
6-32
Video Interface and On-Screen Display
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
COL15
Color 15
[15:0]
A YCbCr triple assigned to the color palette for color 15
in this region.
6.9.4
Alpha Blending
Each color may optionally set the MIX mode bit to cause the foreground
(overlay) and background (image) to be mixed together with weighting
controlled by the MixWeight eld. Foreground pixels are weighted
. Background pixels are weighted
.
6.9.5
High Color
Operation
The L64005 operates in high color mode for every OSD region in which
the high-color bit is set. This allows the OSD to operate with up to 16
colors per region.
6.9.6
Bitmap Storage
The OSD bitmap is stored in packed form immediately following the OSD
header. The rst pixel of the OSD must always start on a word boundary.
The L64005 fetches bitmap data from memory sequentially and stores it
in a small FIFO. The L64005 reads data from the FIFO 2 (or 4) bits at a
time and matches it up against the respective pixel from the video source
before it is mixed together and displayed. Pixels in the same word may
straddle OSD rows, depending on the value of the STARTR and ENDR
header elds. Once the OSD controller determines that the OSD region
is complete (STARTR is out of bounds for the display), it ushes the FIFO
and begins the operation again.
6.9.7
Use of the
OSDA Field
The OSDA eld allows the construction of a linked list of OSD regions in
the memory of the L64005. Selected regions can be resized or updated
without forcing an update of all regions. New regions can be added in
response to user requests without updating all regions. The OSDA
pointer may be updated to point to a new region, allowing animation
effects without signicant CPU intervention. Note that when using the
linked list, each region must be an exact number of 64 bit words wide.
(32 pixels in 2-bpp mode, 16 pixels in 4-bpp mode). When using the OSD
in non-linked list mode, the OSD region itself must contain an exact num-
ber of words, but the regions can be of any width.
Foreground
MixWeight
() 16
×
Background
16
MixWeight
–
() 16
×