1 files changed, 122 insertions, 0 deletions
diff --git a/alacritty/src/display/bell.rs b/alacritty/src/display/bell.rs
new file mode 100644
index 00000000..1aee3ba6
--- /dev/null
+++ b/alacritty/src/display/bell.rs
@@ -0,0 +1,122 @@
+use std::time::{Duration, Instant};
+
+use crate::config::bell::{BellAnimation, BellConfig};
+
+pub struct VisualBell {
+    /// Visual bell animation.
+    animation: BellAnimation,
+
+    /// Visual bell duration.
+    duration: Duration,
+
+    /// The last time the visual bell rang, if at all.
+    start_time: Option<Instant>,
+}
+
+impl VisualBell {
+    /// Ring the visual bell, and return its intensity.
+    pub fn ring(&mut self) -> f64 {
+        let now = Instant::now();
+        self.start_time = Some(now);
+        self.intensity_at_instant(now)
+    }
+
+    /// Get the currently intensity of the visual bell. The bell's intensity
+    /// ramps down from 1.0 to 0.0 at a rate determined by the bell's duration.
+    pub fn intensity(&self) -> f64 {
+        self.intensity_at_instant(Instant::now())
+    }
+
+    /// Check whether or not the visual bell has completed "ringing".
+    pub fn completed(&mut self) -> bool {
+        match self.start_time {
+            Some(earlier) => {
+                if Instant::now().duration_since(earlier) >= self.duration {
+                    self.start_time = None;
+                }
+                false
+            },
+            None => true,
+        }
+    }
+
+    /// Get the intensity of the visual bell at a particular instant. The bell's
+    /// intensity ramps down from 1.0 to 0.0 at a rate determined by the bell's
+    /// duration.
+    pub fn intensity_at_instant(&self, instant: Instant) -> f64 {
+        // If `duration` is zero, then the VisualBell is disabled; therefore,
+        // its `intensity` is zero.
+        if self.duration == Duration::from_secs(0) {
+            return 0.0;
+        }
+
+        match self.start_time {
+            // Similarly, if `start_time` is `None`, then the VisualBell has not
+            // been "rung"; therefore, its `intensity` is zero.
+            None => 0.0,
+
+            Some(earlier) => {
+                // Finally, if the `instant` at which we wish to compute the
+                // VisualBell's `intensity` occurred before the VisualBell was
+                // "rung", then its `intensity` is also zero.
+                if instant < earlier {
+                    return 0.0;
+                }
+
+                let elapsed = instant.duration_since(earlier);
+                let elapsed_f =
+                    elapsed.as_secs() as f64 + f64::from(elapsed.subsec_nanos()) / 1e9f64;
+                let duration_f = self.duration.as_secs() as f64
+                    + f64::from(self.duration.subsec_nanos()) / 1e9f64;
+
+                // Otherwise, we compute a value `time` from 0.0 to 1.0
+                // inclusive that represents the ratio of `elapsed` time to the
+                // `duration` of the VisualBell.
+                let time = (elapsed_f / duration_f).min(1.0);
+
+                // We use this to compute the inverse `intensity` of the
+                // VisualBell. When `time` is 0.0, `inverse_intensity` is 0.0,
+                // and when `time` is 1.0, `inverse_intensity` is 1.0.
+                let inverse_intensity = match self.animation {
+                    BellAnimation::Ease | BellAnimation::EaseOut => {
+                        cubic_bezier(0.25, 0.1, 0.25, 1.0, time)
+                    },
+                    BellAnimation::EaseOutSine => cubic_bezier(0.39, 0.575, 0.565, 1.0, time),
+                    BellAnimation::EaseOutQuad => cubic_bezier(0.25, 0.46, 0.45, 0.94, time),
+                    BellAnimation::EaseOutCubic => cubic_bezier(0.215, 0.61, 0.355, 1.0, time),
+                    BellAnimation::EaseOutQuart => cubic_bezier(0.165, 0.84, 0.44, 1.0, time),
+                    BellAnimation::EaseOutQuint => cubic_bezier(0.23, 1.0, 0.32, 1.0, time),
+                    BellAnimation::EaseOutExpo => cubic_bezier(0.19, 1.0, 0.22, 1.0, time),
+                    BellAnimation::EaseOutCirc => cubic_bezier(0.075, 0.82, 0.165, 1.0, time),
+                    BellAnimation::Linear => time,
+                };
+
+                // Since we want the `intensity` of the VisualBell to decay over
+                // `time`, we subtract the `inverse_intensity` from 1.0.
+                1.0 - inverse_intensity
+            },
+        }
+    }
+
+    pub fn update_config(&mut self, bell_config: &BellConfig) {
+        self.animation = bell_config.animation;
+        self.duration = bell_config.duration();
+    }
+}
+
+impl From<&BellConfig> for VisualBell {
+    fn from(bell_config: &BellConfig) -> VisualBell {
+        VisualBell {
+            animation: bell_config.animation,
+            duration: bell_config.duration(),
+            start_time: None,
+        }
+    }
+}
+
+fn cubic_bezier(p0: f64, p1: f64, p2: f64, p3: f64, x: f64) -> f64 {
+    (1.0 - x).powi(3) * p0
+        + 3.0 * (1.0 - x).powi(2) * x * p1
+        + 3.0 * (1.0 - x) * x.powi(2) * p2
+        + x.powi(3) * p3
+}