Add dependency-free text renderers for go.Figure (text-utf/ascii/ansi/html)

Add four pure-Python, dependency-free plotly.io renderers that draw an existing
go.Figure as plain text:

- text-utf   — braille/block-char (default)
- text-ascii — 7-bit ASCII fallback
- text-ansi  — 24-bit truecolor ANSI escapes
- text-html  — self-contained class-based HTML fragment

Usable via fig.show(renderer="text-utf") (etc.). Supports scatter/scattergl
(lines & markers), bar (honouring orientation, with grouped fan-out), histogram,
and heatmap/histogram2d (colorscale-sampled density shading). Per-series colour is
taken from each trace's marker/line colour or the default qualitative palette.
Unsupported traces and undersized canvases degrade to a one-line note instead of
raising. Adds unit tests and a CHANGELOG entry.

Author: T4rk1n

CHANGELOG.md

@@ -4,6 +4,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Added
+- Add pure-Python, dependency-free text renderers `text-utf` (braille/block-char, default) and `text-ascii` (7-bit fallback) that draw an existing `go.Figure` as plain text — `fig.show(renderer="text-utf")` / `"text-ascii"`. Supports scatter/scattergl (lines & markers), bar (honouring `orientation`), and histogram (bins reproduced client-side, numpy-accelerated when available); multi-series bars fan out into sub-columns, unsupported traces and undersized canvases degrade to a one-line note instead of crashing, and output is written as forced UTF-8.
+- Add colour text renderers `text-ansi` (24-bit truecolor ANSI escapes) and `text-html` (self-contained class-based HTML fragment) — `fig.show(renderer="text-ansi")` / `"text-html"` — and `heatmap` / `histogram2d` trace support (density shaded via a colorscale-sampled ramp, `histogram2d` binned client-side). Each series is coloured from its own `marker`/`line` colour (normalized from `#hex`, `rgb()/rgba()`, or a CSS name) or the default qualitative palette.
+
 
 ## [6.9.0] - 2026-07-09
 

plotly/io/_renderers.py

@@ -467,6 +467,13 @@ def show(fig, renderer=None, validate=True, **kwargs):
 renderers["sphinx_gallery"] = SphinxGalleryHtmlRenderer()
 renderers["sphinx_gallery_png"] = SphinxGalleryOrcaRenderer()
 
+# Text renderers: text-utf (default), text-ascii, and the colour modes
+# text-ansi / text-html.
+# Registered via a hook so the _text subpackage owns its own renderer classes.
+from plotly.io._text import register_text_renderers  # noqa: E402
+
+register_text_renderers(renderers)
+
 # Set default renderer
 # --------------------
 # Version 4 renderer configuration

plotly/io/_text/__init__.py

@@ -0,0 +1,64 @@
+"""Text (Unicode/braille) renderers for ``go.Figure``.
+
+Draws an existing figure as a braille/block-char chart in plain text, as
+registered ``plotly.io`` renderer strings (``text-utf`` default, ``text-ascii``;
+plus the colour modes ``text-ansi`` and ``text-html``). Pure-Python, **no
+external dependency** — the braille + block-char rasterizer is built in here (see
+:mod:`~plotly.io._text.rasterizer`).
+
+Architecture ("one grid, many serializers"):
+
+* :mod:`~plotly.io._text.canvas` — Plotly-agnostic drawing surface -> abstract
+  cell grid.
+* :mod:`~plotly.io._text.serializers` — per-mode grid -> string.
+* :mod:`~plotly.io._text.adapters` — ``go.Figure`` -> Canvas calls.
+* :mod:`~plotly.io._text.renderers` — ``plotly.io`` registration.
+
+This ``__init__`` is the stable public surface of the subpackage;
+:mod:`plotly.io._renderers` imports :func:`register_text_renderers` from here.
+"""
+
+from __future__ import annotations
+
+from plotly.io._text.canvas import (
+    Canvas,
+    Cell,
+    CellGrid,
+    CellRole,
+    Tick,
+)
+from plotly.io._text.serializers import (
+    SERIALIZERS,
+    Serializer,
+    get_serializer,
+    register_serializer,
+)
+from plotly.io._text.adapters import (
+    ADAPTERS,
+    AdapterContext,
+    TraceAdapter,
+    figure_to_canvas,
+    get_adapter,
+    register_adapter,
+)
+from plotly.io._text.renderers import TextRenderer, register_text_renderers
+
+__all__ = [
+    "Canvas",
+    "Cell",
+    "CellGrid",
+    "CellRole",
+    "Tick",
+    "Serializer",
+    "SERIALIZERS",
+    "register_serializer",
+    "get_serializer",
+    "ADAPTERS",
+    "AdapterContext",
+    "TraceAdapter",
+    "register_adapter",
+    "get_adapter",
+    "figure_to_canvas",
+    "TextRenderer",
+    "register_text_renderers",
+]