Re: redisplay code + non-plain-text-only buffers + scroll-conservatively [Re: Bug: ruler-mode breaks scroll-conservatively (HEAD)]

[Richard Stallman]

    Still, there's a difference between scrolling down a buffer with
    partially visible lines and without. With full lines, if you maintain
    <down> pressed, the scroll is totally smooth. With a partially-visible
    last line, the scroll "jumps" slightly every now and then (at more-or-less
    equally distributed intervals, apparently).

That is going to be quite hard to debug, since it can't be reproduced
and happens only occasionally in a series of many similar actions.
The only technique I can think of is to insert debugging log output
code in many places, and record all the output; then, when it fails,
go back and find the log output for that failure and see how it
differs from the usual log output.

I can't afford to do this myself--I am overloaded.  Would someone else
like to do it?

The place to start putting in the debugging printouts is in various places
in the function try_scrolling.