Basically the same effect happened with a lot of DOS shareware drawing programs in the day. The file formats were often instructions like:
Line (20,500) (45, 520) (15)
Line (200,523) (65, 520) (15)
Circle (300, 300) (100) (30)
Fill (50,30) (16)
and so on
If you had a slower computer, or the software wasn't optimized that well, you'd be able to sit and watch your drawing re-draw every time you loaded the file or made certain edits.
Not just DOS, Windows as well. The WMF (Windows Metafile), EMF (Enhanced Metafile) and EMF+ formats are exactly that, except that primitives correspond to GDI or GDI+ calls. And they're still fully supported. Even MSPaint in Win10 can still open them, although it's not listed among supported extensions when you do File -> Open.
