Add visual bell support

This commit adds support for a visual bell. Although the Handler in src/ansi.rs
warns "Hopefully this is never implemented", I wanted to give it a try. A new
config option is added, `visual_bell`, which sets the `duration` and `animation`
function of the visual bell. The default `duration` is 150 ms, and the default
`animation` is `EaseOutExpo`. To disable the visual bell, set its duration to 0.

The visual bell is modeled by VisualBell in src/term/mod.rs. It has a method to
ring the bell, `ring`, and another method, `intensity`. Both return the
"intensity" of the bell, which ramps down from 1.0 to 0.0 at a rate set by
`duration` and `animation`.

Whether or not the Processor waits for events is now configurable in order to
allow for smooth drawing of the visual bell.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/display.rs b/src/display.rs
index 0b242b33..9bfe7339 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -272,7 +272,7 @@ impl Display {
     /// This call may block if vsync is enabled
     pub fn draw(&mut self, mut terminal: MutexGuard<Term>, config: &Config, selection: &Selection) {
         // Clear dirty flag
-        terminal.dirty = false;
+        terminal.dirty = !terminal.visual_bell.completed();
 
         if let Some(title) = terminal.get_next_title() {
             self.window.set_title(&title);
@@ -291,6 +291,8 @@ impl Display {
                 // mutable borrow
                 let size_info = *terminal.size_info();
                 self.renderer.with_api(config, &size_info, |mut api| {
+                    api.set_visual_bell(terminal.visual_bell.intensity() as f32);
+
                     api.clear();
 
                     // Draw the grid