Hi,
A little while ago Lars and I proposed to introduce physical units in the QML
language for use in QtQuick. The idea was to make it easier to write user
interfaces that adapt to different display resolutions by "pinning" your UI to
physical dimensions. For example you could say
Image {
source: "mypprofilephoto.png"
width: 5cm
height: 5cm
}
and the image size in physical pixels would scale accordingly to always produce
a 5cmx5cm profile image on the screen. The proposed units included "px", which
was really an alias for nothing.
We've had some very good discussions around this at last year's contributor
summit as well as in smaller face-to-face discussions. The main feedback I
recall was that this would seem like a nice feature on paper but in practice
people create their resolution independent interfaces using the current
"pixels" and a scale factor that they introduce in a qml file or as a context
property. That's another way of saying that perhaps the feature wouldn't really
find any use, which is fair :). Instead the desire was expressed that making it
_easier_ to scale "logical" pixels in the application would perhaps be better.
So today during a discussion another idea came up:
(1) In order to make it really easy to scale "logical" pixels without having to
introduce your own context property or factor in a .qml file that you multiply
everywhere, we could turn the regular "pixels" in QtQuick into truly logical
pixels that scale with an application wide (or window wide) factor. So Image {
width: 100 ... } will scale automatically from 100 logical pixels to maybe 200
physical pixels on a x2 display. This assumes the availability of API to change
this mapping.
(2) In the events where you still _want_ to use physical pixels, you could use
"px" units.
So at first nothing would change for app developers at all because we map
logical pixels to physical pixels. But
if you'd like to, you could opt into changing this mapping and having a
relatively easy fallback to physical pixels using for example the "px" unit. We
might as well offer the other physical units anyway, that probably causes
little to no harm.
What do you think?
Simon
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