source/PIL/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.
#

"""
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.)
"""
from __future__ import annotations

from math import log, pi, sin, sqrt

from ._binary import o8

TYPE_CHECKING = False
if TYPE_CHECKING:
    from collections.abc import Callable
    from typing import IO

EPSILON = 1e-10
""""""  # Enable auto-doc for data member


def linear(middle: float, pos: float) -> float:
    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: float, pos: float) -> float:
    return pos ** (log(0.5) / log(max(middle, EPSILON)))


def sine(middle: float, pos: float) -> float:
    return (sin((-pi / 2.0) + pi * linear(middle, pos)) + 1.0) / 2.0


def sphere_increasing(middle: float, pos: float) -> float:
    return sqrt(1.0 - (linear(middle, pos) - 1.0) ** 2)


def sphere_decreasing(middle: float, pos: float) -> float:
    return 1.0 - sqrt(1.0 - linear(middle, pos) ** 2)


SEGMENTS = [linear, curved, sine, sphere_increasing, sphere_decreasing]
""""""  # Enable auto-doc for data member


class GradientFile:
    gradient: (
        list[
            tuple[
                float,
                float,
                float,
                list[float],
                list[float],
                Callable[[float, float], float],
            ]
        ]
        | None
    ) = None

    def getpalette(self, entries: int = 256) -> tuple[bytes, str]:
        assert self.gradient is not None
        palette = []

        ix = 0
        x0, x1, xm, rgb0, rgb1, segment = self.gradient[ix]

        for i in range(entries):
            x = i / (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"


class GimpGradientFile(GradientFile):
    """File handler for GIMP's gradient format."""

    def __init__(self, fp: IO[bytes]) -> None:
        if not fp.readline().startswith(b"GIMP Gradient"):
            msg = "not a GIMP gradient file"
            raise SyntaxError(msg)

        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)

        self.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:
                msg = "cannot handle HSV colour space"
                raise OSError(msg)

            self.gradient.append((x0, x1, xm, rgb0, rgb1, segment))