Q40546: LINE Statement with BF Option Outside Window Will Hang

Article: Q40546
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | buglist6.00 fixlist6.00b SR# S881221-109 viewport | mspl13_basic
Last Modified: 17-JAN-1990

If a LINE statement with the BF (box filled) option is executed
outside the boundaries of the physical view port set up by the VIEW
statement, the computer will hang. The program runs properly inside
the QuickBASIC QB.EXE environment, but fails when compiled with BC.EXE
from Microsoft BASIC Compiler Version 6.00.

Microsoft has confirmed this to be a problem with BC.EXE in Microsoft
BASIC Compiler Version 6.00. This problem was corrected in Microsoft
BASIC Compiler Version 6.00b.

This problem does not occur in Microsoft QuickBASIC Versions 4.00,
4.00b, and 4.50, or in Microsoft BASIC Professional Development System
(PDS) Version 7.00.

The following program sets up a physical view port with the VIEW
statement and then draws a line using the BF option, starting inside
the box and moving outside the window's boundaries. If the program is
compiled with Version 6.00 of Microsoft BASIC Compiler, the program
will hang upon attempting to draw the first box that lies outside the
window view port.

The following is a code example:

SCREEN 2
xmin = 0: ymin = 0
xmax = 1000: ymax = 1000
dx = (xmax - xmin) / 10
dy = (ymax - ymin) / 10
VIEW (200, 50)-(400, 150)
WINDOW SCREEN (xmin, ymin)-(xmax, ymax)
LINE (xmin, ymin)-(xmax, ymax), 1, B
x0 = xmin
loop1:  x0 = x0 + dx
        LOCATE 5, 35: PRINT USING "x0=####"; x0
        LINE (x0, ymin + dy)-(x0 + 5, ymax - dy), 1, BF
stall:  x$ = INKEY$: IF x$ = "" THEN GOTO stall
        IF x$ = CHR$(27) THEN END
        GOTO loop1

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