When you’re animating characters or scenes in Flash, you may discover times when the background needs to move as well. This allows the character to appear to move over distances greater than the width of the frame. Creating a background as wide as the total animation space can be a pain unless you learn to loop simple backgrounds. You can get a lot of mileage out of a small graphic.
1. Open your animation in Flash. Draw your background graphic on the bottom layer. Don’t get complicated; a mountain horizon or a series of buildings or rooftops will do.
2. Select your background drawing and convert it to a symbol (F8). Make sure the symbol type is “Movie Clip.” Double-click on your new movie clip to open an editing window that superimposes your background onto the movie stage.
3. Duplicate your background graphic. Choose “Flip Horizontal” from the Modify menu Transform submenu. Drag the copy so that its left edge is exactly aligned with the original’s right edge. The two should match perfectly, but if they don’t, modify both graphics until they tile seamlessly.
4. Group the two background objects (Command+G). Select any frame further down the layer timeline and add a keyframe (F6). You should now see two black circles (keyframes) with gray frames in between.
5. Make sure the layer is selected, and choose “Create Motion Tween” from the Timeline submenu of the Insert Menu. You should see an arrow connecting both key frames.
6. Drag the background in the last keyframe so that the far-right edge is only 10 or 12 pixels to the right of the right-stage edge. You don’t want the graphic even with the edge or you will create a pause in the animation playback where two consecutive frames will appear exactly the same.
7. Return to the stage and play your animation back. Your background should loop seamlessly. If it seems to pause at the beginning of playback, reposition the background in the last keyframe until the play is smooth.