Plasma and QML, considerations

[Alessandro Diaferia]

2010/6/11 Marco Martin <notmart at gmail.com>

> Hi all,
>
> Since i've been working a bit in the Plasma Qml bindings I want to share
> some
> of the problems i encountered, hoping there is still time to have a soluion
> to
> it.
> Since is something that -iff done right- could be a qiute important part of
> plasma, is something i want got right from all parts involved before is too
> late(tm) (even if maybe already is for some things).
> So what's the status of QML plama bindings right now:
>
> * graphics:
> -qml has some primitive shae of its own, like rectangles, circles, with
> gradients and whatnot, they are QGraphicsDeclarativeItems, this means you
> don't get a decent api if ever accessed by  "real" language, have to
> reimplement all from scratch, don't have the usual properties we're
> accustomed
> to since qgraphicswidgets (sucks for using our animations, sucks even for
> using its -internal- javascript bindings)
> -it has also its idea of anchor-based layouts: while it's quite nice to use
> forget any meaningful size hints, so forget it will ever work correctly
> when a
> qml plasmoid is in qml layouts
>
> But the situation is not ugly as it seems (greatly due Alexis, yay!) now is
> possible to use quite conveniently any QGraphicsWidget from QML, it's
> possible
> to position them with the weird anchor based qml thng, or with
> QGraphicsLayouts.
>
> Now as QGraphicsLayouts there is a little problem, because there aren't
> bindings for them by default, they a re just shipped as examples, i had to
> include them in the plasma bindings code (with potential licensing problems
> since thy are BSD) they were in the default api for a while, then removed
> :/
> Anyways, the result works quite good (well, as buggy as the usual
> qgrahicslayouts, so uaual administration, yay:) and is actually possible to
> have a QML root item with a real proper size hint:p
>
> Another problem is colors: it is possible to bind/access Plasma colors
> somehow? probably by binding an object that exposes just that? or could be
> the
> SystemPalette element used? (i.e. could it be written to with Plasma theme
> colors intead?)
>
> For graphics i think that's it, once those 2 problems are solved, tha's
> good
> to go :)
>
> * data:
> In playground right now there is a working implementation of dataengine
> bindings: there are a clock and a rss reader that use dataengines and ar
> written in qml.
> However there is a (big) problem: in orderto work, it makes use of a
> private
> Qt object: QDeclarativeOpenMetaObject: is this going to be private forever?
> and if yes, there should be -really- another way to export dataengine data,
> otherwise is not possible for it to go in libplasma, -really-
>
> Listviews: the qml rss feed reader in playground uses a qml item view to
> show
> the single rss items. Is a thing is really important to me because as i
> like
> to repeat every like 3.23 seconds, we don't have a real item view in
> plasma:
> while the standard qt views are old ugly and a disaster in proxy widget, on
> the other hand our implementations again and again are a bunch of duplicate
> code, quite inefficient and hard to maintain.
> The one that goes more near to a real item view is the netbook sal,


There's also the one from PMC actually :p


> but i
> really don't want to export it in libplasma, like never ever, because
> should
> become feature complete (code way bigger than it is) and would have to be
> maintained for years.
> Now while QML views a are quite limited, they are a good looking, not too
> bad
> working, easy maintainance compromise, so i would like to use those until
> (and
> if) a real graphicsscene based item view will be in Qt.
>
> now, common of many engines, when the result is intended for an item view
> the
> data is done like that:
> the engine calls setData with a data in this form: a key whose value is a
> qvariant that contains a -list- of Data, that would be the news items, the
> microblog entries, the opendesktop list of people, whatever...
>
> in my example qml news reader the binding to a qml list is quite rough and
> ugly, to say the least, but it works, a good way i think would be to map
> those
> lists to models or something like that, or find at least some way to make
> it
> less ugly, but the current way would be already prettier than the current
> completely by hand way :p
>
>
> ok, those were my concerns, i hope you made it till there, what i'm
> interested
> is to understand what is possible to do by ourselves, and what would still
> require modifications to Qt (like now, or maybe too late anyways or never
> ever)
>
> Cheers,
> Marco Martin
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>



-- 
Alessandro Diaferia
KDE Developer
KDE e.V. member
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