Sixel and iterm formats not working in Termux built with Sixel support

[Kabouik]

There is a PR for Termux that supports Sixel and iterm2 and some users have reported it to work with both imgcat (which uses iterm2) and chafa, and I could reproduce the working behaviour with imgcat but somehow chafa doesn't work for me, although I tried both formats with it.

I don't know if this is a version issue and whether something changed in chafa since the positive reports are somewhat old now, but thought it would be good to ask here if anyone understands what could be wrong and why it still works with imgcat.

I reported the issue in the Termux PR too but I don't know which side the issue comes from: termux/termux-app#2973 (comment)

imcat:

chafa -f sixels:

chafa -f iterm:

[hpjansson]

Hi, thanks for the report. Which version of Chafa are you using (chafa --version)?

Does it work with smaller images, or is the issue the same?

[Kabouik]

The version I have (installed in Termux using pkg add) is 1.18.2. I tried a smaller image (and jpg instead of png) but got the same issue.

Chafa version 1.18.2

Loaders:  AVIF GIF HEIF JPEG JXL PNG QOI SVG TIFF WebP XWD
Features: none
Applying: none

[agnostic-apollo]

Have commented about the issues here.

termux/termux-app#2973 (comment)

[hpjansson]

Have commented about the issues here.

termux/termux-app#2973 (comment)

Thanks, @agnostic-apollo. So to sum this up, it sounds like the issue with sixels can be fixed on your end.

Regarding iTerm images, I think we can do a better job in Chafa. I chose TIFF initially because it was easy to do without an external dep. I wanted something that would save CPU time in the loopback case, and it seemed better supported than BMP on the decoder end (libtiff handles alpha correctly).

I've done some more analysis now, and I think we may want to switch to PNG. In order to preserve loopback efficiency we can use a low compression factor. On sparse images this could actually speed things up, since there will be less for the other layers to do (base64, kernel and recipient copies, etc). And it's better supported.

[Kabouik]

Thanks to both of you, this indeed fixed it on my end and I can now use Sixel with chafa in Termux and use my TUI program on both desktop and mobile.

For now, I was using Sixel because it seemed to be the most widespread standard, but if it's significantly slower than iterm and if iterm format can be used to display images with exactly the same constraints as sixels when using chafa, i.e., if it's a drop-in replacement in most cases, then I'll be happy to switch to it. As a end-user of chafa, it's just important to me that the different formats have as little peculiarities as possible when used with chafa, to avoid having to change redraw functions to reduce issues such as flickering and so on. I'll probably do some testing at some point and if it's easy to switch, I'll happily do it. ❤️

[Edit] Whoopsie, no I won't just now, chafa -f iterm /path/to/image still shows nothing on Termux.

[hpjansson]

I'll make the switch to PNG in Chafa at some point, but I can't say exactly when that will be yet. Stay tuned.