win32 content changed but doesn't show update unless window is moved

Question

My win32 GUI content changes every second but it doesn't show update unless the window is manually moved. I tried to pop up a messagebox every second to trigger the window to refresh and it worked. Hence it proves that my content really changes but the window doesnt update. I want the window to refresh without popping up a messagebox everytime, is there a windows function for this? Thanks

case WM_PAINT:


RECT fingerprintSection;
fingerprintSection.left=500;
fingerprintSection.top=300;
fingerprintSection.bottom=540;
fingerprintSection.right=660;

    wmId    = LOWORD(wParam);
    hdc = BeginPaint(hWnd, &ps);

    refresh=!refresh;
    if((start==true)&&(refresh==true)&&(stop!=true))
    {       

    windowName = MultiByteStringToWideString(name1, CP_ACP);
    LoadAndBlitBitmap(windowName.c_str(), hdc,500,0);//loading a picture that doesnt change
    fingerprint();
    LoadAndBlitBitmap(TEXT("outresized.bmp"), hdc,500,300);//loading a picture that constantly change
    refresh=!refresh;

//RedrawWindow(hWnd,&fingerprintSection,NULL,RDW_INTERNALPAINT|RDW_VALIDATE|RDW_UPDATENOW|RDW_NOCHILDREN);

InvalidateRect( hWnd, &fingerprintSection, TRUE );
    }
    EndPaint(hWnd, &ps);
    break;

Answer 1

If you are drawing in a window outside of WM_PAINT (I guess in this case you are probably doing some GDI drawing on a timer when you get a WM_TIMER message), then you should call InvalidateRect() e.g.

InvalidateRect( hWnd, NULL, FALSE );   // invalidate whole window

This should cause Windows to redraw the whole window. If you have only written a small area, pass a RECT describing the area you have written.

If you want to draw when your windows procedure receives a WM_PAINT message AND for example, want to force that to happen every second, then set a timer...

#define SECOND_TIMER 1000

case WM_INITDIALOG:
   SetTimer( hWnd, SECOND_TIMER, SECOND_TIMER, NULL );
   //other initialisation stuff
   break;

case WM_TIMER:
   if( wParam == SECOND_TIMER )
   { 
       InvalidateRect( hWnd, NULL, FALSE );   // invalidate whole window
   }
   break;

In this simple case the whole window should be redrawn every second since Windows will send a WM_PAINT message due to the InvalidateRect. Ideally you should only invalidate the part you are redrawing.