Call WallpaperManager.setWallpaperOffsets
to instruct the wallpaper to scroll.
So this should center the wallpaper:
WallpaperManager.setWallpaperOffsets(getWindowToken(), 0.5f, 0f);
This should scroll it to the side:
WallpaperManager.setWallpaperOffsets(getWindowToken(), 0f, 0f);
This should scroll it to the other side:
WallpaperManager.setWallpaperOffsets(getWindowToken(), 1f, 0f);
If you're going to do this, you ought to ensure that you know that the wallpaper can actually be scrolled, or that the user has asked you to enable scrolling. Many devices are configured with wallpaper that is the same size as the screen and does not scroll.