cm.py

"""
Builtin colormaps, colormap handling utilities, and the `ScalarMappable` mixin.

.. seealso::

  :doc:`/gallery/color/colormap_reference` for a list of builtin colormaps.

  :doc:`/tutorials/colors/colormap-manipulation` for examples of how to
  make colormaps.

  :doc:`/tutorials/colors/colormaps` an in-depth discussion of
  choosing colormaps.

  :doc:`/tutorials/colors/colormapnorms` for more details about data
  normalization.
"""

from collections.abc import Mapping
import functools

import numpy as np
from numpy import ma

import matplotlib as mpl
from matplotlib import _api, colors, cbook, scale
from matplotlib._cm import datad
from matplotlib._cm_listed import cmaps as cmaps_listed


_LUTSIZE = mpl.rcParams['image.lut']


def _gen_cmap_registry():
    """
    Generate a dict mapping standard colormap names to standard colormaps, as
    well as the reversed colormaps.
    """
    cmap_d = {**cmaps_listed}
    for name, spec in datad.items():
        cmap_d[name] = (  # Precache the cmaps at a fixed lutsize..
            colors.LinearSegmentedColormap(name, spec, _LUTSIZE)
            if 'red' in spec else
            colors.ListedColormap(spec['listed'], name)
            if 'listed' in spec else
            colors.LinearSegmentedColormap.from_list(name, spec, _LUTSIZE))
    # Generate reversed cmaps.
    for cmap in list(cmap_d.values()):
        rmap = cmap.reversed()
        cmap_d[rmap.name] = rmap
    return cmap_d


class ColormapRegistry(Mapping):
    r"""
    Container for colormaps that are known to Matplotlib by name.

    The universal registry instance is `matplotlib.colormaps`. There should be
    no need for users to instantiate `.ColormapRegistry` themselves.

    Read access uses a dict-like interface mapping names to `.Colormap`\s::

        import matplotlib as mpl
        cmap = mpl.colormaps['viridis']

    Returned `.Colormap`\s are copies, so that their modification does not
    change the global definition of the colormap.

    Additional colormaps can be added via `.ColormapRegistry.register`::

        mpl.colormaps.register(my_colormap)
    """
    def __init__(self, cmaps):
        self._cmaps = cmaps
        self._builtin_cmaps = tuple(cmaps)
        # A shim to allow register_cmap() to force an override
        self._allow_override_builtin = False

    def __getitem__(self, item):
        try:
            return self._cmaps[item].copy()
        except KeyError:
            raise KeyError(f"{item!r} is not a known colormap name") from None

    def __iter__(self):
        return iter(self._cmaps)

    def __len__(self):
        return len(self._cmaps)

    def __str__(self):
        return ('ColormapRegistry; available colormaps:\n' +
                ', '.join(f"'{name}'" for name in self))

    def __call__(self):
        """
        Return a list of the registered colormap names.

        This exists only for backward-compatibility in `.pyplot` which had a
        ``plt.colormaps()`` method. The recommended way to get this list is
        now ``list(colormaps)``.
        """
        return list(self)

    def register(self, cmap, *, name=None, force=False):
        """
        Register a new colormap.

        The colormap name can then be used as a string argument to any ``cmap``
        parameter in Matplotlib. It is also available in ``pyplot.get_cmap``.

        The colormap registry stores a copy of the given colormap, so that
        future changes to the original colormap instance do not affect the
        registered colormap. Think of this as the registry taking a snapshot
        of the colormap at registration.

        Parameters
        ----------
        cmap : matplotlib.colors.Colormap
            The colormap to register.

        name : str, optional
            The name for the colormap. If not given, ``cmap.name`` is used.

        force : bool, default: False
            If False, a ValueError is raised if trying to overwrite an already
            registered name. True supports overwriting registered colormaps
            other than the builtin colormaps.
        """
        _api.check_isinstance(colors.Colormap, cmap=cmap)

        name = name or cmap.name
        if name in self:
            if not force:
                # don't allow registering an already existing cmap
                # unless explicitly asked to
                raise ValueError(
                    f'A colormap named "{name}" is already registered.')
            elif (name in self._builtin_cmaps
                    and not self._allow_override_builtin):
                # We don't allow overriding a builtin unless privately
                # coming from register_cmap()
                raise ValueError("Re-registering the builtin cmap "
                                 f"{name!r} is not allowed.")

            # Warn that we are updating an already existing colormap
            _api.warn_external(f"Overwriting the cmap {name!r} "
                               "that was already in the registry.")

        self._cmaps[name] = cmap.copy()

    def unregister(self, name):
        """
        Remove a colormap from the registry.

        You cannot remove built-in colormaps.

        If the named colormap is not registered, returns with no error, raises
        if you try to de-register a default colormap.

        .. warning::

            Colormap names are currently a shared namespace that may be used
            by multiple packages. Use `unregister` only if you know you
            have registered that name before. In particular, do not
            unregister just in case to clean the name before registering a
            new colormap.

        Parameters
        ----------
        name : str
            The name of the colormap to be removed.

        Raises
        ------
        ValueError
            If you try to remove a default built-in colormap.
        """
        if name in self._builtin_cmaps:
            raise ValueError(f"cannot unregister {name!r} which is a builtin "
                             "colormap.")
        self._cmaps.pop(name, None)

    def get_cmap(self, cmap):
        """
        Return a color map specified through *cmap*.

        Parameters
        ----------
        cmap : str or `~matplotlib.colors.Colormap` or None

            - if a `.Colormap`, return it
            - if a string, look it up in ``mpl.colormaps``
            - if None, return the Colormap defined in :rc:`image.cmap`

        Returns
        -------
        Colormap
        """
        # get the default color map
        if cmap is None:
            return self[mpl.rcParams["image.cmap"]]

        # if the user passed in a Colormap, simply return it
        if isinstance(cmap, colors.Colormap):
            return cmap
        if isinstance(cmap, str):
            _api.check_in_list(sorted(_colormaps), cmap=cmap)
            # otherwise, it must be a string so look it up
            return self[cmap]
        raise TypeError(
            'get_cmap expects None or an instance of a str or Colormap . ' +
            f'you passed {cmap!r} of type {type(cmap)}'
        )


# public access to the colormaps should be via `matplotlib.colormaps`. For now,
# we still create the registry here, but that should stay an implementation
# detail.
_colormaps = ColormapRegistry(_gen_cmap_registry())
globals().update(_colormaps)


@_api.deprecated("3.7", alternative="``matplotlib.colormaps.register(name)``")
def register_cmap(name=None, cmap=None, *, override_builtin=False):
    """
    Add a colormap to the set recognized by :func:`get_cmap`.

    Register a new colormap to be accessed by name ::

        LinearSegmentedColormap('swirly', data, lut)
        register_cmap(cmap=swirly_cmap)

    Parameters
    ----------
    name : str, optional
       The name that can be used in :func:`get_cmap` or :rc:`image.cmap`

       If absent, the name will be the :attr:`~matplotlib.colors.Colormap.name`
       attribute of the *cmap*.

    cmap : matplotlib.colors.Colormap
       Despite being the second argument and having a default value, this
       is a required argument.

    override_builtin : bool

        Allow built-in colormaps to be overridden by a user-supplied
        colormap.

        Please do not use this unless you are sure you need it.
    """
    _api.check_isinstance((str, None), name=name)
    if name is None:
        try:
            name = cmap.name
        except AttributeError as err:
            raise ValueError("Arguments must include a name or a "
                             "Colormap") from err
    # override_builtin is allowed here for backward compatibility
    # this is just a shim to enable that to work privately in
    # the global ColormapRegistry
    _colormaps._allow_override_builtin = override_builtin
    _colormaps.register(cmap, name=name, force=override_builtin)
    _colormaps._allow_override_builtin = False


def _get_cmap(name=None, lut=None):
    """
    Get a colormap instance, defaulting to rc values if *name* is None.

    Parameters
    ----------
    name : `~matplotlib.colors.Colormap` or str or None, default: None
        If a `.Colormap` instance, it will be returned. Otherwise, the name of
        a colormap known to Matplotlib, which will be resampled by *lut*. The
        default, None, means :rc:`image.cmap`.
    lut : int or None, default: None
        If *name* is not already a Colormap instance and *lut* is not None, the
        colormap will be resampled to have *lut* entries in the lookup table.

    Returns
    -------
    Colormap
    """
    if name is None:
        name = mpl.rcParams['image.cmap']
    if isinstance(name, colors.Colormap):
        return name
    _api.check_in_list(sorted(_colormaps), name=name)
    if lut is None:
        return _colormaps[name]
    else:
        return _colormaps[name].resampled(lut)

# do it in two steps like this so we can have an un-deprecated version in
# pyplot.
get_cmap = _api.deprecated(
    '3.7',
    name='get_cmap',
    alternative=(
        "``matplotlib.colormaps[name]`` " +
        "or ``matplotlib.colormaps.get_cmap(obj)``"
    )
)(_get_cmap)


@_api.deprecated("3.7",
                 alternative="``matplotlib.colormaps.unregister(name)``")
def unregister_cmap(name):
    """
    Remove a colormap recognized by :func:`get_cmap`.

    You may not remove built-in colormaps.

    If the named colormap is not registered, returns with no error, raises
    if you try to de-register a default colormap.

    .. warning::

      Colormap names are currently a shared namespace that may be used
      by multiple packages. Use `unregister_cmap` only if you know you
      have registered that name before. In particular, do not
      unregister just in case to clean the name before registering a
      new colormap.

    Parameters
    ----------
    name : str
        The name of the colormap to be un-registered

    Returns
    -------
    ColorMap or None
        If the colormap was registered, return it if not return `None`

    Raises
    ------
    ValueError
       If you try to de-register a default built-in colormap.
    """
    cmap = _colormaps.get(name, None)
    _colormaps.unregister(name)
    return cmap


def _auto_norm_from_scale(scale_cls):
    """
    Automatically generate a norm class from *scale_cls*.

    This differs from `.colors.make_norm_from_scale` in the following points:

    - This function is not a class decorator, but directly returns a norm class
      (as if decorating `.Normalize`).
    - The scale is automatically constructed with ``nonpositive="mask"``, if it
      supports such a parameter, to work around the difference in defaults
      between standard scales (which use "clip") and norms (which use "mask").

    Note that ``make_norm_from_scale`` caches the generated norm classes
    (not the instances) and reuses them for later calls.  For example,
    ``type(_auto_norm_from_scale("log")) == LogNorm``.
    """
    # Actually try to construct an instance, to verify whether
    # ``nonpositive="mask"`` is supported.
    try:
        norm = colors.make_norm_from_scale(
            functools.partial(scale_cls, nonpositive="mask"))(
            colors.Normalize)()
    except TypeError:
        norm = colors.make_norm_from_scale(scale_cls)(
            colors.Normalize)()
    return type(norm)


class ScalarMappable:
    """
    A mixin class to map scalar data to RGBA.

    The ScalarMappable applies data normalization before returning RGBA colors
    from the given colormap.
    """

    def __init__(self, norm=None, cmap=None):
        """
        Parameters
        ----------
        norm : `.Normalize` (or subclass thereof) or str or None
            The normalizing object which scales data, typically into the
            interval ``[0, 1]``.
            If a `str`, a `.Normalize` subclass is dynamically generated based
            on the scale with the corresponding name.
            If *None*, *norm* defaults to a *colors.Normalize* object which
            initializes its scaling based on the first data processed.
        cmap : str or `~matplotlib.colors.Colormap`
            The colormap used to map normalized data values to RGBA colors.
        """
        self._A = None
        self._norm = None  # So that the setter knows we're initializing.
        self.set_norm(norm)  # The Normalize instance of this ScalarMappable.
        self.cmap = None  # So that the setter knows we're initializing.
        self.set_cmap(cmap)  # The Colormap instance of this ScalarMappable.
        #: The last colorbar associated with this ScalarMappable. May be None.
        self.colorbar = None
        self.callbacks = cbook.CallbackRegistry(signals=["changed"])

    def _scale_norm(self, norm, vmin, vmax):
        """
        Helper for initial scaling.

        Used by public functions that create a ScalarMappable and support
        parameters *vmin*, *vmax* and *norm*. This makes sure that a *norm*
        will take precedence over *vmin*, *vmax*.

        Note that this method does not set the norm.
        """
        if vmin is not None or vmax is not None:
            self.set_clim(vmin, vmax)
            if isinstance(norm, colors.Normalize):
                raise ValueError(
                    "Passing a Normalize instance simultaneously with "
                    "vmin/vmax is not supported.  Please pass vmin/vmax "
                    "directly to the norm when creating it.")

        # always resolve the autoscaling so we have concrete limits
        # rather than deferring to draw time.
        self.autoscale_None()

    def to_rgba(self, x, alpha=None, bytes=False, norm=True):
        """
        Return a normalized rgba array corresponding to *x*.

        In the normal case, *x* is a 1D or 2D sequence of scalars, and
        the corresponding `~numpy.ndarray` of rgba values will be returned,
        based on the norm and colormap set for this ScalarMappable.

        There is one special case, for handling images that are already
        rgb or rgba, such as might have been read from an image file.
        If *x* is an `~numpy.ndarray` with 3 dimensions,
        and the last dimension is either 3 or 4, then it will be
        treated as an rgb or rgba array, and no mapping will be done.
        The array can be uint8, or it can be floating point with
        values in the 0-1 range; otherwise a ValueError will be raised.
        If it is a masked array, the mask will be ignored.
        If the last dimension is 3, the *alpha* kwarg (defaulting to 1)
        will be used to fill in the transparency.  If the last dimension
        is 4, the *alpha* kwarg is ignored; it does not
        replace the preexisting alpha.  A ValueError will be raised
        if the third dimension is other than 3 or 4.

        In either case, if *bytes* is *False* (default), the rgba
        array will be floats in the 0-1 range; if it is *True*,
        the returned rgba array will be uint8 in the 0 to 255 range.

        If norm is False, no normalization of the input data is
        performed, and it is assumed to be in the range (0-1).

        """
        # First check for special case, image input:
        try:
            if x.ndim == 3:
                if x.shape[2] == 3:
                    if alpha is None:
                        alpha = 1
                    if x.dtype == np.uint8:
                        alpha = np.uint8(alpha * 255)
                    m, n = x.shape[:2]
                    xx = np.empty(shape=(m, n, 4), dtype=x.dtype)
                    xx[:, :, :3] = x
                    xx[:, :, 3] = alpha
                elif x.shape[2] == 4:
                    xx = x
                else:
                    raise ValueError("Third dimension must be 3 or 4")
                if xx.dtype.kind == 'f':
                    if norm and (xx.max() > 1 or xx.min() < 0):
                        raise ValueError("Floating point image RGB values "
                                         "must be in the 0..1 range.")
                    if bytes:
                        xx = (xx * 255).astype(np.uint8)
                elif xx.dtype == np.uint8:
                    if not bytes:
                        xx = xx.astype(np.float32) / 255
                else:
                    raise ValueError("Image RGB array must be uint8 or "
                                     "floating point; found %s" % xx.dtype)
                return xx
        except AttributeError:
            # e.g., x is not an ndarray; so try mapping it
            pass

        # This is the normal case, mapping a scalar array:
        x = ma.asarray(x)
        if norm:
            x = self.norm(x)
        rgba = self.cmap(x, alpha=alpha, bytes=bytes)
        return rgba

    def set_array(self, A):
        """
        Set the value array from array-like *A*.

        Parameters
        ----------
        A : array-like or None
            The values that are mapped to colors.

            The base class `.ScalarMappable` does not make any assumptions on
            the dimensionality and shape of the value array *A*.
        """
        if A is None:
            self._A = None
            return

        A = cbook.safe_masked_invalid(A, copy=True)
        if not np.can_cast(A.dtype, float, "same_kind"):
            raise TypeError(f"Image data of dtype {A.dtype} cannot be "
                            "converted to float")

        self._A = A

    def get_array(self):
        """
        Return the array of values, that are mapped to colors.

        The base class `.ScalarMappable` does not make any assumptions on
        the dimensionality and shape of the array.
        """
        return self._A

    def get_cmap(self):
        """Return the `.Colormap` instance."""
        return self.cmap

    def get_clim(self):
        """
        Return the values (min, max) that are mapped to the colormap limits.
        """
        return self.norm.vmin, self.norm.vmax

    def set_clim(self, vmin=None, vmax=None):
        """
        Set the norm limits for image scaling.

        Parameters
        ----------
        vmin, vmax : float
             The limits.

             The limits may also be passed as a tuple (*vmin*, *vmax*) as a
             single positional argument.

             .. ACCEPTS: (vmin: float, vmax: float)
        """
        # If the norm's limits are updated self.changed() will be called
        # through the callbacks attached to the norm
        if vmax is None:
            try:
                vmin, vmax = vmin
            except (TypeError, ValueError):
                pass
        if vmin is not None:
            self.norm.vmin = colors._sanitize_extrema(vmin)
        if vmax is not None:
            self.norm.vmax = colors._sanitize_extrema(vmax)

    def get_alpha(self):
        """
        Returns
        -------
        float
            Always returns 1.
        """
        # This method is intended to be overridden by Artist sub-classes
        return 1.

    def set_cmap(self, cmap):
        """
        Set the colormap for luminance data.

        Parameters
        ----------
        cmap : `.Colormap` or str or None
        """
        in_init = self.cmap is None

        self.cmap = _ensure_cmap(cmap)
        if not in_init:
            self.changed()  # Things are not set up properly yet.

    @property
    def norm(self):
        return self._norm

    @norm.setter
    def norm(self, norm):
        _api.check_isinstance((colors.Normalize, str, None), norm=norm)
        if norm is None:
            norm = colors.Normalize()
        elif isinstance(norm, str):
            try:
                scale_cls = scale._scale_mapping[norm]
            except KeyError:
                raise ValueError(
                    "Invalid norm str name; the following values are "
                    "supported: {}".format(", ".join(scale._scale_mapping))
                ) from None
            norm = _auto_norm_from_scale(scale_cls)()

        if norm is self.norm:
            # We aren't updating anything
            return

        in_init = self.norm is None
        # Remove the current callback and connect to the new one
        if not in_init:
            self.norm.callbacks.disconnect(self._id_norm)
        self._norm = norm
        self._id_norm = self.norm.callbacks.connect('changed',
                                                    self.changed)
        if not in_init:
            self.changed()

    def set_norm(self, norm):
        """
        Set the normalization instance.

        Parameters
        ----------
        norm : `.Normalize` or str or None

        Notes
        -----
        If there are any colorbars using the mappable for this norm, setting
        the norm of the mappable will reset the norm, locator, and formatters
        on the colorbar to default.
        """
        self.norm = norm

    def autoscale(self):
        """
        Autoscale the scalar limits on the norm instance using the
        current array
        """
        if self._A is None:
            raise TypeError('You must first set_array for mappable')
        # If the norm's limits are updated self.changed() will be called
        # through the callbacks attached to the norm
        self.norm.autoscale(self._A)

    def autoscale_None(self):
        """
        Autoscale the scalar limits on the norm instance using the
        current array, changing only limits that are None
        """
        if self._A is None:
            raise TypeError('You must first set_array for mappable')
        # If the norm's limits are updated self.changed() will be called
        # through the callbacks attached to the norm
        self.norm.autoscale_None(self._A)

    def changed(self):
        """
        Call this whenever the mappable is changed to notify all the
        callbackSM listeners to the 'changed' signal.
        """
        self.callbacks.process('changed', self)
        self.stale = True


# The docstrings here must be generic enough to apply to all relevant methods.
mpl._docstring.interpd.update(
    cmap_doc="""\
cmap : str or `~matplotlib.colors.Colormap`, default: :rc:`image.cmap`
    The Colormap instance or registered colormap name used to map scalar data
    to colors.""",
    norm_doc="""\
norm : str or `~matplotlib.colors.Normalize`, optional
    The normalization method used to scale scalar data to the [0, 1] range
    before mapping to colors using *cmap*. By default, a linear scaling is
    used, mapping the lowest value to 0 and the highest to 1.

    If given, this can be one of the following:

    - An instance of `.Normalize` or one of its subclasses
      (see :doc:`/tutorials/colors/colormapnorms`).
    - A scale name, i.e. one of "linear", "log", "symlog", "logit", etc.  For a
      list of available scales, call `matplotlib.scale.get_scale_names()`.
      In that case, a suitable `.Normalize` subclass is dynamically generated
      and instantiated.""",
    vmin_vmax_doc="""\
vmin, vmax : float, optional
    When using scalar data and no explicit *norm*, *vmin* and *vmax* define
    the data range that the colormap covers. By default, the colormap covers
    the complete value range of the supplied data. It is an error to use
    *vmin*/*vmax* when a *norm* instance is given (but using a `str` *norm*
    name together with *vmin*/*vmax* is acceptable).""",
)


def _ensure_cmap(cmap):
    """
    Ensure that we have a `.Colormap` object.

    For internal use to preserve type stability of errors.

    Parameters
    ----------
    cmap : None, str, Colormap

        - if a `Colormap`, return it
        - if a string, look it up in mpl.colormaps
        - if None, look up the default color map in mpl.colormaps

    Returns
    -------
    Colormap

    """
    if isinstance(cmap, colors.Colormap):
        return cmap
    cmap_name = cmap if cmap is not None else mpl.rcParams["image.cmap"]
    # use check_in_list to ensure type stability of the exception raised by
    # the internal usage of this (ValueError vs KeyError)
    _api.check_in_list(sorted(_colormaps), cmap=cmap_name)
    return mpl.colormaps[cmap_name]