1. A system comprising: one or more integrated circuits configured to provide: a touch path module to receive a plurality of touch events and to generate an output based on the touch events; and a rendering module to: receive a video image; receive the output of the touch path module; determine a plurality of points defining a boundary of a shape, the shape being determined based on the output of the touch path module; generate a mask in accordance with the shape; combine the video image with overlay data in accordance with the mask to generate a combined display image; and output the combined display image, wherein the combined display image comprises a plurality of rows, wherein each of the points comprises a row coordinate, the rendering module being further to: classify the points as one or more of left-edge points and right-edge points; sort the left-edge points by the row coordinate; and sort the right-edge points by the row coordinate, and the rendering module further, for a current row of the plurality of rows of the combined display image, to: determine a start entry based on an left intersection between the current row and a left edge defined by a first left-edge point of the left-edge points and a second left-edge point of the left-edge points; determine a stop entry based on a right intersection between the current row and a line defined by a first right-edge point of the right-edge points and a second right-edge point of the right-edge points; generate a row mask comprising a plurality of entries for the current row based on the start entry and the stop entry; and combine the video image with the overlay data for the current row in accordance with the row mask.