Fix ratatui-image tmux detection when used with a configured image protocol

[Nemo157]

I finally tracked down part of the problems from #345, ratatui-image only does its tmux detection when guess_protocol is called.

This is required for kitty (and presumably iterm2) protocol to work inside tmux, for sixel it's not required since tmux actually implements sixel support itself, but it does appear to give better results by bypassing tmux and passing the sixel data directly to the terminal.

[benjajaja]

Thank you!

[reynoldsme]

I will agree that with this patch, sixel in tmux is significantly more usable. Images are consistently visible and the performance issues appear to be gone. The only downside I can see is that it looks as if tmux is no longer tracking the placement of the sixels internally and as a result, terminal layout starts to break as soon as you add tmux splits as sixels can end up getting placed wherever the cursor is.

In particular, if a sixel gets renders past the current bottom of the terminal, the terminal itself will scroll instead of tmux, and that breaks layout pretty badly (Note how the tmux status line is moving up the screen on every sixel refresh in the next screenshot).

[Nemo157]

Right, that makes a lot of sense, and actually seems to happen with the iTerm2 protocol as well, since the cursor is not under the apps control when it's not the active pane and so since the passthrough'd escape sequences are cursor dependent they render in the wrong place. Kitty seems to be the only protocol that actually renders correctly in that situation since its escape sequence isn't related to placement, the placement happens purely through the unicode characters.

[ulyssa]

@Nemo157 Thank you for looking into this and figuring out the fix, and thank you to @benjajaja for reviewing it!

It sounds like from @reynoldsme that this is a net improvement when running in tmux so I'm going to go ahead and merge it. There is code that should prevent drawing images past the bottom of the window, but if I understand right it sounds like the image doesn't get cleared when the window gets resized during the tmux split. That will probably require a follow-up change to improve the situation.