Enable/disable hover_fill_alpha on multi_polygons

Community Support
,
1

Hello,

i have a code where i plot a large amount of polygons using the multi_polygons glyph. If i use the hover_fill_alpha parameter, things get laggy as the whole glyph gets redrawn everythime the mouse goes to another polygon, which is acceptable. I would like to be able to enable/disable this feature.

I first thought of having two glyphs, one with it, and one without the alpha.

The glyph without the alpha runs smooth on its own, but if it has a glyph with the alpha, even though it is hidden, things are laggy. Is there a way to disable those computation when a the glyph is hidden? How would you do it?

from bokeh.plotting import figure
from bokeh.models import (
    HoverTool,
    ColumnDataSource,
)
import panel as pn


def get_shapes():
    shapes_list = []
    colors_list = []

    count_x = 230

    for i in range(count_x):
        for j in range(count_x):
            shapes_list.append(([i, i + 1, i + 1, i], [j, j, j + 1, j + 1]))
            colors_list.append(
                (
                    int(255 * i / count_x),
                    int(255 * j / count_x),
                    int(255 * i / count_x),
                    255,
                )
            )

    return shapes_list, colors_list


coords, colors = get_shapes()
xs = [c[0] for c in coords]
ys = [c[1] for c in coords]

edge_colors = [(c[0] * 0.9, c[1] * 0.9, c[2] * 0.9, c[3]) for c in colors]

TOOLTIPS = [
    ("Volume ID", "@volume_name"),
]

display_as_polygons = True

MyHover = HoverTool(tooltips=TOOLTIPS)
xs_dict = [[{"exterior": e, "holes": []}] for e in xs]

ys_dict = [[{"exterior": e, "holes": []}] for e in ys]

xs = [[[p["exterior"], *p["holes"]] for p in mp] for mp in xs_dict]
ys = [[[p["exterior"], *p["holes"]] for p in mp] for mp in ys_dict]

source_polygons = ColumnDataSource(
    {
        "xs": xs,
        "ys": ys,
        "color": colors,
        "edge_color": edge_colors,
        "volume_name": list(range(len(colors))),
    }
)

# Create a new figure with specified tools
p = figure(
    tools="pan,wheel_zoom,box_select,reset",
    width_policy="max",
    height_policy="max",
    match_aspect=True,
)
p.add_tools(MyHover)

p.multi_polygons(
    xs="xs",
    ys="ys",
    line_width=2,
    color="color",
    # hover_fill_alpha=.6,
    # hover_fill_color="edge_color",
    line_color="edge_color",
    source=source_polygons,
)
p.multi_polygons(
    xs="xs",
    ys="ys",
    line_width=2,
    color="color",
    hover_fill_alpha=.6,
    # hover_fill_color="edge_color",
    line_color="edge_color",
    source=source_polygons,
    visible=False
)

p.title.text = "Plot with polygons"

pn.pane.Bokeh(p, sizing_mode="stretch_both").show()

Thanks,
Thibault

2

This version is super performant for me:

r = p.multi_polygons(
    xs="xs",
    ys="ys",
    line_width=2,
    color="color",
    line_color="edge_color",
    source=source_polygons,
)

r.hover_glyph = None  # explicitly disable a hover glyph entirely

# p.multi_polygons(
#     xs="xs",
#     ys="ys",
#     line_width=2,
#     color="color",
#     hover_fill_alpha=.6,
#     hover_fill_color="edge_color",
#     line_color="edge_color",
#     source=source_polygons,
#     visible=False
# )

But if I uncomment the second block, things slow down. I suppose I might consider that a bug considering the visible=False. Please open a GitHub Issue with full details.

All that said, is this output with quads actually representative of your real use-case? If your actual need is to draw quads you will see better performance with quad or block or one of the other glyphs optiomized for drawing axis-aligned boxes.

3

I had thought possibly that restricting the hover tool to just the first renderer might help:

MyHover.renderers = [r]

i.e. maybe it was the inspection event that was errantly being responded to regardless of overall visibility, but this did not seem to make a difference. More investigation will be necessary.

4

As a brute-force workaround, you might try having two separate plots rather than separate glyphs on one plot, and toggling the visibility of the plots themselves.

5

Hey,

thanks for your answer,

Yes this is exactly my point it works fine without it, i just openned the issue then (Multi_polygons glyph hover alpha still computed when non visible · Issue #14678 · bokeh/bokeh · GitHub).

No the real use case actually uses the polygons eventually with holes too, so the multi_polygons does a good job here :slight_smile:

I tried editing the renderers, but my understanding on the non conclusive result is that the hover alpha feature is working with another hover tool.

I will go on the brute force solution in the mean time indeed

Thibault

1 Like