enh: Add hover filter

[hoxbro]

Fixes the last point in #6515

WIP, but to test if everything works with bokeh/bokeh#14484 (comment)

Screencast.From.2025-06-26.15-13-19.mp4

Details

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 = (rasterize,)
aggs = (ds.min("s"), )
sels = (ds.min("s"),)
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()