Re: Flicker on MS Windows

[Po Lu <luangruo@yahoo.com>]

Eli Zaretskii <eliz@gnu.org> writes:

> If I increase pulse-iterations to 1000 (from the default of 10), then
> in an unoptimized build I see a rare and barely-visible flickering of
> the tool bar images, as if they are redrawn.
>
> However, I cannot find where this redrawing comes from.  Both xdisp.c
> and dispnew.c do their jobs correctly, and the tool bar is never
> actually redrawn on these levels.  If I put a breakpoint where
> dispnew.c actually writes to the glass using the terminal-specific
> write_glyphs method, as part of the update_frame call, that breakpoint
> never breaks in all those 1000 iterations, not once.  Which means that
> we correctly decide that the tool bar didn't change and does not need
> to be redrawn.
>
> So it sounds like it's some very low-level Windows-specific code,
> perhaps triggered by messages we send to the GUI thread or something?
> This is an area in Emacs about which I know very little.  Ideas
> regarding what could cause this are welcome.
>
> And again, it's barely perceptible here, even with this non-trivial
> setup and a relatively slow Emacs.  I have no idea why it's so
> prominent in your case (assuming it's the same issue that I see, which
> is not certain, since what I see looks like redrawing of the images on
> the tool-bar buttons).

That is quite odd.  Unfortunately, I know next to nothing about Windows
programming, so I probably can't help.

But I wonder if implementing double buffering on MS-Windows would help
to alleviate the problem somewhat.

Thanks.