Linear "cracks" spaced evenly throughout the viewing frame. With
each additional "step" more cracks are superimposed.
The options are as follows:
steps
valid values are whole numbers from 1 to 20.
steps density
valid density values are whole numbers from 10 to 500.
EXAMPLES
fissure 4 500
fissure
In the first example, 4 layers of cracks with the (maximum)
density value of 500 are drawn. When no argument is given, 1 set of
cracks is drawn with density value 400.