Class OffsetFrom

lib/matplotlib/text.py:1605–1676

Callable helper class for working with `Annotation`.

class OffsetFrom:
    """Callable helper class for working with `Annotation`."""

    def __init__(self, artist, ref_coord, unit="points"):
        """
        Parameters
        ----------
        artist : `~matplotlib.artist.Artist` or `.BboxBase` or `.Transform`
            The object to compute the offset from.

        ref_coord : (float, float)
            If *artist* is an `.Artist` or `.BboxBase`, this values is
            the location to of the offset origin in fractions of the
            *artist* bounding box.

            If *artist* is a transform, the offset origin is the
            transform applied to this value.

        unit : {'points, 'pixels'}, default: 'points'
            The screen units to use (pixels or points) for the offset input.
        """
        self._artist = artist
        x, y = ref_coord  # Make copy when ref_coord is an array (and check the shape).
        self._ref_coord = x, y
        self.set_unit(unit)

    def set_unit(self, unit):
        """
        Set the unit for input to the transform used by ``__call__``.

        Parameters
        ----------
        unit : {'points', 'pixels'}
        """
        _api.check_in_list(["points", "pixels"], unit=unit)
        self._unit = unit

    def get_unit(self):
        """Return the unit for input to the transform used by ``__call__``."""
        return self._unit

    def __call__(self, renderer):
        """
        Return the offset transform.

        Parameters
        ----------
        renderer : `RendererBase`
            The renderer to use to compute the offset

        Returns
        -------
        `Transform`
            Maps (x, y) in pixel or point units to screen units
            relative to the given artist.
        """
        if isinstance(self._artist, Artist):
            bbox = self._artist.get_window_extent(renderer)