Re: [hackers] [dmenu|libsl][PATCH] optimize drw_text() for large strings

From: Silvan Jegen <>
Date: Sat, 19 Mar 2022 15:29:56 +0100


On Sat, Mar 19, 2022 at 12:59 PM Stein Gunnar Bakkeby <> wrote:
> Hi NRK,
> I was tinkering with this for a few hours earlier this week and there are several issues with this area of code and not specifically related to this modification of the patch.
> The handling of adding the ellipsis (...) when the text is too long is rather hacky and can cause several issues.
> The general idea is that:
> - we work out how many consecutive characters we can print for the same font
> - then we check if the length of the string exceeds the remaining drawable space
> - if it is too long then we check the length of the string for every character until we find that it no longer fits
> - then we replace the last three bytes with periods (.)
> These are the problematic areas I have found:
> 1. In the original code the text is allowed to bleed into the right padding as long as it fits (I presume this is intentional). If you add one more character then the text is too long and it will crop of four characters to add the ellipsis. This has to do with that the for loop reduces len once more than necessary.
> 2. The adding of the ellipsis naively assumes that the last characters in the string are single-byte UTF-8 characters. As such when it replaces the last bytes of the string then you can end up with split multi-byte UTF-8 characters which can have various effects.

I *think* I somewhat improved this issue in `vis-menu` (which is based
on `dmenu`, IIRC):

Note that this is not well tested and still has issues though.


Received on Sat Mar 19 2022 - 15:29:56 CET

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