What is scanline coherence and edge line coherence?

Answer 1

With a rectangle we notice that we can exploit coherence

-If the fill is solid black (say) then all the pixels are shaded the same

-Each of the length of each span is the same

o(this is scan-line coherence)

-It is possible also to exploit spatial coherence up to the edges

oi.e., if point (x,y) is inside the polygon then so is the point to the left and the right (unless it is an edge/ boundary point )

-Thus we can draw horizontal spans for every y point in the rectangle