1 files changed, 97 insertions, 0 deletions
diff --git a/alacritty/src/display/meter.rs b/alacritty/src/display/meter.rs
new file mode 100644
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+++ b/alacritty/src/display/meter.rs
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+//! Rendering time meter.
+//!
+//! Used to track rendering times and provide moving averages.
+//!
+//! # Examples
+//!
+//! ```rust
+//! // create a meter
+//! let mut meter = alacritty_terminal::meter::Meter::new();
+//!
+//! // Sample something.
+//! {
+//!     let _sampler = meter.sampler();
+//! }
+//!
+//! // Get the moving average. The meter tracks a fixed number of samples, and
+//! // the average won't mean much until it's filled up at least once.
+//! println!("Average time: {}", meter.average());
+//! ```
+
+use std::time::{Duration, Instant};
+
+const NUM_SAMPLES: usize = 10;
+
+/// The meter.
+#[derive(Default)]
+pub struct Meter {
+    /// Track last 60 timestamps.
+    times: [f64; NUM_SAMPLES],
+
+    /// Average sample time in microseconds.
+    avg: f64,
+
+    /// Index of next time to update..
+    index: usize,
+}
+
+/// Sampler.
+///
+/// Samplers record how long they are "alive" for and update the meter on drop..
+pub struct Sampler<'a> {
+    /// Reference to meter that created the sampler.
+    meter: &'a mut Meter,
+
+    /// When the sampler was created.
+    created_at: Instant,
+}
+
+impl<'a> Sampler<'a> {
+    fn new(meter: &'a mut Meter) -> Sampler<'a> {
+        Sampler { meter, created_at: Instant::now() }
+    }
+
+    #[inline]
+    fn alive_duration(&self) -> Duration {
+        self.created_at.elapsed()
+    }
+}
+
+impl<'a> Drop for Sampler<'a> {
+    fn drop(&mut self) {
+        self.meter.add_sample(self.alive_duration());
+    }
+}
+
+impl Meter {
+    /// Create a meter.
+    pub fn new() -> Meter {
+        Default::default()
+    }
+
+    /// Get a sampler.
+    pub fn sampler(&mut self) -> Sampler<'_> {
+        Sampler::new(self)
+    }
+
+    /// Get the current average sample duration in microseconds.
+    pub fn average(&self) -> f64 {
+        self.avg
+    }
+
+    /// Add a sample.
+    ///
+    /// Used by Sampler::drop.
+    fn add_sample(&mut self, sample: Duration) {
+        let mut usec = 0f64;
+
+        usec += f64::from(sample.subsec_nanos()) / 1e3;
+        usec += (sample.as_secs() as f64) * 1e6;
+
+        let prev = self.times[self.index];
+        self.times[self.index] = usec;
+        self.avg -= prev / NUM_SAMPLES as f64;
+        self.avg += usec / NUM_SAMPLES as f64;
+        self.index = (self.index + 1) % NUM_SAMPLES;
+    }
+}