ff-erosion.1

.Dd 2024-04-30
.Dt FF-EROSION 1
.Os farbfeld-utils
.Sh NAME
.Nm ff-erosion
.Nd farbfeld filter that generates erosion by raining
.Sh SYNOPSIS
.Nm
<?opt=value?> <?opt=value?> ...
.Sh DESCRIPTION
.Nm
reads a
.Xr farbfeld 5
image from stdin, applies the erosion filter and writes the result to stdout.
.Pp
This farbfeld filter is used to generate erosion by raining.

Only the red channel of the input is used; the output is same red, green, blue
channels, and all pixels are opaque.
.Pp
In case of an error
.Nm
writes a diagnostic message to stderr.
.Sh EXIT STATUS
.Bl -tag -width Ds
.It 0
Image processed successfully.
.It 1
An error occurred.
.El
.Sh OPTIONS
The filter takes zero or more arguments, where each argument is a letter
followed by an equal sign and a value. Many values can be floating numbers,
but not all.

The possible options are:
   b -- output level (default 1.0)
   c -- output colours (default 0)
   d -- deposit speed (default 0.2)
   e -- threshold for random directions (default 1.0e-8)
   g -- gravity (default 40.0)
   i -- inertia (default 0.1)
   m -- slope limit (default 0.05)
   n -- number of iterations (default 1)
   q -- carrying capacity (default 10.0)
   r -- erosion speed (default 0.9)
   s -- random number seed (default 1)
   w -- water evaporation speed (default 0.001)
   x -- erosion multiplier (default 0.1591549430918953)
   z -- maximum steps per iteration (default 4 * MAX(width,height))
.Sh EXAMPLES
$
.Nm
< image.ff > image-erosion.ff
.Pp
$
.Nm
c=1 b=1.5 < image.ff > image-erosion.ff
.Sh SEE ALSO
.Xr farbfeld 5 ,
.Xr farbfeld-utils 7