How do you make a window float above all others?

Here's a sample program showing floating windows (derived from dvipm). The advantages over the WM_TIMER approach [which was presented in v2.2 -ed] are:

o

there's no delay

repainting is minimized

avoids timing problems

the floating windows are not unconditionally moved to the very top (that is, when moving the base window B (with floating window F) behind a window W, the order of the windows is this: BFW, not BWF!)

The excessive repainting caused by other solutions was quite annoying with dvipm as recomputing the dvipm status window is slow.

Credit: Eberhard Mattes

/* floatwin.c */
/* This program shows how to implement floating windows.  The source
   code works with both 16-bit and 32-bit C compilers.

   If the Z-order of the base window is changed, the floating window
   will be moved on top of the base window.

   Generalizing this approach to many windows floating on many windows
   (floating on many windows ...) is left as exercise. */

#define INCL_WIN
#define INCL_GPI
#include <os2.h>

/* Syntactic sugar for supporting both 16-bit and 32-bit compilers. */

#ifdef __32BIT__
#define MSG ULONG
#define FLAGS fl
#else
#define MSG USHORT
#define FLAGS fs
#endif
#ifndef NULLHANDLE
#define NULLHANDLE NULL
#endif

/* The original frame window procedure. */
static PFNWP pfOldBaseFrameProc = NULL;

/* The handle of the floating window. */
static HWND hwndFloat = NULLHANDLE;

/* This frame window procedure is used for subclassing base windows.
   When changing the Z-order of the frame window, the floating window
   is moved instead of the base window and the hwndInsertBehind field
   is modified to move the base window behind the floating window. */

MRESULT EXPENTRY
BaseFrameProc (HWND hwnd, MSG msg, MPARAM mp1, MPARAM mp2)
{
  PSWP pswp;

  switch (msg)
    {
    case WM_ADJUSTWINDOWPOS:
      pswp = PVOIDFROMMP (mp1);
      if ((pswp->FLAGS & SWP_ZORDER) && hwndFloat != NULLHANDLE
           && WinIsWindowVisible (hwndFloat))
        {
          WinSetWindowPos (hwndFloat, pswp->hwndInsertBehind,
                           0, 0, 0, 0, SWP_ZORDER);
          /* This is the trick! */
          pswp->hwndInsertBehind = hwndFloat;
        }
      break;
    }
  return pfOldBaseFrameProc (hwnd, msg, mp1, mp2);
}


/* Common client window procedure for base windows and floating
   windows.  Display TXT and use CLR for filling the background. */

MRESULT CommonClientWndProc (HWND hwnd, MSG msg, MPARAM mp1, MPARAM mp2,
                             PCH txt, COLOR clr)
{
  HPS hps;
  RECTL rcl;

  switch (msg)
    {
    case WM_PAINT:
      hps = WinBeginPaint (hwnd, 0L, 0L);
      WinQueryWindowRect (hwnd, &rcl);
      GpiSetColor (hps, CLR_DARKCYAN);
      GpiSetBackColor (hps, clr);
      WinDrawText (hps, -1, txt, &rcl, 0, 0,
                   DT_TEXTATTRS | DT_CENTER | DT_VCENTER | DT_ERASERECT);
      WinEndPaint (hps);
      return 0;
    }
  return WinDefWindowProc (hwnd, msg, mp1, mp2);
}


/* Client window procedure for floating windows. */

MRESULT EXPENTRY FloatClientWndProc (HWND hwnd, MSG msg, MPARAM mp1, MPARAM mp2)
{
  return CommonClientWndProc (hwnd, msg, mp1, mp2, "Floating Window", CLR_RED);
}

/* Client window procedure for base windows. */

MRESULT EXPENTRY BaseClientWndProc (HWND hwnd, MSG msg, MPARAM mp1, MPARAM mp2)
{
  return CommonClientWndProc (hwnd, msg, mp1, mp2, "Base Window", CLR_YELLOW);
}


/* Start here. */

int main (void)
{
  static char szBaseClientClass[] = "floatwin.base";
  static char szFloatClientClass[] = "floatwin.float";
  ULONG flFrameFlags;
  HAB hab;
  HMQ hmq;
  QMSG qmsg;
  HWND hwndBase;

  /* Initialize Presentation Manager. */

  hab = WinInitialize (0);
  hmq = WinCreateMsgQueue (hab, 0);

  /* Create client window classes. */

  WinRegisterClass (hab, szBaseClientClass, BaseClientWndProc,
                    CS_SIZEREDRAW, 0);
  WinRegisterClass (hab, szFloatClientClass, FloatClientWndProc,
                    CS_SIZEREDRAW, 0);

  /* Create the base window and the floating window.  Note: the
     windows are initially invisible. */

  flFrameFlags = (FCF_TITLEBAR      | FCF_SYSMENU |
                  FCF_SIZEBORDER    | FCF_MINMAX  |
                  FCF_TASKLIST);

  /* Create and subclass the base window. */

  hwndBase = WinCreateStdWindow (HWND_DESKTOP, 0,
                                 &flFrameFlags, szBaseClientClass,
                                 "floatwin - Base Window",
                                 0L, 0, 1, NULL);
  pfOldBaseFrameProc = WinSubclassWindow (hwndBase, BaseFrameProc);

  /* Create the floating window. */

  hwndFloat = WinCreateStdWindow (HWND_DESKTOP, 0,
                                  &flFrameFlags, szFloatClientClass,
                                  "floatwin - Floating Window",
                                  0L, 0, 1, NULL);

  /* Set the position, size and Z-order of the windows and make them
     visible.  It's important to use SWP_ZORDER for the base
     window. */

  WinSetWindowPos (hwndFloat, HWND_TOP, 10, 10, 300, 80,
                   SWP_SHOW | SWP_MOVE | SWP_SIZE | SWP_ZORDER);
  WinSetWindowPos (hwndBase, HWND_TOP, 100, 50, 300, 80,
                   SWP_SHOW | SWP_MOVE | SWP_SIZE | SWP_ZORDER | SWP_ACTIVATE);

  /* The message loop. */

  while (WinGetMsg (hab, &qmsg, 0L, 0, 0))
    WinDispatchMsg (hab, &qmsg);

  /* Clean up. */

  WinDestroyWindow (hwndBase);
  WinDestroyWindow (hwndFloat);
  WinDestroyMsgQueue (hmq);
  WinTerminate (hab);

  return 0;
}