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.
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)])