C++ Header Guard

#ifndef _0C46500C_084D_44ac_8C26_37E38BED2714_
#define _0C46500C_084D_44ac_8C26_37E38BED2714_
#pragma once

#ifdef __ATLBASE_H__
#include <atlmisc.h>
template <class T> class CSnapWindow
#else
class CSnapWindow
#endif
{
public:
       int snap_Margin, snap_ModifierKey;

#ifdef __ATLBASE_H__
	BEGIN_MSG_MAP(CSnapWindow<T>)
		MESSAGE_HANDLER(WM_MOVING, OnSnapMoving)
		MESSAGE_HANDLER(WM_ENTERSIZEMOVE, OnSnapEnterSizeMove)
	END_MSG_MAP()
#endif

#ifdef __ATLBASE_H__                                                                 
	virtual LRESULT OnSnapEnterSizeMove(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)
#else
	virtual LRESULT OnSnapEnterSizeMove(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
#endif
					{
						snap_cur_pos.x=0;
						snap_cur_pos.y=0;

						snap_rcWindow.bottom=0;
						snap_rcWindow.left=0;
						snap_rcWindow.right=0;
						snap_rcWindow.top=0;

					#ifdef __ATLBASE_H__ 
						T* pT = static_cast<T*>(this);
						GetWindowRect(pT->m_hWnd, &snap_rcWindow );
					#else
						GetWindowRect(hWnd, &snap_rcWindow );
					#endif

						GetCursorPos( &snap_cur_pos );

						snap_x = snap_cur_pos.x - snap_rcWindow.left;
						snap_y = snap_cur_pos.y - snap_rcWindow.top;
					return 0;
					}

#ifdef __ATLBASE_H__ 
	virtual LRESULT OnSnapMoving(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)
#else
	virtual LRESULT OnSnapMoving(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
#endif
					{
						//no snap if shift key pressed
						if (GetAsyncKeyState(snap_ModifierKey) < 0) return FALSE;

						snap_prc = (LPRECT)lParam;

						snap_cur_pos.x=0;
						snap_cur_pos.y=0;
						snap_rcWindow.bottom=0;
						snap_rcWindow.left=0;
						snap_rcWindow.right=0;
						snap_rcWindow.top=0;

						GetCursorPos( &snap_cur_pos );
						OffsetRect( snap_prc,
							snap_cur_pos.x - (snap_prc->left + snap_x) ,
							snap_cur_pos.y - (snap_prc->top  + snap_y) );

						//it may change during app lifetime
						SystemParametersInfo( SPI_GETWORKAREA, 0, &snap_wa, 0 );

						if (isSnapClose( snap_prc->left, snap_wa.left )) {OffsetRect( snap_prc, snap_wa.left - snap_prc->left, 0);}
						else 
							if (isSnapClose( snap_wa.right, snap_prc->right )) {OffsetRect( snap_prc, snap_wa.right - snap_prc->right, 0);}

						if (isSnapClose( snap_prc->top, snap_wa.top )) {OffsetRect( snap_prc, 0, snap_wa.top - snap_prc->top );}
						else 
							if (isSnapClose( snap_wa.bottom, snap_prc->bottom )) {OffsetRect( snap_prc, 0, snap_wa.bottom - snap_prc->bottom );}
					return TRUE;
					}

	virtual BOOL isSnapClose( int a, int b ) { return (abs( a - b ) < snap_Margin);}

	CSnapWindow()
		{
		snap_ModifierKey=VK_SHIFT;
		NONCLIENTMETRICS ncm = { 0 };
		ncm.cbSize = sizeof ncm;
		SystemParametersInfo( SPI_GETNONCLIENTMETRICS, 0, &ncm, 0 );
		snap_Margin=ncm.iCaptionHeight;
		}
private:
	POINT snap_cur_pos;
	RECT snap_rcWindow, snap_wa, *snap_prc;
	int snap_x, snap_y;
};
#endif//_0C46500C_084D_44ac_8C26_37E38BED2714_