Metadata-Version: 2.4
Name: curved-text
Version: 0.5.0
Summary: Draw text along an arbitrary curve in matplotlib, with arc-length positioning and a perpendicular offset.
Author-email: "Joseph J. Thiebes" <joseph@thiebes.org>
License-Expression: MIT
Project-URL: Homepage, https://github.com/thiebes/curved-text
Project-URL: Documentation, https://thiebes.github.io/curved-text/
Project-URL: Source, https://github.com/thiebes/curved-text
Project-URL: Issues, https://github.com/thiebes/curved-text/issues
Project-URL: Changelog, https://github.com/thiebes/curved-text/blob/main/CHANGELOG.md
Keywords: matplotlib,text,annotation,label,curve,visualization
Classifier: Development Status :: 4 - Beta
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.9
Classifier: Programming Language :: Python :: 3.10
Classifier: Programming Language :: Python :: 3.11
Classifier: Programming Language :: Python :: 3.12
Classifier: Programming Language :: Python :: 3.13
Classifier: Framework :: Matplotlib
Classifier: Topic :: Scientific/Engineering :: Visualization
Classifier: Intended Audience :: Science/Research
Requires-Python: >=3.9
Description-Content-Type: text/markdown
License-File: LICENSE
Requires-Dist: matplotlib>=3.5
Requires-Dist: numpy>=1.20
Provides-Extra: test
Requires-Dist: pytest>=7.0; extra == "test"
Provides-Extra: examples
Requires-Dist: seaborn>=0.11; extra == "examples"
Requires-Dist: pandas>=1.3; extra == "examples"
Provides-Extra: docs
Requires-Dist: sphinx>=7.0; extra == "docs"
Requires-Dist: myst-parser>=2.0; extra == "docs"
Requires-Dist: furo>=2024.1.29; extra == "docs"
Dynamic: license-file

# curved-text

[![CI](https://github.com/thiebes/curved-text/actions/workflows/ci.yml/badge.svg)](https://github.com/thiebes/curved-text/actions/workflows/ci.yml)
[![Docs](https://github.com/thiebes/curved-text/actions/workflows/docs.yml/badge.svg)](https://thiebes.github.io/curved-text/)

Draw text that follows an arbitrary curve in [matplotlib](https://matplotlib.org/).

Label a curve along its own path instead of in a legend, so the reader's eye
never leaves the data to read a colour key. The figure below shows the
difference: a legend on the left, and the same lines labelled along their paths
on the right.

![A legend on the left, the same lines labelled along their paths on the right](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/01_direct_labeling.png)

The label is recomputed every time the figure is drawn, so it keeps following
the curve through layout changes, resizing, and interactive panning or zooming.

## When it fits

- The curve `(x, y)` must be ordered along its length, so each point comes after
  the one before it, and it must have at least two points.
- The curve should be smooth relative to the text size. Label a smoothed or
  fitted trend line, not raw noisy samples. Each letter follows the direction of
  the curve under it, so where the curve turns back on itself within the width of
  a single letter, as noisy data does, the letters overlap.

## Install

```bash
pip install curved-text
```

To work from a clone, install it in editable mode:

```bash
pip install -e .
```

## Usage

```python
import numpy as np
import matplotlib.pyplot as plt
from curved_text import curved_text

x = np.linspace(0, 2 * np.pi, 400)
y = np.sin(x)

fig, ax = plt.subplots()
ax.plot(x, y)
curved_text(ax, x, y, "text that follows the curve",
            pos=0.5, anchor="center", offset=6.0, color="C3")
plt.show()
```

![A label following a sine wave](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/02_sine_hello.png)

### Placement

Three independent parameters control where the label sits:

- `pos` sets where the label is anchored along the curve, as a fraction of the
  curve's length. `0.0` is the first point, `1.0` is the last.
- `anchor` sets which part of the label lands at `pos`: `"start"`, `"center"`,
  or `"end"`.
- `offset` shifts the label off the curve, measured in typographic points. The
  shift is perpendicular to the curve. A positive value sits above a
  left-to-right curve.

The figure below sweeps `pos` from the first point to the last. The green dot
marks the anchor point in each panel.

![A label at five positions along a curve](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/03_pos_sweep.png)

If the label runs past either end of the curve, it is not cut off. The curve
continues straight in the direction it had at that end, and the extra letters
sit on that straight line.

### The function and the class

The object form is also available:

```python
from curved_text import CurvedText

CurvedText(x, y, "along the curve", ax, pos=0.2, anchor="start", offset=4.0)
```

Note the order of the axes argument. The `CurvedText` class takes it after `x,
y, text`, matching `matplotlib.text.Text`. The `curved_text` function takes it
first, matching matplotlib's axes-first helper functions.

Any extra keyword arguments (`color`, `fontsize`, `alpha`, `fontfamily`, ...)
pass through to each per-character glyph and each mathtext run.

## Features

### Mathtext

A `$...$` run in the label is laid out by matplotlib's
[mathtext](https://matplotlib.org/stable/users/explain/text/mathtext.html)
engine and then bent along the curve the same way plain text is. Every part of
the expression follows the curve, down to the bars in fractions and the
overlines in radicals, so fractions, radicals, and large brackets stay joined
together at any curvature. Plain and math runs mix freely in one string:

```python
curved_text(ax, x, y, r"flux $\propto \sqrt{D_{\mathrm{eff}}}\,(L/L_0)^2$",
            pos=0.5, anchor="center", offset=8.0)
```

![A mathtext expression following a sine wave](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/10_mathtext.png)

Pass `parse_math=False` to treat dollar signs literally. Tall expressions
compress vertically on the inside of tight bends, so choose the text size to
suit the curvature. `text.usetex` is not supported.

Plain words and math runs in one label share a single baseline, so the math
symbols sit level with the surrounding letters and a superscript lifts only the
exponent, not the body -- the alignment is built in, not tuned:

```python
curved_text(ax, x, y, r"mass $m$ and speed $c$ give $E = mc^2$")
```

![Plain words and math runs on one shared baseline along a curve](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/15_mixed_alignment.png)

### Casing behind the label

Set `box` to draw a casing behind the label. The casing is a band that follows
the curve under the letters, at the label's height. It keeps the label readable
where it crosses the lines it labels. Because it is a single fill, it covers
plain text and mathtext alike:

```python
curved_text(ax, x, y, r"signal $s(t) = A\,e^{-t/\tau}$", box=True)
```

`box` accepts `True`, a colour string, or a dict with these keys:

| Key | Meaning | Default |
| ------- | ------------- | ------------- |
| `color` | Fill colour of the band | white |
| `pad` | Band height, as a multiple of the tallest glyph's height | `1.1` |
| `alpha` | Opacity of the band | `1.0` |

![A label cleared from the lines it crosses by a white casing](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/11_box.png)

For a lighter casing that hugs each letter instead, pass a white `withStroke`
through matplotlib's
[`path_effects`](https://matplotlib.org/stable/users/explain/artists/patheffects_guide.html).
Path effects reach every letter and every mathtext run, as they do on any
`Text`. Because each letter is stroked on its own, a wide stroke makes
neighbouring letters blur together, so use `box` for solid coverage under plain
text:

```python
import matplotlib.patheffects as pe

curved_text(ax, x, y, r"signal $s(t) = A\,e^{-t/\tau}$",
            path_effects=[pe.withStroke(linewidth=4, foreground="white")])
```

The figure below shows the difference on the same plain-text label: a wide
stroke per character on top, the single `box` fill on the bottom.

![A wide per-character stroke leaves gaps; a box fill covers cleanly](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/12_box_vs_stroke.png)

### Even spacing on tight bends

Letters are placed one after another by their own widths, so where the curve
bends sharply they crowd together on the inside of the bend, because each rigid
letter box fans into its neighbour there. Set `crowding="curvature"` to open an
even letterspacing gap that grows with the local curvature, so the inside edges
stop colliding:

```python
curved_text(ax, x, y, "winding", crowding="curvature")
```

The gap is the same between every pair of letters, so the tracking stays even.
It also has a deadband: a gentle bend or a straight run stays below it and is
left unchanged, so only genuinely crowded text is spaced out. The default is
`crowding="none"`, which leaves the spacing as the letters' own widths set it.

The figure below shows both regimes. Top row: a sharp bend, where the correction
visibly separates the letters. Bottom row: a gentle bend of the same letters,
left untouched because it falls below the deadband.

![A sharp bend with crowded letters spaced out, a gentle bend left unchanged](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/13_crowding.png)

### Choosing what rides the curve

By default the text straddles the curve (`valign="center"`). Use `valign` to pick
a different line: `"baseline"` runs the text baseline along the curve so the body
sits above it, while `"ascender"` and `"descender"` ride the top or bottom of the
text -- handy for hanging a label below a curve or sitting it above one:

```python
curved_text(ax, x, y, "Amplitude", valign="baseline")
```

The shift is a single font metric applied to the whole label, so it never
disturbs the spacing or the alignment of plain text with mathtext. Combine it
with `offset` to lift the chosen line clear of the curve.

![The same word on a curve under each valign option](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/14_valign.png)

### Works with seaborn, pandas, and other matplotlib-backed libraries

`curved_text` needs only a `matplotlib.axes.Axes`, so it works with any library
that draws on matplotlib. seaborn's axes-level functions return an `Axes`, its
figure-level functions expose one through `.axes`, and `pandas`
`DataFrame.plot` returns an `Axes` as well. Pass that axes in directly:

```python
import seaborn as sns

ax = sns.lineplot(data=df, x="x", y="y")
curved_text(ax, df["x"], df["y"], "along the curve",
            pos=0.5, anchor="center", offset=6.0)
```

![A label drawn on a seaborn axes](https://raw.githubusercontent.com/thiebes/curved-text/main/examples/images/09_seaborn_pandas.png)

## How it works

Each character (and each `$...$` run) is a child artist drawn from its glyph
outline and placed so a single shared text baseline follows the curve. A plain
character is turned rigidly to follow the line: instead of reading the curve's
slope at a single point, the package draws a straight line across the width of
that one letter and tips the letter to match. Averaging over the letter's width
this way keeps neighbouring letters smooth even when the curve is drawn from only
a few points, and sharing one baseline keeps plain text and mathtext level.

All of this is measured in display space, that is, in pixels on the final figure
after every scaling step. So the spacing and the perpendicular offset stay
correct at any DPI and figure size. The layout is redone on every draw, which is
why the label keeps up with resizing and with interactive pan or zoom.

## Related

[matplotlib-label-lines](https://github.com/cphyc/matplotlib-label-lines) labels
one or many lines inline at a chosen or automatically picked point, each label
rotated to the local slope. It is the quickest way to replace a legend across a
set of lines. `curved-text` solves the adjacent problem: making a single string
(plain or mathtext) follow the curve character by character, with arc-length
placement and a perpendicular offset, redone on every draw. Reach for
label-lines to drop legend labels onto several lines, and for curved-text to
make text ride a path. In the ggplot2 world,
[geomtextpath](https://github.com/AllanCameron/geomtextpath) covers similar
text-on-path ground.

For matplotlib users coming from LaTeX: this is matplotlib's version of TikZ's
`text along path` decoration (from `decorations.text`). The mapping is close.
`pos` and `anchor` do the work of `text align` and the indents, `offset` does
the work of `raise`, and overrunning text rides the straight tangent extension
instead of being cut off at the path's end.

## Documentation

Full documentation, including the API reference and the design notes, is at
[thiebes.github.io/curved-text](https://thiebes.github.io/curved-text/). More
worked examples are in the
[example gallery](https://github.com/thiebes/curved-text/tree/main/examples).

## Contributing

Bug reports, feature requests, and pull requests are welcome. See
[CONTRIBUTING.md](https://github.com/thiebes/curved-text/blob/main/CONTRIBUTING.md)
for the development install, how to run the tests, linting, and the rest of the
workflow. By participating you agree to the
[Code of Conduct](https://github.com/thiebes/curved-text/blob/main/CODE_OF_CONDUCT.md).

## Development and AI use

Generative AI tools were used to develop and maintain this package. The author
(the sole maintainer) directed the design and reviewed, tested, and approved
every change before committing it.

- **Design and direction.** The architecture and the design decisions were the
  maintainer's: the chord-across-advance placement, the `_CurveFrame`
  display-space geometry, tangent-extension overflow, and the choice to support
  mathtext by bending glyph outlines along the curve. The mathtext feature was
  iterated against real problems found in use, including the baseline-alignment
  fix and the move from a per-character stroke to a single box casing once the
  per-letter halo was found to leave gaps. AI assisted in drafting the design
  documents and the implementation against these decisions.
- **Code.** The implementation in `src/curved_text/` was drafted with
  substantial AI assistance against that design, then reviewed and revised by
  the maintainer. Correctness, cross-version compatibility (the test suite runs
  against a matplotlib floor and a pre-release), packaging, and the release
  process were the maintainer's responsibility.
- **Tests.** The test suite in `tests/` was drafted with AI assistance and
  reviewed by the maintainer, and is run in CI on every change.
- **Documentation.** The README, API reference, and example gallery prose were
  drafted with AI assistance and edited by the maintainer.
- **How AI was used.** Primarily conversational and agentic drafting with
  Anthropic's Claude. The maintainer provided the problem framing, the design
  decisions, and the final review.

No AI-generated content was committed without human review.

## License

MIT
