SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
The overlay mechanism consists of displaying more than one layer (VID and/or VIDL1 pipeline layers) using:
The overlay manager is configured using the Z-order parameter. The Z-order value defined for each pipeline indicates the visibility order to the window on the screen. If the Z-order value of window A is lower than the Z-order to layer B, then layer A is displayed below layer B. The transparency color keys and the alpha blending factors are then used to blend the layers together (see Section 12.9.1.4.1.9.2.1, Overlay Alpha Blender, and Section 12.9.1.4.1.9.2.2, Overlay Transparency Color Keys).
Figure 12-508 gives an example of how input pipeline frame outputs are merged together to generate the final display output.
As shown in Figure 12-508, each input pipeline generates one rectangular sub-frame output in ARGB48 format. The overlay is responsible for positioning the sub-frame in the display output frame (specified by DSS0_VP_SIZE_SCREEN[11-0] PPL and [27-16] LPP video port register fields), using the overlay window position parameters (specified by DISPC_OVR_ATTRIBUTES_0/DISPC_OVR_ATTRIBUTES_1 [17-6] POSX and [30-19] POSY overlay register fields), and the window size parameters (specified by DSS0_VID_SIZE[11-0] SIZEX and [27-16] SIZEY pipeline register fields). When the overlay manager does not require the input pipeline data (either because it is currently outputting the background color pixel or it is being stalled by the VP output module), the overlay manager stalls the input pipeline.
When there are no video-encoded pixels at a specific position, the programmable solid background color appears. The solid background color is set in the DSS0_OVR_DEFAULT_COLOR and DSS0_OVR_DEFAULT_COLOR2 registers.
The entire pixels of the video window have to be inside the display screen. Depending on the width of the buffer to be displayed in the video layer and the position, the width must be adjusted by software to limit the right edge of the window inside the display screen. The same is also true for the video layer height in the input pipe line configuration.