Transparent backgrounds (alpha channel) no longer working

[aerogt3]

Hello,

In vtk,js 19.2.5, I could set transparent background for the renderWindow:

renderer = vtkRenderer.newInstance({ background:(1,1,1,1)});

However, in 24.8.0, this same line no longer works, producing an error:
Uncaught RangeError: Invalid initial number of values for array (background)

Is there any reason the alpha channel was dropped? This was a very cool feature, especially for "dark mode" where the transparency allowed for the page/user to effectively set the background.

[jourdain]

The issue is probably coming from the setter but technically we still expect rgba.

Thanks for reporting that issue.

[floryst]

We likely need to directly implement setBackground and getBackground in Viewport/Renderer instead of using the macros. Reason being is that we support setBackground(r, g, b, a = 1), so optional alpha value. The macro setGetArray currently doesn't support such functionality, nor do I think it's a good idea to add such complexity for such a specific use-case...

The alpha channel was never dropped. Instead, the setGetArray mixin was updated with stricter array handling, and setBackground relied on loose array handling (i.e. can take a 3-tuple or 4-tuple).

[finetjul]

Currently the implemented signature is setBackground(r = 1, g = 1, b =1, a = 1) or setBackground(rgba) where rgba is an array of 0 to 4 elements.

You can do the following to have a transparent background:

renderer = vtkRenderer.newInstance({ background:[1,1,1,0]});

[aerogt3]

Hi Julien,

This works in v19.2.5, but not in v24.8.0. At some point, this functionality was removed or altered. The line you have suggested produces the following messages:

[finetjul]

Ah, gotcha.

This is because setBackground() is first defined in motherclass vtkViewport as array of 3 (hence the error) and then redefined in child class vtkRenderer as array of 4.

Here are 3 options:

• Quick fix: do not initialize background in constructor but via the setter: renderer = vtkRenderer.newInstance(); renderer.setBackground(1,1,1,0);
• wait until Refactor constructors #2409 is merged (not so quick)
• Reconsider usefulness of deriving vtkViewport background member variable in vtkRenderer: @aronhelser, @martinken, @jourdain