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