MACROMEDIA FLASH 8-LEARNING ACTIONSCRIPT 2.0 IN FLASH, Руководство пользователя

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504 Animation, Filters, and Drawings
About error handling, performance, and filters
One problem that arises if you use too many filters in an application is the potential to use
large amounts of memory and cause Flash Player performance to suffer. Because a movie clip
with filters attached has two bitmaps that are both 32-bit, these bitmaps can cause your
application to use a significant amount of memory if you use many bitmaps. You might see an
out-of-memory error generated by the computer’s operating system. On a modern computer,
out-of-memory errors should be rare, unless you are using filter effects extensively in an
application (for example, you have thousands of bitmaps on the Stage).
However, if you do encounter an out-of-memory error, the following occurs:
■
The filters array is ignored.
■
The movie clip is drawn using the regular vector renderer.
■
No bitmaps are cached for the movie clip.
After you see an out-of-memory error, a movie clip never attempts to use a filters array or a
bitmap cache. Another factor that affects player performance is the value that you use for the
quality
parameter for each filter that you apply. Higher values require more CPU and
memory for the effect to render, whereas setting the
quality
parameter to a lower value
requires less computer resources. Therefore, you should avoid using an excessive number of
filters, and use a lower
quality
setting when possible.
You can also encounter errors if you use invalid parameter types. Some filter parameters also
have a particular valid range. If you set a value that’s outside of the valid range, the value
changes to a valid value that’s within the range. For example,
quality
should be a value from
1 to 3 for a standard operation, and can only be set to 0 to 15. Anything higher than 15 is set
to 15.
Also, some constructors have restrictions on the length of arrays required as input parameters.
If a convolution filter or color matrix filter is created with an invalid array (not the right size),
the constructor fails and the filter is not created successfully. If the filter object is then used as
an entry on a movie clip’s filters array, it is ignored.
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If a 100 pixel by 100 pixel object is zoomed in once, it uses four times the memory since
the content’s dimensions are now 200 pixels by 200 pixels. If you zoom another two
times, the shape is drawn as an 800 pixel by 800 pixel object which uses 64 times the
memory as the original 100 pixel by 100 pixel object. Whenever you use filters in a SWF
file, it is always a good idea to disable the zoom menu options from the SWF file’s
context menu.
TIP
When using a blur filter, using values for blurX and blurY that are powers of 2 (such as 2,
4, 8, 16, and 32) can be computed faster and give a 20% to 30% performance
improvement.