I want to know how slicer can display two sets of images in a vtk window and can set Opacity. And they can interact with the slicer at the same time, I want to display two sets of mpr images in a vtk window. I ran into some difficulty, I tried reslicing the images by blending them, but they are not aligned in physical space. I also tried to fuse the data before reslicing, but there is no way to meet the speed requirements of manual registration.
Slicer is free, open-source software, so you can have a look at the source code and see how everything is implemented.
You can even copy any parts of it into your software, but if you want to use Slicer features then we generally recommend to customize and extend Slicer instead of reimplement or copy it piece by piece. You can fully customize the user interface to only show what you need and add any additional features - see Slicer Custom Application Template for details.