generating at length an array of scanlines, in which each is
represented by a list of steps. Each step holds an X coordinate
and a coverage value, which contributes to the coverage of each
- pixel within the scanline leftwards or equal to the pixel with its
- X coordinate within.
+ pixel within the scanline rightwards or equal to the pixel with its
+ X coordinate.
Such a coverage value can be positive or negative; when the winding
direction of the span it derives from is positive, so is the