8000 I changed the offset code for draw_text for RendererAgg fixing issue #13044 by safdarzareef · Pull Request #20057 · matplotlib/matplotlib · GitHub
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I changed the offset code for draw_text for RendererAgg fixing issue #13044 #20057

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I changed the offset code for draw_text for RendererAgg fixing issue #13044 #20057

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7 changes: 5 additions & 2 deletions lib/matplotlib/backends/backend_agg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@
except ImportError:
import dummy_threading as threading
from contextlib import nullcontext
from math import radians, cos, sin
from math import radians, cos, sin, sqrt

import numpy as np
from PIL import Image
Expand Down Expand Up @@ -208,10 +208,13 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
xo, yo = font.get_bitmap_offset()
xo /= 64.0
yo /= 64.0
h = sqrt(xo**2 + yo**2)
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Personally, I prefer using hypot() instead, but I don't know if it really matters in the context of bounding box calculations.

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I don't know if it will matter, but we could still change it.

xd = d * sin(radians(angle))
yd = d * cos(radians(angle))
xo = h * cos(radians(angle))
yo = h * sin(radians(angle))
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If we are going to calculate radians(angle) four times, might as well just do it once and store it in a variable.

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Also, these four lines here would greatly benefit from a comment explaining the trigonometry. Usually, cos() goes with x, and y goes with sin(). Seeing it two different ways here for the offset and the descent is confusing.

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I can explain the offset trigonometry, but I just left the code for the descent as it was before. The descent seems wrong - but I am unaware of the reason why it was like that before so I left it there. Basic trigonometry suggests that x components should be calculated by multiplying a number by the cosine of its angle and y components should be calculated by multiplying a number by the sine of its angle - so that is why I used that for the offset but I do think the descent should be in the same form too.

x = round(x + xo + xd)
y = round(y + yo + yd)
y = round(y + yo - yd)
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much like the trig above, I think this will also need a quick proof in the comments.

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I don't think I have a proof for this at the moment except that in the draw_mathtext function the y is calculated in a similar manner and by subtracting the y offset we get a satisfactory result.

self._renderer.draw_text_image(font, x, y + 1, angle, gc)

def get_text_width_height_descent(self, s, prop, ismath):
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