Line to rectangle clipping

clip.cpp

	//http://stackoverflow.com/questions/99353/how-to-test-if-a-line-segment-intersects-an-axis-aligned-rectange-in-2d

	enum {
		OUT_LEFT = 1,
		OUT_TOP = 2,
		OUT_RIGHT = 4,
		OUT_BOTTOM = 8
	};

    INT _ThroughCode(LONGPOSITION pt) 
	{
        INT out = 0;
        if (pt.lX < m_rcBound.lLeft) {
            out |= OUT_LEFT;
        } else if (pt.lX > m_rcBound.lRight) {
            out |= OUT_RIGHT;
        }
		if (pt.lY > m_rcBound.lTop) {
            out |= OUT_TOP;
        } else if (pt.lY < m_rcBound.lBottom) {
            out |= OUT_BOTTOM;
        }
        return out;
    }

	BOOL32 _Through( const LONGPOSITION& ptA, const LONGPOSITION& ptB, LONGPOSITION& ptResultP, LONGPOSITION& ptResultQ )
	{
		_ASSERT( m_rcBound.GetWidth() > 0 );
		_ASSERT( m_rcBound.GetHeight() > 0 );
        INT out1, out2;
        if ( (out2 = _ThroughCode( ptB ) ) == 0 ) 
		{
			// je vovnutri - neni splnena podmienka
			_ASSERT( 0 );
			return FALSE;
		}

		ptResultQ = ptB;
		ptResultP = ptA;
        while ( (out1 = _ThroughCode( ptResultP ) ) != 0 ) 
		{
            if ( out1 & out2 )
                return FALSE;

            if ( out1 & (OUT_LEFT | OUT_RIGHT) ) 
			{
				LONG x = (out1 & OUT_RIGHT) ? m_rcBound.lRight : m_rcBound.lLeft;
                ptResultP.lY = SMULDIV( ptResultP.lY, (x - ptResultP.lX), (ptResultQ.lY - ptResultP.lY), (ptResultQ.lX - ptResultP.lX) );
				ptResultP.lX = x;
            } else 
			{
				LONG y = (out1 & OUT_BOTTOM) ? m_rcBound.lBottom : m_rcBound.lTop;
                ptResultP.lX = SMULDIV( ptResultP.lX, (y - ptResultP.lY), (ptResultQ.lX - ptResultP.lX), (ptResultQ.lY - ptResultP.lY) );
				ptResultP.lY = y;
            }
        }
		// ptA (ptResultP) aligned

		while ( (out2 = _ThroughCode( ptResultQ ) ) != 0 ) 
		{
            if ( out2 & (OUT_LEFT | OUT_RIGHT) ) 
			{
				LONG x = (out2 & OUT_RIGHT) ? m_rcBound.lRight : m_rcBound.lLeft;
                ptResultQ.lY = SMULDIV( ptResultQ.lY, (x - ptResultQ.lX), (ptResultP.lY - ptResultQ.lY), (ptResultP.lX - ptResultQ.lX) );
				ptResultQ.lX = x;
			} else 
			{
				LONG y = (out2 & OUT_BOTTOM) ? m_rcBound.lBottom : m_rcBound.lTop;
                ptResultQ.lX = SMULDIV( ptResultQ.lX, (y - ptResultQ.lY), (ptResultP.lX - ptResultQ.lX), (ptResultP.lY - ptResultQ.lY) );
				ptResultQ.lY = y;
            }
        }
		// ptB (ptResultQ) aligned

        return TRUE;
    }