bangla-render 0.1.1

Bengali text rendering for Matplotlib & Seaborn using Qt/HarfBuzz

🇧🇩 bangla-render

Bengali Text Rendering for Matplotlib & Seaborn (with full OpenType shaping)

bangla-render is the first open-source Python library that enables fully correct Bengali text rendering inside Matplotlib and Seaborn.

Matplotlib cannot shape Bengali text — it does not use HarfBuzz and therefore fails with:

• Matra (ি, ী, ু, ূ, ৃ)
• Reph (র্)
• Juktakkhor (জ্ঞ, ক্ষ, ন্দ, ত্ম, ন্ত …)
• GSUB/GPOS OpenType shaping

So Bengali titles, axis labels, annotations, and heatmap text become broken, disjoint, or scrambled.

💡 bangla-render solves this completely. It uses Qt’s HarfBuzz engine to shape Bengali correctly, renders it into an RGBA image, and overlays it into Matplotlib using OffsetImage, bypassing Matplotlib’s broken text renderer entirely.

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✨ Features

✔ Full Bengali OpenType shaping

• Correct matra placement
• Proper conjunct formation
• Reph, rafar, vowel signs
• Multi-line paragraph shaping
• True Unicode (no ANSI/Bijoy hacks)

✔ High-level Matplotlib API

br.set_bangla_title(ax, "বাংলা শিরোনাম")
br.set_bangla_xlabel(ax, "এক্স অক্ষ")
br.set_bangla_ylabel(ax, "ওয়াই অক্ষ")
br.text(ax, 0.5, 0.5, "মাঝখানে", coord="axes")

✔ Heatmap and confusion-matrix support

br.add_bangla_in_cell(ax, row, col, "খুশি", rows, cols)

✔ Automatic layout engine

apply_bangla_layout() adjusts margins so titles & labels never overlap.

✔ Works everywhere

• Matplotlib
• Seaborn
• Jupyter / VS Code
• Windows, Mac, Linux
• Any backend (Agg, Tk, Qt, etc.)

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🔍 Before & After Comparison

Line Plot

Default Matplotlib	With bangla-render

Heatmap

Before	After

Confusion Matrix

Before	After

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🔥 Why This Library Exists

Matplotlib cannot shape Indic scripts. Even with Bangla fonts installed, it produces:

• Disjoint characters
• Wrong glyph order
• Broken juktakkhor
• Incorrect matra positioning

Existing “solutions” only work for very simple words like ভয়, রাগ — but fail completely for:

• খুশি
• দৃষ্টিভঙ্গি
• শ্রদ্ধা
• ব্যবস্থাপনা
• হাস্যোজ্জ্বল
• পর্যালোচনায়
• And any real paragraph

Before bangla-render, there was:

• No PyPI library
• No correct Bengali shaping
• No Seaborn heatmap support
• No way to set Bengali xlabel/ylabel/title
• No Unicode-safe method

People relied on:

• Bijoy/ANSI hacks
• Exporting PNG text manually
• Inconsistent positioning
• Broken glyph rendering

bangla-render fills this gap for the first time.

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🎯 Our Contributions

1️⃣ First fully working Bengali renderer for Matplotlib

Using a complete pipeline:

• Qt (PySide6)
• HarfBuzz shaping
• QPainter → QImage
• NumPy array
• Matplotlib AnnotationBbox overlay

2️⃣ Easy-to-use Bengali plotting API

Drop-in replacements:

• Title
• X-axis label
• Y-axis label
• Arbitrary annotations (br.text)
• Cell text for heatmaps / confusion matrices

3️⃣ Automatic layout correction

apply_bangla_layout() balances left/right/bottom/top margins automatically.

4️⃣ Seaborn integration

Works naturally with Seaborn heatmaps.

5️⃣ Complete test suite

Covers:

• Simple words
• Complex conjuncts
• Paragraphs
• Line plots
• Heatmaps
• Confusion matrices
• Before/after rendering comparison

6️⃣ Fully Unicode-based

No image hacks or external binaries.

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📦 Installation

(Currently for local use; PyPI version coming soon.)

pip install PySide6
git clone https://github.com/mbs57/bangla-render.git
cd bangla-render
pip install -e .

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🧪 Example — Line Plot

import matplotlib.pyplot as plt
import bangla_render as br

fig, ax = plt.subplots(figsize=(5,4))
br.apply_bangla_layout(fig)

ax.plot([1,2,3], [3,1,4])

br.set_bangla_title(ax, "বাংলা লাইন প্লট")
br.set_bangla_xlabel(ax, "এক্স অক্ষ")
br.set_bangla_ylabel(ax, "ওয়াই অক্ষ")

plt.show()

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🎨 Example — Heatmap

import seaborn as sns
import numpy as np
import matplotlib.pyplot as plt
import bangla_render as br

data = np.random.rand(3,3)
words = [
    ["খুশি","রাগ","আশা"],
    ["ভয়","বিস্ময়","শান্তি"],
    ["ঘৃণা","আনন্দ","সুখ"]
]

fig, ax = plt.subplots(figsize=(6,6))
br.apply_bangla_layout(fig)

sns.heatmap(data, ax=ax, cbar=True, xticklabels=False, yticklabels=False)

rows, cols = data.shape
for i in range(rows):
    for j in range(cols):
        br.add_bangla_in_cell(ax, i, j, words[i][j], rows, cols)

br.set_bangla_title(ax, "বাংলা হিটম্যাপ")
br.set_bangla_xlabel(ax, "প্রেডিক্টেড ক্লাস")
br.set_bangla_ylabel(ax, "সত্যিকারের ক্লাস")

plt.show()

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🧩 API Overview

Title / Axis Labels

• set_bangla_title(ax, text, font_size=...)
• set_bangla_xlabel(ax, text, font_size=...)
• set_bangla_ylabel(ax, text, font_size=...)

General Text

• bangla_text(ax, x, y, text, coord="axes", ...)

Heatmap / Matrix Text

• add_bangla_in_cell(ax, row, col, text, rows, cols)

Layout

• apply_bangla_layout(fig, left=..., right=..., bottom=..., top=...)

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🏗 How It Works

• Qt Text Engine (PySide6) → HarfBuzz
• Renders shaped text into QImage
• Converted to NumPy RGBA array
• Inserted into Matplotlib with AnnotationBbox
• Layout corrected via figure metrics

This bypasses Matplotlib’s broken Indic rendering pipeline entirely.

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🧪 Test Suite

Included under tests/:

• Simple words
• Complex juktakkhor
• Paragraphs
• Line plot
• Heatmap
• Confusion matrix
• Before/after images

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📚 Roadmap

• PyPI release
• Extend to Hindi / Tamil / Telugu / Malayalam
• Mixed Bengali + MathText support
• Level-B backend integration for direct native support
• Submit paper to JOSS (Journal of Open Source Software)

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📄 License

MIT License — free for personal, academic, and commercial use.

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⭐ Acknowledgement

This project aims to make scientific and data visualization more accessible for millions of Bengali speakers, helping students, educators, analysts, and researchers present data in their native language.