Hardware and software working together in tandem. That’s what makes Apple special.
Of course one can critique it now and point out well what happens when you add color. And when you have a resizable window? But remember, this was the age of the Mac 128k, running on a 68k at 8Mhz. The ROM itself was just 64k and all of the core graphics (Quickdraw) was squeezed into 24k. This was an algorithm born of necessity. Without this optimization the original MacPaint would have been sluggish in many of its operations (the ScrnToBuf and the BufToScreen are foundational to MacPaint).