#
# Python Imaging Library
# $Id$
#
# stuff to read (and render) GIMP gradient files
#
# History:
# 97-08-23 fl Created
#
# Copyright (c) Secret Labs AB 1997.
# Copyright (c) Fredrik Lundh 1997.
#
# See the README file for information on usage and redistribution.
#
from math import pi,log,sin,sqrt
import string
# --------------------------------------------------------------------
# Stuff to translate curve segments to palette values (derived from
# the corresponding code in GIMP, written by Federico Mena Quintero.
# See the GIMP distribution for more information.)
#
EPSILON = 1e-10
def linear(middle, pos):
if pos <= middle:
if middle < EPSILON:
return 0.0
else:
return 0.5 * pos / middle
else:
pos = pos - middle
middle = 1.0 - middle
if middle < EPSILON:
return 1.0
else:
return 0.5 + 0.5 * pos / middle
def curved(middle, pos):
return pos ** (log(0.5) / log(max(middle, EPSILON)))
def sine(middle, pos):
return (sin((-pi / 2.0) + pi * linear(middle, pos)) + 1.0) / 2.0
def sphere_increasing(middle, pos):
return sqrt(1.0 - (linear(middle, pos) - 1.0) ** 2)
def sphere_decreasing(middle, pos):
return 1.0 - sqrt(1.0 - linear(middle, pos) ** 2)
SEGMENTS = [ linear, curved, sine, sphere_increasing, sphere_decreasing ]
class GradientFile:
gradient = None
def getpalette(self, entries = 256):
palette = []
ix = 0
x0, x1, xm, rgb0, rgb1, segment = self.gradient[ix]
for i in range(entries):
x = i / float(entries-1)
while x1 < x:
ix = ix + 1
x0, x1, xm, rgb0, rgb1, segment = self.gradient[ix]
w = x1 - x0
if w < EPSILON:
scale = segment(0.5, 0.5)
else:
scale = segment((xm - x0) / w, (x - x0) / w)
# expand to RGBA
r = chr(int(255 * ((rgb1[0] - rgb0[0]) * scale + rgb0[0]) + 0.5))
g = chr(int(255 * ((rgb1[1] - rgb0[1]) * scale + rgb0[1]) + 0.5))
b = chr(int(255 * ((rgb1[2] - rgb0[2]) * scale + rgb0[2]) + 0.5))
a = chr(int(255 * ((rgb1[3] - rgb0[3]) * scale + rgb0[3]) + 0.5))
# add to palette
palette.append(r + g + b + a)
return string.join(palette, ""), "RGBA"
##
# File handler for GIMP's gradient format.
class GimpGradientFile(GradientFile):
def __init__(self, fp):
if fp.readline()[:13] != "GIMP Gradient":
raise SyntaxError, "not a GIMP gradient file"
count = int(fp.readline())
gradient = []
for i in range(count):
s = string.split(fp.readline())
w = map(float, s[:11])
x0, x1 = w[0], w[2]
xm = w[1]
rgb0 = w[3:7]
rgb1 = w[7:11]
segment = SEGMENTS[int(s[11])]
cspace = int(s[12])
if cspace != 0:
raise IOError, "cannot handle HSV colour space"
gradient.append((x0, x1, xm, rgb0, rgb1, segment))
self.gradient = gradient
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