Previously, this code would create a bitmap with the size of the screen
resolution, draw the new wallpaper into it, and then scale it down for
display inside the MonitorWidget.
This was done on every paint event, which made the code quite slow and
allocation-happy.
Instead of this, we now scale down the new wallpaper to a miniature
of the same scale as the little MonitorWidget screen. The miniature is
then used for tiling, etc. The miniature is cached and reused across
paint events if nothing else changes.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
For now, only support 1x and 2x scale.
I tried doing something "smarter" first where the UI would try
to keep the physical resolution constant when toggling between
1x and 2x, but many of the smaller 1x resolutions map to 2x
logical resolutions that Compositor rejects (e.g. 1024x768 becomes
512x384, which is less than the minimum 640x480 that Compositor
wants) and it felt complicated and overly magical.
So this instead just gives you a 1x/2x toggle and a dropdown
with logical (!) resolutions. That is, 800x600 @ 2x gives you
a physical resolution of 1600x1200.
If we don't like this after trying it for a while, we can change
the UI then.
