Processor-based method for rasterizing polygons at an arbitrary precision

Abstract

An image processor is provided which rasterizes polygons with a minimum of computation. Pixels are tested for being inside a triangle by sorting the vertices by their values in one coordinate, rounding the vertices to the nearest pixels, and calculating two characteristic functions for pixels one scan line at a time, thereby identifying two end pixels for the scan line, where the particular functions used are edge characteristic functions for the two edges which bound pixels in the scan line within the triangle defined by the rounded vertices. To avoid ambiguity, pixels on one end of a scan line are deemed outside the triangle if they are exactly on the edge. Alternatively, only one function per pixel is used, the edge function for the nearest edge. The rasterization process is extensible to polygons of more than three sides, by taking into account that only two sides of the polygon need to be considered for a given scan line, and thus only two characteristic functions are needed at any one time. Using just the fractional part of an edge's intersection with a scan line to detect whether a pixel is inside or outside is also possible. Where a characteristic function is used, the value of the function can be used as an anti-aliasing value, which would be a measure of how much of the pixel lies inside the triangle.