Add frame clock

Tracks the presentation time and allows querying the next presentation
time.

6 files changed, 118 insertions, 10 deletions

diff --git a/src/frame_clock.rs b/src/frame_clock.rs
new file mode 100644
index 00000000..5d540f8d
--- /dev/null
+++ b/src/frame_clock.rs
@@ -0,0 +1,60 @@
+use std::num::NonZeroU64;
+use std::time::Duration;
+
+use crate::utils::get_monotonic_time;
+
+#[derive(Debug)]
+pub struct FrameClock {
+    last_presentation_time: Option<Duration>,
+    refresh_interval_ns: Option<NonZeroU64>,
+}
+
+impl FrameClock {
+    pub fn new(refresh_interval: Option<Duration>) -> Self {
+        let refresh_interval_ns = if let Some(interval) = &refresh_interval {
+            assert_eq!(interval.as_secs(), 0);
+            Some(NonZeroU64::new(interval.subsec_nanos().into()).unwrap())
+        } else {
+            None
+        };
+
+        Self {
+            last_presentation_time: None,
+            refresh_interval_ns,
+        }
+    }
+
+    pub fn presented(&mut self, presentation_time: Duration) {
+        if presentation_time.is_zero() {
+            // Not interested in these.
+            return;
+        }
+
+        self.last_presentation_time = Some(presentation_time);
+    }
+
+    pub fn next_presentation_time(&self) -> Duration {
+        let mut now = get_monotonic_time();
+
+        let Some(refresh_interval_ns) = self.refresh_interval_ns else {
+            return now;
+        };
+        let Some(last_presentation_time) = self.last_presentation_time else {
+            return now;
+        };
+
+        let refresh_interval_ns = refresh_interval_ns.get();
+
+        if now <= last_presentation_time {
+            // Got an early VBlank.
+            now += Duration::from_nanos(refresh_interval_ns);
+            // Assume two-frame early VBlanks don't happen. Overflow checks will catch them.
+        }
+
+        let since_last = now - last_presentation_time;
+        let since_last_ns =
+            since_last.as_secs() * 1_000_000_000 + u64::from(since_last.subsec_nanos());
+        let to_next_ns = (since_last_ns / refresh_interval_ns + 1) * refresh_interval_ns;
+        last_presentation_time + Duration::from_nanos(to_next_ns)
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 5da2cf5a..49a8598d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,11 +4,13 @@ extern crate tracing;
 mod handlers;
 
 mod backend;
+mod frame_clock;
 mod grabs;
 mod input;
 mod layout;
 mod niri;
 mod tty;
+mod utils;
 mod winit;
 
 use std::env;
diff --git a/src/niri.rs b/src/niri.rs
index a55811f6..905f0738 100644
--- a/src/niri.rs
+++ b/src/niri.rs
@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 use std::os::unix::io::AsRawFd;
 use std::sync::Arc;
+use std::time::Duration;
 
 use smithay::backend::renderer::element::render_elements;
 use smithay::backend::renderer::element::solid::{SolidColorBuffer, SolidColorRenderElement};
@@ -27,6 +28,7 @@ use smithay::wayland::shm::ShmState;
 use smithay::wayland::socket::ListeningSocketSource;
 
 use crate::backend::Backend;
+use crate::frame_clock::FrameClock;
 use crate::layout::MonitorSet;
 use crate::LoopData;
 
@@ -71,6 +73,7 @@ pub struct OutputState {
     // Set to `true` when the output was redrawn and is waiting for a VBlank. Upon VBlank a redraw
     // will always be queued, so you cannot queue a redraw while waiting for a VBlank.
     pub waiting_for_vblank: bool,
+    pub frame_clock: FrameClock,
 }
 
 impl Niri {
@@ -164,7 +167,7 @@ impl Niri {
         }
     }
 
-    pub fn add_output(&mut self, output: Output) {
+    pub fn add_output(&mut self, output: Output, refresh_interval: Option<Duration>) {
         let x = self
             .global_space
             .outputs()
@@ -180,6 +183,7 @@ impl Niri {
             global: output.create_global::<Niri>(&self.display_handle),
             queued_redraw: None,
             waiting_for_vblank: false,
+            frame_clock: FrameClock::new(refresh_interval),
         };
         let rv = self.output_state.insert(output, state);
         assert!(rv.is_none(), "output was already tracked");
diff --git a/src/tty.rs b/src/tty.rs
index 59ff104a..82e121e5 100644
--- a/src/tty.rs
+++ b/src/tty.rs
@@ -1,13 +1,14 @@
 use std::collections::{HashMap, HashSet};
 use std::os::fd::FromRawFd;
 use std::path::{Path, PathBuf};
+use std::time::Duration;
 
 use anyhow::anyhow;
 use smithay::backend::allocator::dmabuf::Dmabuf;
 use smithay::backend::allocator::gbm::{GbmAllocator, GbmBufferFlags, GbmDevice};
 use smithay::backend::allocator::{Format as DrmFormat, Fourcc};
 use smithay::backend::drm::compositor::DrmCompositor;
-use smithay::backend::drm::{DrmDevice, DrmDeviceFd, DrmEvent};
+use smithay::backend::drm::{DrmDevice, DrmDeviceFd, DrmEvent, DrmEventTime};
 use smithay::backend::egl::{EGLContext, EGLDisplay};
 use smithay::backend::libinput::{LibinputInputBackend, LibinputSessionInterface};
 use smithay::backend::renderer::gles::{GlesRenderer, GlesTexture};
@@ -17,7 +18,9 @@ use smithay::backend::session::{Event as SessionEvent, Session};
 use smithay::backend::udev::{self, UdevBackend, UdevEvent};
 use smithay::output::{Mode, Output, OutputModeSource, PhysicalProperties, Subpixel};
 use smithay::reexports::calloop::{LoopHandle, RegistrationToken};
-use smithay::reexports::drm::control::{connector, crtc, ModeTypeFlags};
+use smithay::reexports::drm::control::{
+    connector, crtc, Mode as DrmMode, ModeFlags, ModeTypeFlags,
+};
 use smithay::reexports::input::Libinput;
 use smithay::reexports::nix::fcntl::OFlag;
 use smithay::reexports::nix::libc::dev_t;
@@ -248,6 +251,16 @@ impl Tty {
                             error!("error marking frame as submitted: {err}");
                         }
 
+                        let presentation_time = match metadata.as_mut().unwrap().time {
+                            DrmEventTime::Monotonic(time) => time,
+                            DrmEventTime::Realtime(_) => {
+                                // Not supported.
+
+                                // This value will be ignored in the frame clock code.
+                                Duration::ZERO
+                            }
+                        };
+
                         // Send presentation time feedback.
                         // catacomb
                         //     .windows
@@ -263,11 +276,9 @@ impl Tty {
                             })
                             .unwrap()
                             .clone();
-                        data.niri
-                            .output_state
-                            .get_mut(&output)
-                            .unwrap()
-                            .waiting_for_vblank = false;
+                        let output_state = data.niri.output_state.get_mut(&output).unwrap();
+                        output_state.waiting_for_vblank = false;
+                        output_state.frame_clock.presented(presentation_time);
                         data.niri.queue_redraw(output);
                     }
                     DrmEvent::Error(error) => error!("DRM error: {error}"),
@@ -425,7 +436,7 @@ impl Tty {
         let res = device.surfaces.insert(crtc, compositor);
         assert!(res.is_none(), "crtc must not have already existed");
 
-        niri.add_output(output.clone());
+        niri.add_output(output.clone(), Some(refresh_interval(*mode)));
         niri.queue_redraw(output);
 
         Ok(())
@@ -464,3 +475,27 @@ impl Tty {
         }
     }
 }
+
+fn refresh_interval(mode: DrmMode) -> Duration {
+    let clock = mode.clock() as u64;
+    let htotal = mode.hsync().2 as u64;
+    let vtotal = mode.vsync().2 as u64;
+
+    let mut numerator = htotal * vtotal * 1_000_000;
+    let mut denominator = clock;
+
+    if mode.flags().contains(ModeFlags::INTERLACE) {
+        denominator *= 2;
+    }
+
+    if mode.flags().contains(ModeFlags::DBLSCAN) {
+        numerator *= 2;
+    }
+
+    if mode.vscan() > 1 {
+        numerator *= mode.vscan() as u64;
+    }
+
+    let refresh_interval = (numerator + denominator / 2) / denominator;
+    Duration::from_nanos(refresh_interval)
+}
diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 00000000..9a7d8092
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,7 @@
+use std::time::Duration;
+
+use smithay::reexports::nix::time::{clock_gettime, ClockId};
+
+pub fn get_monotonic_time() -> Duration {
+    Duration::from(clock_gettime(ClockId::CLOCK_MONOTONIC).unwrap())
+}
diff --git a/src/winit.rs b/src/winit.rs
index 2dda23b3..ef02f5b4 100644
--- a/src/winit.rs
+++ b/src/winit.rs
@@ -110,7 +110,7 @@ impl Winit {
         {
             warn!("error binding renderer wl_display: {err}");
         }
-        niri.add_output(self.output.clone());
+        niri.add_output(self.output.clone(), None);
     }
 
     fn dispatch(&mut self, niri: &mut Niri) {