39.6.10.1 Window Overlay

The LCD module provides hardware support for multiple “overlay plane” that can be used to display windows on top of the image without destroying the image located below. The overlay image can use any color depth. Using the overlay alleviates the need to re-render the occluded portion of the image. When pixels are combined together through the alpha blending unit, a new color is created. This new pixel is called an iterated pixel and is passed to the next blending stage. Then, this pixel may be combined again with another pixel. The VIDPRI bit located in the LCDC_HEOCFG12 register configures the video priority algorithm used to display the layers. When the VIDPRI bit is written to ‘0’, the OVR1 layer is located above the HEO layer. When the VIDPRI bit is written to ‘1’, OVR1 is located below the HEO layer.