Next you should click on the "+” symbol next to Slide to access the modifier's sub-properties and select the Slice Plane option. With that being done, we can use the Align tool to align the Slice with our camera. Then, after activating Align, click on the camera and align the position and orientation using the pivot point as base (Fig.21).
Now we are removing the geometry part that stands behind the camera, but we still need to make the Slice follow the camera while it moves or rotates. For that to work, we're using the Wire Parameter. To access it, right-click over the object to open the floating menu. Next, click on the Wire Parameter option. In the new menu that will open, follow the steps as shown on the image below (Fig.22).
After selecting X Position, you should click over your camera so we can connect the Slice information to the camera (Fig.23).
With that being done, the configuration window from the Wire Parameter will open. Here we will indicate who is controlling who using the arrows that are located at the middle of the screen. Let's make the control for the X and Y axes, because we don't want the Slice to move on the Z axis.
Select the cameras and Slice > X Position, turn on the position arrow in a way that the camera is Master, and, in the Expression field, make a simple math expression to move the Slice a little further behind the camera. All you have to do is type "-25" right after X Position (or the value that adapts best to your scene because, as I've said before, values may vary according to the scene's scale and proportions) and click on "Connect”. Do the same to the Y axis. Remember that we should always connect each axis to its pair, therefore Y to Y (Fig.24).
Now the Slice is already moving with the camera, but we also need it to spin with it, so we'll connect the three axes Rotation, but this time we don't need to use an expression (Fig.25).
Now the Slice is following the same orientation as the camera. Try spinning the camera to check the result (Fig.26 – 27).
After this last step our tools are complete and ready to use. I hope you've liked this tutorial and that this technique will be very useful for you all. Soon I intend to transform it into a script to have an easier application.
I would give special thanks to Lucas Kazakevicius for his suggestions for achieving this technique, and Ana Flávia Maestri for having translated this tutorial.