dedicated to the overlay. The graphics card will render the DVD playback only inside the purple area. If another window moves over top of the purple area and obscures a part of it, then the graphics hardware performs the clipping by itself. In practice, the actual color "purple" is not used - rather, either a nondescript near-black color is used (as the system often has thousands of such shades to choose from), or the mask region is denoted using some similar masking method not involving colors.

Screen shots

As a consequence

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