ENVIRONMENTS
CHARLES PETZOLD
Vol. 9, No. 11

---------------------------------------------------------
 THREADS2.C -- Demonstrates drawing from a second thread
               (c) 1990, Ziff Communications Co.
               PC Magazine * Charles Petzold, 1/90
---------------------------------------------------------

#define INCL_WIN
#define INCL_GPI
#include <os2.h>
#include <mt\process.h>

#define STACKSIZE 4096 * sizeof (int)

typedef struct
     {
     HPS   hps ;
     BOOL  fContinue ;
     BOOL  fTerminate ;
     SHORT cxClient ;
     SHORT cyClient ;
     ULONG semTriggerDraw ;
     ULONG semDoingDraw ;
     }
     THREADPARAMS ;

MRESULT EXPENTRY ClientWndProc (HWND, USHORT, MPARAM, MPARAM) ;
VOID    FAR      SecondThread (THREADPARAMS *) ;
VOID             DrawPattern (HPS, SHORT, SHORT, BOOL *) ;
VOID             DrawLine (HPS, SHORT, SHORT, SHORT, SHORT) ;

HAB  hab ;

int main (void)
     {
     static CHAR  szClientClass [] = "Threads2" ;
     static ULONG flFrameFlags = FCF_TITLEBAR      | FCF_SYSMENU |
                                 FCF_SIZEBORDER    | FCF_MINMAX  |
                                 FCF_SHELLPOSITION | FCF_TASKLIST ;
     HMQ          hmq ;
     HWND         hwndFrame, hwndClient ;
     QMSG         qmsg ;

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

     WinRegisterClass (hab, szClientClass, ClientWndProc, CS_SIZEREDRAW, 0) ;

     hwndFrame = WinCreateStdWindow (HWND_DESKTOP, WS_VISIBLE,
                                     &flFrameFlags, szClientClass, NULL,
                                     0L, NULL, 0, &hwndClient) ;

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

     WinDestroyWindow (hwndFrame) ;
     WinDestroyMsgQueue (hmq) ;
     WinTerminate (hab) ;
     return 0 ;
     }

MRESULT EXPENTRY ClientWndProc (HWND hwnd, USHORT msg, MPARAM mp1, MPARAM mp2)
     {
     static int          aiThreadStack [STACKSIZE / sizeof (int)] ;
     static THREADPARAMS tp ;
     HDC                 hdc ;
     SIZEL               sizl ;

     switch (msg)
          {
          case WM_CREATE:
                              // create a presentation space for the window

               hdc = WinOpenWindowDC (hwnd) ;
               sizl.cx = 0 ;
               sizl.cy = 0 ;
               tp.hps = GpiCreatePS (hab, hdc, &sizl,
                                     PU_PELS    | GPIF_DEFAULT |
                                     GPIT_MICRO | GPIA_ASSOC) ;

                              // start the thread after initialization

               tp.fTerminate = FALSE ;

               DosSemSet (&tp.semTriggerDraw) ;
               DosSemClear (&tp.semDoingDraw) ;

               if (_beginthread (SecondThread, aiThreadStack,
                                 STACKSIZE, &tp) == -1)
                    {
                    WinMessageBox (HWND_DESKTOP, hwnd,
                                   "Cannot create second thread!", "Threads2",
                                   0, MB_OK | MB_ICONEXCLAMATION) ;
                    return 0 ;
                    }

               return 0 ;

          case WM_SIZE:
                              // stop the thread from drawing

               tp.fContinue = FALSE ;
               DosSemWait (&tp.semDoingDraw, SEM_INDEFINITE_WAIT) ;

               tp.cxClient = SHORT1FROMMP (mp2) ;
               tp.cyClient = SHORT2FROMMP (mp2) ;
               return 0 ;

          case WM_PAINT:
                              // stop the thread from drawing

               tp.fContinue = FALSE ;
               DosSemWait (&tp.semDoingDraw, SEM_INDEFINITE_WAIT) ;

                              // erase the whole window

               WinInvalidateRect (hwnd, NULL, FALSE) ;

               WinBeginPaint (hwnd, tp.hps, NULL) ;
               GpiErase (tp.hps) ;
               WinEndPaint (tp.hps) ;

                              // let the thread start again at the beginning

               tp.fContinue = TRUE ;
               DosSemSet (&tp.semDoingDraw) ;
               DosSemClear (&tp.semTriggerDraw) ;
               return 0 ;

          case WM_DESTROY:
                              // stop the thread and clean up

               tp.fTerminate = TRUE ;
               tp.fContinue  = FALSE ;
               DosSemWait (&tp.semDoingDraw, SEM_INDEFINITE_WAIT) ;

               GpiDestroyPS (tp.hps) ;
               return 0 ;
          }
     return WinDefWindowProc (hwnd, msg, mp1, mp2) ;
     }

VOID _CDECL FAR SecondThread (THREADPARAMS * ptp)
     {
     HAB  hab ;

     hab = WinInitialize (0) ;

     while (!ptp->fTerminate)
          {
                              // wait for the semaphore to be cleared

          DosSemWait (&ptp->semTriggerDraw, SEM_INDEFINITE_WAIT) ;

                              // draw the pattern until stopped

          while (ptp->fContinue)
               DrawPattern (ptp->hps, ptp->cxClient,
                                      ptp->cyClient, &ptp->fContinue) ;

          DosSemSet (&ptp->semTriggerDraw) ;
          DosSemClear (&ptp->semDoingDraw) ;
          }

     WinTerminate (hab) ;
     _endthread () ;
     }

VOID DrawPattern (HPS hps, SHORT cxClient, SHORT cyClient, BOOL *pfContinue)
     {
     SHORT x, y ;

     GpiSetMix (hps, FM_INVERT) ;

     for (x = 0 ; *pfContinue && x < cxClient ; x++)
          DrawLine (hps, 0, 0, x, cyClient) ;

     for (y = cyClient ; *pfContinue && y > 0 ; y--)
          DrawLine (hps, 0, 0, cxClient, y) ;

     for (y = 0 ; *pfContinue && y < cyClient ; y++)
          DrawLine (hps, cxClient, 0, 0, y) ;

     for (x = 0 ; *pfContinue && x < cxClient ; x++)
          DrawLine (hps, cxClient, 0, x, cyClient) ;

     for (x = cxClient ; *pfContinue && x > 0 ; x--)
          DrawLine (hps, cxClient, cyClient, x, 0) ;

     for (y = 0 ; *pfContinue && y < cyClient ; y++)
          DrawLine (hps, cxClient, cyClient, 0, y) ;

     for (y = cyClient ; *pfContinue && y > 0 ; y--)
          DrawLine (hps, 0, cyClient, cxClient, y) ;

     for (x = cxClient ; *pfContinue && x > 0 ; x--)
          DrawLine (hps, 0, cyClient, x, 0) ;
     }

VOID DrawLine (HPS hps, SHORT x1, SHORT y1, SHORT x2, SHORT y2)
     {
     POINTL ptl ;

     ptl.x = x1 ; ptl.y = y1 ; GpiMove (hps, &ptl) ;
     ptl.x = x2 ; ptl.y = y2 ; GpiLine (hps, &ptl) ;
     }