GimpGradientFile.py

#
# 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
from PIL._binary import o8

# --------------------------------------------------------------------
# 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(object):

    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 += 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))

            # add to palette
            palette.append(r + g + b + a)

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


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

class GimpGradientFile(GradientFile):

    def __init__(self, fp):

        if fp.readline()[:13] != b"GIMP Gradient":
            raise SyntaxError("not a GIMP gradient file")

        line = fp.readline()

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

        count = int(line)

        gradient = []

        for i in range(count):

            s = fp.readline().split()
            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))

        self.gradient = gradient