Agg appears to cut off the last column of the recording?

[AhoyISki]

Describe the bug
When I record with asciinema rec, and play it with asciinema play, it shows all the columns that were recorded. When I pass it to agg, it cuts out the last column for some reason

To Reproduce
Steps to reproduce the behavior:

1. asciinema rec test
2. `agg test test.gif
3. See error

Expected behavior
It should not cut out the last column

Versions:

• OS: Arch Linux x86_64
• agg: 1.7.0

Additional context
Here's an example of a generated gif:

And the recording that generated it:

rec.zip

You will notice that at the bottom right corner, in the recording it shows the number of lines, but in the gif, that's cut out for some reason.

[ku1ik]

I found out that this is related to cursor positioning at the edge with auto-wrap mode off, followed by EL sequence.

I replayed your recording in several terminal emulators, all set to 96x25 size (the same as your recording) to see how they handle this case:

• Ghostty - last column cut off
• iTerm2 - last column visible
• Terminal.app - last column cut off
• xterm - last column cut off
• alacritty - last column visible
• Gnome Console - last column visible
• kitty - last column visible
• WezTerm - last column cut off

It's 50/50... 😅

avt (agg's virtual terminal) typically follows the majority's behavior, and in this case there isn't a clear consensus between terminal emulator implementers it seems. I don't remember if avt's current behavior was intentional or just happened to be implemented like this....

Anyway, there isn't a good answer here I'm afraid.

[ku1ik]

Turned this into a discussions since it's about an ambiguous behaviour, which needs more discussions (if we are to act on this).

[AhoyISki]

I mean, tbh, I don't really see how this could be ambiguous? If the recorded application shows the last column, shouldn't the recording also do that?

[ku1ik]

Well, the thing is, asciinema doesn't record terminal contents as in full cell grid - it records what gets printed to a terminal. Then, the player or agg runs the captured output stream through a virtual terminal emulator (avt), which is different emulator than yours.

If you replay your recording with asciinema play inside xterm, Terminal.app or Ghostty you will also observe the last column is cut off there, because during playback it's the actual terminal performing the interpretation of the captured session. It's the same problem as with agg / asciinema player.

[AhoyISki]

This is something that has frustrated me for a bit, mostly because I prefer using gifs to showcase my projects, and the last column being cut off makes it look like my app is broken in some way

[ku1ik]

I get it, and I understand your frustration. The only way for asciinema/agg to handle this correctly would be to have avt emulate quirks of a specific terminal you used when recording (this information is in the header of the v3 cast file already). But I would rather not go this path, feels like a rabbit hole :)

[AhoyISki]

Ahah, it turns out my application was broken, but moreso that maybe kitty was doing a fix for a specific
scenario, while other terminals weren't.

In my editor, I placed a \x1b[0K at the end of every line, in order to flush out what was there before.
This worked fine on kitty, even on lines which already ended at the very right edge of the terminal.

However, a behavior that is standard across terminals is that typing characters at the rightmost edge will simply replace the rightmost character with whatever you typed. Therefore, following that logic, a \x1b[0K should clear that character, because your cursor is still in the same position.

This is what was causing the bug, but it's fixed now in AhoyISki/duat@493ba58.

Anyways, sorry for the bother, it wasn't my intention to be a hindrance or anything like that, thanks for the attention!

[ku1ik]

No worried! I'm glad you figured it out.