I believe that what you are trying to accomplish can be done using two overlays of the same image. You can use this command to get a duplicate overlay:
&overlay OVERLAY create from FOG INTRO
OVERLAY can then be treated like a normal overlay.
By having another overlay like the first, you can have them alternate their movements so that it appears to have a solid motion. The positions of the overlays should be somewhat like this:
- The first overlay begins from off-screen on one side of the scene and travels off-screen to the other side while the second overlay follows directly behind it.
- Once the first overlay is completely off-screen, it travels back instantly to the original position and continues it’s movement, followed by the second overlay.
- This should create the illusion of one fluid motion between overlays (which may take some experimenting.)
A better, similar example and explanation of this can be found by looking up how to create looping backgrounds, but feel free to ask if you need better clarification.
I hope this helps.