Code in the per_pixel section of MilkDrop is not actually re-evaluated at every pixel as the name would suggest, rather the screen is divided into a grid and the code is evaluated at each grid point. The pixels in-between these points interpolate their values from the surrounding four points on the grid. The size of the grid is 32×24 by default, but can be set higher or lower by the user. Per_Pixel equations allow the preset author to alter some of MilkDrop's parameters differently in certain areas of the screen based upon x and y values, distance from the center of the screen, and the angle.