SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
The overlay mechanism consists of displaying more than one input layer (graphics and/or video layers) using:
The overlay manager is configured by using the Z-order parameter. The Z-order value defined for each pipeline indicates the visibility order of the window on the screen. If the Z-order value of window A is lower than the Z-order of 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 12.6.3.10.2.1, Overlay Alpha Blender, and Section 12.6.3.10.2.2, Overlay Transparency Color Keys).
Figure 12-353 gives an simplified example of how two input pipeline frame outputs are merged together to generate the final display output.
As shown in Figure 12-353, 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[13-0] PPL and [29-16] LPP video port register fields), using the overlay window position parameters (specified by the [13-0] POSX and [29-16] POSY overlay fields in the DSS0_OVR_ATTRIBUTES2_0 through DSS0_OVR_ATTRIBUTES2_4 registers), and the window size parameters (specified by the [13-0] SIZEX and [29-16] SIZEY input pipeline fields in the DSS0_VID_SIZE registers). 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 can be 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.