Method and apparatus for rendering of fractional pixel lists for anti-aliasing and transparency

A method for displaying images in a raster display using a plurality of pixels, with each image having an edge and each pixel having an area, the method which comprises the steps of:

• identifying said pixels comprising each said image;
• assigning a plurality of image parameters to each said pixel in each said image, said image parameters including X, Y, Z, R, G, B, T, and A factors wherein said X and Y factors are indicative of a location for said respective pixel, said Z factor is indicative of a viewing distance from said image, said R, G and B factors are collectively indicative of a color for said pixel, said T factor is indicative of a transparency for said image, and said A factor is a pixel area factor;
• determining said A factor for each said pixel as a function of area of each said pixel covered by said image, with partial coverage being determined by establishing a slope for said edge of each said image through each said pixel intersected by said edge to divide said pixel into a covered portion and an uncovered portion and addressing said covered portion of said pixel as a polygon, calculating a subarea for said polygon, and ratioing said subarea to said area to obtain said area factor;
• creating an alpha value for each pixel of each said image, said alpha value being a function of both said A factor and said T factor;
• weighing said image parameters of each said pixel with a respective alpha value to generate a pixlink;
• inserting each said pixlink according to said Z factor thereof into a pixlink list for said pixel;
• altering respective said alpha values of all pixlinks in said list having a lower Z factor than said inserted pixlink, said altering being done according to said alpha value of said inserted pixlink;
• and
• combining pixlinks of respective pixels for each said image to create said display.

An apparatus for antialiasing an edge of an image to be presented in a raster display, the image being formed using a plurality of pixels with each pixel having an area, the method which comprises:

• means for establishing a slope for said edge of said image through a pixel intersected by said edge to divide said pixel into a covered portion and an uncovered portion;
• means for computing an area factor for said pixel, said computing step being accomplished by addressing said covered portion of said pixel as a polygon, calculating a subarea for said polygon, and ratioing said subarea to said area to obtain said area factor;
• means for assigning a plurality of image parameters to said pixel, said plurality of image parameters being characteristic of said image at said pixel and including at least a Z factor indicative of a viewing distance from said image, a T factor indicative of a transparency for said image, an X factor and a Y factor, said X factor and said Y factor each being indicative of a location for said pixel in said image, and said plurality of image parameters further including an R factor, a G factor and a B factor collectively indicative of a color for said pixel and said apparatus further comprises means for adding said respective R, G and B factors of all pixlinks in said pixlink list to establish said R, G and B factors for said pixlink in said list having a highest said Z factor;
• means for weighing said plurality of image parameters at each said pixel according to said computed area factor and said T factor to create a pixlink having an alpha value;
• means for inserting said pixlink according to said Z factor thereof into a pixlink list for said pixel;
• means for altering respective said alpha values of all pixlinks in said list having a lower Z factor than said inserted pixlink, said altering being done according to said alpha value of said inserted pixlink;
• and
• means for discarding all pixlinks from said pixlink list having a Z factor below said Z factor of said pixlink in said list which causes said alpha value of said pixlink having said highest Z factor to have a limit value.