection
-                            0,
+                                .shm_put_image(
-                        )
+                                    imp.window,
-                        .push_err()
+                                    imp.gc,
-                        .map(|c| c.ignore_error())
+                                    surface_width.get(),
+                                    surface_height.get(),
+                                    src_x,
+                                    src_y,
+                                    width,
+                                    height,
+                                    dst_x,
+                                    dst_y,
+                                    imp.depth,
+                                    xproto::ImageFormat::Z_PIXMAP.into(),
+                                    false,
+                                    segment_id,
+                                    0,
+                                )
+                                .push_err()
+                                .map(|c| c.ignore_error())
+                                .swbuf_err("Failed to draw image to window")
+                        })
                         .and_then(|()| {
                             // Send a short request to act as a notification for when the X server is done processing the image.
                             shm.begin_wait(&imp.display.connection)
-                        })
+                                .swbuf_err("Failed to draw image to window")
-                } else {
+                        })?;
-                    Ok(())
                 }
             }
-        };
+        }
 
-        result.swbuf_err("Failed to draw image to window")
+        imp.buffer_presented = true;
+
+        Ok(())
+    }
+
+    pub fn present(self) -> Result<(), SoftBufferError> {
+        let (width, height) = self
+            .0
+            .size
+            .expect("Must set size of surface before calling `present()`");
+        self.present_with_damage(&[Rect {
+            x: 0,
+            y: 0,
+            width: width.into(),
+            height: height.into(),
+        }])
     }
 }