Add a test program for text viewports.

tests/viewport.bas

@@ -0,0 +1,69 @@
+   10 REM Text Viewport Example using VDU 28
+   20 :
+   30 CLS
+   40 :
+   50 cols%=FN_getScreenCols - 1
+   60 rows%=FN_getScreenRows - 1
+   70 :
+   80 REM Create a border around the screen
+   90 :
+  100 REM Top line
+  110 PROC_fill(0,0,cols%,0)
+  120 REM Left side
+  130 PROC_fill(0,rows%-1,0,1)
+  140 REM Right side
+  150 PROC_fill(cols%,rows%-1,cols%,1)
+  160 REM Bottom line
+  170 PROC_fill(0,rows%,cols%,rows%)
+  180 :
+  190 REM Display some text in various sizes of viewport
+  200 t% = 2
+  210 b% = 2
+  220 l% = 2
+  230 r% = cols% - 2
+  240 size% = 1
+  250 REPEAT
+  260   PROC_stars(l%,b%,r%,t%)
+  270   t% = b% + 2
+  280   size% = size% + 1
+  290   r% = r% - 1
+  300   b% = t% + size%
+  310 UNTIL b% > rows% - 1 OR r% < l%
+  320 :
+  330 k%=GET
+  480 END
+  490 :
+  500 DEF PROC_fill(L%,B%,R%,T%)
+  510 VDU 28,L%,B%,R%,T%
+  520 VDU 17,191,17,0
+  530 VDU 12
+  540 VDU 17,128,17,63
+  550 VDU 26
+  560 ENDPROC
+  570 :
+  600 DEF FN_getScreenCols
+  610 REM A% is the OSBYTE command to run
+  620 A%=&A0
+  630 REM L% is the sysvar to fetch
+  640 L%=&13
+  650 =USR(&FFF4)
+  660 :
+  700 DEF FN_getScreenRows
+  710 REM A% is the OSBYTE command to run
+  720 A%=&A0
+  730 REM L% is the sysvar to fetch
+  740 L%=&14
+  750 =USR(&FFF4)
+  760 :
+  800 DEF PROC_stars(L%,B%,R%,T%)
+  810 VDU 28,L%,B%,R%,T%
+  820 C% = (R% -L% + 1) * (B% - T% + 1) * 2 - 1
+  830 PATTERN$ = "/-|\*"
+  840 J% = 1
+  850 FOR I% = 1 TO C%
+  860   PRINT MID$(PATTERN$, J%, 1);
+  870   J% = J% + 1
+  880   IF J% = 6 THEN J% = 1
+  890 NEXT I%
+  900 VDU 26
+  910 ENDPROC