Calculating the window coordinate

┌──────────────────────────────────────────────────────────────────────┐
│To calculate the window coordinate of your execution environment, use │
│WinQuerySysValue and obtain a resolution of the display.              │
└──────────────────────────────────────────────────────────────────────┘

DBCS OS/2 supports various display resolutions just like on SBCS OS/2. To draw graphical objects on PS/55 the way they are shown on PS/2, you need to calculates the window coordinate for PS/55. For this purpose, you need to know the display resolution of the run-time environment. Use WinQuerySysValue to obtain its value.

┌──────────────────────────────────────────────────────────────────────┐
│Use GpiQueryFontMetrics to find the font size at the runtime          │
│environment.                                                          │
└──────────────────────────────────────────────────────────────────────┘

To calculate how many characters you can present in a PM control such as a list-box, you need to know the width and the height of the current font. This can be obtained by using GpiQueryFontMetrics.
Calculating a window size (source: MISCMAIN.C)

   ...
static LONG desk_cx, desk_cy;
   ...

    GetFontSize( hpsMain, &lAveWidth, &lFontHeight );

    hwndFrame = WinQueryWindow(hwnd, QW_PARENT);

    desk_cx = WinQuerySysValue( HWND_DESKTOP, SV_CXSCREEN );
    desk_cy = WinQuerySysValue( HWND_DESKTOP, SV_CYSCREEN );

    /* set window width to show MAIN_WIN_WIDTH SBCS characters */
    cx = (lAveWidth*MAIN_WIN_WIDTH>desk_cx) ? desk_cx : lAveWidth*MAIN_WIN_WIDTH;

    /* set window height large enough to show a string pointed to by sText.*/
    cy = (((strlen(sText)/MAIN_WIN_WIDTH)+10)*lFontHeight>desk_cy) ?
          desk_cy : ((strlen(sText)/MAIN_WIN_WIDTH) + 10)*lFontHeight;

    x = (cx<desk_cx) ? (desk_cx-cx)/2 : 0;
    y = (cy<desk_cy) ? (desk_cy-cy)/2 : 0;

    WinSetWindowPos(hwndFrame,
                    HWND_BOTTOM,
                    x, y, cx, cy,
                    SWP_MOVE | SWP_SIZE | SWP_ACTIVATE);
   ...
/************************************************/
/* GetFontSize:                                 */
/* Get the following system value from PM APIs. */
/*   Average character width                    */
/*   Character height                           */
/************************************************/
void GetFontSize(HPS hps, LONG *lWidth, LONG *lHeight)
{
  FONTMETRICS fm;

  GpiQueryFontMetrics(hps, (LONG)sizeof(FONTMETRICS), &fm);
  *lWidth = fm.lAveCharWidth;
  *lHeight = fm.lMaxBaselineExt + fm.lExternalLeading;
}