Flash CS3 Documentation

Learning ActionScript 2.0 in Adobe Flash > Animation, Filters, and Drawings > Using filter effects > Working with filters, caching, and the MovieClip class

Working with filters, caching, and the MovieClip class

If a movie clip has an associated filter, it's marked to cache itself as a transparent bitmap when the SWF file loads. As long as the movie clip has at least one filter applied to it, Flash Player caches the movie clip as a bitmap at runtime by forcing the cacheAsBitmap property to be true. The cached bitmap is used as a source image for the filter effects. Each movie clip usually has two bitmaps: one bitmap is the original unfiltered source movie clip, the second bitmap is the final image after filtering. If you do not change the appearance of the movie clip at runtime, the final image does not need to update, which helps improve performance.

You can access filters applied to an instance by calling the MovieClip.filters property. Calling this property returns an array that contains each filter object currently associated with the movie clip instance. A filter itself has a set of properties unique to that filter, such as the following:

trace(my_mc.filters[0].angle); // 45.0
trace(my_mc.filters[0].distance); // 4

You can access and modify filters as you would a regular array object. Setting and getting the filters by using the property returns a duplicate of the filters object, not a reference.

To modify an existing filter, you can use code similar to the code in the following procedure.

To modify a filter's properties when applied to a movie clip instance:

1. Create a new Flash document and save the file as modifyFilter.fla.
2. Add the following ActionScript to Frame 1 of the Timeline:

   this.createEmptyMovieClip("my_mc", 10);
   // draw square
   with (my_mc) {
       beginFill(0xFF0000, 100);
       moveTo(0, 0);
       lineTo(100, 0);
       lineTo(100, 100);
       lineTo(0, 100);
       lineTo(0, 0);
       endFill();
   }
   my_mc._x = 100;
   my_mc._y = 100;
   
   // use default DropShadowFilter values
   my_mc.filters = [new flash.filters.DropShadowFilter()];
   trace(my_mc.filters[0].distance); // 4
   var filter_array:Array = my_mc.filters;
   filter_array[0].distance = 10;
   my_mc.filters = filter_array;
   trace(my_mc.filters[0].distance); // 10
   

   The first section of this code uses the Drawing API to create a red square, and positions the shape on the Stage. The second section of code applies a drop shadow filter to the square. Next, the code creates a temporary array to hold the current filters to apply to the red square on the Stage. The distance property of the first filter is set to 10 pixels, and the modified filter is reapplied to the my_mc movie clip instance.

3. Select Control > Test Movie to test the document.

   NOTE

   Currently, no support is available for having any filters perform rotation based upon their parent's rotation or some sort of other rotation. The blur filter always blurs perfectly horizontally or vertically, independently of the rotation or skew of any item in the parent object tree.

   TIP

   Filtered content has the same restrictions on size as content with its cacheAsBitmap property set to true. If the author zooms in too far on the SWF file, the filters are no longer visible when the bitmap representation is greater than 2880 pixels in either direction. When you publish SWF files with filters, it is a good idea to disable the zoom menu options.

For a source sample of using ActionScript to apply filters, Filters.fla, see the Flash Samples page at www.adobe.com/go/learn_fl_samples. Download the Samples zip file and navigate to the ActionScript2.0/Filters folder to access this sample.

Flash CS3