X11: Split off the event loop into a separate module (#183)

This PR splits off the X11 event loop logic into a separate module. It also changes the X11 implementation of the `Window` type to take only a shared reference to the inner type (`&WindowInner` instead of `&mut WindowInner`), bringing it in line with the other backends.

This does not change any of the logic however, it only separates some of the window state from the event loop state, to make sure they don't step on each other's toes in the future (particularly around the WindowHandler).

This is part of the effort to split up #174 into smaller pieces.

src/x11/event_loop.rs

@@ -0,0 +1,303 @@
+use crate::x11::keyboard::{convert_key_press_event, convert_key_release_event, key_mods};
+use crate::x11::{ParentHandle, Window, WindowInner};
+use crate::{
+    Event, MouseButton, MouseEvent, PhyPoint, PhySize, ScrollDelta, WindowEvent, WindowHandler,
+    WindowInfo,
+};
+use std::error::Error;
+use std::os::fd::AsRawFd;
+use std::time::{Duration, Instant};
+use x11rb::connection::Connection;
+use x11rb::protocol::Event as XEvent;
+
+pub(super) struct EventLoop {
+    handler: Box<dyn WindowHandler>,
+    window: WindowInner,
+    parent_handle: Option<ParentHandle>,
+
+    new_physical_size: Option<PhySize>,
+    frame_interval: Duration,
+    event_loop_running: bool,
+}
+
+impl EventLoop {
+    pub fn new(
+        window: WindowInner, handler: impl WindowHandler + 'static,
+        parent_handle: Option<ParentHandle>,
+    ) -> Self {
+        Self {
+            window,
+            handler: Box::new(handler),
+            parent_handle,
+            frame_interval: Duration::from_millis(15),
+            event_loop_running: false,
+            new_physical_size: None,
+        }
+    }
+
+    #[inline]
+    fn drain_xcb_events(&mut self) -> Result<(), Box<dyn Error>> {
+        // the X server has a tendency to send spurious/extraneous configure notify events when a
+        // window is resized, and we need to batch those together and just send one resize event
+        // when they've all been coalesced.
+        self.new_physical_size = None;
+
+        while let Some(event) = self.window.xcb_connection.conn.poll_for_event()? {
+            self.handle_xcb_event(event);
+        }
+
+        if let Some(size) = self.new_physical_size.take() {
+            self.window.window_info =
+                WindowInfo::from_physical_size(size, self.window.window_info.scale());
+
+            let window_info = self.window.window_info;
+
+            self.handler.on_event(
+                &mut crate::Window::new(Window { inner: &self.window }),
+                Event::Window(WindowEvent::Resized(window_info)),
+            );
+        }
+
+        Ok(())
+    }
+
+    // Event loop
+    // FIXME: poll() acts fine on linux, sometimes funky on *BSD. XCB upstream uses a define to
+    // switch between poll() and select() (the latter of which is fine on *BSD), and we should do
+    // the same.
+    pub fn run(&mut self) -> Result<(), Box<dyn Error>> {
+        use nix::poll::*;
+
+        let xcb_fd = self.window.xcb_connection.conn.as_raw_fd();
+
+        let mut last_frame = Instant::now();
+        self.event_loop_running = true;
+
+        while self.event_loop_running {
+            // We'll try to keep a consistent frame pace. If the last frame couldn't be processed in
+            // the expected frame time, this will throttle down to prevent multiple frames from
+            // being queued up. The conditional here is needed because event handling and frame
+            // drawing is interleaved. The `poll()` function below will wait until the next frame
+            // can be drawn, or until the window receives an event. We thus need to manually check
+            // if it's already time to draw a new frame.
+            let next_frame = last_frame + self.frame_interval;
+            if Instant::now() >= next_frame {
+                self.handler.on_frame(&mut crate::Window::new(Window { inner: &self.window }));
+                last_frame = Instant::max(next_frame, Instant::now() - self.frame_interval);
+            }
+
+            let mut fds = [PollFd::new(xcb_fd, PollFlags::POLLIN)];
+
+            // Check for any events in the internal buffers
+            // before going to sleep:
+            self.drain_xcb_events()?;
+
+            // FIXME: handle errors
+            poll(&mut fds, next_frame.duration_since(Instant::now()).subsec_millis() as i32)
+                .unwrap();
+
+            if let Some(revents) = fds[0].revents() {
+                if revents.contains(PollFlags::POLLERR) {
+                    panic!("xcb connection poll error");
+                }
+
+                if revents.contains(PollFlags::POLLIN) {
+                    self.drain_xcb_events()?;
+                }
+            }
+
+            // Check if the parents's handle was dropped (such as when the host
+            // requested the window to close)
+            //
+            // FIXME: This will need to be changed from just setting an atomic to somehow
+            // synchronizing with the window being closed (using a synchronous channel, or
+            // by joining on the event loop thread).
+            if let Some(parent_handle) = &self.parent_handle {
+                if parent_handle.parent_did_drop() {
+                    self.handle_must_close();
+                    self.window.close_requested.set(false);
+                }
+            }
+
+            // Check if the user has requested the window to close
+            if self.window.close_requested.get() {
+                self.handle_must_close();
+                self.window.close_requested.set(false);
+            }
+        }
+
+        Ok(())
+    }
+
+    fn handle_xcb_event(&mut self, event: XEvent) {
+        // For all the keyboard and mouse events, you can fetch
+        // `x`, `y`, `detail`, and `state`.
+        // - `x` and `y` are the position inside the window where the cursor currently is
+        //   when the event happened.
+        // - `detail` will tell you which keycode was pressed/released (for keyboard events)
+        //   or which mouse button was pressed/released (for mouse events).
+        //   For mouse events, here's what the value means (at least on my current mouse):
+        //      1 = left mouse button
+        //      2 = middle mouse button (scroll wheel)
+        //      3 = right mouse button
+        //      4 = scroll wheel up
+        //      5 = scroll wheel down
+        //      8 = lower side button ("back" button)
+        //      9 = upper side button ("forward" button)
+        //   Note that you *will* get a "button released" event for even the scroll wheel
+        //   events, which you can probably ignore.
+        // - `state` will tell you the state of the main three mouse buttons and some of
+        //   the keyboard modifier keys at the time of the event.
+        //   http://rtbo.github.io/rust-xcb/src/xcb/ffi/xproto.rs.html#445
+
+        match event {
+            ////
+            // window
+            ////
+            XEvent::ClientMessage(event) => {
+                if event.format == 32
+                    && event.data.as_data32()[0]
+                        == self.window.xcb_connection.atoms.WM_DELETE_WINDOW
+                {
+                    self.handle_close_requested();
+                }
+            }
+
+            XEvent::ConfigureNotify(event) => {
+                let new_physical_size = PhySize::new(event.width as u32, event.height as u32);
+
+                if self.new_physical_size.is_some()
+                    || new_physical_size != self.window.window_info.physical_size()
+                {
+                    self.new_physical_size = Some(new_physical_size);
+                }
+            }
+
+            ////
+            // mouse
+            ////
+            XEvent::MotionNotify(event) => {
+                let physical_pos = PhyPoint::new(event.event_x as i32, event.event_y as i32);
+                let logical_pos = physical_pos.to_logical(&self.window.window_info);
+
+                self.handler.on_event(
+                    &mut crate::Window::new(Window { inner: &self.window }),
+                    Event::Mouse(MouseEvent::CursorMoved {
+                        position: logical_pos,
+                        modifiers: key_mods(event.state),
+                    }),
+                );
+            }
+
+            XEvent::EnterNotify(event) => {
+                self.handler.on_event(
+                    &mut crate::Window::new(Window { inner: &self.window }),
+                    Event::Mouse(MouseEvent::CursorEntered),
+                );
+                // since no `MOTION_NOTIFY` event is generated when `ENTER_NOTIFY` is generated,
+                // we generate a CursorMoved as well, so the mouse position from here isn't lost
+                let physical_pos = PhyPoint::new(event.event_x as i32, event.event_y as i32);
+                let logical_pos = physical_pos.to_logical(&self.window.window_info);
+                self.handler.on_event(
+                    &mut crate::Window::new(Window { inner: &self.window }),
+                    Event::Mouse(MouseEvent::CursorMoved {
+                        position: logical_pos,
+                        modifiers: key_mods(event.state),
+                    }),
+                );
+            }
+
+            XEvent::LeaveNotify(_) => {
+                self.handler.on_event(
+                    &mut crate::Window::new(Window { inner: &self.window }),
+                    Event::Mouse(MouseEvent::CursorLeft),
+                );
+            }
+
+            XEvent::ButtonPress(event) => match event.detail {
+                4..=7 => {
+                    self.handler.on_event(
+                        &mut crate::Window::new(Window { inner: &self.window }),
+                        Event::Mouse(MouseEvent::WheelScrolled {
+                            delta: match event.detail {
+                                4 => ScrollDelta::Lines { x: 0.0, y: 1.0 },
+                                5 => ScrollDelta::Lines { x: 0.0, y: -1.0 },
+                                6 => ScrollDelta::Lines { x: -1.0, y: 0.0 },
+                                7 => ScrollDelta::Lines { x: 1.0, y: 0.0 },
+                                _ => unreachable!(),
+                            },
+                            modifiers: key_mods(event.state),
+                        }),
+                    );
+                }
+                detail => {
+                    let button_id = mouse_id(detail);
+                    self.handler.on_event(
+                        &mut crate::Window::new(Window { inner: &self.window }),
+                        Event::Mouse(MouseEvent::ButtonPressed {
+                            button: button_id,
+                            modifiers: key_mods(event.state),
+                        }),
+                    );
+                }
+            },
+
+            XEvent::ButtonRelease(event) => {
+                if !(4..=7).contains(&event.detail) {
+                    let button_id = mouse_id(event.detail);
+                    self.handler.on_event(
+                        &mut crate::Window::new(Window { inner: &self.window }),
+                        Event::Mouse(MouseEvent::ButtonReleased {
+                            button: button_id,
+                            modifiers: key_mods(event.state),
+                        }),
+                    );
+                }
+            }
+
+            ////
+            // keys
+            ////
+            XEvent::KeyPress(event) => {
+                self.handler.on_event(
+                    &mut crate::Window::new(Window { inner: &self.window }),
+                    Event::Keyboard(convert_key_press_event(&event)),
+                );
+            }
+
+            XEvent::KeyRelease(event) => {
+                self.handler.on_event(
+                    &mut crate::Window::new(Window { inner: &self.window }),
+                    Event::Keyboard(convert_key_release_event(&event)),
+                );
+            }
+
+            _ => {}
+        }
+    }
+
+    fn handle_close_requested(&mut self) {
+        // FIXME: handler should decide whether window stays open or not
+        self.handle_must_close();
+    }
+
+    fn handle_must_close(&mut self) {
+        self.handler.on_event(
+            &mut crate::Window::new(Window { inner: &self.window }),
+            Event::Window(WindowEvent::WillClose),
+        );
+
+        self.event_loop_running = false;
+    }
+}
+
+fn mouse_id(id: u8) -> MouseButton {
+    match id {
+        1 => MouseButton::Left,
+        2 => MouseButton::Middle,
+        3 => MouseButton::Right,
+        8 => MouseButton::Back,
+        9 => MouseButton::Forward,
+        id => MouseButton::Other(id),
+    }
+}

src/x11/mod.rs

@@ -5,5 +5,6 @@ mod window;
 pub use window::*;
 
 mod cursor;
+mod event_loop;
 mod keyboard;
 mod visual_info;

src/x11/visual_info.rs

@@ -63,7 +63,7 @@ impl WindowVisualConfig {
 
 // For this 32-bit depth to work, you also need to define a color map and set a border
 // pixel: https://cgit.freedesktop.org/xorg/xserver/tree/dix/window.c#n818
-pub fn create_color_map(
+fn create_color_map(
     connection: &XcbConnection, visual_id: Visualid,
 ) -> Result<Colormap, Box<dyn Error>> {
     let colormap = connection.conn.generate_id()?;