[Toybox] [PATCH] vi: changes to buffer drawing

[Rob Landley]

n 9/19/19 2:52 PM, Jarno Mäkipää wrote:
> Actually I think that current crunch_str prints trailing zero width
> combining chars just fine?
> 
> since when width==columns its still >= 0
> 
> .................................................
> for (end = start = *str; *end; columns += col, end += bytes) {
>     wchar_t wc;
> 
>     if ((bytes = utf8towc(&wc, end, 4))>0 && (col = wcwidth(wc))>=0) {
>       if (!escmore || wc>255 || !strchr(escmore, wc)) {
>         if (width-columns<col) break;
> <------col is 0 when U-0x300-0x36f
>         if (out) fwrite(end, bytes, 1, out);
> 
>         continue;
>       }
>     }
> ......................
> 

The problem is when you ask it how many bytes of input will fit in a given
number of columns (or to print up to this many columns), it doesn't give the
trailing combining characters. It stops right after the last printing character
that fits.

And the callers need to be adjusted to ask "how many bytes will fit into 0
chars" so they can add combining characters to an existing column when
characters are coming in incrementally (from some outside source you're reading
in chunks, or which is delivering individual characters like serial ports), and
they've filled up the space _but_ there may be more combining characters coming
in in future that attach to the existing space.

> And yeah UTF-8 is good because it was originally written on napkin at
> dinner table
> by Ken Thompson and Rob Pike. Unicode on the other hand... not written
> in napkin.

Unicode is insane. When characters come in incrementally, you have to redraw the
same glyph repeatedly because you _can't_ know when you're done until you overshoot.

Rob