Writing GUI applications on the Raspberry Pi without a desktop environment↗

Because I had been previously using my Pi as a headless server, I hadn’t installed a desktop environment. I wanted to add a lightweight heads-up display to the server, and I wanted a graphical application that could operate without X, the usual graphical system on Linux.
Writing such a lightweight application required understanding how to interact more directly with my new screen, the learnings from which I’ll share here. This article is a summary of multiple sources I pieced together.