Support per-window background color and opacity via OSC escape sequences (kitty color protocol)

[coopbri]

Feature Request

Add support for setting background color with opacity on a per-window basis via escape sequences, similar to kitty's OSC 21 color protocol.

Current Behavior

Rio supports [window] opacity in config, but this:

• Affects all windows globally
• Requires restart to take effect
• Cannot be changed dynamically per-window

OSC 11 works for setting background color, but doesn't support alpha/opacity.

Requested Behavior

Support kitty's OSC 21 color protocol for per-window colors with opacity:

# Set background with 80% opacity
printf '\e]21;background=#1a1b26@0.8\007'

# Reset to default
printf '\e]21;background\007'

Use Case

Dynamic per-window theming based on context (e.g., different opacity for different projects/tasks) without affecting other terminal windows.

Reference

• Kitty color control documentation

[JRBros2346]

I believe kitty is not yet fully implemented..
Kitty is being developed in the zero-dot-three branch

[xxxserxxx]

I'd like to have this as a function I can bind keys to, specifically to increase or decrease a single window's background opacity. More useful would be a way to specify it in the configuration for a single window as defined by WM_NAME, or alternatively through a command line option, so I can auto-start a specific window in this mode. The use case is that, for many windows, having a transparent background is a distraction, but if I'm running something like catnip (a terminal audio visualizer) I'd like that window to have a fully transparent background. transset through a compositor is not useful for these cases, because transset makes the entire window contents tansparent, not just the background color.