GSX-86: Graphics
for
the
APe
Virtual Device Interface (VOl)
GSX-86
uses a
standard
method
to
access graphics capabilities. It is called the
Virtual Device Interface (VDI) since it makes all graphics devices
appear
"virtually"
identical.
The
implementation
of
the
VDI
employs the
conventional
BDOS
calling
sequence.
The
application
program
calls
GDOS
via
interrupt
#224 with
function
code
0473H in register CX. Registers
DS
and
DX
contain
the segment base
and
offset, respectively,
of
the
parameter
list (PB). The
parameter
list consists
of
five
double-word
addresses, the addresses
of
five
arrays,
as follows.
PB
PB+4
PB+8
PB+12
PB+16
adQress
of
input
control
array
address
of
input
parameter
array
address
of
input
point
coordinate
array
address
of
output
parameter
array
address
of
output
point
coordinate
array
The
specific
graphics
function
to
be
performed
by
GDOS
is
indicated
by
an
operation
code
in the
input
control
array.
All
data
passed
to
the device driver
are
assumed to be two-byte integers.
The
GDOS
preserves the
BP
(base
pointer)
and
DS
(data
segment) registers. All
other
registers are subject
to
change when
returned
from
GDOS.
INPUT
CONTROL
ARRAY
The
control
array
contains
the
following values when the function is called.
control
(1)
control
(2)
control
(4)
control
(6-n)
Opcode
Number
of
vertices in
input
coordinate
point
array
(ptsin)
Length
of
input
parameter
array
Opcode-dependent
(intin)
INPUT
PARAMETER
ARRAY
The
input
parameter
array
contains
the
following values when the
function
is called.
intin
Array
of
input
parameters.
Length
of
array
is
opcode-dependent
and
specified in
control
(4).
9-9
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