1. A method for generating three dimensional computer graphics images using multisample antialiasing by sequentially processing a plurality of primitives, comprising: dividing at least a first pixel into a plurality of sample areas; processing a first primitive, by determining that all the sample areas of the first pixel are located within said first primitive, storing a value for the first primitive in a multisample memory for a smaller number of the sample areas of the first pixel than the total number of the sample areas of the first pixel, and storing data indicating that all the sample areas of the first pixel are located within the first primitive; subsequently processing a second primitive, by reading the stored data for the first pixel to determine that all the sample areas of the first pixel are located within the first primitive, determining that only some of the sample areas of the first pixel are located within the second primitive, determining whether the value for the first primitive is already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, if it is determined that the value for the first primitive is already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, storing a value for the second primitive in the multisample memory for each sample area of the first pixel which is located within the second primitive without reading from the multisample memory the value for the first primitive; and if it is determined that the value for the first primitive is not already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, reading from the multisample memory the value for the first primitive, writing to the multisample memory the value for the first primitive for each sample area of the first pixel which is not located within the second primitive for which the value for the first primitive is not already stored, and storing a value for the second primitive in the multisample memory for each sample area of the first pixel which is located within the second primitive.