> On Dec 6, 2023, at 7:25 AM, Eli Zaretskii wrote: > >> From: JD Smith >> Date: Tue, 5 Dec 2023 23:33:42 -0500 >> Cc: 67604@debbugs.gnu.org >> >> Not really, no. But reproducing the problem is just a step towards >> debugging it, so the alternative is for you to step through next-line >> and its subroutines >> >> I stepped through next-line and subroutines via edebug and landed via line-move-visual on: >> >> (vertical-motion (cons (or goal-column >> (if (consp temporary-goal-column) >> (car temporary-goal-column) >> temporary-goal-column)) >> arg)) >> >> So vertical-motion is where all fingers point. > > Did you verify that goal-column and temporary-goal-column have correct > values in the case where the problem happens? Yes. Sometimes the temporary-goal-column is 0 (if I C-a on a text line) or sometimes a fractional number like 66.5 or similar if I start my downward movement by first C-a’ing on the green image line. In both cases the short screen line #3 line is skipped. >> It isn't like I'm the only >> one who should be able to read the code and understand where it fails. >> >> I agree with that, but unfortunately am not setup for it here and have next to no familiarity with Emacs’ >> C code. I’m sorry I can’t be of more help. But similar to how you were unable to work with dvisvgm >> and other packages, I don’t have access to gdb, as it is not supported on my architecture. > > If someone can reproduce and debug the problem on a system other than > macOS, that would be some progress. (If the problem is specific to > macOS, it is much less interesting, at least to me, since the display > code on macOS behaves differently in significant ways, and because > macOS is in general an idiosyncratic platform.) I have made progress. I built master on a remote Linux server and ran it via X forwarding. With an 8x17 font, the bug is found at offset 2 = 148 pixel width of the red SVG, for the specific frame-width = 74. I verified that (vertical-motion 1) causes the same line-skip error, when starting from the green image. This makes me think that your difficulty reproducing the bug on your system may result from a miscommunication. To be sure, I’ve recorded a session of me (re-)discovering the bug at this comment . Hopefully that’s useful. If not, I did the build on my Linux server with debug options, and can run over gdb. If you can give me a simple recipe for where I should break and what I should look at, I’m happy to try. But I suspect it will be 25x more efficient for you to have a look if you can reproduce. Re MacOS, I’m surprised you wouldn’t say that Windows is similarly an idiosyncratic system for display and other purposes.