Creating Background Tiles
Lesson 2: GBA Sprite Making Tutorial
By Adam C. Tierney
Depending on video mode, the Gameboy Advance has a number of background layers it can use. But regardless of what mode you're in, they're always split up into 8x8 pixel units called tiles.
Many other game platforms can do backgrounds in a similar way - the NES, SNES, Genesis and the other Gameboys all do, and there are others. Even in software renderers, backgrounds are often done in this way.
Castlevania, Golden Sun - just about any 2D Gameboy game does backgrounds this way. Now, we're doing something a little different for our big project, but this is still a good example of the way things are usually done, and is the way just about any SNES game worked.
First, we need something to build. I'm going to build a segment of fence, something that could be used in a game like Chrono Trigger. First, we need an area of tiles, divisible by 8. A 88x120 area will do. I've created one, and made a checkerboard pattern so we can see the individual 8x8 parts. The size of these examples has been doubled so that you can more easily see it for the example.
Now, I'm going to place a green field on this background, this is the area of grass around the fence.
The Gameboy can support a different amount of colors per background depending on how the individual game is set up, but the total amount of colors you can use is always going to be an issue. The key is to use as few colors as possible to get your idea across. What I tend to do is figure out a small pallet (set of colors) for each item, and use several shades in that color set. For example, a wooden signpost would use mostly shades of brown. For this fence, I'm going for a fantasy stone look, so I'm going to use greys and purples. I'm going to stick by a basic rule of, say, 8 colors per tile. This isn't a hardware limit, but it'll allow more colors to be used elsewhere.
First, I'm going to make the endpoint of the fence - it'll end in a pillar. As I said, I'm going with some bluish grey and dark purple. I'm going to make it 32x64 pixels in size, as that's about the right scale for most GBA sprites. Here's the result:
You can see that the fence could be repeaded, and that it would line up horizontally.
That's exactly what we're going to do next. We copy the fence again, and begin to cut it off where it hits the pillar, making a joint. Note that the pillar and fence could be horizontally mirrored so that it can be used for other things. Anyway, the fence extended to the pillar, and the joint drawn where it meets the pillar:
The fence is pretty much finished, but it doesn't really look like it's connected to the ground. To solve this, we're going to give the grass some texture, add a few rocks - just make it obvious that there's a connection there. Be mindful of the color count, but having 5-6 greens wouldn't be a problem. Here's what I did:
Now the fence is pretty much ready to be used, but there's an issue you still need to address. If you want characters in whatever game you're working on to be able to walk behind the fence, you need to split it into two layers. The top parts of the fence would reside on a different layer than the bottom parts and the grass, so that a character could walk behind the fence from the top. What you'll end up with is two different images:
Now, you can also finish off the top of the fence and pillar with something, so that they can be used on their own, but really, this is ready to be used in a game. Of course, if you're working on a project with a coder, you'll need to talk to them to find out what the exact limitations will be for you. That's about it.
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