1. A method performed by at least one computing system, the method comprising: receiving a design database specifying a polygonal feature; receiving a pixel grid corresponding to a lithographic system, wherein the pixel grid includes an array of pixels; decomposing the polygonal feature into a set of rectangles; and converting the polygonal feature into a map of exposure intensities based on the set of rectangles, wherein the converting includes: determining areas of the pixels of the pixel grid overlapped by the polygonal feature based on the set of rectangles, and assigning exposure intensities to the pixels of the pixel grid overlapped by the polygonal feature based on the determined areas.