Event Loop 2.0 API and Windows implementation (#638)

* Rename EventsLoop and associated types to EventLoop

* Rename WindowEvent::Refresh to WindowEvent::Redraw

* Remove second thread from win32 backend

* Update run_forever to hijack thread

* Replace windows Mutex with parking_lot Mutex

* Implement new ControlFlow and associated events

* Add StartCause::Init support, timer example

* Add ability to send custom user events

* Fully invert windows control flow so win32 calls into winit's callback

* Add request_redraw

* Rename platform to platform_impl

* Rename os to platform, add Ext trait postfixes

* Add platform::desktop module with EventLoopExt::run_return

* Re-organize into module structure

* Improve documentation

* Small changes to examples

* Improve docs for run and run_return

* Change instances of "events_loop" to "event_loop"

* Rename MonitorId to MonitorHandle

* Add CHANGELOG entry

* Improve WaitUntil timer precision

* When SendEvent is called during event closure, buffer events

* Fix resize lag when waiting in some situations

* Update send test and errors that broke some examples/APIs

* Improve clarity/fix typos in docs

* Fix unreachable panic after setting ControlFlow to Poll during some RedrawRequested events.

* Fix crash when running in release mode

* Remove crossbeam dependency and make drop events work again

* Remove serde implementations from ControlFlow

* Fix 1.24.1 build

* Fix freeze when setting decorations

* Replace &EventLoop in callback with &EventLoopWindowTarget

* Document and implement Debug for EventLoopWindowTarget

* Fix some deadlocks that could occur when changing window state

* Fix thread executor not executing closure when called from non-loop thread

* Fix buffered events not getting dispatched

* Fix crash with runner refcell not getting dropped

* Address review feedback

* Fix CHANGELOG typo

* Catch panics in user callback

src/platform_impl/linux/x11/util/atom.rs

@@ -0,0 +1,72 @@
+use std::collections::HashMap;
+use std::ffi::{CStr, CString};
+use std::fmt::Debug;
+use std::os::raw::*;
+
+use parking_lot::Mutex;
+
+use super::*;
+
+type AtomCache = HashMap<CString, ffi::Atom>;
+
+lazy_static! {
+    static ref ATOM_CACHE: Mutex<AtomCache> = Mutex::new(HashMap::with_capacity(2048));
+}
+
+impl XConnection {
+    pub fn get_atom<T: AsRef<CStr> + Debug>(&self, name: T) -> ffi::Atom {
+        let name = name.as_ref();
+        let mut atom_cache_lock = ATOM_CACHE.lock();
+        let cached_atom = (*atom_cache_lock).get(name).cloned();
+        if let Some(atom) = cached_atom {
+            atom
+        } else {
+            let atom = unsafe { (self.xlib.XInternAtom)(
+                self.display,
+                name.as_ptr() as *const c_char,
+                ffi::False,
+            ) };
+            if atom == 0 {
+                let msg = format!(
+                    "`XInternAtom` failed, which really shouldn't happen. Atom: {:?}, Error: {:#?}",
+                    name,
+                    self.check_errors(),
+                );
+                panic!(msg);
+            }
+            /*println!(
+                "XInternAtom name:{:?} atom:{:?}",
+                name,
+                atom,
+            );*/
+            (*atom_cache_lock).insert(name.to_owned(), atom);
+            atom
+        }
+    }
+
+    pub unsafe fn get_atom_unchecked(&self, name: &[u8]) -> ffi::Atom {
+        debug_assert!(CStr::from_bytes_with_nul(name).is_ok());
+        let name = CStr::from_bytes_with_nul_unchecked(name);
+        self.get_atom(name)
+    }
+
+    // Note: this doesn't use caching, for the sake of simplicity.
+    // If you're dealing with this many atoms, you'll usually want to cache them locally anyway.
+    pub unsafe fn get_atoms(&self,  names: &[*mut c_char]) -> Result<Vec<ffi::Atom>, XError> {
+        let mut atoms = Vec::with_capacity(names.len());
+        (self.xlib.XInternAtoms)(
+            self.display,
+            names.as_ptr() as *mut _,
+            names.len() as c_int,
+            ffi::False,
+            atoms.as_mut_ptr(),
+        );
+        self.check_errors()?;
+        atoms.set_len(names.len());
+        /*println!(
+            "XInternAtoms atoms:{:?}",
+            atoms,
+        );*/
+        Ok(atoms)
+    }
+}

src/platform_impl/linux/x11/util/client_msg.rs

@@ -0,0 +1,95 @@
+use super::*;
+
+pub type ClientMsgPayload = [c_long; 5];
+
+impl XConnection {
+    pub fn send_event<T: Into<ffi::XEvent>>(
+        &self,
+        target_window: c_ulong,
+        event_mask: Option<c_long>,
+        event: T,
+    ) -> Flusher {
+        let event_mask = event_mask.unwrap_or(ffi::NoEventMask);
+        unsafe {
+            (self.xlib.XSendEvent)(
+                self.display,
+                target_window,
+                ffi::False,
+                event_mask,
+                &mut event.into(),
+            );
+        }
+        Flusher::new(self)
+    }
+
+    pub fn send_client_msg(
+        &self,
+        window: c_ulong,        // The window this is "about"; not necessarily this window
+        target_window: c_ulong, // The window we're sending to
+        message_type: ffi::Atom,
+        event_mask: Option<c_long>,
+        data: ClientMsgPayload,
+    ) -> Flusher {
+        let mut event: ffi::XClientMessageEvent = unsafe { mem::uninitialized() };
+        event.type_ = ffi::ClientMessage;
+        event.display = self.display;
+        event.window = window;
+        event.message_type = message_type;
+        event.format = c_long::FORMAT as c_int;
+        event.data = unsafe { mem::transmute(data) };
+        self.send_event(target_window, event_mask, event)
+    }
+
+    // Prepare yourself for the ultimate in unsafety!
+    // You should favor `send_client_msg` whenever possible, but some protocols (i.e. startup notification) require you
+    // to send more than one message worth of data.
+    pub fn send_client_msg_multi<T: Formattable>(
+        &self,
+        window: c_ulong,        // The window this is "about"; not necessarily this window
+        target_window: c_ulong, // The window we're sending to
+        message_type: ffi::Atom,
+        event_mask: Option<c_long>,
+        data: &[T],
+    ) -> Flusher {
+        let format = T::FORMAT;
+        let size_of_t = mem::size_of::<T>();
+        debug_assert_eq!(size_of_t, format.get_actual_size());
+        let mut event: ffi::XClientMessageEvent = unsafe { mem::uninitialized() };
+        event.type_ = ffi::ClientMessage;
+        event.display = self.display;
+        event.window = window;
+        event.message_type = message_type;
+        event.format = format as c_int;
+
+        let t_per_payload = format.get_payload_size() / size_of_t;
+        assert!(t_per_payload > 0);
+        let payload_count = data.len() / t_per_payload;
+        let payload_remainder = data.len() % t_per_payload;
+        let payload_ptr = data.as_ptr() as *const ClientMsgPayload;
+
+        let mut payload_index = 0;
+        while payload_index < payload_count {
+            let payload = unsafe { payload_ptr.offset(payload_index as isize) };
+            payload_index += 1;
+            event.data = unsafe { mem::transmute(*payload) };
+            self.send_event(target_window, event_mask, &event).queue();
+        }
+
+        if payload_remainder > 0 {
+            let mut payload: ClientMsgPayload = [0; 5];
+            let t_payload = payload.as_mut_ptr() as *mut T;
+            let invalid_payload = unsafe { payload_ptr.offset(payload_index as isize) };
+            let invalid_t_payload = invalid_payload as *const T;
+            let mut t_index = 0;
+            while t_index < payload_remainder {
+                let valid_t = unsafe { invalid_t_payload.offset(t_index as isize) };
+                unsafe { (*t_payload.offset(t_index as isize)) = (*valid_t).clone() };
+                t_index += 1;
+            }
+            event.data = unsafe { mem::transmute(payload) };
+            self.send_event(target_window, event_mask, &event).queue();
+        }
+
+        Flusher::new(self)
+    }
+}

src/platform_impl/linux/x11/util/format.rs

@@ -0,0 +1,58 @@
+use std::fmt::Debug;
+use std::mem;
+use std::os::raw::*;
+
+// This isn't actually the number of the bits in the format.
+// X11 does a match on this value to determine which type to call sizeof on.
+// Thus, we use 32 for c_long, since 32 maps to c_long which maps to 64.
+// ...if that sounds confusing, then you know why this enum is here.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub enum Format {
+    Char = 8,
+    Short = 16,
+    Long = 32,
+}
+
+impl Format {
+    pub fn from_format(format: usize) -> Option<Self> {
+        match format {
+            8 => Some(Format::Char),
+            16 => Some(Format::Short),
+            32 => Some(Format::Long),
+            _ => None,
+        }
+    }
+
+    pub fn is_same_size_as<T>(&self) -> bool {
+        mem::size_of::<T>() == self.get_actual_size()
+    }
+
+    pub fn get_actual_size(&self) -> usize {
+        match self {
+            &Format::Char => mem::size_of::<c_char>(),
+            &Format::Short => mem::size_of::<c_short>(),
+            &Format::Long => mem::size_of::<c_long>(),
+        }
+    }
+
+    pub fn get_payload_size(&self) -> usize {
+        match self {
+            // Due to the wonders of X11, half the space goes unused if you're not using longs (on 64-bit).
+            &Format::Char => mem::size_of::<c_char>() * 20,
+            &Format::Short => mem::size_of::<c_short>() * 10,
+            &Format::Long => mem::size_of::<c_long>() * 5,
+        }
+    }
+}
+
+pub trait Formattable: Debug + Clone + Copy + PartialEq + PartialOrd {
+    const FORMAT: Format;
+}
+
+// You might be surprised by the absence of c_int, but not as surprised as X11 would be by the presence of it.
+impl Formattable for c_schar { const FORMAT: Format = Format::Char; }
+impl Formattable for c_uchar { const FORMAT: Format = Format::Char; }
+impl Formattable for c_short { const FORMAT: Format = Format::Short; }
+impl Formattable for c_ushort { const FORMAT: Format = Format::Short; }
+impl Formattable for c_long { const FORMAT: Format = Format::Long; }
+impl Formattable for c_ulong { const FORMAT: Format = Format::Long; }

src/platform_impl/linux/x11/util/geometry.rs

@@ -0,0 +1,387 @@
+use std::cmp;
+
+use super::*;
+use {LogicalPosition, LogicalSize};
+
+// Friendly neighborhood axis-aligned rectangle
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AaRect {
+    x: i64,
+    y: i64,
+    width: i64,
+    height: i64,
+}
+
+impl AaRect {
+    pub fn new((x, y): (i32, i32), (width, height): (u32, u32)) -> Self {
+        let (x, y) = (x as i64, y as i64);
+        let (width, height) = (width as i64, height as i64);
+        AaRect { x, y, width, height }
+    }
+
+    pub fn contains_point(&self, x: i64, y: i64) -> bool {
+        x >= self.x && x <= self.x + self.width && y >= self.y && y <= self.y + self.height
+    }
+
+    pub fn get_overlapping_area(&self, other: &Self) -> i64 {
+        let x_overlap = cmp::max(
+            0,
+            cmp::min(self.x + self.width, other.x + other.width) - cmp::max(self.x, other.x),
+        );
+        let y_overlap = cmp::max(
+            0,
+            cmp::min(self.y + self.height, other.y + other.height) - cmp::max(self.y, other.y),
+        );
+        x_overlap * y_overlap
+    }
+}
+
+#[derive(Debug)]
+pub struct TranslatedCoords {
+    pub x_rel_root: c_int,
+    pub y_rel_root: c_int,
+    pub child: ffi::Window,
+}
+
+#[derive(Debug)]
+pub struct Geometry {
+    pub root: ffi::Window,
+    // If you want positions relative to the root window, use translate_coords.
+    // Note that the overwhelming majority of window managers are reparenting WMs, thus the window
+    // ID we get from window creation is for a nested window used as the window's client area. If
+    // you call get_geometry with that window ID, then you'll get the position of that client area
+    // window relative to the parent it's nested in (the frame), which isn't helpful if you want
+    // to know the frame position.
+    pub x_rel_parent: c_int,
+    pub y_rel_parent: c_int,
+    // In that same case, this will give you client area size.
+    pub width: c_uint,
+    pub height: c_uint,
+    // xmonad and dwm were the only WMs tested that use the border return at all.
+    // The majority of WMs seem to simply fill it with 0 unconditionally.
+    pub border: c_uint,
+    pub depth: c_uint,
+}
+
+#[derive(Debug, Clone)]
+pub struct FrameExtents {
+    pub left: c_ulong,
+    pub right: c_ulong,
+    pub top: c_ulong,
+    pub bottom: c_ulong,
+}
+
+impl FrameExtents {
+    pub fn new(left: c_ulong, right: c_ulong, top: c_ulong, bottom: c_ulong) -> Self {
+        FrameExtents { left, right, top, bottom }
+    }
+
+    pub fn from_border(border: c_ulong) -> Self {
+        Self::new(border, border, border, border)
+    }
+
+    pub fn as_logical(&self, factor: f64) -> LogicalFrameExtents {
+        let logicalize = |value: c_ulong| value as f64 / factor;
+        LogicalFrameExtents {
+            left: logicalize(self.left),
+            right: logicalize(self.right),
+            top: logicalize(self.top),
+            bottom: logicalize(self.bottom),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct LogicalFrameExtents {
+    pub left: f64,
+    pub right: f64,
+    pub top: f64,
+    pub bottom: f64,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum FrameExtentsHeuristicPath {
+    Supported,
+    UnsupportedNested,
+    UnsupportedBordered,
+}
+
+#[derive(Debug, Clone)]
+pub struct FrameExtentsHeuristic {
+    pub frame_extents: FrameExtents,
+    pub heuristic_path: FrameExtentsHeuristicPath,
+}
+
+impl FrameExtentsHeuristic {
+    pub fn inner_pos_to_outer(&self, x: i32, y: i32) -> (i32, i32) {
+        use self::FrameExtentsHeuristicPath::*;
+        if self.heuristic_path != UnsupportedBordered {
+            (x - self.frame_extents.left as i32, y - self.frame_extents.top as i32)
+        } else {
+            (x, y)
+        }
+    }
+
+    pub fn inner_pos_to_outer_logical(&self, mut logical: LogicalPosition, factor: f64) -> LogicalPosition {
+        use self::FrameExtentsHeuristicPath::*;
+        if self.heuristic_path != UnsupportedBordered {
+            let frame_extents = self.frame_extents.as_logical(factor);
+            logical.x -= frame_extents.left;
+            logical.y -= frame_extents.top;
+        }
+        logical
+    }
+
+    pub fn inner_size_to_outer(&self, width: u32, height: u32) -> (u32, u32) {
+        (
+            width.saturating_add(
+                self.frame_extents.left.saturating_add(self.frame_extents.right) as u32
+            ),
+            height.saturating_add(
+                self.frame_extents.top.saturating_add(self.frame_extents.bottom) as u32
+            ),
+        )
+    }
+
+    pub fn inner_size_to_outer_logical(&self, mut logical: LogicalSize, factor: f64) -> LogicalSize {
+        let frame_extents = self.frame_extents.as_logical(factor);
+        logical.width += frame_extents.left + frame_extents.right;
+        logical.height += frame_extents.top + frame_extents.bottom;
+        logical
+    }
+}
+
+impl XConnection {
+    // This is adequate for get_inner_position
+    pub fn translate_coords(&self, window: ffi::Window, root: ffi::Window) -> Result<TranslatedCoords, XError> {
+        let mut translated_coords: TranslatedCoords = unsafe { mem::uninitialized() };
+        unsafe {
+            (self.xlib.XTranslateCoordinates)(
+                self.display,
+                window,
+                root,
+                0,
+                0,
+                &mut translated_coords.x_rel_root,
+                &mut translated_coords.y_rel_root,
+                &mut translated_coords.child,
+            );
+        }
+        //println!("XTranslateCoordinates coords:{:?}", translated_coords);
+        self.check_errors().map(|_| translated_coords)
+    }
+
+    // This is adequate for get_inner_size
+    pub fn get_geometry(&self, window: ffi::Window) -> Result<Geometry, XError> {
+        let mut geometry: Geometry = unsafe { mem::uninitialized() };
+        let _status = unsafe {
+            (self.xlib.XGetGeometry)(
+                self.display,
+                window,
+                &mut geometry.root,
+                &mut geometry.x_rel_parent,
+                &mut geometry.y_rel_parent,
+                &mut geometry.width,
+                &mut geometry.height,
+                &mut geometry.border,
+                &mut geometry.depth,
+            )
+        };
+        //println!("XGetGeometry geo:{:?}", geometry);
+        self.check_errors().map(|_| geometry)
+    }
+
+    fn get_frame_extents(&self, window: ffi::Window) -> Option<FrameExtents> {
+        let extents_atom = unsafe { self.get_atom_unchecked(b"_NET_FRAME_EXTENTS\0") };
+
+        if !hint_is_supported(extents_atom) {
+            return None;
+        }
+
+        // Of the WMs tested, xmonad, i3, dwm, IceWM (1.3.x and earlier), and blackbox don't
+        // support this. As this is part of EWMH (Extended Window Manager Hints), it's likely to
+        // be unsupported by many smaller WMs.
+        let extents: Option<Vec<c_ulong>> = self.get_property(
+            window,
+            extents_atom,
+            ffi::XA_CARDINAL,
+        ).ok();
+
+        extents.and_then(|extents| {
+            if extents.len() >= 4 {
+                Some(FrameExtents {
+                    left: extents[0],
+                    right: extents[1],
+                    top: extents[2],
+                    bottom: extents[3],
+                })
+            } else {
+                None
+            }
+        })
+    }
+
+    pub fn is_top_level(&self, window: ffi::Window, root: ffi::Window) -> Option<bool> {
+        let client_list_atom = unsafe { self.get_atom_unchecked(b"_NET_CLIENT_LIST\0") };
+
+        if !hint_is_supported(client_list_atom) {
+            return None;
+        }
+
+        let client_list: Option<Vec<ffi::Window>> = self.get_property(
+            root,
+            client_list_atom,
+            ffi::XA_WINDOW,
+        ).ok();
+
+        client_list.map(|client_list| client_list.contains(&window))
+    }
+
+    fn get_parent_window(&self, window: ffi::Window) -> Result<ffi::Window, XError> {
+        let parent = unsafe {
+            let mut root: ffi::Window = mem::uninitialized();
+            let mut parent: ffi::Window = mem::uninitialized();
+            let mut children: *mut ffi::Window = ptr::null_mut();
+            let mut nchildren: c_uint = mem::uninitialized();
+
+            // What's filled into `parent` if `window` is the root window?
+            let _status = (self.xlib.XQueryTree)(
+                self.display,
+                window,
+                &mut root,
+                &mut parent,
+                &mut children,
+                &mut nchildren,
+            );
+
+            // The list of children isn't used
+            if children != ptr::null_mut() {
+                (self.xlib.XFree)(children as *mut _);
+            }
+
+            parent
+        };
+        self.check_errors().map(|_| parent)
+    }
+
+    fn climb_hierarchy(&self, window: ffi::Window, root: ffi::Window) -> Result<ffi::Window, XError> {
+        let mut outer_window = window;
+        loop {
+            let candidate = self.get_parent_window(outer_window)?;
+            if candidate == root {
+                break;
+            }
+            outer_window = candidate;
+        }
+        Ok(outer_window)
+    }
+
+    pub fn get_frame_extents_heuristic(&self, window: ffi::Window, root: ffi::Window) -> FrameExtentsHeuristic {
+        use self::FrameExtentsHeuristicPath::*;
+
+        // Position relative to root window.
+        // With rare exceptions, this is the position of a nested window. Cases where the window
+        // isn't nested are outlined in the comments throghout this function, but in addition to
+        // that, fullscreen windows often aren't nested.
+        let (inner_y_rel_root, child) = {
+            let coords = self.translate_coords(window, root).expect("Failed to translate window coordinates");
+            (
+                coords.y_rel_root,
+                coords.child,
+            )
+        };
+
+        let (width, height, border) = {
+            let inner_geometry = self.get_geometry(window).expect("Failed to get inner window geometry");
+            (
+                inner_geometry.width,
+                inner_geometry.height,
+                inner_geometry.border,
+            )
+        };
+
+        // The first condition is only false for un-nested windows, but isn't always false for
+        // un-nested windows. Mutter/Muffin/Budgie and Marco present a mysterious discrepancy:
+        // when y is on the range [0, 2] and if the window has been unfocused since being
+        // undecorated (or was undecorated upon construction), the first condition is true,
+        // requiring us to rely on the second condition.
+        let nested = !(window == child || self.is_top_level(child, root) == Some(true));
+
+        // Hopefully the WM supports EWMH, allowing us to get exact info on the window frames.
+        if let Some(mut frame_extents) = self.get_frame_extents(window) {
+            // Mutter/Muffin/Budgie and Marco preserve their decorated frame extents when
+            // decorations are disabled, but since the window becomes un-nested, it's easy to
+            // catch.
+            if !nested {
+                frame_extents = FrameExtents::new(0, 0, 0, 0);
+            }
+
+            // The difference between the nested window's position and the outermost window's
+            // position is equivalent to the frame size. In most scenarios, this is equivalent to
+            // manually climbing the hierarchy as is done in the case below. Here's a list of
+            // known discrepancies:
+            // * Mutter/Muffin/Budgie gives decorated windows a margin of 9px (only 7px on top) in
+            //   addition to a 1px semi-transparent border. The margin can be easily observed by
+            //   using a screenshot tool to get a screenshot of a selected window, and is
+            //   presumably used for drawing drop shadows. Getting window geometry information
+            //   via hierarchy-climbing results in this margin being included in both the
+            //   position and outer size, so a window positioned at (0, 0) would be reported as
+            //   having a position (-10, -8).
+            // * Compiz has a drop shadow margin just like Mutter/Muffin/Budgie, though it's 10px
+            //   on all sides, and there's no additional border.
+            // * Enlightenment otherwise gets a y position equivalent to inner_y_rel_root.
+            //   Without decorations, there's no difference. This is presumably related to
+            //   Enlightenment's fairly unique concept of window position; it interprets
+            //   positions given to XMoveWindow as a client area position rather than a position
+            //   of the overall window.
+
+            FrameExtentsHeuristic {
+                frame_extents,
+                heuristic_path: Supported,
+            }
+        } else if nested {
+            // If the position value we have is for a nested window used as the client area, we'll
+            // just climb up the hierarchy and get the geometry of the outermost window we're
+            // nested in.
+            let outer_window = self.climb_hierarchy(window, root).expect("Failed to climb window hierarchy");
+            let (outer_y, outer_width, outer_height) = {
+                let outer_geometry = self.get_geometry(outer_window).expect("Failed to get outer window geometry");
+                (
+                    outer_geometry.y_rel_parent,
+                    outer_geometry.width,
+                    outer_geometry.height,
+                )
+            };
+
+            // Since we have the geometry of the outermost window and the geometry of the client
+            // area, we can figure out what's in between.
+            let diff_x = outer_width.saturating_sub(width);
+            let diff_y = outer_height.saturating_sub(height);
+            let offset_y = inner_y_rel_root.saturating_sub(outer_y) as c_uint;
+
+            let left = diff_x / 2;
+            let right = left;
+            let top = offset_y;
+            let bottom = diff_y.saturating_sub(offset_y);
+
+            let frame_extents = FrameExtents::new(
+                left.into(),
+                right.into(),
+                top.into(),
+                bottom.into(),
+            );
+            FrameExtentsHeuristic {
+                frame_extents,
+                heuristic_path: UnsupportedNested,
+            }
+        } else {
+            // This is the case for xmonad and dwm, AKA the only WMs tested that supplied a
+            // border value. This is convenient, since we can use it to get an accurate frame.
+            let frame_extents = FrameExtents::from_border(border.into());
+            FrameExtentsHeuristic {
+                frame_extents,
+                heuristic_path: UnsupportedBordered,
+            }
+        }
+    }
+}

src/platform_impl/linux/x11/util/hint.rs

@@ -0,0 +1,236 @@
+use std::sync::Arc;
+
+use super::*;
+
+pub const MWM_HINTS_DECORATIONS: c_ulong = 2;
+
+#[derive(Debug)]
+pub enum StateOperation {
+    Remove = 0, // _NET_WM_STATE_REMOVE
+    Add = 1,    // _NET_WM_STATE_ADD
+    Toggle = 2, // _NET_WM_STATE_TOGGLE
+}
+
+impl From<bool> for StateOperation {
+    fn from(op: bool) -> Self {
+        if op {
+            StateOperation::Add
+        } else {
+            StateOperation::Remove
+        }
+    }
+}
+
+/// X window type. Maps directly to
+/// [`_NET_WM_WINDOW_TYPE`](https://specifications.freedesktop.org/wm-spec/wm-spec-1.5.html).
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum WindowType {
+    /// A desktop feature. This can include a single window containing desktop icons with the same dimensions as the
+    /// screen, allowing the desktop environment to have full control of the desktop, without the need for proxying
+    /// root window clicks.
+    Desktop,
+    /// A dock or panel feature. Typically a Window Manager would keep such windows on top of all other windows.
+    Dock,
+    /// Toolbar windows. "Torn off" from the main application.
+    Toolbar,
+    /// Pinnable menu windows. "Torn off" from the main application.
+    Menu,
+    /// A small persistent utility window, such as a palette or toolbox.
+    Utility,
+    /// The window is a splash screen displayed as an application is starting up.
+    Splash,
+    /// This is a dialog window.
+    Dialog,
+    /// A dropdown menu that usually appears when the user clicks on an item in a menu bar.
+    /// This property is typically used on override-redirect windows.
+    DropdownMenu,
+    /// A popup menu that usually appears when the user right clicks on an object.
+    /// This property is typically used on override-redirect windows.
+    PopupMenu,
+    /// A tooltip window. Usually used to show additional information when hovering over an object with the cursor.
+    /// This property is typically used on override-redirect windows.
+    Tooltip,
+    /// The window is a notification.
+    /// This property is typically used on override-redirect windows.
+    Notification,
+    /// This should be used on the windows that are popped up by combo boxes.
+    /// This property is typically used on override-redirect windows.
+    Combo,
+    /// This indicates the the window is being dragged.
+    /// This property is typically used on override-redirect windows.
+    Dnd,
+    /// This is a normal, top-level window.
+    Normal,
+}
+
+impl Default for WindowType {
+    fn default() -> Self {
+        WindowType::Normal
+    }
+}
+
+impl WindowType {
+    pub(crate) fn as_atom(&self, xconn: &Arc<XConnection>) -> ffi::Atom {
+        use self::WindowType::*;
+        let atom_name: &[u8] = match self {
+            &Desktop => b"_NET_WM_WINDOW_TYPE_DESKTOP\0",
+            &Dock => b"_NET_WM_WINDOW_TYPE_DOCK\0",
+            &Toolbar => b"_NET_WM_WINDOW_TYPE_TOOLBAR\0",
+            &Menu => b"_NET_WM_WINDOW_TYPE_MENU\0",
+            &Utility => b"_NET_WM_WINDOW_TYPE_UTILITY\0",
+            &Splash => b"_NET_WM_WINDOW_TYPE_SPLASH\0",
+            &Dialog => b"_NET_WM_WINDOW_TYPE_DIALOG\0",
+            &DropdownMenu => b"_NET_WM_WINDOW_TYPE_DROPDOWN_MENU\0",
+            &PopupMenu => b"_NET_WM_WINDOW_TYPE_POPUP_MENU\0",
+            &Tooltip => b"_NET_WM_WINDOW_TYPE_TOOLTIP\0",
+            &Notification => b"_NET_WM_WINDOW_TYPE_NOTIFICATION\0",
+            &Combo => b"_NET_WM_WINDOW_TYPE_COMBO\0",
+            &Dnd => b"_NET_WM_WINDOW_TYPE_DND\0",
+            &Normal => b"_NET_WM_WINDOW_TYPE_NORMAL\0",
+        };
+        unsafe { xconn.get_atom_unchecked(atom_name) }
+    }
+}
+
+pub struct NormalHints<'a> {
+    size_hints: XSmartPointer<'a, ffi::XSizeHints>,
+}
+
+impl<'a> NormalHints<'a> {
+    pub fn new(xconn: &'a XConnection) -> Self {
+        NormalHints { size_hints: xconn.alloc_size_hints() }
+    }
+
+    pub fn has_flag(&self, flag: c_long) -> bool {
+        has_flag(self.size_hints.flags, flag)
+    }
+
+    fn getter(&self, flag: c_long, field1: &c_int, field2: &c_int) -> Option<(u32, u32)> {
+        if self.has_flag(flag) {
+            Some((*field1 as _, *field2 as _))
+        } else {
+            None
+        }
+    }
+
+    pub fn get_size(&self) -> Option<(u32, u32)> {
+        self.getter(ffi::PSize, &self.size_hints.width, &self.size_hints.height)
+    }
+
+    // WARNING: This hint is obsolete
+    pub fn set_size(&mut self, size: Option<(u32, u32)>) {
+        if let Some((width, height)) = size {
+            self.size_hints.flags |= ffi::PSize;
+            self.size_hints.width = width as c_int;
+            self.size_hints.height = height as c_int;
+        } else {
+            self.size_hints.flags &= !ffi::PSize;
+        }
+    }
+
+    pub fn get_max_size(&self) -> Option<(u32, u32)> {
+        self.getter(ffi::PMaxSize, &self.size_hints.max_width, &self.size_hints.max_height)
+    }
+
+    pub fn set_max_size(&mut self, max_size: Option<(u32, u32)>) {
+        if let Some((max_width, max_height)) = max_size {
+            self.size_hints.flags |= ffi::PMaxSize;
+            self.size_hints.max_width = max_width as c_int;
+            self.size_hints.max_height = max_height as c_int;
+        } else {
+            self.size_hints.flags &= !ffi::PMaxSize;
+        }
+    }
+
+    pub fn get_min_size(&self) -> Option<(u32, u32)> {
+        self.getter(ffi::PMinSize, &self.size_hints.min_width, &self.size_hints.min_height)
+    }
+
+    pub fn set_min_size(&mut self, min_size: Option<(u32, u32)>) {
+        if let Some((min_width, min_height)) = min_size {
+            self.size_hints.flags |= ffi::PMinSize;
+            self.size_hints.min_width = min_width as c_int;
+            self.size_hints.min_height = min_height as c_int;
+        } else {
+            self.size_hints.flags &= !ffi::PMinSize;
+        }
+    }
+
+    pub fn get_resize_increments(&self) -> Option<(u32, u32)> {
+        self.getter(ffi::PResizeInc, &self.size_hints.width_inc, &self.size_hints.height_inc)
+    }
+
+    pub fn set_resize_increments(&mut self, resize_increments: Option<(u32, u32)>) {
+        if let Some((width_inc, height_inc)) = resize_increments {
+            self.size_hints.flags |= ffi::PResizeInc;
+            self.size_hints.width_inc = width_inc as c_int;
+            self.size_hints.height_inc = height_inc as c_int;
+        } else {
+            self.size_hints.flags &= !ffi::PResizeInc;
+        }
+    }
+
+    pub fn get_base_size(&self) -> Option<(u32, u32)> {
+        self.getter(ffi::PBaseSize, &self.size_hints.base_width, &self.size_hints.base_height)
+    }
+
+    pub fn set_base_size(&mut self, base_size: Option<(u32, u32)>) {
+        if let Some((base_width, base_height)) = base_size {
+            self.size_hints.flags |= ffi::PBaseSize;
+            self.size_hints.base_width = base_width as c_int;
+            self.size_hints.base_height = base_height as c_int;
+        } else {
+            self.size_hints.flags &= !ffi::PBaseSize;
+        }
+    }
+}
+
+impl XConnection {
+    pub fn get_wm_hints(&self, window: ffi::Window) -> Result<XSmartPointer<ffi::XWMHints>, XError> {
+        let wm_hints = unsafe { (self.xlib.XGetWMHints)(self.display, window) };
+        self.check_errors()?;
+        let wm_hints = if wm_hints.is_null() {
+            self.alloc_wm_hints()
+        } else {
+            XSmartPointer::new(self, wm_hints).unwrap()
+        };
+        Ok(wm_hints)
+    }
+
+    pub fn set_wm_hints(&self, window: ffi::Window, wm_hints: XSmartPointer<ffi::XWMHints>) -> Flusher {
+        unsafe {
+            (self.xlib.XSetWMHints)(
+                self.display,
+                window,
+                wm_hints.ptr,
+            );
+        }
+        Flusher::new(self)
+    }
+
+    pub fn get_normal_hints(&self, window: ffi::Window) -> Result<NormalHints, XError> {
+        let size_hints = self.alloc_size_hints();
+        let mut supplied_by_user: c_long = unsafe { mem::uninitialized() };
+        unsafe {
+            (self.xlib.XGetWMNormalHints)(
+                self.display,
+                window,
+                size_hints.ptr,
+                &mut supplied_by_user,
+            );
+        }
+        self.check_errors().map(|_| NormalHints { size_hints })
+    }
+
+    pub fn set_normal_hints(&self, window: ffi::Window, normal_hints: NormalHints) -> Flusher {
+        unsafe {
+            (self.xlib.XSetWMNormalHints)(
+                self.display,
+                window,
+                normal_hints.size_hints.ptr,
+            );
+        }
+        Flusher::new(self)
+    }
+}

src/platform_impl/linux/x11/util/icon.rs

@@ -0,0 +1,34 @@
+use {Icon, Pixel, PIXEL_SIZE};
+use super::*;
+
+impl Pixel {
+    pub fn to_packed_argb(&self) -> Cardinal {
+        let mut cardinal = 0;
+        assert!(CARDINAL_SIZE >= PIXEL_SIZE);
+        let as_bytes = &mut cardinal as *mut _ as *mut u8;
+        unsafe {
+            *as_bytes.offset(0) = self.b;
+            *as_bytes.offset(1) = self.g;
+            *as_bytes.offset(2) = self.r;
+            *as_bytes.offset(3) = self.a;
+        }
+        cardinal
+    }
+}
+
+impl Icon {
+    pub(crate) fn to_cardinals(&self) -> Vec<Cardinal> {
+        assert_eq!(self.rgba.len() % PIXEL_SIZE, 0);
+        let pixel_count = self.rgba.len() / PIXEL_SIZE;
+        assert_eq!(pixel_count, (self.width * self.height) as usize);
+        let mut data = Vec::with_capacity(pixel_count);
+        data.push(self.width as Cardinal);
+        data.push(self.height as Cardinal);
+        let pixels = self.rgba.as_ptr() as *const Pixel;
+        for pixel_index in 0..pixel_count {
+            let pixel = unsafe { &*pixels.offset(pixel_index as isize) };
+            data.push(pixel.to_packed_argb());
+        }
+        data
+    }
+}

src/platform_impl/linux/x11/util/input.rs

@@ -0,0 +1,159 @@
+use std::str;
+
+use super::*;
+use events::ModifiersState;
+
+pub const VIRTUAL_CORE_POINTER: c_int = 2;
+pub const VIRTUAL_CORE_KEYBOARD: c_int = 3;
+
+// A base buffer size of 1kB uses a negligible amount of RAM while preventing us from having to
+// re-allocate (and make another round-trip) in the *vast* majority of cases.
+// To test if `lookup_utf8` works correctly, set this to 1.
+const TEXT_BUFFER_SIZE: usize = 1024;
+
+impl From<ffi::XIModifierState> for ModifiersState {
+    fn from(mods: ffi::XIModifierState) -> Self {
+        let state = mods.effective as c_uint;
+        ModifiersState {
+            alt: state & ffi::Mod1Mask != 0,
+            shift: state & ffi::ShiftMask != 0,
+            ctrl: state & ffi::ControlMask != 0,
+            logo: state & ffi::Mod4Mask != 0,
+        }
+    }
+}
+
+pub struct PointerState<'a> {
+    xconn: &'a XConnection,
+    root: ffi::Window,
+    child: ffi::Window,
+    pub root_x: c_double,
+    pub root_y: c_double,
+    win_x: c_double,
+    win_y: c_double,
+    buttons: ffi::XIButtonState,
+    modifiers: ffi::XIModifierState,
+    group: ffi::XIGroupState,
+    relative_to_window: bool,
+}
+
+impl<'a> PointerState<'a> {
+    pub fn get_modifier_state(&self) -> ModifiersState {
+        self.modifiers.into()
+    }
+}
+
+impl<'a> Drop for PointerState<'a> {
+    fn drop(&mut self) {
+        if !self.buttons.mask.is_null() {
+            unsafe {
+                // This is why you need to read the docs carefully...
+                (self.xconn.xlib.XFree)(self.buttons.mask as _);
+            }
+        }
+    }
+}
+
+impl XConnection {
+    pub fn select_xinput_events(&self, window: c_ulong, device_id: c_int, mask: i32) -> Flusher {
+        let mut event_mask = ffi::XIEventMask {
+            deviceid: device_id,
+            mask: &mask as *const _ as *mut c_uchar,
+            mask_len: mem::size_of_val(&mask) as c_int,
+        };
+        unsafe {
+            (self.xinput2.XISelectEvents)(
+                self.display,
+                window,
+                &mut event_mask as *mut ffi::XIEventMask,
+                1, // number of masks to read from pointer above
+            );
+        }
+        Flusher::new(self)
+    }
+
+    #[allow(dead_code)]
+    pub fn select_xkb_events(&self, device_id: c_uint, mask: c_ulong) -> Option<Flusher> {
+        let status = unsafe {
+            (self.xlib.XkbSelectEvents)(
+                self.display,
+                device_id,
+                mask,
+                mask,
+            )
+        };
+        if status == ffi::True {
+            Some(Flusher::new(self))
+        } else {
+            None
+        }
+    }
+
+    pub fn query_pointer(&self, window: ffi::Window, device_id: c_int) -> Result<PointerState, XError> {
+        unsafe {
+            let mut pointer_state: PointerState = mem::uninitialized();
+            pointer_state.xconn = self;
+            pointer_state.relative_to_window = (self.xinput2.XIQueryPointer)(
+                self.display,
+                device_id,
+                window,
+                &mut pointer_state.root,
+                &mut pointer_state.child,
+                &mut pointer_state.root_x,
+                &mut pointer_state.root_y,
+                &mut pointer_state.win_x,
+                &mut pointer_state.win_y,
+                &mut pointer_state.buttons,
+                &mut pointer_state.modifiers,
+                &mut pointer_state.group,
+            ) == ffi::True;
+            if let Err(err) = self.check_errors() {
+                // Running the destrutor would be bad news for us...
+                mem::forget(pointer_state);
+                Err(err)
+            } else {
+                Ok(pointer_state)
+            }
+        }
+    }
+
+    fn lookup_utf8_inner(
+        &self,
+        ic: ffi::XIC,
+        key_event: &mut ffi::XKeyEvent,
+        buffer: &mut [u8],
+    ) -> (ffi::KeySym, ffi::Status, c_int) {
+        let mut keysym: ffi::KeySym = 0;
+        let mut status: ffi::Status = 0;
+        let count = unsafe {
+            (self.xlib.Xutf8LookupString)(
+                ic,
+                key_event,
+                buffer.as_mut_ptr() as *mut c_char,
+                buffer.len() as c_int,
+                &mut keysym,
+                &mut status,
+            )
+        };
+        (keysym, status, count)
+    }
+
+    pub fn lookup_utf8(&self, ic: ffi::XIC, key_event: &mut ffi::XKeyEvent) -> String {
+        let mut buffer: [u8; TEXT_BUFFER_SIZE] = unsafe { mem::uninitialized() };
+        let (_, status, count) = self.lookup_utf8_inner(ic, key_event, &mut buffer);
+        // The buffer overflowed, so we'll make a new one on the heap.
+        if status == ffi::XBufferOverflow {
+            let mut buffer = Vec::with_capacity(count as usize);
+            unsafe { buffer.set_len(count as usize) };
+            let (_, _, new_count) = self.lookup_utf8_inner(ic, key_event, &mut buffer);
+            debug_assert_eq!(count, new_count);
+            str::from_utf8(&buffer[..count as usize])
+                .unwrap_or("")
+                .to_string()
+        } else {
+            str::from_utf8(&buffer[..count as usize])
+                .unwrap_or("")
+                .to_string()
+        }
+    }
+}

src/platform_impl/linux/x11/util/memory.rs

@@ -0,0 +1,62 @@
+use std::ops::{Deref, DerefMut};
+
+use super::*;
+
+pub struct XSmartPointer<'a, T> {
+    xconn: &'a XConnection,
+    pub ptr: *mut T,
+}
+
+impl<'a, T> XSmartPointer<'a, T> {
+    // You're responsible for only passing things to this that should be XFree'd.
+    // Returns None if ptr is null.
+    pub fn new(xconn: &'a XConnection, ptr: *mut T) -> Option<Self> {
+        if !ptr.is_null() {
+            Some(XSmartPointer {
+                xconn,
+                ptr,
+            })
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, T> Deref for XSmartPointer<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.ptr }
+    }
+}
+
+impl<'a, T> DerefMut for XSmartPointer<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.ptr }
+    }
+}
+
+impl<'a, T> Drop for XSmartPointer<'a, T> {
+    fn drop(&mut self) {
+        unsafe {
+            (self.xconn.xlib.XFree)(self.ptr as *mut _);
+        }
+    }
+}
+
+impl XConnection {
+    pub fn alloc_class_hint(&self) -> XSmartPointer<ffi::XClassHint> {
+        XSmartPointer::new(self, unsafe { (self.xlib.XAllocClassHint)() })
+            .expect("`XAllocClassHint` returned null; out of memory")
+    }
+
+    pub fn alloc_size_hints(&self) -> XSmartPointer<ffi::XSizeHints> {
+        XSmartPointer::new(self, unsafe { (self.xlib.XAllocSizeHints)() })
+            .expect("`XAllocSizeHints` returned null; out of memory")
+    }
+
+    pub fn alloc_wm_hints(&self) -> XSmartPointer<ffi::XWMHints> {
+        XSmartPointer::new(self, unsafe { (self.xlib.XAllocWMHints)() })
+            .expect("`XAllocWMHints` returned null; out of memory")
+    }
+}

src/platform_impl/linux/x11/util/mod.rs

@@ -0,0 +1,104 @@
+// Welcome to the util module, where we try to keep you from shooting yourself in the foot.
+// *results may vary
+
+mod atom;
+mod client_msg;
+mod format;
+mod geometry;
+mod hint;
+mod icon;
+mod input;
+mod memory;
+mod randr;
+mod window_property;
+mod wm;
+
+pub use self::atom::*;
+pub use self::client_msg::*;
+pub use self::format::*;
+pub use self::geometry::*;
+pub use self::hint::*;
+pub use self::icon::*;
+pub use self::input::*;
+pub use self::memory::*;
+pub use self::randr::*;
+pub use self::window_property::*;
+pub use self::wm::*;
+
+use std::mem;
+use std::ptr;
+use std::ops::BitAnd;
+use std::os::raw::*;
+
+use super::{ffi, XConnection, XError};
+
+pub fn reinterpret<'a, A, B>(a: &'a A) -> &'a B {
+    let b_ptr = a as *const _ as *const B;
+    unsafe { &*b_ptr }
+}
+
+pub fn maybe_change<T: PartialEq>(field: &mut Option<T>, value: T) -> bool {
+    let wrapped = Some(value);
+    if *field != wrapped {
+        *field = wrapped;
+        true
+    } else {
+        false
+    }
+}
+
+pub fn has_flag<T>(bitset: T, flag: T) -> bool
+where T:
+    Copy + PartialEq + BitAnd<T, Output = T>
+{
+    bitset & flag == flag
+}
+
+#[must_use = "This request was made asynchronously, and is still in the output buffer. You must explicitly choose to either `.flush()` (empty the output buffer, sending the request now) or `.queue()` (wait to send the request, allowing you to continue to add more requests without additional round-trips). For more information, see the documentation for `util::flush_requests`."]
+pub struct Flusher<'a> {
+    xconn: &'a XConnection,
+}
+
+impl<'a> Flusher<'a> {
+    pub fn new(xconn: &'a XConnection) -> Self {
+        Flusher { xconn }
+    }
+
+    // "I want this request sent now!"
+    pub fn flush(self) -> Result<(), XError> {
+        self.xconn.flush_requests()
+    }
+
+    // "I want the response now too!"
+    pub fn sync(self) -> Result<(), XError> {
+        self.xconn.sync_with_server()
+    }
+
+    // "I'm aware that this request hasn't been sent, and I'm okay with waiting."
+    pub fn queue(self) {}
+}
+
+impl XConnection {
+    // This is impoartant, so pay attention!
+    // Xlib has an output buffer, and tries to hide the async nature of X from you.
+    // This buffer contains the requests you make, and is flushed under various circumstances:
+    // 1. `XPending`, `XNextEvent`, and `XWindowEvent` flush "as needed"
+    // 2. `XFlush` explicitly flushes
+    // 3. `XSync` flushes and blocks until all requests are responded to
+    // 4. Calls that have a return dependent on a response (i.e. `XGetWindowProperty`) sync internally.
+    //    When in doubt, check the X11 source; if a function calls `_XReply`, it flushes and waits.
+    // All util functions that abstract an async function will return a `Flusher`.
+    pub fn flush_requests(&self) -> Result<(), XError> {
+        unsafe { (self.xlib.XFlush)(self.display) };
+        //println!("XFlush");
+        // This isn't necessarily a useful time to check for errors (since our request hasn't
+        // necessarily been processed yet)
+        self.check_errors()
+    }
+
+    pub fn sync_with_server(&self) -> Result<(), XError> {
+        unsafe { (self.xlib.XSync)(self.display, ffi::False) };
+        //println!("XSync");
+        self.check_errors()
+    }
+}

src/platform_impl/linux/x11/util/randr.rs

@@ -0,0 +1,111 @@
+use std::{env, slice};
+use std::str::FromStr;
+
+use validate_hidpi_factor;
+use super::*;
+
+pub fn calc_dpi_factor(
+    (width_px, height_px): (u32, u32),
+    (width_mm, height_mm): (u64, u64),
+) -> f64 {
+    // Override DPI if `WINIT_HIDPI_FACTOR` variable is set
+    let dpi_override = env::var("WINIT_HIDPI_FACTOR")
+        .ok()
+        .and_then(|var| f64::from_str(&var).ok());
+    if let Some(dpi_override) = dpi_override {
+        if !validate_hidpi_factor(dpi_override) {
+            panic!(
+                "`WINIT_HIDPI_FACTOR` invalid; DPI factors must be normal floats greater than 0. Got `{}`",
+                dpi_override,
+            );
+        }
+        return dpi_override;
+    }
+
+    // See http://xpra.org/trac/ticket/728 for more information.
+    if width_mm == 0 || width_mm == 0 {
+        warn!("XRandR reported that the display's 0mm in size, which is certifiably insane");
+        return 1.0;
+    }
+
+    let ppmm = (
+        (width_px as f64 * height_px as f64) / (width_mm as f64 * height_mm as f64)
+    ).sqrt();
+    // Quantize 1/12 step size
+    let dpi_factor = ((ppmm * (12.0 * 25.4 / 96.0)).round() / 12.0).max(1.0);
+    assert!(validate_hidpi_factor(dpi_factor));
+    dpi_factor
+}
+
+pub enum MonitorRepr {
+    Monitor(*mut ffi::XRRMonitorInfo),
+    Crtc(*mut ffi::XRRCrtcInfo),
+}
+
+impl MonitorRepr {
+    pub unsafe fn get_output(&self) -> ffi::RROutput {
+        match *self {
+            // Same member names, but different locations within the struct...
+            MonitorRepr::Monitor(monitor) => *((*monitor).outputs.offset(0)),
+            MonitorRepr::Crtc(crtc) => *((*crtc).outputs.offset(0)),
+        }
+    }
+
+    pub unsafe fn get_dimensions(&self) -> (u32, u32) {
+        match *self {
+            MonitorRepr::Monitor(monitor) => ((*monitor).width as u32, (*monitor).height as u32),
+            MonitorRepr::Crtc(crtc) => ((*crtc).width as u32, (*crtc).height as u32),
+        }
+    }
+
+    pub unsafe fn get_position(&self) -> (i32, i32) {
+        match *self {
+            MonitorRepr::Monitor(monitor) => ((*monitor).x as i32, (*monitor).y as i32),
+            MonitorRepr::Crtc(crtc) => ((*crtc).x as i32, (*crtc).y as i32),
+        }
+    }
+}
+
+impl From<*mut ffi::XRRMonitorInfo> for MonitorRepr {
+    fn from(monitor: *mut ffi::XRRMonitorInfo) -> Self {
+        MonitorRepr::Monitor(monitor)
+    }
+}
+
+impl From<*mut ffi::XRRCrtcInfo> for MonitorRepr {
+    fn from(crtc: *mut ffi::XRRCrtcInfo) -> Self {
+        MonitorRepr::Crtc(crtc)
+    }
+}
+
+impl XConnection {
+    pub unsafe fn get_output_info(
+        &self,
+        resources: *mut ffi::XRRScreenResources,
+        repr: &MonitorRepr,
+    ) -> Option<(String, f64)> {
+        let output_info = (self.xrandr.XRRGetOutputInfo)(
+            self.display,
+            resources,
+            repr.get_output(),
+        );
+        if output_info.is_null() {
+            // When calling `XRRGetOutputInfo` on a virtual monitor (versus a physical display)
+            // it's possible for it to return null.
+            // https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=816596
+            let _ = self.check_errors(); // discard `BadRROutput` error
+            return None;
+        }
+        let name_slice = slice::from_raw_parts(
+            (*output_info).name as *mut u8,
+            (*output_info).nameLen as usize,
+        );
+        let name = String::from_utf8_lossy(name_slice).into();
+        let hidpi_factor = calc_dpi_factor(
+            repr.get_dimensions(),
+            ((*output_info).mm_width as u64, (*output_info).mm_height as u64),
+        );
+        (self.xrandr.XRRFreeOutputInfo)(output_info);
+        Some((name, hidpi_factor))
+    }
+}

src/platform_impl/linux/x11/util/window_property.rs

@@ -0,0 +1,144 @@
+use std;
+
+use super::*;
+
+pub type Cardinal = c_long;
+pub const CARDINAL_SIZE: usize = mem::size_of::<c_long>();
+
+#[derive(Debug, Clone)]
+pub enum GetPropertyError {
+    XError(XError),
+    TypeMismatch(ffi::Atom),
+    FormatMismatch(c_int),
+    NothingAllocated,
+}
+
+impl GetPropertyError {
+    pub fn is_actual_property_type(&self, t: ffi::Atom) -> bool {
+        if let GetPropertyError::TypeMismatch(actual_type) = *self {
+            actual_type == t
+        } else {
+            false
+        }
+    }
+}
+
+// Number of 32-bit chunks to retrieve per iteration of get_property's inner loop.
+// To test if `get_property` works correctly, set this to 1.
+const PROPERTY_BUFFER_SIZE: c_long = 1024; // 4k of RAM ought to be enough for anyone!
+
+#[derive(Debug)]
+pub enum PropMode {
+    Replace = ffi::PropModeReplace as isize,
+    Prepend = ffi::PropModePrepend as isize,
+    Append = ffi::PropModeAppend as isize,
+}
+
+impl XConnection {
+    pub fn get_property<T: Formattable>(
+        &self,
+        window: c_ulong,
+        property: ffi::Atom,
+        property_type: ffi::Atom,
+    ) -> Result<Vec<T>, GetPropertyError> {
+        let mut data = Vec::new();
+        let mut offset = 0;
+
+        let mut done = false;
+        while !done {
+            unsafe {
+                let mut actual_type: ffi::Atom = mem::uninitialized();
+                let mut actual_format: c_int = mem::uninitialized();
+                let mut quantity_returned: c_ulong = mem::uninitialized();
+                let mut bytes_after: c_ulong = mem::uninitialized();
+                let mut buf: *mut c_uchar = ptr::null_mut();
+                (self.xlib.XGetWindowProperty)(
+                    self.display,
+                    window,
+                    property,
+                    // This offset is in terms of 32-bit chunks.
+                    offset,
+                    // This is the quanity of 32-bit chunks to receive at once.
+                    PROPERTY_BUFFER_SIZE,
+                    ffi::False,
+                    property_type,
+                    &mut actual_type,
+                    &mut actual_format,
+                    // This is the quantity of items we retrieved in our format, NOT of 32-bit chunks!
+                    &mut quantity_returned,
+                    // ...and this is a quantity of bytes. So, this function deals in 3 different units.
+                    &mut bytes_after,
+                    &mut buf,
+                );
+
+                if let Err(e) = self.check_errors() {
+                    return Err(GetPropertyError::XError(e));
+                }
+
+                if actual_type != property_type {
+                    return Err(GetPropertyError::TypeMismatch(actual_type));
+                }
+
+                let format_mismatch = Format::from_format(actual_format as _) != Some(T::FORMAT);
+                if format_mismatch {
+                    return Err(GetPropertyError::FormatMismatch(actual_format));
+                }
+
+                if !buf.is_null() {
+                    offset += PROPERTY_BUFFER_SIZE;
+                    let new_data = std::slice::from_raw_parts(
+                        buf as *mut T,
+                        quantity_returned as usize,
+                    );
+                    /*println!(
+                        "XGetWindowProperty prop:{:?} fmt:{:02} len:{:02} off:{:02} out:{:02}, buf:{:?}",
+                        property,
+                        mem::size_of::<T>() * 8,
+                        data.len(),
+                        offset,
+                        quantity_returned,
+                        new_data,
+                    );*/
+                    data.extend_from_slice(&new_data);
+                    // Fun fact: XGetWindowProperty allocates one extra byte at the end.
+                    (self.xlib.XFree)(buf as _); // Don't try to access new_data after this.
+                } else {
+                    return Err(GetPropertyError::NothingAllocated);
+                }
+
+                done = bytes_after == 0;
+            }
+        }
+
+        Ok(data)
+    }
+
+    pub fn change_property<'a, T: Formattable>(
+        &'a self,
+        window: c_ulong,
+        property: ffi::Atom,
+        property_type: ffi::Atom,
+        mode: PropMode,
+        new_value: &[T],
+    ) -> Flusher<'a> {
+        debug_assert_eq!(mem::size_of::<T>(), T::FORMAT.get_actual_size());
+        unsafe {
+            (self.xlib.XChangeProperty)(
+                self.display,
+                window,
+                property,
+                property_type,
+                T::FORMAT as c_int,
+                mode as c_int,
+                new_value.as_ptr() as *const c_uchar,
+                new_value.len() as c_int,
+            );
+        }
+        /*println!(
+            "XChangeProperty prop:{:?} val:{:?}",
+            property,
+            new_value,
+        );*/
+        Flusher::new(self)
+    }
+}

src/platform_impl/linux/x11/util/wm.rs

@@ -0,0 +1,141 @@
+use parking_lot::Mutex;
+
+use super::*;
+
+// This info is global to the window manager.
+lazy_static! {
+    static ref SUPPORTED_HINTS: Mutex<Vec<ffi::Atom>> = Mutex::new(Vec::with_capacity(0));
+    static ref WM_NAME: Mutex<Option<String>> = Mutex::new(None);
+}
+
+pub fn hint_is_supported(hint: ffi::Atom) -> bool {
+    (*SUPPORTED_HINTS.lock()).contains(&hint)
+}
+
+pub fn wm_name_is_one_of(names: &[&str]) -> bool {
+    if let Some(ref name) = *WM_NAME.lock() {
+        names.contains(&name.as_str())
+    } else {
+        false
+    }
+}
+
+impl XConnection {
+    pub fn update_cached_wm_info(&self, root: ffi::Window) {
+        *SUPPORTED_HINTS.lock() = self.get_supported_hints(root);
+        *WM_NAME.lock() = self.get_wm_name(root);
+    }
+
+    fn get_supported_hints(&self, root: ffi::Window) -> Vec<ffi::Atom> {
+        let supported_atom = unsafe { self.get_atom_unchecked(b"_NET_SUPPORTED\0") };
+        self.get_property(
+            root,
+            supported_atom,
+            ffi::XA_ATOM,
+        ).unwrap_or_else(|_| Vec::with_capacity(0))
+    }
+
+    fn get_wm_name(&self, root: ffi::Window) -> Option<String> {
+        let check_atom = unsafe { self.get_atom_unchecked(b"_NET_SUPPORTING_WM_CHECK\0") };
+        let wm_name_atom = unsafe { self.get_atom_unchecked(b"_NET_WM_NAME\0") };
+
+        // Mutter/Muffin/Budgie doesn't have _NET_SUPPORTING_WM_CHECK in its _NET_SUPPORTED, despite
+        // it working and being supported. This has been reported upstream, but due to the
+        // inavailability of time machines, we'll just try to get _NET_SUPPORTING_WM_CHECK
+        // regardless of whether or not the WM claims to support it.
+        //
+        // Blackbox 0.70 also incorrectly reports not supporting this, though that appears to be fixed
+        // in 0.72.
+        /*if !supported_hints.contains(&check_atom) {
+            return None;
+        }*/
+
+        // IceWM (1.3.x and earlier) doesn't report supporting _NET_WM_NAME, but will nonetheless
+        // provide us with a value for it. Note that the unofficial 1.4 fork of IceWM works fine.
+        /*if !supported_hints.contains(&wm_name_atom) {
+            return None;
+        }*/
+
+        // Of the WMs tested, only xmonad and dwm fail to provide a WM name.
+
+        // Querying this property on the root window will give us the ID of a child window created by
+        // the WM.
+        let root_window_wm_check = {
+            let result = self.get_property(
+                root,
+                check_atom,
+                ffi::XA_WINDOW,
+            );
+
+            let wm_check = result
+                .ok()
+                .and_then(|wm_check| wm_check.get(0).cloned());
+
+            if let Some(wm_check) = wm_check {
+                wm_check
+            } else {
+                return None;
+            }
+        };
+
+        // Querying the same property on the child window we were given, we should get this child
+        // window's ID again.
+        let child_window_wm_check = {
+            let result = self.get_property(
+                root_window_wm_check,
+                check_atom,
+                ffi::XA_WINDOW,
+            );
+
+            let wm_check = result
+                .ok()
+                .and_then(|wm_check| wm_check.get(0).cloned());
+
+            if let Some(wm_check) = wm_check {
+                wm_check
+            } else {
+                return None;
+            }
+        };
+
+        // These values should be the same.
+        if root_window_wm_check != child_window_wm_check {
+            return None;
+        }
+
+        // All of that work gives us a window ID that we can get the WM name from.
+        let wm_name = {
+            let utf8_string_atom = unsafe { self.get_atom_unchecked(b"UTF8_STRING\0") };
+
+            let result = self.get_property(
+                root_window_wm_check,
+                wm_name_atom,
+                utf8_string_atom,
+            );
+
+            // IceWM requires this. IceWM was also the only WM tested that returns a null-terminated
+            // string. For more fun trivia, IceWM is also unique in including version and uname
+            // information in this string (this means you'll have to be careful if you want to match
+            // against it, though).
+            // The unofficial 1.4 fork of IceWM still includes the extra details, but properly
+            // returns a UTF8 string that isn't null-terminated.
+            let no_utf8 = if let Err(ref err) = result {
+                err.is_actual_property_type(ffi::XA_STRING)
+            } else {
+                false
+            };
+
+            if no_utf8 {
+                self.get_property(
+                    root_window_wm_check,
+                    wm_name_atom,
+                    ffi::XA_STRING,
+                )
+            } else {
+                result
+            }
+        }.ok();
+
+        wm_name.and_then(|wm_name| String::from_utf8(wm_name).ok())
+    }
+}