Comment by lizzylot

For simple SPI displays it's the transfer bandwidth that dominates, so for best performance you wanna minimize the number of pixels you need to send. So for eaxmple: if you wanna draw a 100 pixel long horizontal line, if you ever send more than 100 pixels of data you're not gonna hit the speed of light. And if you wanna draw an angled line you're gonna have to do something like bresenham and pixel by pixel because drawing NxN blocks for a 45 degree line would be insane.