Creating LaTeX labels¶
This example shows how to create a custom LatexLabel
class that uses a
third-party JavaScript library, KaTeX, to render LaTeX onto the
plot.
import numpy as np
from bokeh.models import Label
from bokeh.plotting import figure, show
from bokeh.util.compiler import TypeScript
TS_CODE = """
import * as p from "core/properties"
import {Label, LabelView} from "models/annotations/label"
declare const katex: any
export class LatexLabelView extends LabelView {
model: LatexLabel
render(): void {
//--- Start of copied section from ``Label.render`` implementation
// Here because AngleSpec does units tranform and label doesn't support specs
let angle: number
switch (this.model.angle_units) {
case "rad": {
angle = -this.model.angle
break
}
case "deg": {
angle = (-this.model.angle * Math.PI) / 180.0
break
}
default:
throw new Error("unreachable code")
}
const panel = this.layout ?? this.plot_view.layout.center_panel
let sx = this.model.x_units == "data" ? this.coordinates.x_scale.compute(this.model.x) : panel.xview.compute(this.model.x)
let sy = this.model.y_units == "data" ? this.coordinates.y_scale.compute(this.model.y) : panel.yview.compute(this.model.y)
sx += this.model.x_offset
sy -= this.model.y_offset
//--- End of copied section from ``Label.render`` implementation
// Must render as superpositioned div (not on canvas) so that KaTex
// css can properly style the text
this._css_text(this.layer.ctx, "", sx, sy, angle)
// ``katex`` is loaded into the global window at runtime
// katex.renderToString returns a html ``span`` element
katex.render(this.model.text, this.el, {displayMode: true})
}
}
export namespace LatexLabel {
export type Attrs = p.AttrsOf<Props>
export type Props = Label.Props
}
export interface LatexLabel extends LatexLabel.Attrs {}
export class LatexLabel extends Label {
properties: LatexLabel.Props
__view_type__: LatexLabelView
constructor(attrs?: Partial<LatexLabel.Attrs>) {
super(attrs)
}
static {
this.prototype.default_view = LatexLabelView
}
}
"""
class LatexLabel(Label):
"""A subclass of the Bokeh built-in `Label` that supports rendering
LaTex using the KaTex typesetting library.
Only the render method of LabelView is overloaded to perform the
text -> latex (via katex) conversion. Note: ``render_mode="canvas``
isn't supported and certain DOM manipulation happens in the Label
superclass implementation that requires explicitly setting
`render_mode='css'`).
"""
__javascript__ = ["https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.6.0/katex.min.js"]
__css__ = ["https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.6.0/katex.min.css"]
__implementation__ = TypeScript(TS_CODE)
x = np.arange(0.0, 1.0 + 0.01, 0.01)
y = np.cos(2 * 2 * np.pi * x) + 2
p = figure(title="LaTex Demonstration", width=500, height=500)
p.line(x, y)
# Note: must set ``render_mode="css"``
latex = LatexLabel(
text="f = \\sum_{n=1}^\\infty\\frac{-e^{i\\pi}}{2^n}!",
x=40,
y=420,
x_units="screen",
y_units="screen",
render_mode="css",
text_font_size="21px",
background_fill_alpha=0,
)
p.add_layout(latex)
show(p)
See also
Extended examples of using KaTeX LaTeX with Bokeh labels are available in examples/custom/wrapped_extension_base/ and examples/custom/wrapped_extension_full/.
A similar example using MathJax to render LaTeX in a Bokeh label is available in examples/models/file/latex_extension_mathjax.py