It was but it was borderline. A typical trick was to do the division at the start and end of a span, and interpolate linearly, rather than per pixel. This work

It was but it was borderline. A typical trick was to do the division at the start and end of a span, and interpolate linearly, rather than per pixel. This worked well enough if the triangle was seen fairly straight on and was not too large. Quake popularized the per-8 pixels technique, which is close enough in most cases.