OpenGL Programming Guide

Chapter 10The Framebuffer

The Accumulation Buffer

Jittering

If you need to take nine or sixteen samples to antialias an image, you might think that the best choice of points is an equally spaced grid across the pixel. Surprisingly, this is not necessarily true. In fact, sometimes it's a good idea to take points that lie in adjacent pixels. You might want a uniform distribution or a normalized distribution, clustering toward the center of the pixel. The SIGGRAPH paper discusses these issues. In addition, Table 10-5 shows a few sets of reasonable jittering values to be used for some selected sample counts. Most of the examples in the table are uniformly distributed in the pixel, and all lie within the pixel.

Table 10-5 : Sample Jittering Values

Count	Values
2	{0.25, 0.75}, {0.75, 0.25}
3	{0.5033922635, 0.8317967229}, {0.7806016275, 0.2504380877}, {0.2261828938, 0.4131553612}
4	{0.375, 0.25}, {0.125, 0.75}, {0.875, 0.25}, {0.625, 0.75}
5	{0.5, 0.5}, {0.3, 0.1}, {0.7, 0.9}, {0.9, 0.3}, {0.1, 0.7}
6	{0.4646464646, 0.4646464646}, {0.1313131313, 0.7979797979}, {0.5353535353, 0.8686868686}, {0.8686868686, 0.5353535353}, {0.7979797979, 0.1313131313}, {0.2020202020, 0.2020202020}
8	{0.5625, 0.4375}, {0.0625, 0.9375}, {0.3125, 0.6875}, {0.6875, 0.8125}, {0.8125, 0.1875}, {0.9375, 0.5625}, {0.4375, 0.0625}, {0.1875, 0.3125}
9	{0.5, 0.5}, {0.1666666666, 0.9444444444}, {0.5, 0.1666666666}, {0.5, 0.8333333333}, {0.1666666666, 0.2777777777}, {0.8333333333, 0.3888888888}, {0.1666666666, 0.6111111111}, {0.8333333333, 0.7222222222}, {0.8333333333, 0.0555555555}
12	{0.4166666666, 0.625}, {0.9166666666, 0.875}, {0.25, 0.375}, {0.4166666666, 0.125}, {0.75, 0.125}, {0.0833333333, 0.125}, {0.75, 0.625}, {0.25, 0.875}, {0.5833333333, 0.375}, {0.9166666666, 0.375}, {0.0833333333, 0.625}, { 0.583333333, 0.875}
16	{0.375, 0.4375}, {0.625, 0.0625}, {0.875, 0.1875}, {0.125, 0.0625}, {0.375, 0.6875}, {0.875, 0.4375}, {0.625, 0.5625}, {0.375, 0.9375}, {0.625, 0.3125}, {0.125, 0.5625}, {0.125, 0.8125}, {0.375, 0.1875}, {0.875, 0.9375}, {0.875, 0.6875}, {0.125, 0.3125}, {0.625, 0.8125}

OpenGL Programming Guide