Creating Latex Labels¶
This example shows how to create a custom LatexLabel
class that uses a
third party Javascript library, KaTeX, in order to render LaTeX onto the plot.
import numpy as np
from bokeh.models import Label
from bokeh.plotting import figure, show
JS_CODE = """
import {Label, LabelView} from "models/annotations/label"
export class LatexLabelView extends LabelView
render: () ->
#--- Start of copied section from ``Label.render`` implementation
# Here because AngleSpec does units tranform and label doesn't support specs
switch @model.angle_units
when "rad" then angle = -1 * @model.angle
when "deg" then angle = -1 * @model.angle * Math.PI/180.0
panel = @model.panel ? @plot_view.frame
xscale = @plot_view.frame.xscales[@model.x_range_name]
yscale = @plot_view.frame.yscales[@model.y_range_name]
sx = if @model.x_units == "data" then xscale.compute(@model.x) else panel.xview.compute(@model.x)
sy = if @model.y_units == "data" then yscale.compute(@model.y) else panel.yview.compute(@model.y)
sx += @model.x_offset
sy -= @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
@_css_text(@plot_view.canvas_view.ctx, "", sx, sy, angle)
# ``katex`` is loaded into the global window at runtime
# katex.renderToString returns a html ``span`` element
katex.render(@model.text, @el, {displayMode: true})
export class LatexLabel extends Label
type: 'LatexLabel'
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__ = JS_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", plot_width=500, plot_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=35, y=445, x_units='screen', y_units='screen',
render_mode='css', text_font_size='16pt',
background_fill_color='#ffffff')
p.add_layout(latex)
show(p)