There is at least two bugs in the blog post, here:

Next simple task would be to fill the complete framebuffer with a solid colour:

    memset(f->buf, rgb, f->width*f->height*sizeoof(uint32_t));

The first is the obvious typo around `sizeof`, which I didn't even see at first (edit: this).

The second is that code will only work for 8-bit colors, i.e. only the 8 (technically CHAR_BIT, "a byte") least-significant bits of `rgb` will be used. This is a quirk of the `memset()` standard C function, which has the prototype:

    void *memset(void s[.n], int c, size_t n);

but then the man page [1] says:

The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c.

[1]: https://man7.org/linux/man-pages/man3/memset.3.html