> That way you get speed up without needing the y-buffer memory. I mean, the "Y-buffer" memory is just one integer per column, pretty trivial even for a softwa

> That way you get speed up without needing the y-buffer memory. I mean, the "Y-buffer" memory is just one integer per column, pretty trivial even for a software rasterizer on an early 90s machine with a limited cache hierarchy. Pretty much any algorithm that has overdraw will lose to that. That's why this technique was so popular in the nineties—what Doom did was just a generalization of this idea to allow multiple sparse pixel spans per column instead of just one. (For comparison, Z-buffer bandwidth is expensive because it's an extra 16/24/32 bits per pixel, which can double your fill rate requirements.)