Parameter block contents.
PB Address of control array
PB+2 Address of input parameter array
PB+4 Address of input point coordinate array
PB+6 Address of output parameter array.
PB+8 Address of output point coordinate array
This area is used by the GDOS and GIOS for control of the selected
function. For example control(1) will contain the number of the required
graphics routine (Remember open workstation – opcode 1). The remaining fields
are used to contain values representing the amount of valid data contained in
the other arrays on both entry to, and return from, the GIOS. These are
usually extracted by the GIOS and used as loop counters.
Contains information to be’used by the GIOS in a called function. These
are not usually point coordinates but colour change values, text strings,
input device modes and the suchlike.
Contains point coordinates passed to the GIOS from the calling program.
Used to contain line coordinates for example. This array is scaled to device
coordinates by the GDOS before control is passed to the GIOS.
Similar to intin but used by the GIOS to return data to the calling
program. Typical entries are text rotation achieved as opposed to rotation
asked for, input samples flagged as successful or not, linestyle selected etc.
Similar to ptsin but used by the GIOS to pass coordinates back to the
calling program. This array is also scaled by the GDOS before control is
passed back to the caller, but this time to the 32k X 32k virtual frame size.
The GSX standard dictates that all array elements are 16 bit values, even
ASCII text strings. Ail array references in the documentation are 1 based,
which can be a source of bugs if you forget that array(l) is really array(0).
Those of you au fait with the CP/M map may care to take a look at fig 2,
which shows where the GDOS and GIOS live when at home. All calls to BDOS are
rerouted through the GDOS first (via a modified 0005h) and passed on to the
BDOS if it is not a graphics request.