bug#61667: 29.0.60; Failure to redisplay

[Dmitry Gutov]

On 25/02/2023 07:35, Po Lu wrote:
> I now think I know an easy way to test this theory for sure.  Create
> another frame, place it so that it is above the frame you are trying to
> test, set its Z group to above and its alpha-background parameter to
> 0.9, run some command that updates that frame once per second, and place
> it above the first frame.
>
> Then, see if the text inserted appears only once an update happens to
> the other frame.  To be extra sure, run the other frame in another Emacs
> process.

OK, here's what I did: set frame parameters as you described and added a 
timer which inserts a character at the end of the buffer one per second.

Then I launched a separate Emacs and positioned it entirely "below" the 
first one (fully covered, aside from the transparency effect). And 
started typing in it.

Both frames were updated as expected. And the top one continued to be 
updated with character insertions even when I paused typing in the 
bottom one.

Screenshot from 2023-02-26 02-29-53.png
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