feat(bokeh): Server side HoverTool for rasterized/datashaded plots with selector

[hoxbro]

Previously, we sent all hover data to the front end, which could lead to significant overhead on larger plots. With this PR, the data is pushed server-side to the hover tool with a custom data model.

script

import itertools

import datashader as ds
import numpy as np
import pandas as pd
import panel as pn

import holoviews as hv
from holoviews.operation.datashader import datashade, dynspread, rasterize

hv.extension("bokeh")

num = 10000
seed = np.random.default_rng(1)


dists = {
    cat: pd.DataFrame(
        {
            "x": seed.normal(x, s, num),
            "y": seed.normal(y, s, num),
            "s": s,
            "val": val,
            "cat": cat,
        }
    )
    for x, y, s, val, cat in [
        (2, 2, 0.03, 0, "d1"),
        (2, -2, 0.10, 1, "d2"),
        (-2, -2, 0.50, 2, "d3"),
        (-2, 2, 1.00, 3, "d4"),
        (0, 0, 3.00, 4, "d5"),
    ]
}

df = pd.concat(dists, ignore_index=True)
df["y"] += 100  # Offset to distinguish x from y
points = hv.Points(df)


def dynspread_datashade(*args, **kwargs):
    return dynspread(datashade(*args, **kwargs))


def dynspread_rasterize(*args, **kwargs):
    return dynspread(rasterize(*args, **kwargs))


ops = (rasterize, dynspread_rasterize, datashade, dynspread_datashade)
aggs = (ds.min("s"), ds.by("cat"))
sels = (None, ds.min("s"))
# ops = (datashade,)
# aggs = (ds.by("cat"),)
# sels = (None,)
combinations = itertools.product(ops, aggs, sels)
plots = []
for op, agg, sel in combinations:
    title = f"{op.__name__.replace('_','+')}(agg={type(agg).__name__}, sel={type(sel).__name__ if sel else None})"
    plot = op(points, aggregator=agg, selector=sel).opts(
        tools=["hover"], title=title, width=400, height=400
    )
    plots.append(plot)

pn.panel(hv.Layout(plots).cols(4).opts(shared_axes=False)).servable()

[codecov]

Codecov Report

Attention: Patch coverage is 94.52055% with 16 lines in your changes missing coverage. Please review.

Project coverage is 88.79%. Comparing base (1a73b88) to head (48f91a5).

Files with missing lines	Patch %	Lines
holoviews/plotting/bokeh/raster.py	83.33%	10 Missing ⚠️
holoviews/operation/datashader.py	95.41%	5 Missing ⚠️
holoviews/element/raster.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6422      +/-   ##
==========================================
+ Coverage   88.76%   88.79%   +0.02%     
==========================================
  Files         323      323              
  Lines       68679    68885     +206     
==========================================
+ Hits        60963    61166     +203     
- Misses       7716     7719       +3     

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[hoxbro]

Don't understand this.

[philippjfr]

Not that it wasn't already but that's getting quite unwieldy.

[hoxbro]

Agree.

[philippjfr]

In that case please refactor 🙂

[hoxbro]

I'm not sure what you mean. Do you want it to be put into a method?

[hoxbro]

Refactored in 8f4378e

Which is what I think you mean

[philippjfr]

Let's remove the RGBA value by default when the index layer is enabled.

[hoxbro]

Let's remove the RGBA value by default when the index layer is enabled.

Done in 48f91a5