[Development] Scalable UIs in QtQuick (take 2)

Michael Brasser michael.brasser at live.com
Thu Feb 25 01:41:01 CET 2016


Hi,

Regarding (2), last time around I had concerns about the proposed limitations associated with language-level unit support (see some of the discussion at https://codereview.qt-project.org/98288). I'd be interested to hear the particulars of what unit support might look like this time around.

Regards,
Michael

________________________________________
From: Development <development-bounces+michael.brasser=live.com at qt-project.org> on behalf of Hausmann Simon <Simon.Hausmann at theqtcompany.com>
Sent: Thursday, February 18, 2016 4:50 AM
To: development at qt-project.org
Subject: [Development] Scalable UIs in QtQuick (take 2)

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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