Gradients in gnuplot

gradient.plt

set terminal png size 640,480
set output 'gradient.png'
set xrange [-5:5]
set yrange [-5:5]
set cbrange [0:1]
unset colorbox
unset key
set palette gray negative
set object 1 rectangle from 1,-10 to 10,10 behind fillcolor rgb 'black' fillstyle noborder
plot '< python gradient.py -x -1 1 -10 10 64' with image

gradient.py

import argparse
import sys

def parseArgs():
    parser = argparse.ArgumentParser(description = "Generate gradient data suitable for use in gnuplot.")
    parser.add_argument("xMin", metavar = "X_MIN", type = float, help = "minimum x-coordinate")
    parser.add_argument("xMax", metavar = "X_MAX", type = float, help = "maximum x-coordinate")
    parser.add_argument("yMin", metavar = "Y_MIN", type = float, help = "minimum y-coordinate")
    parser.add_argument("yMax", metavar = "Y_MAX", type = float, help = "maximum y-coordinate")
    parser.add_argument("stepCount", metavar = "STEPS", type = int, help = "number of steps")
    axis = parser.add_mutually_exclusive_group(required = True)
    axis.add_argument("-x", action = "store_true", default = False, help = "grade along x-axis")
    axis.add_argument("-y", action = "store_true", default = False, help = "grade along y-axis")
    return parser.parse_args()

def grade(min, max, step, stepCount):
    return min + step * (max - min) / stepCount

def write(x, y, z):
    sys.stdout.write("{0} {1} {2}\n".format(x, y, z))

args = parseArgs()
for step in range(args.stepCount + 1):
    if args.x:
        x1 = x2 = grade(args.xMin, args.xMax, step, args.stepCount)
        y1 = args.yMin
        y2 = args.yMax
    elif args.y:
        x1 = args.xMin
        x2 = args.xMax
        y1 = y2 = grade(args.yMin, args.yMax, step, args.stepCount)
    z = step / args.stepCount
    write(x1, y1, z)
    write(x2, y2, z)
    sys.stdout.write("\n")

output.png