#
# Python Imaging Library
# $Id$
#
#
# 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
from ._binary import o8

# --------------------------------------------------------------------
# Stuff to translate curve segments to palette values (derived from
# the corresponding code in GIMP, written by Federico Mena Quintero.
#

EPSILON = 1e-10

[docs]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

[docs]def curved(middle, pos):
return pos ** (log(0.5) / log(max(middle, EPSILON)))

[docs]def sine(middle, pos):
return (sin((-pi / 2.0) + pi * linear(middle, pos)) + 1.0) / 2.0

[docs]def sphere_increasing(middle, pos):
return sqrt(1.0 - (linear(middle, pos) - 1.0) ** 2)

[docs]def sphere_decreasing(middle, pos):
return 1.0 - sqrt(1.0 - linear(middle, pos) ** 2)

SEGMENTS = [linear, curved, sine, sphere_increasing, sphere_decreasing]

[docs]    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 += 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 = o8(int(255 * ((rgb1[0] - rgb0[0]) * scale + rgb0[0]) + 0.5))
g = o8(int(255 * ((rgb1[1] - rgb0[1]) * scale + rgb0[1]) + 0.5))
b = o8(int(255 * ((rgb1[2] - rgb0[2]) * scale + rgb0[2]) + 0.5))
a = o8(int(255 * ((rgb1[3] - rgb0[3]) * scale + rgb0[3]) + 0.5))

palette.append(r + g + b + a)

return b"".join(palette), "RGBA"

##
# File handler for GIMP's gradient format.

def __init__(self, fp):

raise SyntaxError("not a GIMP gradient file")

# GIMP 1.2 gradient files don't contain a name, but GIMP 1.3 files do
if line.startswith(b"Name: "):

count = int(line)

for i in range(count):

w = [float(x) for x in 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))