non-zero winding number fill r

To determine if a pixel should be filled using this rule draw a line from here to infinity (in any direction) and count the number of times contours cross this line. If the contour crosses the line in a clockwise direction add 1, of the contour crosses in a counter clockwise direction subtract one. If the result is non-zero then fill the pixel. If it is zero leave it blank. This method is used for rasterizing fonts by truetype and older (before version 2) postscript. See Also Even-Odd Fill Rule