Vedo: Color map with alpha values disables interaction events

[nantille]

In the recent example called slice-plane, the code works as expected.

However, if you set a color map with alpha values, it doesn't work anymore.

In my case, I created a color map with hundreds of opaque (alpha 1.0) rgb colors and only one transparent (alpha 0.0) color. Then I built a LUT with that color map. Setting this color map disables interaction events, even if pickable(True) is set.

I tried first setting a LUT with slice._mapper.SetLookupTable(lut) and then with vedo's cmap slice.cmap(color_map, alpha=alpha_map).

[nantille]

Here's the modified code of the above example to reproduce the issue:

"""Slice a Volume with an arbitrary plane
click the plane to get the scalar value"""
from vedo import *

vol = Volume(datadir+'embryo.slc').alpha([0,0,0.5]).c('hot_r')
vol.pickable(False).addScalarBar3D(title='Voxel intensity', c='k')

# Fails to be pickable because of alpha map
sl = vol.slicePlane(origin=vol.center(), normal=(0,1,1))
# Hide black
alpha_map = [0.0, 1.0, 1.0, 1.0, 1.0]
sl.cmap('viridis', alpha=alpha_map).lighting('ambient').addScalarBar(title='Slice')
sl.pickable(True)

plt = show(vol, sl, __doc__, axes=3, interactive=False)

def func(mesh):
    print('Hey', mesh.name)
    ptid = mesh.closestPoint(mesh.picked3d, returnPointId=True)
    val = arr[ptid]
    txt = precision(mesh.picked3d, 3) + f"\nvalue = {val}"
    vpt = Sphere(mesh.points(ptid), r=1, c='pink').pickable(0)
    vig = vpt.vignette(txt, s=5, offset=(20,10)).followCamera()
    msg = Text2D(txt, pos='bottom-left', font="VictorMono")
    plt.remove(plt.actors[-3:], render=False) # remove the last 3
    plt.add([vpt, vig, msg])                  # add the new ones

arr = sl.getPointArray()
plt.actors += [None,None,None] # holds sphere, vignette, text2d
plt.mouseLeftClickFunction = func
plt.resetcam = False
interactive()

[marcomusy]

Hi Nicolas - unfortunately this seems to be a bug in vtk9 versions.
In fact your above example (nice idea btw to hide low values in the slice!) works fine in vtk 8.1.2 | python 3.7
I'll investigate it with vtk people but I need to make sure it's not related to vedo.
I'll keep you informed.

PS: your output image seems to lack antialising...

do you know why so?

[nantille]

Hi Marco, thanks for investigating this nasty bug! Ugh...then I suppose I'll install vtk 8 and py37 temporarily. Good to know that it's a regression.

I need to be able to clip and hide parts of a volume (even on a slice like this) with a color map. And then I can do more advanced stuff with that.

I don't know why AA is off by default, but I can turn it on with settings.useFXAA = True

[nantille]

I confirm it works with vtk8, py37 and latest vedo (pip install -U git+https://github.com/marcomusy/vedo.git).

[marcomusy]

I found the problem and submitted an issue to vtk developers... if they cannot fix it , it shouldnt be difficult to have a work around in vedo..

[marcomusy]

As a temporary fix you can set

# Hide black
alpha_map = [0.0, 1.0, 1.0, 1.0, 1.0]
sl.cmap('viridis', alpha=alpha_map).lighting('ambient').addScalarBar(title='Slice')
sl.ForceOpaqueOn()

[nantille]

Great fix for VTK 9, thank you! I feared that ForceOpaqueOn would also force black to opaque but it keeps transparency as desired. I suppose we can close this because there's a way to fix the regression.