Overlay Surface

What is overlay surface?开发者_JAVA百科 I have to work currently on overlay surface and for which i should know the concept of overlay surface? As i have to wrok on converting YUV444->RGB888

Thanks in advance

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Wiki article. I guess you can find many other sources on the web.
My short explanation is:
An overlay is a hardware characteristic. It means that you have another image plane that pictures are displayed on. It is not part of the main "regular" frame buffer. You basically have the ability to display 2 "desktop" images independently of each other. Once you turn off the overlay you get the normal view of the frame buffer.

Overlay is used to display images over the current view OR to play movies in many cases. That is why you get a black image when trying to capture a screen shot of a movie frame. Because the screen shot is of the frame buffer and not of the overlay buffer.

You can read the implementation for the Overlay by Marvell for the PXA3xx to get a better understanding of how it is implemented. Read Vol III chapter 1.4.7.