This is more like "by communicating with the X server", which is not exactly the level of "from scratch" I was expecting, but then again, it's more involved than the equivalent in Win32 that's not much more than filling in some structures and invoking a few functions.

This reminds me of the time I was a young, naïve idiot, and decided I would learn GTK by writing some basic app in GTK. In x86 (not x86-64) assembly. Like all of my other project ideas from that era, never went anywhere, and I horribly underappreciated just how complicated things were.

Kudos for actually getting somewhere in their attempt to do this, a further state than I ever managed.

I learned X86 ASM by sinking my teeth into the Intel 8085 manual, then lighting up LEDs on a hardware emulator and later on a 8085 simulator that me and my brother built.

What certainly helped was that I had did some digital design and instruction set architecture, etc.

Later on, I did some real-world assembly programming for the PIC microcontrollers and some inlined assembly in C, which I did not find daunting at all because of my previous experience.

I guess the best prerequisite for this material is having done some low-level C, the kind where you know about text/data sections and being comfortable with calling conventions, the run time and the linking process.