Understanding composition

Composition is the process of combining multiple content sources into a single image. The following forms of transparency are used for composition:

Destination view port
Allows any content on layers below to be displayed. This transparency mode has an implicit transparency in that anything outside the specified view port is transparent.
Source chroma
Allows source pixels of a particular color to be interpreted as transparent. Unlike a destination view port, source chroma allows for transparent pixels within the buffer.
Source alpha blending
Allows pixel blending based on the alpha channel of the source pixel. Source alpha blending is one of the most powerful forms of transparency because it can blend in the range from fully opaque to fully transparent.

Screen composition

You use Screen composition to manage composition capabilities for your application.

The Composition Manager combines multiple window buffers into one resultant buffer. This is the composite buffer (Screen> framebuffer).

An image showing an example of Screen composition with two windows and only one supported pipeline.

This Screen composition example shows two windows; each window posts a different image. Those images are composed into one composite framebuffer, which binds to the single pipeline. This output is then fed into the associated display port and then onto the display hardware.

Last modified: 2015-03-31

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