First _pg_chartscatter Call May Not Use Specified plotchar

MS-DOS                 | OS/2       | WINDOWS

The information in this article applies to:

• The C Run-time (CRT), included with:

      - Microsoft C for MS-DOS, versions 6.0, 6.0a, and 6.0ax
      - Microsoft C for OS/2, versions 6.0, and 6.0a
      - Microsoft C/C++ for MS-DOS, versions 7.0
      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

SUMMARY

In Microsoft C versions 6.0, 6.0a, 6.0ax, C/C++ version 7.0, and Visual C/C++ version 1.0, when producing scatter charts with the Presentation Graphics function _pg_chartscatter(), the first scatter chart created in a program may be drawn with the default plotting character even if a different character was specified. This usually results from calling _pg_initchart() before setting the graphics video mode with _setvideomode().

MORE INFORMATION

The problem stems from an initialization sequence for the palette that is used whenever a new video mode is set. If the call to _pg_initchart is made AFTER a call to _setvideomode(), then the palette should not be affected.

The sample program below demonstrates this problem and the workaround. The program draws two scatter charts. For the first chart, the '$' character is specified for the plotting character. For the second chart, the '#' character is the plotting character. The second chart uses the '#' character as specified, but the first chart is drawn with the '*' character, which is the default plotting character.

If the program is altered, so that the call to _pg_initchart is moved down a few lines to after the call to _setvideomode(), then the problem goes away and the first chart is drawn correctly with the '$' character.

This is expected behavior. After entering a new video mode, a call to _pg_initchart() should be made, then the palette should be changed. The current plot character is considered to be part of the palette and requires a valid video mode to be set before the palette is set.

Sample Code

/* TEST.C
   Compile line: CL test.c graphics.lib pgchart.lib  */

#include <conio.h>
#include <graph.h>
#include <string.h>
#include <stdlib.h>
#include <pgchart.h>

void main(void)

    chartenv env;
    palettetype pal;
    int i;

    /* Move the following line to after the call to _setvideomode() */
    _pg_initchart();
    if( !_setvideomode( _MAXRESMODE ) )
        exit( 1 );

    _pg_defaultchart (&env, _PG_SCATTERCHART, _PG_POINTONLY );
    strcpy( env.maintitle.title, "Scatter Test" );
    strcpy( env.xaxis.axistitle.title, "X Amount" );
    strcpy( env.yaxis.axistitle.title, "Y Amount" );

    strcpy( env.subtitle.title, "\"plotchar\" should be '$'" );
    _pg_getpalette(pal);
    for(i=0; i < _PG_PALETTELEN; i++)
        pal[i].plotchar = '$';
    _pg_setpalette(pal);
    _pg_chartscatter( &env, x[0], y[0], 5 );
    getch();
    _clearscreen( _GCLEARSCREEN );

    strcpy( env.subtitle.title, "\"plotchar\" should be '#'" );
    _pg_getpalette(pal);
    for(i=0; i < _PG_PALETTELEN; i++)
        pal[i].plotchar = '#';
    _pg_setpalette(pal);
    _pg_chartscatter( &env, x[0], y[0], 5 );
    getch();
    _clearscreen( _GCLEARSCREEN );

    _setvideomode( _DEFAULTMODE );