About runtime bitmap caching movie clip and button symbols

Runtime bitmap caching lets you optimize playback performance by specifying that a static movie clip (for example, a background image) or button symbol be cached as a bitmap at runtime. Caching a movie clip as a bitmap prevents Flash Player from having to continually redraw the image, which provides a significant improvement in playback performance.

For example, when you create animations with a complex background, create a movie clip for the background. The background is rendered as a bitmap stored at the current screen depth. It can be drawn quickly, letting the animation play faster and more smoothly.

Without bitmap caching, the animation might play back too slowly.

Bitmap caching lets you use a movie clip and freeze it in place automatically. If a region changes, vector data updates the bitmap cache. This process minimizes the number of redraws that Flash Player must perform, and provides smoother, faster playback performance.

Only use runtime bitmap caching on static, complex movie clips in which the position, but not the content, of the movie clip changes on each frame in an animation. The playback or runtime performance improvement from using runtime bitmap caching is only noticeable on complex-content movie clips. Runtime bitmap caching with simple movie clips does not enhance performance.

For more information, see When to enable caching in Learning ActionScript 2.0 in Adobe Flash.

Under the following circumstances, a movie clip does not use a bitmap (even if Use Runtime Bitmap Caching is selected) but instead renders the movie clip or button symbol by using vector data:

• The bitmap is too large (greater than 2880 pixels in either direction).

• The bitmap fails to allocate (producing an out of memory error).