Storage of QML defined properties explained (Part 1)

How much does a property you define in QML code cost in terms of memory? This simple question led me down a merry chase into the source of the QML engine. The result is this article and in the end a contribution to Qt5.6.

Before we get started, let’s do a quick recap of what we know about Qt properties on the C++ side. Qt has compile time properties which can be added to QObject derived classes. The various methods associated with such a property (read/write/reset/notify/…) are specified using the Q_PROPERTY macro. The properties themselves are typically stored as C++ member variables. They integrate with the meta object system and are therefore also accessible from the QML-side.

Back to the initial question: how much memory is needed for a QML defined property? To answer this, one first needs to figure out how and where they are Continue reading Storage of QML defined properties explained (Part 1)

Introducing QtOpcUa

basysKom has been working on the new Qt module QtOpcUa which brings support for the industrial communication standard OPC UA into the Qt world. We recently have offered this module as a contribution to the Qt-project. It is currently under review, we aim to make it a tech preview in Qt 5.7.

basysKom will show QtOpcUa based demos at the Qt World Summit 06./07.10.2015 in Berlin. We are happy to discuss use cases, improvements and OPC UA in general. Looking forward to see you in Berlin.

What is OPC UA?

OPC UA is a communication suite for industrial applications like process or factory automation. Its specification is developed and maintained by the OPC Foundation. The first version has been released in 2008. OPC UA is the successor of the popular original OPC standard (which is now OPC Classic). Unlike its predecessor which was based on Microsoft DCOM, OPC UA is designed with the focus on platform independence and scalability. Beside others, it includes features such as data modeling and much improved security mechanisms. This lines the vision of OPC UA to provide a standard communication protocol to be used on all levels of an industrial plant, ranging from field devices to the ERP system. The involvement of companies like Bosch, Siemens and Honeywell within the OPC Foundation as well as the development of the OPC UA specification itself shows that OPC UA will play an important role in future projects and products.

Continue reading Introducing QtOpcUa