A small change has been made at Atlas to the DEC Fortran graphics routines VTPRIM. A problem arises with the existing version because the routines allow items to be added to a display file while the file is being screened. This is a useful facility, but in order to prevent a corrupt display file being screened while the PDP15 is in the middle of updating it, the VT15 is turned off. (see SPROGS papers 1 and 4). When it is turned on again, the VP15 processor screens the display file from the beginning. Therefore if the time between updates is less than the time the VP15 takes to display a complete file, only a portion of the picture is screened. This switching on and off occurs even if the file is not actually being displayed.
The solution adopted arises out of a conversation with FRAH and ensures that the display file is always well-formed; the VT15 can then be left on. The picture then appears evenly.
Routines affected by the change are those which add display orders to the end of a display file, i.e. :
COPY
LINE
PRAMTR
TEXT the subpicture routines
and PLOT the main picture routine.
There is no apparent change to REPLOT which replaces display orders in the middle of a display file.
The binary file incorporating the change is VTPRIM BIN and is located on my disc area. To obtain it (assuming DOS is being used), enter PI and type:-
T DK +-DK <JRG> VTPRIM BIN return
When running your display program (after transferring VTPRIM to your file space), the name VPPRIM must be included in the list of file names given to LOAD - for example:-
MAIN, SUB1, SUB2, VTPRIM altmode
It will appear as VTPRIM 00 if a core map list is produced (option P).
In due course, it will be put into the file .LIBR BIN, the Fortran library, and will then be loaded automatically.
Please inform me of any problems.
The DEC account of VTPRIM is: Graphic 15 programming manual .
Some lab-produced comments and flow-charts can be found in
SPROGS paper 1 The PDP15 Fortran Graphic Routines: VTPFIM
SPROGS paper 4 Changes to VTPRIM