[Interest] To QML or not to QML...

Preet prismatic.project at gmail.com
Tue Mar 6 00:18:29 CET 2012

On Mon, Mar 5, 2012 at 12:54 PM, Jason H <scorp1us at yahoo.com> wrote:
> It is my understanding that the major differences between 4 and 5 are that 5
> assumes (and requires) a hardware GL implementation (scenegraph), where 4
> does not.

I was under the impression that the legacy QtQuick 1 stuff would be
available in Qt5 as is with software rasterization under the existing
'QDeclarative' classes/module. The QtQuick 2 stuff all seems to be
under the 'QQuick' module.

In terms of your coding, his largely comes down to the import
> statements that are used.
> ________________________________
> From: BRM <bm_witness at yahoo.com>
> To: Interests Qt <interest at qt-project.org>
> Sent: Monday, March 5, 2012 12:39 PM
> Subject: [Interest] To QML or not to QML...
> I'm working on an application that presently uses Qt 4.7 for a front-end to
> a larger system. One of its main tasks is to display data in the system
> which requires rendering up to around a thousand or so points and overlaying
> a template of the ideal against the actual. Presently it does all the work
> in a custom QWidget class and implements the drawing in
> QWidget::paintEvent(QPaintEvent *event). However, I am getting ready to do a
> major rewrite of this functionality - namely I want to add some text labels,
> values, and lines for some of the measurements related to it, and am trying
> to determine the best possible path of two that are available.
> No matter what I do, there will be some major rework to my application as
> things are just changing a lot to do the new functionality I am seeking
> (can't be helped).
> The below are the options I am aware of:
> 1. Rework the painting to be done to a QImage/QPixMap/etc, and then use
> QGraphScene to display the data, do the overlays, etc.
> 2. Use QML (Qt Quick 1) similar to #1
> 3. Use QML (Qt Quick 1) similar to present operation
> My main requirements are that I need to be able to update at least a few
> times a second (typically 3-5 times a second; possibly higher), and adding
> the new text with lines and numbers for the measurements.
> As I have not yet touched QML, and there are many on this list who have,
> what you recommend?
> Would it be worth trying to do this in QML - either #2 or #3 - or should I
> just stick to #1?
> For those involved with Qt5, will there likely be big changes in the
> functionality in moving this to Qt5 when the time comes? I understand (from
> the development list) that QML1 is generally easy to port to QML2 but that
> it depends on what you do with QML; am I likely to run into a big issue in
> the port given what I need to do?

It's not clear why you want to move to QML... is it because you want
to draw stuff (text and other graph elements) in QML directly (and
think this might be easier)? If your current app is setup using
'form-style' widgets  and has a traditional desktop GUI, then it might
be a lot of additional effort to move it to QML.

There's this QML canvas project:
http://qt.gitorious.org/qt-labs/qmlcanvas, that might make it easier
for you to draw your graph. But really this depends on the complexity
of what you're trying to do. There are also projects like Qwt:
http://qwt.sourceforge.net/, which use widget-based Qt to draw
complicated graphs.



> TIA,
> Ben
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