You can set the transparency threshold for the slice rendering in the Volumes module. If that’s what you are looking for you can access the corresponding functionality with
thanks pieper .
i find the code to render slice in 3d view , it looks like to convert slice volume into a texture then combine the texture into a vtkPlaneSource,render the 3d plane source use ModelDisplayNode
i try to add the follow code to make the 3d rendering black area transparent,but it make no sense