Mask layers are frequently used throughout Flash projects to partially reveal content sitting on layers directly beneath the mask. The mask itself can be a filled shape, text, an instance of a graphic symbol, or a movie clip. Dynamic effects can even be created by applying shape or motion tweening to your masks.
This level of flexibility and sophistication can place a lot of demand on the CPU, leading to a drop in frame rate. Although desktop computers can handle most masking operations, the same effects will degrade the performance of your iOS apps. Wherever possible, limit your use of masks. For existing projects, rather than use masks, obscure your content with other clips that sit on top of it.
In this recipe we will do just that; removing a mask layer and instead using two movie clips to obscure the content that was previously clipped by the mask.