[Qt-qml] QML must love binding programmers

[Kristian Mueller]

Hi Hugo,

we are actually working on something similar here at mixd.tv. Our
approach is to map Python objects directly into QML using the Qt Meta
Object System (QDeclarativeOpenMetaObject) and by accessing the
QScripEngine.

We are using QML for our frontend and the business logic is mostly done
in Python. Qt is used here for things like:

 - Window Creation (+ setting the QML main file)
 - TrayIcon stuff
 - Window movement
 - Drag & Drop Cursor Icons
 - Setting the Mouse Cursor Pixmap

Some of those could actually be implemented as part of QML.

What we'd like our Python <-> QML project to become is a pure QML UI
Binding for Python. With the modulatization of Qt maybe only needing a
subset of Qt.

Our approch is not to control QML from Python, but to allow access to
"normal" Python objects from QML. So actually we don't need
qmlRegisterType, because we don't need to subclass Qt objects in
Python. 

Our strategy is to keep direct access to QML from Python low. To convert
types we are currently using Python-Boost but will remove Boost
dependencies over time.

We'd see a public release of our code in maybe a month from now.


Greetings from Berlin
Georg & Kristian
--
mixd.tv


Am Montag, den 25.10.2010, 19:18 -0200 schrieb Hugo Parente Lima:
> Hi;
> 
> I'm working on getting Python (PySide) able to export Python types to QML the 
> same way you can do with C++ types, i.e.:
> 
> class Foo(QObject):
> 	...
> 
> qmlRegisterType(Foo, "foo.bar.com", 1, 0, "FooOnQml_huhu")
> 
> I took a look on QtDeclarative sources and faced some issues to integrate 
> Python or any other language to QML.
> 
> First, QML uses qmlRegisterType<T> function to register a type, this function 
> just fills a struct with some info and pass it to the depths of QML, one of 
> these fields is a function pointer, this function pointer is used as a factory 
> function by QML to create instances of the exported type T. So what's the 
> problem?
> 
> Using a template function everything can be decided at compile time, so we 
> have a different factory function for each type exported to QML, perfect for 
> C++ but Qt bindings doesn't have the information about user created types at 
> compile time, so we can't have a factory function for each type created by the 
> user as we have on C++.
> 
> One way to ease the work of people doing Qt bindings to support QML is adding 
> a bit more info on this factory function, so we can use a Proxy object to 
> decide what type need to be instantiated.
> 
> I attached a pseudo-patch that implements this idea, pseudo because I wrote it 
> just to show what changes are needed, if I get a thumbs up about it I can 
> work, test and create a merge request for it.
> 
> Any comments? Any chances to get it or something like it into the mainline for 
> Qt4.7.1?
> 
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