sixel: Implement DEC-accurate calculation of cursor position for jumping

[hzeller]

Right now only known to be implemented by development version of Windows Terminal.
Until we can detect that this is the terminal we're running, requires to set environment variable TIMG_SIXEL_FULL_CELL_JUMP=1

Issues: #145

[hzeller]

@j4james this implements the calculation suggested in #145 (comment)
Can you patch this in your local copy and and test if it works for you (possibly also @gestate-8 ) ?

Right now, you need to set both environment variables TIMG_SIXEL_FULL_CELL_JUMP=1 and TIMG_SIXEL_NEWLINE_WORKAROUND=1 as we can't autodetect yet hat we're under the windows terminal

[j4james]

@hzeller It works for me. Although I think it would have been nicer if you just extended the TIMG_SIXEL_NEWLINE_WORKAROUND variable so it's range of options instead of a bool (i.e. the DEC compatible option would now be 2). That way users only have one variable they need to set, and if you want to support more terminals in the future, you can easily add another option to the list. Not a big deal though.

[gestate-8]

Works very well with envs.
The images are arranged slightly overlapping each other without envs.

[hzeller]

Thanks everyone for playing with the option, sounds like the way to go then.

...Although I think it would have been nicer if you just extended the TIMG_SIXEL_NEWLINE_WORKAROUND variable

Since the values are somewhat independent behaviours it would need to be a bitset, so it could have values

• 1 = TIMG_SIXEL_NEWLINE_WORKAROUND
• 2 = TIMG_SIXEL_FULL_CELL_JUMP
• 3 = TIMG_SIXEL_NEWLINE_WORKAROUND | TIMG_SIXEL_FULL_CELL_JUMP

Const: it might be harder to understand what exactly is modified.
Pros: it would be easier to just set a single environment variable and try out all possible values much more easily. And users probably don't care about the exact details as long as they can stop incrementing numbers once it works :)

Let me think about it, but now I also lean towards a single environment variable.

[hzeller]

Ok, made it now the single environment variable TIMG_SIXEL_NEWLINE_WORKAROUND again, which can have values 0..3. For WindowsTerminal, the value should be set to 3.