Advantages of Tile-Based Scrolling

There are several advantages of using tile-based scrolling in your work: data compactness, image scrolling, and interactivity.

Data Compactness

You can already see one advantage of this technique. It "compresses" the bitmap by storing only its smaller common denominator, thus eliminating redundancy. In the example shown previously in Figure 1, the original bitmap is 144 pixels wide by 80 pixels high. This amounts to storing 11,520 "squared pixels." Using the tile-based scrolling technique, you store only three images—each one 16 x 16 pixels—which amounts to storing just 768 squared pixels. Of course you still have to subtract the Run Length Encoding compression of Director from that amount, but there is still a big benefit.

Another great advantage of this technique is that your bitmap can be huge and yet occupy only a few kilobytes of space, as long as it's made up of just a few items. Moreover, by using vertical and horizontal flipping, rotations, ink effects, and other effects, you can use a single graphic item to create varied image pieces without ever increasing the loading time.

The other interesting point to note is that the micro items (tiles) must have a unique size for this technique to be applicable. In most games, the size of the tiles is 16 x 16 pixels for video memory purposes. I recommend that you to stick to this standard even though it's not necessary for the technique to work in Director. By doing so, however, your format will be compatible with games that use this scrolling technique—and also with the different C sources, as well as with freeware graphics you can find on the web. In short, although sticking to 16 x 16 pixels is not essential, it's not worth it not to do it.

Image Scrolling

A second advantage of this technique concerns image scrolling. Imagine that the bitmap is a lot larger than the display area. All you have to do is recreate the bitmap in the size of the display area and draw a column of additional tiles. Once the image scrolls by an amount of 16 pixels, you erase the first tile column of the bitmap and redraw another one on the other side of the bitmap. Keep repeating this until you reach the end of the bitmap. This means you redraw just a very small portion of the image at each update.

For example, the following Shockwave file containing the whole first level of "Super Mario Bros." takes only a little bit of time to scroll through:

Note: The playback speed of this file is determined by the speed of your computer (processor speed, clock speed, memory available). Your results will vary.

Interactivity

The third advantage of tile-based scrolling essentially concerns its application in the field of video games. You can use the cartography of a game level (the bitmap's map) to determine how it interacts with a character.

For example, if a character doesn't stand on a brick-type tile, he'll fall; or if he falls on a water-type tile, he'll die. Of course this implies that each tile has one—and only one—property. If you wish to have some nonsolid brick tile (for instance, to create secret areas), you'll have to use a property list with varying properties.

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