Graphics Programming
TVP4020
Programmers Reference Manual
58
to be copied. P
ERMEDIA
copy works by adding a linear offset to the
destination fragment's address to find the source fragment's address.
The calculation of the offset value is as shown in the diagram below:
Note that the offset is independent of the origin of the buffer or window,
as it is added to the destination address. Care must be taken when the
source and destination overlap to choose the source scanning direction
so that the overlapping area is not overwritten before it has been moved.
This may be done by swapping the values written to the StartXDom and
StartXSub, or by changing the sign of dY and setting StartY to be the
opposite side of the rectangle.
Source
Rectangle
X O ffset
Y O ffset * Screen W idth + X O ffset
Destination
Rectangle
Screen Width
Increasing
Physical
Address
Offset = -
Offset
Y Offset
Figure 5.7
Copy Operation
P
ERMEDIA
buffer upload/downloads are very similar to copies in that the
region of interest is generated in the Rasterizer. However, the localbuffer
and framebuffer are generally configured to read
or to write only, rather
than both read
and write. The host out unit should be set to output data
to the FIFO for image uploads. For downloads, the Rasterizer should be
set to sync on the appropriate data type. This means that the Rasterizer
will not generate the next fragment address until data is supplied from
the host processor.
Units which can generate fragment values, the Color DDA unit for
example, should generally be disabled for any copy/upload/download
operations.
Warning: During image upload, all the returned fragments must be read
from the Host Out FIFO, otherwise the P
ERMEDIA
pipeline will stall. In
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