enhance performance of color mapping

[muendlein]

• issues: fixes Improve color mapping performance #14555
• tests added / passed

[muendlein]

Due to string operations the current code path for color mapping is not really efficient.
Speed up with this PR is roughly 5x.

Before firefox:

After firefox:

Before chrome:

After chrome:

Code:

import numpy as np

from bokeh.io import curdoc
from bokeh.models.sources import ColumnDataSource
from bokeh.plotting import figure
from bokeh.transform import linear_cmap

n_samples = 500000

x = np.linspace(0, 10, n_samples)
y = np.sin(x)
c = np.sin(x)

cds = ColumnDataSource(data={"x": x, "y": y, "c": c})

colors = ["#37bf06", "#a0bf06", "#bfb006", "#eb9809", "#d12008", "#a80505", "#400303"]

p = figure(output_backend="webgl")
p.scatter(x="x", y="y", source=cds, line_color=None, size=5, fill_color=linear_cmap(
    "c",
    palette=colors,
    nan_color= 'rgba(255, 0, 0, 0.5)',
    low=-1,
    high=1))


curdoc().add_root(p)

[codecov]

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[mattpap]

The main reason for that existing approach is to preserve color values as much as possible in the output, e.g. for SVG backend. But I think performance is more important in the case of color mapping than other concerns.

[philippjfr]

But I think performance is more important in the case of color mapping than other concerns.

Agree!

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.