Thread: novel method of dragging

>>I saw this novel method to initiate dragging of a window<<

It's a variation on a theme; another is:

Code:

SendMessage(hwnd,WM_SYSCOMMAND,HTCAPTION|SC_MOVE, lParam);

(search this board for that one). Ultimately, all that's happening is something like:

Code:

case WM_NCHITTEST:
  if (GetAsyncKeyState(VK_LBUTTON)&0x8000)
    {
    return HT_CAPTION;
    }
  else
    {
    /*return default handling (DefWindowProc,CallWindowProc etc.)*/
    }

(check out WM_NCHITTEST).

From what I understand, WM_NCHITTEST effectively synthesises the other mouse messages so, when you skew its behaviour by telling it it's left-clicked on the caption, this is responsible for the loss of the other mouse messages.

So, you can either

1. synthesise the mouse message of interest yourself, eg for WM_LBUTTONUP, something like:

Code:

case WM_NCHITTEST:
  {
  static BOOL bIsLButtonDown;
  if (GetAsyncKeyState(VK_LBUTTON)&0x8000)
    {
    bIsLButtonDown=TRUE;
    return HTCAPTION;
    }
  else
    {
    if (bIsLButtonDown==TRUE)
      {
      POINT pt={LOWORD(lParam),HIWORD(lParam)};
      UINT uFlags=0;
      
      bIsLButtonDown=FALSE;
      /*need to convert mouse coords*/
      ScreenToClient(hwnd,&pt);
      /*synthesise mouse up event*/
      /*first get state of other mouse buttons; should, ideally get 
        key states of SHIFT and CTRL buttons on keyboard, too.*/ 
      if (GetAsyncKeyState(VK_MBUTTON)&0x8000)
        {
        uFlags|=MK_MBUTTON;
        }
      if (GetAsyncKeyState(VK_RBUTTON)&0x8000)
        {
        uFlags|=MK_RBUTTON;
        }
    SendMessage(hwnd,WM_LBUTTONUP,uFlags,MAKELPARAM( pt.x,pt.y));
    }
  /*return DefWindowProc,CallWindowProc etc*/
  }

or,

2. much simpler, you could just handle the WM_EXITSIZEMOVE message, ie.

Code:

case WM_EXITSIZEMOVE:
  {
  if (!GetAsyncKeyState(VK_LBUTTON)&0x8000)
    {
    /*mouse L-button is up*/
    }
  return 0;
  }

Please note that GetAsyncKeyState works with physical mouse buttons so may not necessarily correspond to the way a user may have configured their mouse (GetSystemMetrics will resolve any uncertainty here).