interface.py

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# This file is part of afw.
#
# Developed for the LSST Data Management System.
# This product includes software developed by the LSST Project
# (https://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
# for details of code ownership.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
__all__ = [
    "WHITE", "BLACK", "RED", "GREEN", "BLUE", "CYAN", "MAGENTA", "YELLOW", "ORANGE", "IGNORE",
    "Display", "Event", "noop_callback", "h_callback",
    "setDefaultBackend", "getDefaultBackend",
    "setDefaultFrame", "getDefaultFrame", "incrDefaultFrame",
    "setDefaultMaskTransparency", "setDefaultMaskPlaneColor",
    "getDisplay", "delAllDisplays",
]
 
import re
import sys
import importlib
import lsst.afw.geom as afwGeom
import lsst.afw.image as afwImage
import lsst.log
 
logger = lsst.log.Log.getLogger(__name__)
 
# Symbolic names for mask/line colors.  N.b. ds9 supports any X11 color for masks
WHITE = "white"
BLACK = "black"
RED = "red"
GREEN = "green"
BLUE = "blue"
CYAN = "cyan"
MAGENTA = "magenta"
YELLOW = "yellow"
ORANGE = "orange"
IGNORE = "ignore"
 
 
def _makeDisplayImpl(display, backend, *args, **kwargs):
    """Return the ``DisplayImpl`` for the named backend
 
    Parameters
    ----------
    display : `str`
        Name of device. Should be importable, either absolutely or relative to lsst.display
    backend : `str`
        The desired backend
    *args
        Arguments passed to DisplayImpl.__init__
    *kwargs
        Keywords arguments passed to DisplayImpl.__init__
 
    Examples
    --------
    E.g.
 
    .. code-block:: py
 
         import lsst.afw.display as afwDisplay
         display = afwDisplay.Display(backend="ds9")
 
     would call
 
    .. code-block:: py
 
         _makeDisplayImpl(..., "ds9", 1)
 
    and import the ds9 implementation of ``DisplayImpl`` from `lsst.display.ds9`
    """
    _disp = None
    exc = None
    candidateBackends = (f"lsst.display.{backend}", backend, f".{backend}", f"lsst.afw.display.{backend}")
    for dt in candidateBackends:
        exc = None
        # only specify the root package if we are not doing an absolute import
        impargs = {}
        if dt.startswith("."):
            impargs["package"] = "lsst.display"
        try:
            _disp = importlib.import_module(dt, **impargs)
            # If _disp doesn't have a DisplayImpl attribute, we probably
            # picked up an irrelevant module due to a name collision
            if hasattr(_disp, "DisplayImpl"):
                break
            else:
                _disp = None
        except (ImportError, SystemError) as e:
            # SystemError can be raised in Python 3.5 if a relative import
            # is attempted when the root package, lsst.display, does not exist.
            # Copy the exception into outer scope
            exc = e
 
    if not _disp or not hasattr(_disp.DisplayImpl, "_show"):
        # If available, re-use the final exception from above
        e = ImportError(f"Could not load the requested backend: {backend} "
                        f"(tried {', '.join(candidateBackends)}, but none worked).")
        if exc is not None:
            raise e from exc
        else:
            raise e
 
    if display:
        _impl = _disp.DisplayImpl(display, *args, **kwargs)
        if not hasattr(_impl, "frame"):
            _impl.frame = display.frame
 
        return _impl
    else:
        return True
 
 
class Display:
    """Create an object able to display images and overplot glyphs.
 
    Parameters
    ----------
    frame
        An identifier for the display.
    backend : `str`
        The backend to use (defaults to value set by setDefaultBackend()).
    **kwargs
        Arguments to pass to the backend.
    """
    _displays = {}
    _defaultBackend = None
    _defaultFrame = 0
    _defaultMaskPlaneColor = dict(
        BAD=RED,
        CR=MAGENTA,
        EDGE=YELLOW,
        INTERPOLATED=GREEN,
        SATURATED=GREEN,
        DETECTED=BLUE,
        DETECTED_NEGATIVE=CYAN,
        SUSPECT=YELLOW,
        NO_DATA=ORANGE,
        # deprecated names
        INTRP=GREEN,
        SAT=GREEN,
    )
    _defaultMaskTransparency = {}
    _defaultImageColormap = "gray"
 
    def __init__(self, frame=None, backend=None, **kwargs):
        if frame is None:
            frame = getDefaultFrame()
 
        if backend is None:
            if Display._defaultBackend is None:
                try:
                    setDefaultBackend("ds9")
                except RuntimeError:
                    setDefaultBackend("virtualDevice")
 
            backend = Display._defaultBackend
 
        self.frame = frame
        self._impl = _makeDisplayImpl(self, backend, **kwargs)
        self.name = backend
 
        self._xy0 = None                # displayed data's XY0
        self.setMaskTransparency(Display._defaultMaskTransparency)
        self._maskPlaneColors = {}
        self.setMaskPlaneColor(Display._defaultMaskPlaneColor)
        self.setImageColormap(Display._defaultImageColormap)
 
        self._callbacks = {}
 
        for ik in range(ord('a'), ord('z') + 1):
            k = f"{ik:c}"
            self.setCallback(k, noRaise=True)
            self.setCallback(k.upper(), noRaise=True)
 
        for k in ('Return', 'Shift_L', 'Shift_R'):
            self.setCallback(k)
 
        for k in ('q', 'Escape'):
            self.setCallback(k, lambda k, x, y: True)
 
        def _h_callback(k, x, y):
            h_callback(k, x, y)
 
            for k in sorted(self._callbacks.keys()):
                doc = self._callbacks[k].__doc__
                print("   %-6s %s" % (k, doc.split("\n")[0] if doc else "???"))
 
        self.setCallback('h', _h_callback)
 
        Display._displays[frame] = self
 
    def __enter__(self):
        """Support for python's with statement.
        """
        return self
 
    def __exit__(self, *args):
        """Support for python's with statement.
        """
        self.close()
 
    def __del__(self):
        self.close()
 
    def __getattr__(self, name):
        """Return the attribute of ``self._impl``, or ``._impl`` if it is
        requested.
 
        Parameters:
        -----------
        name : `str`
            name of the attribute requested.
 
        Returns:
        --------
        attribute : `object`
            the attribute of self._impl for the requested name.
        """
 
        if name == '_impl':
            return object.__getattr__(self, name)
 
        if not (hasattr(self, "_impl") and self._impl):
            raise AttributeError("Device has no _impl attached")
 
        try:
            return getattr(self._impl, name)
        except AttributeError:
            raise AttributeError(
                f"Device {self.name} has no attribute \"{name}\"")
 
    def close(self):
        if getattr(self, "_impl", None) is not None:
            self._impl._close()
            del self._impl
            self._impl = None
 
        if self.frame in Display._displays:
            del Display._displays[self.frame]
 
    @property
    def verbose(self):
        """The backend's verbosity.
        """
        return self._impl.verbose
 
    @verbose.setter
    def verbose(self, value):
        if self._impl:
            self._impl.verbose = value
 
    def __str__(self):
        return f"Display[{self.frame}]"
 
    # Handle Displays, including the default one (the frame to use when a user specifies None)
 
    @staticmethod
    def setDefaultBackend(backend):
        try:
            _makeDisplayImpl(None, backend)
        except Exception as e:
            raise RuntimeError(
                f"Unable to set backend to {backend}: \"{e}\"")
 
        Display._defaultBackend = backend
 
    @staticmethod
    def getDefaultBackend():
        return Display._defaultBackend
 
    @staticmethod
    def setDefaultFrame(frame=0):
        """Set the default frame for display.
        """
        Display._defaultFrame = frame
 
    @staticmethod
    def getDefaultFrame():
        """Get the default frame for display.
        """
        return Display._defaultFrame
 
    @staticmethod
    def incrDefaultFrame():
        """Increment the default frame for display.
        """
        Display._defaultFrame += 1
        return Display._defaultFrame
 
    @staticmethod
    def setDefaultMaskTransparency(maskPlaneTransparency={}):
        if hasattr(maskPlaneTransparency, "copy"):
            maskPlaneTransparency = maskPlaneTransparency.copy()
 
        Display._defaultMaskTransparency = maskPlaneTransparency
 
    @staticmethod
    def setDefaultMaskPlaneColor(name=None, color=None):
        """Set the default mapping from mask plane names to colors.
 
        Parameters
        ----------
        name : `str` or `dict`
            Name of mask plane, or a dict mapping names to colors
            If name is `None`, use the hard-coded default dictionary.
        color
            Desired color, or `None` if name is a dict.
        """
 
        if name is None:
            name = Display._defaultMaskPlaneColor
 
        if isinstance(name, dict):
            assert color is None
            for k, v in name.items():
                setDefaultMaskPlaneColor(k, v)
            return
        # Set the individual color values
        Display._defaultMaskPlaneColor[name] = color
 
    @staticmethod
    def setDefaultImageColormap(cmap):
        """Set the default colormap for images.
 
        Parameters
        ----------
        cmap : `str`
            Name of colormap, as interpreted by the backend.
 
        Notes
        -----
        The only colormaps that all backends are required to honor
        (if they pay any attention to setImageColormap) are "gray" and "grey".
        """
 
        Display._defaultImageColormap = cmap
 
    def setImageColormap(self, cmap):
        """Set the colormap to use for images.
 
         Parameters
        ----------
        cmap : `str`
            Name of colormap, as interpreted by the backend.
 
        Notes
        -----
        The only colormaps that all backends are required to honor
        (if they pay any attention to setImageColormap) are "gray" and "grey".
        """
 
        self._impl._setImageColormap(cmap)
 
    @staticmethod
    def getDisplay(frame=None, backend=None, create=True, verbose=False, **kwargs):
        """Return a specific `Display`, creating it if need be.
 
        Parameters
        ----------
        frame
            The desired frame (`None` => use defaultFrame
            (see `~Display.setDefaultFrame`)).
        backend : `str`
            create the specified frame using this backend (or the default if
            `None`) if it doesn't already exist. If ``backend == ""``, it's an
            error to specify a non-existent ``frame``.
        create : `bool`
            create the display if it doesn't already exist.
        verbose : `bool`
            Allow backend to be chatty.
        **kwargs
            keyword arguments passed to `Display` constructor.
        """
 
        if frame is None:
            frame = Display._defaultFrame
 
        if frame not in Display._displays:
            if backend == "":
                raise RuntimeError(f"Frame {frame} does not exist")
 
            Display._displays[frame] = Display(
                frame, backend, verbose=verbose, **kwargs)
 
        Display._displays[frame].verbose = verbose
        return Display._displays[frame]
 
    @staticmethod
    def delAllDisplays():
        """Delete and close all known displays.
        """
        for disp in list(Display._displays.values()):
            disp.close()
        Display._displays = {}
 
    def maskColorGenerator(self, omitBW=True):
        """A generator for "standard" colors.
 
        Parameters
        ----------
        omitBW : `bool`
            Don't include `BLACK` and `WHITE`.
 
        Examples
        --------
 
        .. code-block:: py
 
           colorGenerator = interface.maskColorGenerator(omitBW=True)
           for p in planeList:
               print(p, next(colorGenerator))
        """
        _maskColors = [WHITE, BLACK, RED, GREEN,
                       BLUE, CYAN, MAGENTA, YELLOW, ORANGE]
 
        i = -1
        while True:
            i += 1
            color = _maskColors[i%len(_maskColors)]
            if omitBW and color in (BLACK, WHITE):
                continue
 
            yield color
 
    def setMaskPlaneColor(self, name, color=None):
        """Request that mask plane name be displayed as color.
 
        Parameters
        ----------
        name : `str` or `dict`
            Name of mask plane or a dictionary of name -> colorName.
        color : `str`
            The name of the color to use (must be `None` if ``name`` is a
            `dict`).
 
            Colors may be specified as any X11-compliant string (e.g.
            `"orchid"`), or by one of the following constants in
            `lsst.afw.display` : `BLACK`, `WHITE`, `RED`, `BLUE`,
            `GREEN`, `CYAN`, `MAGENTA`, `YELLOW`.
 
            If the color is "ignore" (or `IGNORE`) then that mask plane is not
            displayed.
 
            The advantage of using the symbolic names is that the python
            interpreter can detect typos.
        """
        if isinstance(name, dict):
            assert color is None
            for k, v in name.items():
                self.setMaskPlaneColor(k, v)
            return
 
        self._maskPlaneColors[name] = color
 
    def getMaskPlaneColor(self, name=None):
        """Return the color associated with the specified mask plane name.
 
        Parameters
        ----------
        name : `str`
            Desired mask plane; if `None`, return entire dict.
        """
        if name is None:
            return self._maskPlaneColors
        else:
            color = self._maskPlaneColors.get(name)
 
            if color is None:
                color = self._defaultMaskPlaneColor.get(name)
 
            return color
 
    def setMaskTransparency(self, transparency=None, name=None):
        """Specify display's mask transparency (percent); or `None` to not set
        it when loading masks.
        """
        if isinstance(transparency, dict):
            assert name is None
            for k, v in transparency.items():
                self.setMaskTransparency(v, k)
            return
 
        if transparency is not None and (transparency < 0 or transparency > 100):
            print(
                "Mask transparency should be in the range [0, 100]; clipping", file=sys.stderr)
            if transparency < 0:
                transparency = 0
            else:
                transparency = 100
 
        if transparency is not None:
            self._impl._setMaskTransparency(transparency, name)
 
    def getMaskTransparency(self, name=None):
        """Return the current display's mask transparency.
        """
        return self._impl._getMaskTransparency(name)
 
    def show(self):
        """Uniconify and Raise display.
 
        Notes
        -----
        Throws an exception if frame doesn't exit.
        """
        return self._impl._show()
 
    def __addMissingMaskPlanes(self, mask):
        """Assign colours to any missing mask planes found in mask.
        """
        maskPlanes = mask.getMaskPlaneDict()
        nMaskPlanes = max(maskPlanes.values()) + 1
 
        # Build inverse dictionary from mask plane index to name.
        planes = {}
        for key in maskPlanes:
            planes[maskPlanes[key]] = key
 
        colorGenerator = self.display.maskColorGenerator(omitBW=True)
        for p in range(nMaskPlanes):
            name = planes[p]            # ordered by plane index
            if name not in self._defaultMaskPlaneColor:
                self.setDefaultMaskPlaneColor(name, next(colorGenerator))
 
    def image(self, data, title="", wcs=None):
        """Display an image on a display, with semi-transparent masks
        overlaid, if available.
 
        Parameters
        ----------
        data : `lsst.afw.image.Exposure` or `lsst.afw.image.MaskedImage` or `lsst.afw.image.Image`
            Image to display; Exposure and MaskedImage will show transparent
            mask planes.
        title : `str`, optional
            Title for the display window.
        wcs : `lsst.afw.geom.SkyWcs`, optional
            World Coordinate System to align an `~lsst.afw.image.MaskedImage`
            or `~lsst.afw.image.Image` to; raise an exception if ``data``
            is an `~lsst.afw.image.Exposure`.
 
        Raises
        ------
        RuntimeError
            Raised if an Exposure is passed with a non-None wcs when the
            ``wcs`` kwarg is also non-None.
        TypeError
            Raised if data is an incompatible type.
        """
        if hasattr(data, "getXY0"):
            self._xy0 = data.getXY0()
        else:
            self._xy0 = None
 
        # It's an Exposure; display the MaskedImage with the WCS
        if isinstance(data, afwImage.Exposure):
            if wcs:
                raise RuntimeError("You may not specify a wcs with an Exposure")
            data, wcs = data.getMaskedImage(), data.wcs
        # it's a DecoratedImage; display it
        elif isinstance(data, afwImage.DecoratedImage):
            try:
                wcs = afwGeom.makeSkyWcs(data.getMetadata())
            except TypeError:
                wcs = None
            data = data.image
 
            self._xy0 = data.getXY0()   # DecoratedImage doesn't have getXY0()
 
        if isinstance(data, afwImage.Image):  # it's an Image; display it
            self._impl._mtv(data, None, wcs, title)
        # It's a Mask; display it, bitplane by bitplane.
        elif isinstance(data, afwImage.Mask):
            self.__addMissingMaskPlanes(data)
            # Some displays can't display a Mask without an image; so display
            # an Image too, with pixel values set to the mask.
            self._impl._mtv(afwImage.ImageI(data.array), data, wcs, title)
        # It's a MaskedImage; display Image and overlay Mask.
        elif isinstance(data, afwImage.MaskedImage):
            self.__addMissingMaskPlanes(data.mask)
            self._impl._mtv(data.image, data.mask, wcs, title)
        else:
            raise TypeError(f"Unsupported type {data!r}")
 
    def mtv(self, data, title="", wcs=None):
        """Display an image on a display, with semi-transparent masks
        overlaid, if available.
 
        Notes
        -----
        Historical note: the name "mtv" comes from Jim Gunn's forth imageprocessing
        system, Mirella (named after Mirella Freni); The "m" stands for Mirella.
        """
        self.image(data, title, wcs)
 
    class _Buffering:
        """Context manager for buffering repeated display commands.
        """
        def __init__(self, _impl):
            self._impl = _impl
 
        def __enter__(self):
            self._impl._buffer(True)
 
        def __exit__(self, *args):
            self._impl._buffer(False)
            self._impl._flush()
 
    def Buffering(self):
        """Return a context manager that will buffer repeated display
        commands, to e.g. speed up displaying points.
 
        Examples
        --------
        .. code-block:: py
 
           with display.Buffering():
               display.dot("+", xc, yc)
        """
        return self._Buffering(self._impl)
 
    def flush(self):
        """Flush any buffering that may be provided by the backend.
        """
        self._impl._flush()
 
    def erase(self):
        """Erase the specified display frame.
        """
        self._impl._erase()
 
    def centroids(self, catalog, *, symbol="o", **kwargs):
        """Draw the sources from a catalog at their pixel centroid positions
        as given by `~lsst.afw.table.Catalog.getX()` and
        `~lsst.afw.table.Catalog.getY()`.
 
        See `dot` for an explanation of ``symbol`` and available args/kwargs,
        which are passed to `dot`.
 
        Parameters
        ----------
        catalog : `lsst.afw.table.Catalog`
            Catalog to display centroids for. Must have valid `slot_Centroid`.
        """
        if not catalog.getCentroidSlot().isValid():
            raise RuntimeError("Catalog must have a valid `slot_Centroid` defined to get X/Y positions.")
 
        with self.Buffering():
            for pt in catalog:
                self.dot(symbol, pt.getX(), pt.getY(), **kwargs)
 
    def dot(self, symb, c, r, size=2, ctype=None, origin=afwImage.PARENT, **kwargs):
        """Draw a symbol onto the specified display frame.
 
        Parameters
        ----------
        symb
            Possible values are:
 
                ``"+"``
                    Draw a +
                ``"x"``
                    Draw an x
                ``"*"``
                    Draw a *
                ``"o"``
                    Draw a circle
                ``"@:Mxx,Mxy,Myy"``
                    Draw an ellipse with moments (Mxx, Mxy, Myy) (argument size is ignored)
                `lsst.afw.geom.ellipses.BaseCore`
                    Draw the ellipse (argument size is ignored). N.b. objects
                    derived from `~lsst.afw.geom.ellipses.BaseCore` include
                    `~lsst.afw.geom.ellipses.Axes` and `~lsst.afw.geom.ellipses.Quadrupole`.
                Any other value
                    Interpreted as a string to be drawn.
        c, r : `float`
            The column and row where the symbol is drawn [0-based coordinates].
        size : `int`
            Size of symbol, in pixels.
        ctype : `str`
            The desired color, either e.g. `lsst.afw.display.RED` or a color name known to X11
        origin : `lsst.afw.image.ImageOrigin`
            Coordinate system for the given positions.
        **kwargs
            Extra keyword arguments to backend.
        """
        if isinstance(symb, int):
            symb = f"{symb:d}"
 
        if origin == afwImage.PARENT and self._xy0 is not None:
            x0, y0 = self._xy0
            r -= y0
            c -= x0
 
        if isinstance(symb, afwGeom.ellipses.BaseCore) or re.search(r"^@:", symb):
            try:
                mat = re.search(r"^@:([^,]+),([^,]+),([^,]+)", symb)
            except TypeError:
                pass
            else:
                if mat:
                    mxx, mxy, myy = [float(_) for _ in mat.groups()]
                    symb = afwGeom.Quadrupole(mxx, myy, mxy)
 
            symb = afwGeom.ellipses.Axes(symb)
 
        self._impl._dot(symb, c, r, size, ctype, **kwargs)
 
    def line(self, points, origin=afwImage.PARENT, symbs=False, ctype=None, size=0.5):
        """Draw a set of symbols or connect points
 
        Parameters
        ----------
        points : `list`
            A list of (col, row)
        origin : `lsst.afw.image.ImageOrigin`
            Coordinate system for the given positions.
        symbs : `bool` or sequence
            If ``symbs`` is `True`, draw points at the specified points using
            the desired symbol, otherwise connect the dots.
 
            If ``symbs`` supports indexing (which includes a string -- caveat
            emptor) the elements are used to label the points.
        ctype : `str`
            ``ctype`` is the name of a color (e.g. 'red').
        size : `float`
            Size of points to create if `symbs` is passed.
        """
        if symbs:
            try:
                symbs[1]
            except TypeError:
                symbs = len(points)*list(symbs)
 
            for i, xy in enumerate(points):
                self.dot(symbs[i], *xy, size=size, ctype=ctype)
        else:
            if len(points) > 0:
                if origin == afwImage.PARENT and self._xy0 is not None:
                    x0, y0 = self._xy0
                    _points = list(points)  # make a mutable copy
                    for i, p in enumerate(points):
                        _points[i] = (p[0] - x0, p[1] - y0)
                    points = _points
 
                self._impl._drawLines(points, ctype)
 
    def scale(self, algorithm, min, max=None, unit=None, **kwargs):
        """Set the range of the scaling from DN in the image to the image
        display.
 
        Parameters
        ----------
        algorithm : `str`
            Desired scaling (e.g. "linear" or "asinh").
        min
            Minimum value, or "minmax" or "zscale".
        max
            Maximum value (must be `None` for minmax|zscale).
        unit
            Units for min and max (e.g. Percent, Absolute, Sigma; `None` if
            min==minmax|zscale).
        **kwargs
            Optional keyword arguments to the backend.
        """
        if min in ("minmax", "zscale"):
            assert max is None, f"You may not specify \"{min}\" and max"
            assert unit is None, f"You may not specify \"{min}\" and unit"
        elif max is None:
            raise RuntimeError("Please specify max")
 
        self._impl._scale(algorithm, min, max, unit, **kwargs)
 
    def zoom(self, zoomfac=None, colc=None, rowc=None, origin=afwImage.PARENT):
        """Zoom frame by specified amount, optionally panning also
        """
        if (rowc and colc is None) or (colc and rowc is None):
            raise RuntimeError(
                "Please specify row and column center to pan about")
 
        if rowc is not None:
            if origin == afwImage.PARENT and self._xy0 is not None:
                x0, y0 = self._xy0
                colc -= x0
                rowc -= y0
 
            self._impl._pan(colc, rowc)
 
        if zoomfac is None and rowc is None:
            zoomfac = 2
 
        if zoomfac is not None:
            self._impl._zoom(zoomfac)
 
    def pan(self, colc=None, rowc=None, origin=afwImage.PARENT):
        """Pan to a location.
 
        Parameters
        ----------
        colc, rowc
            Coordinates to pan to.
        origin : `lsst.afw.image.ImageOrigin`
            Coordinate system for the given positions.
 
        See also
        --------
        Display.zoom
        """
        self.zoom(None, colc, rowc, origin)
 
    def interact(self):
        """Enter an interactive loop, listening for key presses or equivalent
        UI actions in the display and firing callbacks.
 
        Exit with ``q``, ``CR``, ``ESC``, or any equivalent UI action provided
        in the display. The loop may also be exited by returning `True` from a
        user-provided callback function.
        """
        interactFinished = False
 
        while not interactFinished:
            ev = self._impl._getEvent()
            if not ev:
                continue
            k, x, y = ev.k, ev.x, ev.y      # for now
 
            if k not in self._callbacks:
                logger.warn("No callback registered for {0}".format(k))
            else:
                try:
                    interactFinished = self._callbacks[k](k, x, y)
                except Exception as e:
                    logger.error(
                        "Display._callbacks['{0}']({0},{1},{2}) failed: {3}".format(k, x, y, e))
 
    def setCallback(self, k, func=None, noRaise=False):
        """Set the callback for a key.
 
        Backend displays may provide an equivalent graphical UI action, but
        must make the associated key letter visible in the UI in some way.
 
        Parameters
        ----------
        k : `str`
            The key to assign the callback to.
        func : callable
            The callback assigned to ``k``.
        noRaise : `bool`
            Do not raise if ``k`` is already in use.
 
        Returns
        -------
        oldFunc : callable
            The callback previously assigned to ``k``.
        """
 
        if k in "f":
            if noRaise:
                return
            raise RuntimeError(
                f"Key '{k}' is already in use by display, so I can't add a callback for it")
 
        ofunc = self._callbacks.get(k)
        self._callbacks[k] = func if func else noop_callback
 
        self._impl._setCallback(k, self._callbacks[k])
 
        return ofunc
 
    def getActiveCallbackKeys(self, onlyActive=True):
        """Return all callback keys
 
        Parameters
        ----------
        onlyActive : `bool`
            If `True` only return keys that do something
        """
        return sorted([k for k, func in self._callbacks.items() if
                       not (onlyActive and func == noop_callback)])
 
 
# Callbacks for display events
 
 
class Event:
    """A class to handle events such as key presses in image display windows.
    """
 
    def __init__(self, k, x=float('nan'), y=float('nan')):
        self.k = k
        self.x = x
        self.y = y
 
    def __str__(self):
        return f"{self.k} ({self.x:.2f}, {self.y:.2f}"
 
 
# Default fallback function
 
 
def noop_callback(k, x, y):
    """Callback function
 
    Parameters
    ----------
    key
    x
    y
    """
    return False
 
 
def h_callback(k, x, y):
    print("Enter q or <ESC> to leave interactive mode, h for this help, or a letter to fire a callback")
    return False
 
# Handle Displays, including the default one (the frame to use when a user specifies None)
# If the default frame is None, image display is disabled
 
 
def setDefaultBackend(backend):
    Display.setDefaultBackend(backend)
 
 
def getDefaultBackend():
    return Display.getDefaultBackend()
 
 
def setDefaultFrame(frame=0):
    return Display.setDefaultFrame(frame)
 
 
def getDefaultFrame():
    """Get the default frame for display.
    """
    return Display.getDefaultFrame()
 
 
def incrDefaultFrame():
    """Increment the default frame for display.
    """
    return Display.incrDefaultFrame()
 
 
def setDefaultMaskTransparency(maskPlaneTransparency={}):
    return Display.setDefaultMaskTransparency(maskPlaneTransparency)
 
 
def setDefaultMaskPlaneColor(name=None, color=None):
    """Set the default mapping from mask plane names to colors.
 
    Parameters
    ----------
    name : `str` or `dict`
        Name of mask plane, or a dict mapping names to colors.
        If ``name`` is `None`, use the hard-coded default dictionary.
    color : `str`
        Desired color, or `None` if ``name`` is a dict.
    """
 
    return Display.setDefaultMaskPlaneColor(name, color)
 
 
def getDisplay(frame=None, backend=None, create=True, verbose=False, **kwargs):
    """Return a specific `Display`, creating it if need be.
 
    Parameters
    ----------
    frame
        Desired frame (`None` => use defaultFrame (see `setDefaultFrame`)).
    backend : `str`
        Create the specified frame using this backend (or the default if
        `None`) if it doesn't already exist. If ``backend == ""``, it's an
        error to specify a non-existent ``frame``.
    create : `bool`
        Create the display if it doesn't already exist.
    verbose : `bool`
        Allow backend to be chatty.
    **kwargs
        Keyword arguments passed to `Display` constructor.
 
    See also
    --------
    Display.getDisplay
    """
 
    return Display.getDisplay(frame, backend, create, verbose, **kwargs)
 
 
def delAllDisplays():
    """Delete and close all known displays.
    """
    return Display.delAllDisplays()