Dear Florian,

thank you for reporting this bug. For me, it seems like that the layer property has also influence in the 3D rendering window, which shouldn't be the case.

You are right, depth sorting works only within non-opaque objects but not with multiple objects in the scene. This is a general limitation of this approach.

However, we provide another option for correct transparency rendering when using the Standard Multi Widget, which might be helpful for you. The option can be found in the "Window" > "Preferences..." menu.
Select "Editor" > "Standard Multi Widget" and chose "Enable Depth Peeling" in the Rendering Mode drop down menu. Then restart MITK and load your surfaces and change the opacity.

We tried the depth peeling approach with the vtk tooth surfaces you provided and it worked.

Best,
Sandy

Changed status to WORKSFORME.

There are two issues here, which work with correct settings:

(1) Intra-object transparency
You must either enable the depth sorting property or depth peeling in the preferences.

(2) Inter-object transparency
If you are using the depth sorting property you have to ensure that objects in the front have a higher layer (property) than objects in the back. This is a feature (not a bug) but it is not done automatically. Note that this approach cannot work in all cases for overlapping objects (see Painter's algorithm). You can change the layer of an object either by directly changing the layer property or by changing the order of the data nodes in the Data Manager, i.e., via drag and drop. I will attach a screenshot to prove that it's working.

A more robust and convenient approach is to simply enable depth peeling, which also works for inter-object transparency regardless of the layer and which dosn't have the Painter's algorithm flaw. I will also attach a screenshot of the preferences setting.

Enabled depth sorting for both surfaces and set higher layer for front surface.

Depth peeling preference