You can set an opaque background for a display
object. For example, when your SWF has a background that contains
complex vector art, you can set the opaqueBackground property
to a specified color (typically the same color as the Stage). The
color is specified as a number (commonly a hexadecimal color value).
The background is then treated as a bitmap, which helps optimize
When you set cacheAsBitmap to true,
and also set the opaqueBackground property to a
specified color, the opaqueBackground property
allows the internal bitmap to be opaque and rendered faster. If
you do not set cacheAsBitmap to true,
the opaqueBackground property adds an opaque vector-square
shape to the background of the display object. It does not create
a bitmap automatically.
The following example shows how to set the background of a display
object to optimize performance:
myShape.cacheAsBitmap = true;
myShape.opaqueBackground = 0xFF0000;
In this case, the background color of the Shape named myShape is
set to red (0xFF0000). Assuming the Shape instance
contains a drawing of a green triangle, on a Stage with a white
background, this would show up as a green triangle with red in the
empty space in the Shape instance’s bounding box (the rectangle
that completely encloses the Shape).
Of course, this code would make more sense if it were used with
a Stage with a solid red background. On another colored background,
that color would be specified instead. For example, in a SWF with
a white background, the opaqueBackground property
would most likely be set to 0xFFFFFF, or pure white.