ff-gradient.1

.Dd 2024-05-08
.Dt FF-GRADIENT 1
.Os farbfeld-utils
.Sh NAME
.Nm ff-gradient
.Nd farbfeld program that generates a gradient picture
.Sh SYNOPSIS
.Nm
<width> <height> <mode> <colour> <?colour?> ...
.Sh DESCRIPTION
.Nm
generates a gradient
.Xr farbfeld 5
picture and writes the result to stdout.
.Pp
This program does not read from standard in.
.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 four or more arguments:
   - width
   - height
   - mode
   - one or more colours that make up the gradient

The colours can be defined through one of the following patterns:
   rrggbb            three pairs of 8-bit hex values
   rrggbbaa          four pairs of 8-bit hex values
   rrrrggggbbbb      three pairs of 16-bit hex values
   rrrrggggbbbbaaaa  four pairs of 16-bit hex values

The modes available are:
   a  = determine the colour to use according to the angle relative to the
        centre
   d  = diagonal gradient
   f  = a combination horizontal and vertical gradient - the last colour forms
        a gradient with the first colour in the leftmost column, and then that
        forms a horizontal gradient with the rest of the colours
   h  = horizontal gradient
   m* = the gradient is based on the product of the X and Y coordinates - the
        optional number is a bias amount
   n* = random (uniform) noise - the optional number is the random number seed
   q  = make a horziontal gradient using red and green channels, and a
        vertical gradient using blue and alpha channels
        (to mix the channels differently, follow this by ff-matrix)
   r  = the gradient is based on the distance from the centre
        (forming concentric circles)
   v  = vertical gradient
   y* = swirly lines emanating from the middle of the picture - the optional
        number specifies how swirly it is (and need not be an integer)

(* means you can optionally add a number after the mode letter, with no space
 or other delimiter)
.Sh EXAMPLES
$
.Nm
640 480 y9.23 906060 609060 606090 > gradient-swirl.ff
.Sh SEE ALSO
.Xr farbfeld 5 ,
.Xr farbfeld-utils 7