dss-072
Layer composition by hardware
Video1
Video1
Video2
Video2
Public Version
Display Subsystem Functional Description
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The overlay mechanism consists of displaying more than one layer (graphics and video layers) using rules
based on priority and transparency color keys.
When the pixel format is ARGB or RGBA, the color key match logic uses only the RGB value defined by
ARGB or RGBA. The alpha blending factor is ignored.
The overlay managers are based on the same rules for priority and transparency color keys (see
Each data pipeline is assigned a single overlay related to a single display controller output.
The overlay manager is connected to all three outputs of the pipelines (graphics, video1 and video2). The
output of the LCD overlay manger is connected to the Spatial/Temporal Dithering, and Passive Matrix
units and back to the palette unit in the case of Gamma correction.
7.4.2.4.1 Priority Rule
The overlay manager can be configured in two distinct modes:
•
Alpha mode (only source color key with the graphics layer)
•
Normal mode (no alpha support)
The following rules apply in normal mode:
The video1 layer is always on top of the graphics layer. The video2 layer is always on top of the video1
and graphics. The display controller reads the data for each buffer from the system memory and,
depending on the transparency color key values, displays either the pixels in the video layer, the pixels in
the graphics layer, or the solid background color.
Each layer can have any size up to full-display screen. If there are no graphics or video-encoded pixels at
a specific position, the programmable, solid background color appears (see
Figure 7-78. Overlay Manager in Normal Mode
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Display Subsystem
SWPU177N – December 2009 – Revised November 2010
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