bug#40278: 27.0.90; Flickering in Windows 10

[Noam Postavsky]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Noam Postavsky <npostavs@gmail.com>
>> Cc: Nicolas Bértolo <nicolasbertolo@gmail.com>,
>>   40278@debbugs.gnu.org
>> Date: Mon, 30 Mar 2020 12:23:42 -0400
>> 
>> I can see it here, especially on scroll towards the beginning of the
>> file (Emacs is maxing out the CPU while doing this).
>
> If redisplay cannot keep up, you could indeed see partially-redrawn
> window.  But I didn't understand this was the problem, and it doesn't
> sound like "flicker" to me.

The "flicker" part is that it looks like the window turns momentarily
completely blank before redrawing.

>> It kind of looks like the rectangle beneath the child frame gets
>> repainted separately from the rest.
>
> What do you mean by "beneath" in this context?

There's occasionally a rectangle which seems to repainted slower than
its surroundings.  That rectangle is lower down (closer to my desk than
the ceiling) on my monitor than the child frame.  Also, I guess the text
it momentarily contains was previously behind the child frame in terms
of z-order (although it's a bit hard to tell because the repainting is
still too fast to really anything).