Address VisualBell Feedback

[markandrus]

@jonhoo raised some useful feedback in #406, namely

1. Behaviors like "brighten text", "dim text", etc., would be useful.
2. Colors should be customizable to accommodate different color schemes.
3. Non-flashing behaviors like "pixelate" would be useful.

This PR addresses 1 and 2 by converting VisualBellConfig into an enum representing one of three effects:

• None: does nothing
• FlashText: flashes the text a configurable color
• FlashBackground: flashes the background a configurable color

Example video (warning: flashing lights): https://gfycat.com/IdealLazyDairycow

Other changes:

• Renamed VisualBellAnimation to "VisualBellEasing" and animation to easing.
• Moved the cubic_bezier code to src/config.rs and added an ease function to the VisualBellEasing implementation.

The VisualBellConfig enum could be expanded in the future to support a Pixelate option, e.g. something like

visual_bell:
  Pixelate:
    size: 24 # px
    duration: 150

Or perhaps even a Blur could be supported; however, I think these would require adding a rendering pass, so I haven't implemented these yet.

[lord-re]

The flashing background with customizable color is way better than the great white flash ! In fact i was trying to add this feature. Glad you did it.

[jwilm]

Thanks for the PR! I've tried this out, and it all works as described. Having control of the flash color is much nicer than the great white flash.

I'm not sold on having advanced effects like the text flashing or even more complex effects like pixelate. The color overlay can be implemented concisely. Mostly, I worry about taking on a bunch of code for something simple like the bell.

Going to think on this some more.

[markandrus]

I'm not sold on having advanced effects like the text flashing or even more complex effects like pixelate. The color overlay can be implemented concisely. Mostly, I worry about taking on a bunch of code for something simple like the bell.

Understood 👍 FWIW, I'm just playing around with this feature in order to learn a bit more about Rust (and to play to some degree with OpenGL shaders). I'm happy to explore what can be done, even if little or none of it should be merged. I'm also happy to cut the text flashing or other parts of the PR if you'd like to accept some form of it.

[OJFord]

The FlashText option looks fantastic, big 👍 for that.

[NickeZ]

It would have been awesome with some more subtle bell like pixelate or blur, but I fully understand that it feels like bloat..

edit: you could also have like a gradient with some lighter color towards the edges..

[pokey]

@jwilm any updates on this? All I'd be after is configurable background color for the flash. This seems like a good compromise between avoiding bloat / addressing the visually disturbing flash for those who dislike it.

[unphased]

The great white flash is headache-inducing! I'll take anything that can be configured to be as subtle as i need (which is very subtle). Also nice would be if it could play sound like a bell traditionally does, although I COMPLETELY understand if we want to keep everything simple and visual only for dependency/portability/aesthetic reasons.

[chrisduerr]

#963 should implement this.