Mesh3d plot disappears when opacity less than 1

NOTE: When I found and reported this bug, I was working on a Chromebook. After I wrote this, I noted this does not occur from Mac with Chrome (ver 74).

Please see my example code below. I am plotting offline. When I change the opacity to anything other than 1, the plot disappears. As evidenced by the hover info, the plot still exists; it's just not visible.

I tried a number of different colorscales with different alpha values. The result does not change.

I also tried working around the opacity issue by setting the opacity to 1 and then setting the colorscale alpha values to something less than 1. But the alpha values appear to have no effect.

I noticed some similar bugs such as 3741, 3744, and 3492. Despite their similarity, these bugs appear to be different from this issue I am reporting. They are also resolved.

Lastly, I note that this bug occurs on the latest versions of Chrome (i.e. 74). But it does not occur on earlier versions.

Postscript: I have subsequently noticed the occurrence of the same opacity bug for Scatter3d. I also note that there's no opacity problem for Scatter in 2d.

import numpy as np
from numpy import sin, cos, pi
import plotly
import plotly.graph_objs as go

def ellipsoid( a = 4, b = 3, c = 2, num_pts = 40):
    phi = np.linspace(0, 2 * pi, num=num_pts)
    theta = np.linspace(-pi / 2, pi / 2, num=num_pts)
    phi, theta = np.meshgrid(phi, theta)
    x = cos(theta) * sin(phi) * a
    y = cos(theta) * cos(phi) * b
    z = sin(theta) * c

    Ell = np.vstack((x.flatten(), y.flatten(), z.flatten()))

    ell_1 = go.Mesh3d(
        opacity = 0.99,
        colorscale = [ [0.0, 'rgb(255, 0, 0)'], [0.5, 'rgb(0, 255, 0)'], [1.0, 'rgb(0, 0, 255)'] ],
        intensity = z.flatten(),
        name = 'z',
        showscale = False,
        x = Ell[0, :].flatten(),
        y = Ell[1, :].flatten(),
        z = Ell[2, :].flatten(),
        alphahull = 0
    )
    axes_max = np.max( np.abs(Ell) )
    return ell_1, axes_max

def plot_it(data, mr):
    r = [-mr, mr]
    layout = go.Layout(
        autosize = False,
        width = 600,
        height = 600,
        margin = dict(
            l = 0,
            r = 0,
            b = 0,
            t = 0,
            pad = 4),
        scene = dict(
            aspectratio = go.layout.scene.Aspectratio(x=1, y=1, z=1),
            xaxis = dict(
                range=r,
                title='x'),
            yaxis = dict(
                range=r,
                title='y'),
            zaxis = dict(
                range=r,
                title='z' ))
    )

    fig = go.Figure(data=data, layout=layout)
    plotly.offline.plot(fig, filename='/home/chronos/user/Downloads/bug_mesh3d_opac.html')
    return

def test1():
    d, mx = ellipsoid()
    data = [d]
    plot_it(data, mx+2.)
    return

def main():
    test1()
    return

if __name__ == "__main__":
    main()

Riproduci l’esempio usando plotly.offline.plot con una traccia Mesh3d in Chrome, variando l’opacità e i valori alfa di colorscale; verifica anche il caso Scatter3d segnalato. Segui il percorso di rendering 3D per determinare perché la geometria rimane interattiva al passaggio del mouse ma invisibile, e considera conclusa l’issue quando i grafici Mesh3d e Scatter3d parzialmente opachi vengono renderizzati correttamente.