Having explained the above, it’s clear now that it’s all matter of how you implement your code, and that every detail that comes along with it can have a big impact on your application’s performance. Nevertheless this performance drop can be improved dramatically if we pull XmlModel out the Loader component. If you ran the example yourself, you should have noticed that the pink rectangle stopped animating for a while, for as long as the news feed was loading and was feeding the list view with data. This time something looks wrong in QML profiler, as soon as I press the “Press me!” button. NamespaceDeclarations: "declare namespace media = '' "
Now let’s decrease our example’s performance a bit by adding the following code (part is borrowed from the Qt Quick Demo – RSS News) after the pink rectangle: That said, if we remove this binding and profile again, we’ll have a completely different view:ġ.3 QML Profiler basic render loop, scene graph multiple frames view, no further painting In the above example the rectangle’s height has a binding to the “animatedHeight” property that’s being animated continuously hence we have paint calls since the rectangle resizes following the value of that property. It is worth mentioning here that we will actually see data in the Scene Graph section only when something is requesting to paint. Zooming out to take the whole picture, it looks like below with more frames showing up: 1.2 QML Profiler basic render loop, scene graph multiple frames viewīelow is the code used in the above profiling example: 1.1 QML Profiler basic render loop, Scene Graph frame viewĪbove we can see the Scene Graph steps, as they occur when the applications is running. That said, when we stop the profiler, we’ll get the analysis results divided in categories with the first one of them being the Scene Graph. Now that we know about the scene graph and we have an idea of what it does under the hood, we can better understand the data we get in the QML profiler when profiling our applications. The below graphics are representing both single and multi-thread rendering loops respectively. You can dive into more details about the Qt Quick Scene Graph here.
In summary, the basic and windows loops are single threaded and the threaded runs the scene graph rendering on a dedicated thread.
Now when it comes to rendering, there are 3 loop variants available, the basic, the windows and the threaded.
This scene graph takes care about organizing all items (and their state changes) to be rendered in frames, reducing this way the draw calls and hence achieving better performance. However, before going into more details about that, it is useful to explain roughly what is the Scene Graph in Qt applications.įor performance optimization, Qt/QML applications make use of a dedicated Scene Graph that it’s rendered via a graphics API, like for example OpenGL.
This and many other problematic cases we can examine and optimize using the QML profiler. It is not much saying that this may block the UI for a few seconds, until all operations started from when that button was pressed are finished, we’ll also have a look at a similar example later in this article. Now that said, it is really important to not underestimate the risks of fast prototyping or most importantly writing your logic in JavaScript – both can be ‘powerful’ enough to make your UI unresponsive, slow, to freeze, to perform bad or even crash! That said, we’re not referring only to adding some standalone js files into your project and call methods that are implemented there but to every place and in any way JavaScript is used in the entire UI.įor example, imagine a list menu where if pressing the “more” button in the list’s delegate, another component is loaded that contains another smaller list of items as options. Depending on the complexity of the UI application, it often takes a few hours to have the application wireframe fully implemented and a few more to add some JavaScript logic and actually perform some real actions, like for example listen to the radio from the internet.