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.

2 files changed, 5 insertions, 1 deletions

diff --git a/res/text.f.glsl b/res/text.f.glsl
index 770c1a36..70d50b38 100644
--- a/res/text.f.glsl
+++ b/res/text.f.glsl
@@ -15,6 +15,7 @@
 in vec2 TexCoords;
 in vec3 fg;
 in vec3 bg;
+flat in float vb;
 flat in int background;
 
 layout(location = 0, index = 0) out vec4 color;
@@ -26,7 +27,7 @@ void main()
 {
     if (background != 0) {
         alphaMask = vec4(1.0, 1.0, 1.0, 1.0);
-        color = vec4(bg, 1.0);
+        color = vec4(bg + vb, 1.0);
     } else {
         alphaMask = vec4(texture(mask, TexCoords).rgb, 1.0);
         color = vec4(fg, 1.0);
diff --git a/res/text.v.glsl b/res/text.v.glsl
index 99234775..ccb6b8b5 100644
--- a/res/text.v.glsl
+++ b/res/text.v.glsl
@@ -36,10 +36,12 @@ out vec3 bg;
 uniform vec2 termDim;
 uniform vec2 cellDim;
 
+uniform float visualBell;
 uniform int backgroundPass;
 
 // Orthographic projection
 uniform mat4 projection;
+flat out float vb;
 flat out int background;
 
 void main()
@@ -72,6 +74,7 @@ void main()
         TexCoords = uvOffset + vec2(position.x, 1 - position.y) * uvSize;
     }
 
+    vb = visualBell;
     background = backgroundPass;
     bg = backgroundColor / vec3(255.0, 255.0, 255.0);
     fg = textColor / vec3(255.0, 255.0, 255.0);