Re: Flicker on MS Windows

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> Then I'm afraid I cannot reproduce this.  I tried Emacs 27 on 2
> different versions of Windows 10, and I don't see any abnormal
> flickering when I lean on C-v.  The menu bar does flicker once in a
> few seconds (and that is expected, given how eagerly we update our
> menus)), but by that time Emacs scrolled many window-fulls.

Hmm, that's weird.

> Are you trying this with an optimized build or an unoptimized build?
> An unoptimized build cannot keep up with the auto-repeat rate of the
> keyboard, so the first scroll through the file could cause Emacs to
> become stuck until you release the key.  But once you scroll the file
> once (i.e. it is all fontified), even an unoptimized build behaves
> reasonably, and I see no particular flickering, at least not on the
> menu bar.

It's an optimized build, with "-O2 -g3".

> I certainly don't see any artifacts like left-over text -- that smells
> like some "optimization" of your video driver.  Try disabling any
> advanced features of the display adapter you have there.

I meant to say that I guessed that w32_scroll_run is somehow involved by
commenting out w32_scroll_run and observing that old text was left-over
in places which would previously not flicker during scrolling.  (Because
copying the area that can be scrolled is faster than displaying the rest
of the screen contents, so the system displays the scrolled contents
before the rest can be drawn.)

> Ah, you mean the call to w32_scroll_run in dispnew.c...  Does setting
> w32-use-visible-system-caret non-nil help in any way?

It makes it flicker less, but the flicker is still noticable.

BTW, here's another way to reproduce some severe flicker on MS Windows:
just type "M-: (run-hooks 'xref-after-jump-hook) RET", and the tool bar
buttons, cursor and text start to flicker severely.  The tool bar
buttons flicker in a peculiar way: the background is displayed, but the
image itself flickers with interleaved bands of black.

It's also not affected by the setting of w32-use-visible-system-caret.

Thanks.