PXD20RM Datasheet, PDF (532/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

12.4.4.1 Blending priority of layers
The 4 layers available in the DCULite are each fixed in priority order, with layer 0 being the highest
priority, layer 1 being the second highest priority, and so on until layer 3, which is the lowest priority. The
priority is used by the DCULite to define how to blend individual pixels within the layers. For example, if
layer 0 is defined as not being blended with other layers and a pixel on layer 0 overlaps a pixel on layer 1
then the pixel on layer 0 will be visible on the panel unchanged by the pixel on layer 1. However, if layer
0 is defined as being partially transparent, then the DCULite will blend the overlapping pixel such that the
result is a combination of the pixel on layer 0 and the pixel on layer 1. It is possible to blend up to four
layers at each pixel position.
As there is a maximum number of layers that can blended together, then any pixel on a layer that is lower
than the threshold priority will not be included in any blend. If a pixel is on a layer that has the lowest
priority in any blending scheme, then the blending settings for that pixel are ignored and the pixel is treated
as a background pixel. This means that a lower priority layer may have some pixels completely obscured
by those on higher priority layers on one part of the panel, and some other pixels visible or blended on
other parts of the panel.
Figure 12-63 shows how the pixel blend takes place inside the DCULite. The priority of the layers
determines at which stage of the blend the pixel enters. Any pixels lower than the threshold priority are
ignored and, as can be seen, the blend settings for the lowest priority pixel is also ignored.
Higher priority pixel
Lowest priority pixel
Blend1
Two-plane Blending Result
Note: All blend stages use the blending settings
defined for the upper pixel.
Figure 12-63. Pixel blending stack
This priority concept is illustrated in Figure 12-64 and Figure 12-65. In this case, there are five layers
enabled, and each contains a graphic that is a solid rectangular block of a single color. The size and shape
of each layer is different. The background color of the panel is set to grey and layers have been placed such
that they overlap each other.
Figure 12-64 shows the individual source graphics and the case where no layer has any blending enabled.
Here, the highest priority layer (in this case layer 0) is fully visible. Layer 1 is visible where layer 0 does
not overlap it. Layer 2 is visible where layer 1 does not overlap it. Layer 3 is overlapped by layers 0 and 1
and so is only partially visible. Layer 4 is partially obscured by all of the other layers. Note that layer 4 is
higher priority than the background color.
12-70
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor