DOCUMENT:Q118815  02-NOV-1999  [fortran]
TITLE   :BUG: M6101 Drawing a Line Outside Screen Coordinates
PRODUCT :Microsoft Fortran Compiler
PROD/VER::1.0,1.0a
OPER/SYS:
KEYWORDS:

======================================================================
-------------------------------------------------------------------------------
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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