User timer based rendering instead of vsync

Fixes #824.

6 files changed, 138 insertions, 51 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f58f63a..31696c54 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Crash while typing on Wayland
 - Multi-line semantic bracket selection
 - Reduced GPU memory usage
+- Low frame rate when multiple windows render at the same time
+- Redraw hanging until a keypress on X11 in rare cases
 
 ## 0.11.0
 
diff --git a/alacritty/src/display/mod.rs b/alacritty/src/display/mod.rs
index ba6eeae0..605ac3f2 100644
--- a/alacritty/src/display/mod.rs
+++ b/alacritty/src/display/mod.rs
@@ -6,14 +6,14 @@ use std::fmt::{self, Formatter};
 use std::mem::{self, ManuallyDrop};
 use std::num::NonZeroU32;
 use std::ops::{Deref, DerefMut};
-#[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
 use std::sync::atomic::Ordering;
+use std::time::{Duration, Instant};
 
 use glutin::context::{NotCurrentContext, PossiblyCurrentContext};
 use glutin::prelude::*;
 use glutin::surface::{Rect as DamageRect, Surface, SwapInterval, WindowSurface};
 
-use log::{debug, info, warn};
+use log::{debug, info};
 use parking_lot::MutexGuard;
 use serde::{Deserialize, Serialize};
 use winit::dpi::PhysicalSize;
@@ -46,10 +46,11 @@ use crate::display::damage::RenderDamageIterator;
 use crate::display::hint::{HintMatch, HintState};
 use crate::display::meter::Meter;
 use crate::display::window::Window;
-use crate::event::{Mouse, SearchState};
+use crate::event::{Event, EventType, Mouse, SearchState};
 use crate::message_bar::{MessageBuffer, MessageType};
 use crate::renderer::rects::{RenderLine, RenderLines, RenderRect};
 use crate::renderer::{self, GlyphCache, Renderer};
+use crate::scheduler::{Scheduler, TimerId, Topic};
 use crate::string::{ShortenDirection, StrShortener};
 
 pub mod content;
@@ -367,6 +368,9 @@ pub struct Display {
     /// The ime on the given display.
     pub ime: Ime,
 
+    /// The state of the timer for frame scheduling.
+    pub frame_timer: FrameTimer,
+
     // Mouse point position when highlighting hints.
     hint_mouse_point: Option<Point>,
 
@@ -487,13 +491,9 @@ impl Display {
             (Vec::new(), Vec::new())
         };
 
-        // We use vsync everywhere except wayland.
-        if !is_wayland {
-            if let Err(err) =
-                surface.set_swap_interval(&context, SwapInterval::Wait(NonZeroU32::new(1).unwrap()))
-            {
-                warn!("Error setting vsync: {:?}", err);
-            }
+        // Disable vsync.
+        if let Err(err) = surface.set_swap_interval(&context, SwapInterval::DontWait) {
+            info!("Failed to disable vsync: {}", err);
         }
 
         Ok(Self {
@@ -510,6 +510,7 @@ impl Display {
             vi_highlighted_hint: None,
             is_wayland,
             cursor_hidden: false,
+            frame_timer: FrameTimer::new(),
             visual_bell: VisualBell::from(&config.bell),
             colors: List::from(&config.colors),
             pending_update: Default::default(),
@@ -751,6 +752,7 @@ impl Display {
     pub fn draw<T: EventListener>(
         &mut self,
         mut terminal: MutexGuard<'_, Term<T>>,
+        scheduler: &mut Scheduler,
         message_buffer: &MessageBuffer,
         config: &UiConfig,
         search_state: &SearchState,
@@ -966,10 +968,11 @@ impl Display {
             self.draw_hyperlink_preview(config, cursor_point, display_offset);
         }
 
-        // Frame event should be requested before swaping buffers, since it requires surface
-        // `commit`, which is done by swap buffers under the hood.
-        #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
-        self.request_frame(&self.window);
+        // Frame event should be requested before swapping buffers on Wayland, since it requires
+        // surface `commit`, which is done by swap buffers under the hood.
+        if self.is_wayland {
+            self.request_frame(scheduler);
+        }
 
         // Clearing debug highlights from the previous frame requires full redraw.
         self.swap_buffers();
@@ -982,6 +985,12 @@ impl Display {
             self.renderer.finish();
         }
 
+        // XXX: Request the new frame after swapping buffers, so the
+        // time to finish OpenGL operations is accounted for in the timeout.
+        if !self.is_wayland {
+            self.request_frame(scheduler);
+        }
+
         self.damage_rects.clear();
 
         // Append damage rects we've enqueued for the next frame.
@@ -1376,23 +1385,40 @@ impl Display {
     }
 
     /// Requst a new frame for a window on Wayland.
-    #[inline]
-    #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
-    fn request_frame(&self, window: &Window) {
-        let surface = match window.wayland_surface() {
-            Some(surface) => surface,
-            None => return,
-        };
+    fn request_frame(&mut self, scheduler: &mut Scheduler) {
+        // Mark that we've used a frame.
+        self.window.has_frame.store(false, Ordering::Relaxed);
 
-        let should_draw = self.window.should_draw.clone();
+        #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
+        if let Some(surface) = self.window.wayland_surface() {
+            let has_frame = self.window.has_frame.clone();
+            // Request a new frame.
+            surface.frame().quick_assign(move |_, _, _| {
+                has_frame.store(true, Ordering::Relaxed);
+            });
 
-        // Mark that window was drawn.
-        should_draw.store(false, Ordering::Relaxed);
+            return;
+        }
 
-        // Request a new frame.
-        surface.frame().quick_assign(move |_, _, _| {
-            should_draw.store(true, Ordering::Relaxed);
-        });
+        // Get the display vblank interval.
+        let monitor_vblank_interval = 1_000_000.
+            / self
+                .window
+                .current_monitor()
+                .and_then(|monitor| monitor.refresh_rate_millihertz())
+                .unwrap_or(60_000) as f64;
+
+        // Now convert it to micro seconds.
+        let monitor_vblank_interval =
+            Duration::from_micros((1000. * monitor_vblank_interval) as u64);
+
+        let swap_timeout = self.frame_timer.compute_timeout(monitor_vblank_interval);
+
+        let window_id = self.window.id();
+        let timer_id = TimerId::new(Topic::Frame, window_id);
+        let event = Event::new(EventType::Frame, window_id);
+
+        scheduler.schedule(event, swap_timeout, false, timer_id);
     }
 }
 
@@ -1534,6 +1560,54 @@ impl<T> DerefMut for Replaceable<T> {
     }
 }
 
+/// The frame timer state.
+pub struct FrameTimer {
+    /// Base timestamp used to compute sync points.
+    base: Instant,
+
+    /// The last timestamp we synced to.
+    last_synced_timestamp: Instant,
+
+    /// The refresh rate we've used to compute sync timestamps.
+    refresh_interval: Duration,
+}
+
+impl FrameTimer {
+    pub fn new() -> Self {
+        let now = Instant::now();
+        Self { base: now, last_synced_timestamp: now, refresh_interval: Duration::ZERO }
+    }
+
+    /// Compute the delay that we should use to achieve the target frame
+    /// rate.
+    pub fn compute_timeout(&mut self, refresh_interval: Duration) -> Duration {
+        let now = Instant::now();
+
+        // Handle refresh rate change.
+        if self.refresh_interval != refresh_interval {
+            self.base = now;
+            self.last_synced_timestamp = now;
+            self.refresh_interval = refresh_interval;
+            return refresh_interval;
+        }
+
+        let next_frame = self.last_synced_timestamp + self.refresh_interval;
+
+        if next_frame < now {
+            // Redraw immediately if we haven't drawn in over `refresh_interval` microseconds.
+            let elapsed_micros = (now - self.base).as_micros() as u64;
+            let refresh_micros = self.refresh_interval.as_micros() as u64;
+            self.last_synced_timestamp =
+                now - Duration::from_micros(elapsed_micros % refresh_micros);
+            Duration::ZERO
+        } else {
+            // Redraw on the next `refresh_interval` clock tick.
+            self.last_synced_timestamp = next_frame;
+            next_frame - now
+        }
+    }
+}
+
 /// Calculate the cell dimensions based on font metrics.
 ///
 /// This will return a tuple of the cell width and height.
diff --git a/alacritty/src/display/window.rs b/alacritty/src/display/window.rs
index 93e83677..97329d70 100644
--- a/alacritty/src/display/window.rs
+++ b/alacritty/src/display/window.rs
@@ -1,11 +1,5 @@
-#[rustfmt::skip]
 #[cfg(not(any(target_os = "macos", windows)))]
-use {
-    std::sync::atomic::AtomicBool,
-    std::sync::Arc,
-
-    winit::platform::unix::{WindowBuilderExtUnix, WindowExtUnix},
-};
+use winit::platform::unix::{WindowBuilderExtUnix, WindowExtUnix};
 
 #[rustfmt::skip]
 #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
@@ -28,6 +22,8 @@ use {
 };
 
 use std::fmt::{self, Display, Formatter};
+use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
 
 #[cfg(target_os = "macos")]
 use cocoa::base::{id, NO, YES};
@@ -37,6 +33,7 @@ use raw_window_handle::{HasRawWindowHandle, RawWindowHandle};
 
 use winit::dpi::{PhysicalPosition, PhysicalSize};
 use winit::event_loop::EventLoopWindowTarget;
+use winit::monitor::MonitorHandle;
 #[cfg(target_os = "macos")]
 use winit::platform::macos::{WindowBuilderExtMacOS, WindowExtMacOS};
 #[cfg(windows)]
@@ -106,9 +103,8 @@ impl From<crossfont::Error> for Error {
 ///
 /// Wraps the underlying windowing library to provide a stable API in Alacritty.
 pub struct Window {
-    /// Flag tracking frame redraw requests from Wayland compositor.
-    #[cfg(not(any(target_os = "macos", windows)))]
-    pub should_draw: Arc<AtomicBool>,
+    /// Flag tracking that we have a frame we can draw.
+    pub has_frame: Arc<AtomicBool>,
 
     /// Attached Wayland surface to request new frame events.
     #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
@@ -194,8 +190,7 @@ impl Window {
             mouse_visible: true,
             window,
             title: identity.title,
-            #[cfg(not(any(target_os = "macos", windows)))]
-            should_draw: Arc::new(AtomicBool::new(true)),
+            has_frame: Arc::new(AtomicBool::new(true)),
             #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
             wayland_surface,
             scale_factor,
@@ -388,6 +383,10 @@ impl Window {
         }
     }
 
+    pub fn current_monitor(&self) -> Option<MonitorHandle> {
+        self.window.current_monitor()
+    }
+
     #[cfg(target_os = "macos")]
     pub fn set_simple_fullscreen(&self, simple_fullscreen: bool) {
         self.window.set_simple_fullscreen(simple_fullscreen);
diff --git a/alacritty/src/event.rs b/alacritty/src/event.rs
index 25d52e56..2fb60b2a 100644
--- a/alacritty/src/event.rs
+++ b/alacritty/src/event.rs
@@ -10,6 +10,7 @@ use std::fmt::Debug;
 use std::os::unix::io::RawFd;
 use std::path::PathBuf;
 use std::rc::Rc;
+use std::sync::atomic::Ordering;
 use std::time::{Duration, Instant};
 use std::{env, f32, mem};
 
@@ -101,6 +102,7 @@ pub enum EventType {
     BlinkCursor,
     BlinkCursorTimeout,
     SearchNext,
+    Frame,
 }
 
 impl From<TerminalEvent> for EventType {
@@ -1096,6 +1098,9 @@ impl input::Processor<EventProxy, ActionContext<'_, Notifier, EventProxy>> {
 
                     self.ctx.window().scale_factor = scale_factor;
                 },
+                EventType::Frame => {
+                    self.ctx.display.window.has_frame.store(true, Ordering::Relaxed);
+                },
                 EventType::SearchNext => self.ctx.goto_match(None),
                 EventType::Scroll(scroll) => self.ctx.scroll(scroll),
                 EventType::BlinkCursor => {
@@ -1450,11 +1455,6 @@ impl Processor {
                 },
                 // Process all pending events.
                 WinitEvent::RedrawEventsCleared => {
-                    *control_flow = match scheduler.update() {
-                        Some(instant) => ControlFlow::WaitUntil(instant),
-                        None => ControlFlow::Wait,
-                    };
-
                     // Check for pending frame callbacks on Wayland.
                     #[cfg(all(feature = "wayland", not(any(target_os = "macos", windows))))]
                     if let Some(wayland_event_queue) = self.wayland_event_queue.as_mut() {
@@ -1473,6 +1473,13 @@ impl Processor {
                             WinitEvent::RedrawEventsCleared,
                         );
                     }
+
+                    // Update the scheduler after event processing to ensure
+                    // the event loop deadline is as accurate as possible.
+                    *control_flow = match scheduler.update() {
+                        Some(instant) => ControlFlow::WaitUntil(instant),
+                        None => ControlFlow::Wait,
+                    };
                 },
                 // Process config update.
                 WinitEvent::UserEvent(Event { payload: EventType::ConfigReload(path), .. }) => {
diff --git a/alacritty/src/scheduler.rs b/alacritty/src/scheduler.rs
index 3a26322f..ea8e6271 100644
--- a/alacritty/src/scheduler.rs
+++ b/alacritty/src/scheduler.rs
@@ -28,6 +28,7 @@ pub enum Topic {
     DelayedSearch,
     BlinkCursor,
     BlinkTimeout,
+    Frame,
 }
 
 /// Event scheduled to be emitted at a specific time.
diff --git a/alacritty/src/window_context.rs b/alacritty/src/window_context.rs
index 833586ea..79bc918b 100644
--- a/alacritty/src/window_context.rs
+++ b/alacritty/src/window_context.rs
@@ -7,7 +7,6 @@ use std::mem;
 #[cfg(not(windows))]
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::rc::Rc;
-#[cfg(not(any(target_os = "macos", windows)))]
 use std::sync::atomic::Ordering;
 use std::sync::Arc;
 
@@ -478,9 +477,8 @@ impl WindowContext {
             self.mouse.hint_highlight_dirty = false;
         }
 
-        // Skip rendering on Wayland until we get frame event from compositor.
-        #[cfg(not(any(target_os = "macos", windows)))]
-        if self.display.is_wayland && !self.display.window.should_draw.load(Ordering::Relaxed) {
+        // Skip rendering until we get a new frame.
+        if !self.display.window.has_frame.load(Ordering::Relaxed) {
             return;
         }
 
@@ -495,8 +493,14 @@ impl WindowContext {
                 self.display.window.request_redraw();
             }
 
-            // Redraw screen.
-            self.display.draw(terminal, &self.message_buffer, &self.config, &self.search_state);
+            // Redraw the window.
+            self.display.draw(
+                terminal,
+                scheduler,
+                &self.message_buffer,
+                &self.config,
+                &self.search_state,
+            );
         }
     }