Graphics & 3D

Optimizing the Rendering of Qt Quick 2 applications

B05 6.11.2019 13:30 - 14:30

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Giuseppe D’Angelo
Giuseppe D’Angelo

If you have ever wondered how Qt Quick applications are rendered to the screen, and how to use that knowledge to find and fix performance problems, then this talk is for you. Qt Quick 2 applications are notably easy to write. With just a few lines of QML code, we can create compelling, animated, fluid, 60FPS user interfaces. From time to time, however, we may face performance problems in our UI layer, especially in constrained hardware environments (mobile or embedded). In order to tackle these problems, we need to understand the foundations of Qt Quick 2’s rendering, and how to design our code in order to extract the maximum performances from the underlying hardware. And while it is true that premature optimization is the root of all evil, avoding premature pessimization is also extremely important, especially at early stages of design of a complex application. In this talk we will introduce the main principles behind profiling and optimizing the rendering of a Qt Quick 2 application. We will start by discussing how Qt Quick 2 renders a scene – namely, through its scene graph and via OpenGL calls. We will see how to gather information about how effectively Qt Quick is rendering a scene. Some of this information is available via “secret switches”, while other requires the usage of external tools, which is therefore necessary to master. Finally, we will discuss how to fix some of the most common performance problems: poor batching, excessive overdraws, fill rate limitation, and poor texture memory utilization. Practical experience with QML application is required, and some OpenGL knowledge is beneficial (but not necessary).