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

BRM bm_witness at yahoo.com
Mon Mar 5 18:39:20 CET 2012

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?



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