Layered text display mode?

[phantomics]

What do you think about the idea of adding the ability for Kitty to display characters printed atop others? Here is an example:

This is a line of text with a bar graph in the background rendered using the partial block Unicode characters. The letters are the top level, with an orange foreground color while the background color is transparent to reveal the characters below, which have red/green foreground and background colors. It could make sense to support a maximum of three layers, for four colors per pixel in a bit shift-friendly format. One character printed over another character printed over a background.

This could be a simple way to add lots of expressive potential for terminal interfaces. More expressive than one-layer characters with more consistent structure than sixel graphics. Ideally these graphics would be expressed in a way that could default to one-layer display for incompatible terminals.

[kovidgoyal]

Your example is trivially renderable with th eexisitng kityt graphics protocol. As for the general case of layered rendering it will be supported by allowing popup windows with z-index and individual font sizes and is on my TODO list.

[j4james]

@kovidgoyal I suspect you'll prefer to do your own thing for this, but just FYI, there is actually an existing DEC mode that can do layered text that was supported on some of their graphic terminals. It was called overstrike mode (private mode ?20), and when set, any text that was output would only render the foreground pixels, so it was like the background color was transparent.

For example, a sequence like this:

printf "STRIKE OUT\r\e[?20h----------\e[?20l\n"

would result in output like this:

The only modern terminal I'm aware of that supports this mode is mintty.

[kovidgoyal]

Thanks for the pointer, but yes, this is a little too limited for the use cases I have in mind.