The capabilities of Lunar Magic extend beyond mere SMW level editing. It is also the most comprehensive tool for editing Super Mario World's overworld.
A quick reminder first. Remember how before I kept saying that SMW was only ever designed to play SMW and nothing else? Despite how annoying the level editing limitations are, they still allow you a great deal of freedom. Overworld editing is a lot more restrictive and far more complicated. There's plenty of freedom to be found of course, but the process of creating a good overworld is much more painstaking than level editing.
Part of the complexity of this task comes from how the overworld is constructed compared to levels. We won't get into it too much yet, but the main thing is this. You need a strong understanding of how SMW handles images before you can really proceed with editing the overworld. I strongly recommend that you have read and understood the advanced image tutorial before proceeding further.
First, let's open up a fresh copy of the SMW ROM in Lunar Magic. You see good old Yoshi's Island 1. Thankfully, we won't be seeing much more of that for a while. Go to→ , or press the button. This will bring up our new home for the next set of tutorials: the Overworld Editor.
The part on the left should be fairly recognizable as the main portion of SMW's overworld. Ignore the part on the right for now. If you scroll down, you will see some other familiar sights.
These are the six sub-sections of the overworld. If you scroll down even farther than the screenshot shows, you'll see a bunch of random images. Again, ignore these for now.
If you recall from level editing, levels are built in layers. Layer 1 is the foreground, with objects that Mario and other sprites interact with, and Layer 2 is (usually) the background.
The overworld is quite similar. However, a point must be made before we go farther. And that relates to how videogames work in general.
Every videogame, from text adventures and Pong to modern 3D games, is an elaborate lie. To explain this concept, look at a simple Turn block in SMW. This block stops Mario and other sprites from going through it, and it has other effects. And every time you see a turn block, no matter how or where in the game, it has these same consistent properties.
The lie is this: the image doesn't matter. The image of the turn block has no bearing on what the turn block does. You can create entirely invisible blocks that collide with sprites and Mario just like a turn block, and you can create blocks with the turn block image that Mario can pass right through. It is the game designer's imperative to maintain the illusion that what things look like has any bearing on how they behave. So long as this illusion is maintained, the player feels as through the game world is a reasonable consistent place.
The point I'm making is this: just because something looks like it causes something doesn't mean it does. The Map16 code that SMW employs in level editing creates a pretty strict connection between look and function. Certainly, you can violate this by creating blocks with old looks and different functions, or vice versa, but that's your choice as the game designer. The game gives you tools to keep things consistent, and it's your choice to use them properly.
While level editing has the Map16 to link image to gameplay, the overworld has no such thing. The background imagery and the foreground interactable objects are entirely separate from one another. So to maintain the above illusion, you're going to have to do a lot of work on your end to keep things reasonable.
When you beat Yoshi's Island 1, what you see is a new yellow path form that leads upward from the level. You see it going up the mountain until it switches to the overworld to complete the ascent. You also see some hills grow in the background.
Now, here's what the game is thinking. All of the hill growing and yellow path formation? Meaningless. The path that Mario follows is already there and is never directly revealed. You can draw yellow paths anywhere you like; it will have no bearing on where Mario can and cannot go. The paths that determine where Mario can walk are always there; they are not created when you pass a level. The only thing that happens when you beat a level is that the level now allows you to travel in a certain direction that it would not otherwise have allowed before. The paths leading out of a level by that direction determine where Mario ends up.
Everything that you can actually see in the overworld that is not a level, pipe, or star of some kind is the background. It has no impact on the gameplay at all. To see this, scroll back up to the top and press 2 (to turn off viewing the background). This leaves only the foreground objects and sprites. Most of the foreground paths that determine where Mario can walk do not have visible graphics on them. Fortunately Lunar Magic can show them. Press 9 to display the paths, and then press 0 to make the paths translucent (so you can see what's under them).
The above image contains only Mario paths, level entrances, and various overworld sprites. And the sprites have no gameplay function either; only the level entrances and Mario paths do.
In later tutorials, we'll go into detail as to how these paths are constructed and so forth. Right now, we just need an overview of what the overworld is made of. That is, the overworld is made of a background image composed of tiles, some foreground information about levels and paths for Mario, and a number of decorative sprites. The background can be changed by passing a level, but the foreground paths are not affected by this process.
The overworld editor is not nearly as user-friendly as the map editor. It has some very odd eccentricities that you should be aware of.
If you open the overworld editor, make a change, and then load a new ROM (from the level editor), the old overworld will still be loaded. This has the positive effect that you can copy an overworld to another ROM (as a backup), simply by opening the editor, loading the new ROM, and saving the overworld. But there is a pretty strong negative in that you can accidentally do so just by loading another ROM. Even worse, the old overworld will still be in memory even if you have closed the overworld editor.
The way to deal with this is, after you load a new ROM, go to→ or press . Just get in the habit of doing it. This also acts as a very handy undo feature.
Unlike levels, there are no overworld files. Due to the ease of copying overworlds, I strongly suggest you keep a copy of your ROM that contains only your overworld, and copy it to your main testing ROM as needed.
There is one final issue with regard to editing the overworld. If you make any changes to the overworld, the only way to see those changes in the game is to start a new game from scratch. That is, you must start a game that says “empty.” If you did not see level 0xC5 and the introductory message, then you started from a game that had already been played.