Opacity bug fix for point and sphere actors

[SunTzunami]

Fixes #335

Earlier,

Now,

Earlier, opacity argument wasn't manipulating the opacity of point actors and sphere actors. That issue is resolved by this fix. Unit tests are included for the same.

[skoudoro]

Hi @SunTzunami,

It looks good to me. I just need to try it locally and then I will go ahead and merge your PR.

Thank you for this update

[skoudoro]

After looking more in detail into your fix, I think we should avoid using actor.GetProperty().SetOpacity(opacity). It seems not compatible with our architecture.
Ideally, in the function actor.sphere, we would check if opacity != 1. if yes, we should update the color array by adding a dimension if it is an Nx3, or by updating the last dimension if it is an Nx4.

I will merge your PR because it fixes the actor.point but we need a new PR to improve this version.

[skoudoro]

thank you @SunTzunami

[SunTzunami]

Hi @skoudoro. To make these fixes, I read the documentation for line actor (https://fury.gl/latest/_modules/fury/actor.html#line) as transparency worked for line actor. Line actor too uses actor.GetProperty().SetOpacity(opacity) to manipulate opacity so I assumed it'll be fine to use that for sphere and point actors too.

[skoudoro]

In both cases, it needs to be improved @SunTzunami.

if you look here, the 3 spheres have 3 differents opacities : 0.3, 04, 0.99. This is how we setup the opacities. actor.GetProperty().SetOpacity(opacity) do not update this array and override our values. Each object can have a different opacity which is impossible with actor.GetProperty().SetOpacity(opacity).

[SunTzunami]

@skoudoro thanks for the info. I'll try making a better fix.