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[Bug]: Incorrect rendering of Abugida fonts on Matplotlib visualization #29357
Description
Bug summary
While trying to plot a heatmap, with labels in Devanagari script, I observe that words with vowel markers that come before the consonant are being rendered incorrectly in the plot.
The issue seems to lie only within the plot and is correctly rendered outside the plot in other Jupyter notebook output cells. I have imported Noto Serif Devanagari Thin of format ".ttf" in the font_manager of matplotlib.
Code for reproduction
#-------------------------------------Importing font file--------------------------------------------
import matplotlib.pyplot as plt
from matplotlib import font_manager
font_path = r'../NotoSerifDevanagari-Thin.ttf' #Font Download URL https://fonts.google.com/noto/specimen/Noto+Serif+Devanagari
font_manager.fontManager.addfont(font_path)
prop = font_manager.FontProperties(fname=font_path)
plt.rcParams['font.family'] = 'sans-serif'
plt.rcParams['font.sans-serif'] = prop.get_name()
#---------------------------------------Printing the Heatmap------------------------------------------
cols = ['कंऊ', 'कंकन', 'कंकाल', 'कंग', 'कंगण', 'कंगणयाठ', 'कंगणा', 'कंगणी',
'कंगणु', 'कंगयारी', 'कंगर', 'कंगरमाला', 'कंगला', 'कंगाळ',
'कंगावणो', 'कंगियारी', 'कंगूरा', 'कंगोयर', 'कंगड़ोणा', 'कंघू']
import seaborn as sns
distances = [[ 1.00000012, 0.07712191, 0.14661103, -0.04143704, 0.53648712,
0.33697583, 0.53648712, 0.51686014, 0.38120874, 0.50693332,
0.45912105, 0.39092736, 0.37029334, 0.48355384, 0.08494762,
0.2027287 , 0.22532 , -0.13099329, 0.21541182, 0.2619344 ],
[ 0.07712191, 1. , 0.27505046, 0.02465715, 0.19377662,
0.1261098 , 0.19377662, 0.1506419 , 0.35335953, 0.20175425,
0.24165124, 0.28307295, 0.16849031, 0.0239366 , 0.07874829,
0.13574625, 0.20279602, 0.13992496, 0.07440536, 0.29719737],
[ 0.14661103, 0.27505046, 1. , -0.04620013, 0.33248773,
0.15105981, 0.33248773, 0.22782895, 0.32314968, 0.16231962,
0.33643136, 0.33366867, 0.06132669, 0.00628519, 0.31157723,
0.32549456, 0.24985954, 0.08681663, -0.0043968 , 0.30289415],
[-0.04143704, 0.02465715, -0.04620013, 1. , -0.03092548,
0.06609477, -0.03092548, -0.13675212, -0.02324197, -0.24876945,
-0.19765455, -0.09264191, 0.10586093, -0.03386144, -0.07041141,
-0.16070572, -0.11320979, 0.05005207, 0.06435453, -0.04384374],
[ 0.53648712, 0.19377662, 0.33248773, -0.03092548, 1. ,
0.29916139, 1. , 0.65163825, 0.72046704, 0.55254239,
0.57694138, 0.62017921, 0.42146252, 0.40582417, 0.13931256,
0.42310567, 0.34080061, 0.02983071, 0.21334639, 0.47694966],
[ 0.33697583, 0.1261098 , 0.15105981, 0.06609477, 0.29916139,
1. , 0.29916139, 0.54745869, 0.28604334, 0.39199968,
0.36999825, 0.2213295 , 0.26273593, 0.39979477, 0.15303509,
0.33649553, 0.09807743, 0.05601585, 0.2305386 , 0.40991256],
[ 0.53648712, 0.19377662, 0.33248773, -0.03092548, 1. ,
0.29916139, 1. , 0.65163825, 0.72046704, 0.55254239,
0.57694138, 0.62017921, 0.42146252, 0.40582417, 0.13931256,
0.42310567, 0.34080061, 0.02983071, 0.21334639, 0.47694966],
[ 0.51686014, 0.1506419 , 0.22782895, -0.13675212, 0.65163825,
0.54745869, 0.65163825, 1. , 0.71716835, 0.63264708,
0.62838955, 0.47028607, 0.33207874, 0.47275523, 0.16827085,
0.50378844, 0.26850763, -0.06614359, 0.25800855, 0.56002025],
[ 0.38120874, 0.35335953, 0.32314968, -0.02324197, 0.72046704,
0.28604334, 0.72046704, 0.71716835, 1. , 0.50603543,
0.5059674 , 0.52531186, 0.29890772, 0.30439026, 0.31332371,
0.46341207, 0.33670898, 0.1210591 , 0.1456821 , 0.45291205],
[ 0.50693332, 0.20175425, 0.16231962, -0.24876945, 0.55254239,
0.39199968, 0.55254239, 0.63264708, 0.50603543, 1. ,
0.55836697, 0.25994718, 0.31039424, 0.36613216, 0.24675051,
0.465611 , 0.23443568, 0.01218331, 0.37018659, 0.45373405],
[ 0.45912105, 0.24165124, 0.33643136, -0.19765455, 0.57694138,
0.36999825, 0.57694138, 0.62838955, 0.5059674 , 0.55836697,
1. , 0.44948247, 0.25360835, 0.39044196, 0.23445548,
0.59344035, 0.56251523, -0.01464187, 0.22015723, 0.61909768],
[ 0.39092736, 0.28307295, 0.33366867, -0.09264191, 0.62017921,
0.2213295 , 0.62017921, 0.47028607, 0.52531186, 0.25994718,
0.44948247, 1. , 0.3531896 , 0.22887981, 0.06463467,
0.3665741 , 0.42415992, 0.08162159, 0.08619286, 0.39534383],
[ 0.37029334, 0.16849031, 0.06132669, 0.10586093, 0.42146252,
0.26273593, 0.42146252, 0.33207874, 0.29890772, 0.31039424,
0.25360835, 0.3531896 , 1. , 0.76107077, -0.00676973,
0.24680215, 0.09632001, 0.00772719, 0.178872 , 0.29167667],
[ 0.48355384, 0.0239366 , 0.00628519, -0.03386144, 0.40582417,
0.39979477, 0.40582417, 0.47275523, 0.30439026, 0.36613216,
0.39044196, 0.22887981, 0.76107077, 1. , 0.00392713,
0.17269458, 0.0984515 , -0.09089949, 0.12039699, 0.30054512],
[ 0.08494762, 0.07874829, 0.31157723, -0.07041141, 0.13931256,
0.15303509, 0.13931256, 0.16827085, 0.31332371, 0.24675051,
0.23445548, 0.06463467, -0.00676973, 0.00392713, 1.00000012,
0.31029389, 0.00211672, 0.10704701, 0.04611979, 0.17345914],
[ 0.2027287 , 0.13574625, 0.32549456, -0.16070572, 0.42310567,
0.33649553, 0.42310567, 0.50378844, 0.46341207, 0.465611 ,
0.59344035, 0.3665741 , 0.24680215, 0.17269458, 0.31029389,
1. , 0.40896827, 0.10605786, 0.21322685, 0.62610233],
[ 0.22532 , 0.20279602, 0.24985954, -0.11320979, 0.34080061,
0.09807743, 0.34080061, 0.26850763, 0.33670898, 0.23443568,
0.56251523, 0.42415992, 0.09632001, 0.0984515 , 0.00211672,
0.40896827, 1. , 0.08140745, 0.10477526, 0.31258686],
[-0.13099329, 0.13992496, 0.08681663, 0.05005207, 0.02983071,
0.05601585, 0.02983071, -0.06614359, 0.1210591 , 0.01218331,
-0.01464187, 0.08162159, 0.00772719, -0.09089949, 0.10704701,
0.10605786, 0.08140745, 1. , 0.00525283, 0.08305563],
[ 0.21541182, 0.07440536, -0.0043968 , 0.06435453, 0.21334639,
0.2305386 , 0.21334639, 0.25800855, 0.1456821 , 0.37018659,
0.22015723, 0.08619286, 0.178872 , 0.12039699, 0.04611979,
0.21322685, 0.10477526, 0.00525283, 1. , 0.08586092],
[ 0.2619344 , 0.29719737, 0.30289415, -0.04384374, 0.47694966,
0.40991256, 0.47694966, 0.56002025, 0.45291205, 0.45373405,
0.61909768, 0.39534383, 0.29167667, 0.30054512, 0.17345914,
0.62610233, 0.31258686, 0.08305563, 0.08586092, 1. ]]
fig, ax = plt.subplots(figsize=(20, 20))
s = sns.heatmap(distances, square=True, annot=True, cbar=False, cmap='Blues', ax=ax)
s.set_yticklabels(cols)
s.set_xticklabels(cols)
hfont = {'fontname':'Helvetica'}
plt.xlabel('Words', **hfont)
plt.ylabel('Words', **hfont)
plt.xticks(rotation=90)
plt.yticks(rotation=0)
plt.rcParams.update({'font.size': 20})
plt.show()Actual outcome
Expected outcome
In the expected outcome, the highlighted label in the bug summary image should be rendered as कंगियारी. In the current output it is being rendered like कंगयिारी which is wrong.
Additional information
I observe that words with vowel markers that come before the consonant are being rendered incorrectly in the plot. This makes me believe that this might be due to some old font engine which is being used in matplotlib to render Unicode characters.
Operating system
Windows
Matplotlib Version
3.4.3
Matplotlib Backend
module://matplotlib_inline.backend_inline
Python version
3.9.7
Jupyter version
6.4.5
Installation
pip
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tacaswell commented on Dec 20, 2024
This is a known limitation which has on-going work to address.
attn @QuLogic .
QuLogic commented on Apr 10, 2026
The text-overhaul branch is now merged to main.