bug#50112: 28.0.50; ediff help frame does not display text

[David Phillips via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Thanks! That does indeed fix the problem for me. Now I can have my help frame back and not struggle to remember the keys. 

  Thanks again.
    David

> On Aug 21, 2021, at 8:18 AM, Alan Third <alan@idiocy.org> wrote:
> 
> On Thu, Aug 19, 2021 at 03:33:26PM +0200, Lars Ingebrigtsen wrote:
>> David Phillips <dphillips@cfa.harvard.edu> writes:
>> 
>>> I built emacs this morning from the git master branch.
>>> The latest commit was 9b31ad36094666da6b3281025adc163829d89de8 with
>>> a date stamp of Wed Aug 18 20:02:39 2021 +0300.
>>> I am running the macos GUI version.
>>> First I run /Applications/Emacs/Contents/MacOS/Emacs -Q
>>> then I load two files and run 'ediff-buffers' to compare them.
>>> ediff works just fine except that the frame with the help message
>>> is an empty frame. The '?' command changes the frame size but the
>>> text never renders.
>> 
>> I can reproduce this problem on Macos, but not in Debian.
>> 
> <snip>
>> 
>> Perhaps Alan has some insight here; added to the CCs.
> 
> This is a bit weird. When creating the graphics context to draw on we
> need to specify a colorspace, so we just use the one that the (OS)
> window we're drawing for uses.
> 
> However sometimes it seems we get a null from the window instead of a
> legit colorspace which causes the graphics context creation to fail. I
> don't know why we should ever get a null, but anyway, I've pushed a
> change to master that should use a generic colorspace in these
> situations.
> -- 
> Alan Third