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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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