Switch on or off a so-called "patch" mode. In patch mode, all elements are drawn one by one, otherwise all colors are drawn one by one. This patch mode is helpful to draw 3D surfaces with elements sorted from back to front (the simplest hidden surface method for convex bodies). For this purpose there is also a difference in drawing grids ( [Net-2D] or [Net-3D] from the [Draw] menu) - in patch mode, the polygons are filled with the background color on screen or with a light gray in postscript output.