[Interest] Role of `qmlscene` and `qml` command line tools

[Shawn Rutledge]

> On 6 May 2016, at 11:36, Elvis Stansvik <elvstone at gmail.com> wrote:
> 
> Hi all,
> 
> Since some time, the `qmlscene` command has been available for
> debugging QML applications:
> 
> …
> Recently, the `qml` command is also available:
> 
> The tools seem quite similar. What was the rationale for introducing
> `qml`? The old `qmlscene` is described in the docs [1] as:
> 
> "The qmlscene utility is meant to be used for testing your QML
> applications, and not as a launcher in a production environment. To
> launch a QML application in a production environment, develop a custom
> C++ application or bundle the QML file in a module. See Deploying QML
> applications for more information."
> 
> Is there a similar page describing the `qml` tool somewhere (I can't
> see it mentioned anywhere)? Is the `qml` tool also meant only for
> testing/debugging, and not for production use?

The QML tool is a bit more flexible, makes fewer assumptions (e.g. it doesn’t use a QApplication by default, so you don’t end up loading the widgets module into memory if you don’t need it) and is meant as the long-term replacement for qmlscene.  QML can be used for non-graphical purposes if your root object is a plain QObject, not an Item or Window; that’s only practical with the qml tool, not qmlscene.  It is more directly analogous to other language interpreters like python and perl (which also do not load graphical libraries unless you import the relevant modules in your script), and you can even use the shebang mechanism, so that qml files can be marked executable and run from the command line.  You can configure your window system to use it as the default application with which to run any file with the qml extension (e.g. when double-clicking a qml file in your file manager/finder), if you like.  (QTBUG-33659 is a request to set up that association when you install the SDK, but that never got done AFAIK.  It requires someone with Qt Installer expertise, I think.)

Here’s one of Alan’s talks, shortly after he wrote it:

https://www.youtube.com/watch?v=2nnrl1v7LcE

So you could nearly forget about qmlscene, except that it has a few handy command-line options that qml still doesn’t.  OTOH qml can be configured via config files.  And yes I think that should be documented better.  You can see the default configuration in tools/qml/conf/configuration.qml, but it’s not clear enough what else could be declared in your custom config file.

> The reason I'm asking is I'm building a QML application for embedded
> use. The app is QML only, apart from some calls from QML into Python
> using pyotherside [2] when interfacing with the hardware. So in theory
> I could launch my app using `qmlscene` or `qml`, which would free me
> from having to build and distribute a little C++ launcher application
> to launch the app.

That’s what the qml tool is intended for.