Compiling Qt with Docker Using Caching

This is a guest post from Viktor Petersson, CEO of Screenly.io. Screenly is the most popular digital signage product for the Raspberry Pi. Find Viktor on Twitter @vpetersson.

In the previous blog post, we talked about how we compile Qt for Screenly OSE using Docker’s nifty multi-stage and multi-platform features. In this article, we build on this topic further and zoom in on caching. 

Docker does a great job with caching using layers. Each command (e.g., RUN, ADD, etc.) generates a layer, which Docker then reuses in future builds unless something changes. As always, there are exceptions to this process, but this is generally speaking true. Another type of caching is caching for a particular operation, such as compiling source code, inside a container.

At Screenly, we created a Qt build environment inside a Docker container. We created this Qt build to ensure that the build process was reproducible and easy to share among developers. Since the Qt compilation process takes a long time, we leveraged ccache to speed up our Qt compilation. Implementing ccache requires volume mounting a folder from outside of the Docker environment. 

The above steps work well if you Continue reading

Compiling Qt with Docker multi-stage and multi-platform

This is a guest post from Viktor Petersson, CEO of Screenly.io. Screenly is the most popular digital signage product for the Raspberry Pi. Find Viktor on Twitter @vpetersson.

For those not familiar with Qt, it is a cross-platform development framework that is used in a wide range of products, including cars (Tesla), digital signs (Screenly), and airplanes (Lufthansa). Needless to say, Qt is very powerful. One thing you cannot say about the Qt framework, however, is that it is easy to compile — at least for embedded devices. The countless blog posts, forum threads, and Stack Overflow posts on the topic reveal that compiling Qt is a common headache.

As long-term Qt users, we have had our fair share of battles with it at Screenly. We migrated to Qt for our commercial digital signage software a number of years ago, and since then, we have been very happy with both its performance and flexibility. Recently, we decided to migrate our open source digital signage software (Screenly OSE) to Qt as well. Since these projects share no code base, this was a greenfield opportunity that allowed us to start afresh and explore Continue reading