BUG: M6101 Drawing a Line Outside Screen Coordinates (118815)

The information in this article applies to:

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

This article was previously published under Q118815

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

Modification Type:	Major	Last Reviewed:	10/2/2003
Keywords:	KB118815