Coordinate based font sizes in matplotlib

Question

I would like to render text in matplotlib, where the size of the font is specified in terms of coordinates rather than in pt. My use case is to render single letters, whose size matches the size of the underlying box (Patch instance) in the background.

A bonus would be, if I could specify the width and height independently, resulting in scaled letters.

Could you write what you have tried till now and what kind of plot are you trying? — Saket Kumar Singh, Oct 11 '18 at 09:44
Maybe something like [this](https://stackoverflow.com/questions/42615527/sequence-logos-in-matplotlib-aligning-xticks)? — ImportanceOfBeingErnest, Oct 11 '18 at 10:24

score 2 · Accepted Answer · answered Oct 15 '18 at 15:39

Based on the comment of @ImportanceOfBeingErnest, I came to the following solution:

def set_font_size_in_coord(text, width=None, height=None, mode="unlocked"):
    from matplotlib.transforms import Bbox
    from matplotlib.text import Text
    from matplotlib.patheffects import AbstractPathEffect

    class TextScaler(AbstractPathEffect):
        def __init__(self, text, width, height, mode):
            self._text = text
            self._mode = mode
            self._width = width
            self._height = height

        def draw_path(self, renderer, gc, tpath, affine, rgbFace=None):
            ax = self._text.axes
            renderer = ax.get_figure().canvas.get_renderer()
            bbox = text.get_window_extent(renderer=renderer)
            bbox = Bbox(ax.transData.inverted().transform(bbox))

            if self._mode == "proportional":
                if self._width is None:
                    # Proportional scaling based on height
                    scale_y = self._height / bbox.height
                    scale_x = scale_y
                elif self._height is None:
                    # Proportional scaling based on width
                    scale_x = self._width / bbox.width
                    scale_y = scale_x
            elif self._mode == "unlocked":
                scale_x = self._width / bbox.width
                scale_y = self._height / bbox.height
            elif self._mode == "minimum":
                scale_x = self._width / bbox.width
                scale_y = self._height / bbox.height
                scale = max(scale_x, scale_y)
                scale_x, scale_y = scale, scale
            elif self._mode == "maximum":
                scale_x = self._width / bbox.width
                scale_y = self._height / bbox.height
                scale = min(scale_x, scale_y)
                scale_x, scale_y = scale, scale

            affine = affine.identity().scale(scale_x, scale_y) + affine
            renderer.draw_path(gc, tpath, affine, rgbFace)

    if mode in ["unlocked", "minimum", "maximum"]:
        if width is None or height is None:
            raise TypeError(
                f"Width and height must be set in '{mode}' mode"
            )
    elif mode == "proportional":
        if  not (width  is None and height is not None) or \
            not (height is None and width  is not None):
                raise TypeError(
                    f"Either width or height must be set in '{mode}' mode"
                )
    else:
        raise ValueError(
                f"Unknown mode '{mode}'"
            )
    text.set_path_effects([TextScaler(text, width, height, mode)])

Coordinate based font sizes in matplotlib

1 Answers1