ID Number: Q74508
3.00
WINDOWS
Summary:
In Chapter 14 of the "Microsoft Windows Device Development Kit Device
Driver Adaptation Guide," the interpretation of the raster operation
(ROP) code is explained. However, only the higher-order word or most-
significant word (MSW) of the 32-bit ROP code is explained. This word
is an index in the ROP table. The use of the lower-order word or
least-significant word (LSW) of the ROP code is not addressed in the
Windows Device Development Kit (DDK).
The LSW of the ROP code may be used by display drivers to assist in
parsing the ROP. A complete explanation of the LSW of the ROP code can
be found in the file COMMENT.BLT, which is included with the DDK
display driver sample source code. This file is found in the directory
that contains the source code for the BitBlt routine. For example, the
file that relates to the VGA/EGA driver is found in the
DISPLAY\4PLANE\BITBLT directory.
Note: The LSW of the ROP code is NOT used by the VGA/EGA, 8514, and
other display drivers distributed by Microsoft. Windows Graphics
Device Interface (GDI) does not process the LSW. GDI simply passes it
to the display driver.
The relevant section from the COMMENT.BLT file is included below.
More Information:
The low-order word in and of itself does not contain enough
information to generate the ROP code. What it contains is:
1. An index specifying which predefined parse sting to use. A parse
string has a format similar to
SDPSDPSD
or
S+SD-PDS
where S, D, and P represent source, destination, and pattern. The
"+" represents a "push", and the "-" represents a "pop". Sixteen of
the 256 ROPs cannot be represented without using "push" and "pop".
2. Amount to rotate the parse string. If the base string is
SDPSDPSD
and an offset of 2 was given, the new base string will be:
PSDPSDSD
3. Five logic operations. The logic operations could be any of the
following:
NOT
XOR
OR
AND
4. A parity bit used to imply a sixth logic operation of NOT. Pairs of
trailing NOTs are discarded since they cancel.
Example 1: 85, 0085 1E05, PDSPnoaxn,
D = not ((((not P) or S) and D) xor P)
1E08 = 00 01 11 10 00 0 001 01
| | | | | | | |
| | | | | | | |___ bias start by 1
| | | | | | |______ use string 1
| | | | | |_________ parity - no trailing NOT
| | | | |____________ Logic operation #1 is a NOT
| | | |_______________ Logic operation #2 is a OR
| | |__________________ Logic operation #3 is a AND
| |_____________________ Logic operation #4 is a XOR
|________________________ Logic operation #5 is a NOT
String #1 is defined as: SPDSPDSP
After the bias, it will be: PDSPDSPS
The number of binary logic operations + 1 gives an index into the new
string of the first operand. In this case, there are three binary
operations, so the first operand will be the fourth element of the
string (P), the second operand will be the third element (S), and so
forth.
Example 2: 71, 0071 1D5C, SSDxPDxaxn,
D = not (((D xor P) and (D xor S)) xor S)
1E08 = 00 01 11 01 01 0 111 00
| | | | | | | |
| | | | | | | |___ don't bias start
| | | | | | |______ use string 7
| | | | | |_________ parity - no trailing NOT
| | | | |____________ Logic operation #1 is a XOR
| | | |_______________ Logic operation #2 is a XOR
| | |__________________ Logic operation #3 is a AND
| |_____________________ Logic operation #4 is a XOR
|________________________ Logic operation #5 is a NOT
String #7 is defined as: S+SD-PDS
The number of binary logic operations + 1 normally gives an index into
the string of the first operand. When a push/pop is involved, this
must be biased by 2 to account for the encoded push/pop. In this case,
there are four binary operations, plus a push and a pop, so the first
operand will be the seventh element of the string (D), the second
operand will be the sixth element (P), and so forth.