- appl_init

= Initialise the AES. This call must precede any use of VDI or AES.
> Opcode 10

 GEM, AES, AES Application Functions

 C call : id = appl_init()

 long id           This is >=0 if the call worked, and represents the
                   application's id number.

- graf_handle

= Return the VDI handle used by the AES
> Opcode 77

 GEM, AES, AES Graphics Library.

 C call : handle = graf_handle(&cw, &ch, &bw, &bh);

 word cw,ch        Width and height of the system font character cell
 word bw,bh        Width and height of a box large enough to hold a
                   system font character
 long handle       The VDI handle which can be used in subsequent calls
                   to the VDI library.


- v_opnvwk

= Open virtual workstation
> Opcode 100

 GEM, VDI, VDI Control Functions

 C call :  v_opnvwk(work_in, &handle, work_out);

 word work_in[11]   Input array specifying options
 word handle        Pointer to handle returned from AES
 word work_out[57]  Output array

 Input values in work_in are as follows

 work_in[0]      Device id (1 for the screen)
 work_in[1]      Default line type (1 for solid)
 work_in[2]      Polyline colour (1 for black)
 work_in[3]      Marker type (1)
 work_in[4]      Polymarker colour (1 for black)
 work_in[5]      Text font (1)
 work_in[6]      Text colour (1 for black)
 work_in[7]      Fill interior style (1)
 work_in[8]      Fill style (1)
 work_in[9]      Fill colour (1 for black)
 work_in[10]     Coordinate type (0 for normalised, 2 for raster)

 Various values are placed in work_out. Some of the more interesting
 are detailed below. Note that values are filled in to work_out up to
 work_out[56].

 work_out[0]     Max x coordinate
 work_out[1]     Max y coordinate
 work_out[13]    Max number of colours available
 work_out[45]    Min character width
 work_out[46]    Min character height
 work_out[47]    Max character width
 work_out[48]    Max character height


- form_alert

= Display an alert message on the screen
> Opcode 52

 GEM, AES, AES Form Library.

 C call : button = form_alert(defbutton, text);

 long defbutton    The default exit button for the form. This is 0 for
                   no exit button, 1 for the first and so on.
 byte *text        The text to be displayed
 long button       The exit button selected by the user (as above).

- v_clsvwk

= Close virtual workstation
> Opcode 101

 GEM, VDI, VDI Control Functions

 C call :  v_clsvwk(handle);

 word handle       Handle returned by v_opnvwk

- appl_exit

= Close down the application library
> Opcode 19

 GEM, AES, AES Application Functions

 C call : rc = appl_exit()

 long rc           Returns >0 if no error.