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Q118815: BUG: M6101 Drawing a Line Outside Screen Coordinates

Article: Q118815
Product(s): Microsoft Fortran Compiler
Version(s): 1.0,1.0a
Operating System(s): 
Keyword(s): 
Last Modified: 02-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft FORTRAN PowerStation for MS-DOS, versions 1.0, 1.0a 
-------------------------------------------------------------------------------

SYMPTOMS
========

When a program draws a line with an endpoint outside the screen coordinates, the
line is not clipped and the following error message is generated:

  run-time error M6101: MATH
  - floating-point error: invalid

CAUSE
=====

The limit seems to be related to converting to an int. In the sample code below,
the extent of X in the window coordinates is 1.0, the screen coordinate is 639,
and the line is drawn to 51.28. For example:

     639 * 51.28 / 1.0 = 32,767.92 > 32,767

In the preceding example, a line drawn to 51.27 succeeds (639 * 51.27 / 1.0 =
32,761.53 < 32,767).

RESOLUTION
==========

Do not draw outside the screen coordinates. Clip the endpoints of lines before
calling the LINETO_W routine. If you clip to values within 10 times the size of
the window, the code should work in any resolution.

STATUS
======

Microsoft has confirmed this to be a bug with Microsoft FORTRAN PowerStation for
MS-DOS, versions 1.0 and 1.0a.

MORE INFORMATION
================

To demonstrate this problem, compile the following sample code and run it from a
full-screen MS-DOS prompt in Windows (not Windows NT) or directly from MS-DOS.

Sample Code
-----------

  C Compile options needed: none
        INCLUDE  'FGRAPH.FI'
        INCLUDE  'FGRAPH.FD'
        INTEGER*2 status
        status = SETVIDEOMODE( $VRES16COLOR )
        status = setwindow(.TRUE.,0D0,1.D0,1.D0,0.D0 )
        status = LINETO_W( 51.28d0, 0.0d0 )
        status = SETVIDEOMODE( $DEFAULTMODE )
        END

Additional query words: 1.00 1.00a

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbFortranSearch kbZNotKeyword3 kbFORTRANPower100DOS kbFORTRANPower100aDOS
Version           : :1.0,1.0a

=============================================================================

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