Avoid filters, including filters processed
through Pixel Bender.
Try to minimize the use of effects like filters, including filters
processed in mobile devices through Pixel Bender. When a filter
is applied to a display object, the runtime creates two bitmaps
in memory. The first is created as a rasterized version of the display
object, which in turn is used to produce a second bitmap with the
Modifying one of the properties of a filter involves some CPU
processing and can use a significant amount of memory.
The bitmaps are not of the same size. Certain filters create images that are larger than the original image, as the kernel in many filters exceeds the bounds of the source image and produces an output that is larger than the original image.
Flash Player 10.1 and AIR 2.5 introduce a new filtering behavior
on all platforms. If the filter is not modified within 30 seconds,
or if it is hidden or offscreen, the memory used by the non-filtered
bitmap is freed. This feature saves half the memory used by a filter on all platforms.
For example, consider a text object with a blur filter applied.
The text in this case is used for simple decoration and is not modified.
After 30 seconds, the non-filtered bitmap in memory is freed. The
same result occurs if the text is hidden for 30 seconds or is offscreen.
When one of the filter properties is modified, the non-filtered
bitmap in memory is recreated. This feature is called dynamic bitmap
unloading. Even with these optimizations, be cautious with filters;
they still require extensive CPU or GPU processing when being modified.
As a best practice, use bitmaps created through an authoring
tool, such as Adobe® Photoshop®,
to emulate filters when possible. Avoid using dynamic bitmaps created
at runtime in ActionScript. Using externally authored bitmaps helps
the runtime to reduce the CPU or GPU load, especially when the filter properties
do not change over time. If possible, create any effects that you
need on a bitmap in an authoring tool. You can then display the
bitmap in the runtime without performing any processing on it, which
can be much faster.