A term originally derived from photography, masking defines the method to protect specific portions of a photograph from alteration. Masking can also be described from a painter’s perspective. It is the process of using masking tape to mask out the parts of the painting that you want to protect from accidental damage.
ActionScript provides a mechanism for creating masks to hide pictures, just as painters use masking tape to hide areas. Masking is an important concept used in building puzzle games. You need to have a solid grasp of how masks are created and manipulated with ActionScript. You can apply masking techniques to hide or show different parts of a picture. Figure 11.1 shows a picture without a mask.