bug#37932: [PATCH] Support hidpi fringes and images with Cairo

[Robert Pluim]

>>>>> On Sat, 26 Oct 2019 12:14:19 +0300, Eli Zaretskii <eliz@gnu.org> said:
    >> * It removes the auto :scale property. I think this is the right thing
    >> to do, applications that want to use the :scale parameter to transform
    >> their images shouldn't lose the hidpi scaling nor explicitly call
    >> image-compute-scaling-factor.

If I read the patch correctly, you now auto-scale inside image.c,
which shouldn't change anything when not using :scale. What's the
effect when code passes in eg :scale 2? Autoscaling + frame scaling,
so for a frame where scale == 2 we get * 4? I guess that would be
sensible, but weʼd need to explain it clearly. [1]

    Eli> I don't think I'm qualified to make an intelligent decision on this by
    Eli> myself (and you just asked the question not long ago, and proceeded to
    Eli> coding without giving anyone any time to answer it :-().  I don't know
    Eli> enough about this to make such a decision.  maybe Robert, Alan, and
    Eli> others would chime in and voice their opinions.  failing that, please
    Eli> tell more about the pro's and con's here, so that we could see what
    Eli> kind of trade-offs are we talking about.

I think Lars did the autoscaling work. If things continue to work as
before for the normal case, and we explain the interaction between
:scale and frame scale I have no objections.

Robert

Footnotes:
[1]  And it would get people out of the "1 physical display pixel == 1
     logical display pixel" mindset that needed to be fixed in so many
     places in the X backend.