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()

Reproduisez l’exemple avec plotly.offline.plot et un trace Mesh3d dans Chrome, en faisant varier l’opacité et les valeurs alpha de colorscale ; vérifiez également le cas Scatter3d signalé. Suivez le chemin de rendu 3D afin de déterminer pourquoi la géométrie reste interactive au survol mais demeure invisible, et considérez l’issue comme terminée lorsque les graphiques Mesh3d et Scatter3d partiellement opaques se rendent correctement.