CGDI - Simple GDI Set And Reset

In MFC, GDI Objects need to be selected and then destroyed. CGDI and its derived classes take care of this by selecting the object in the constructor and deselecting it in the destructor. CGDIObject is a template class which takes as its parameter the CGdiObject-derived class. This class library only accounts for a few of the set/get function pairs. This could be extended by creating classes for each of the CDC Set/Get functions. Examples:

// Example to draw a line using the BLACK_PEN stock object
void DrawLine(CDC* pDC)
{
    CStockObject theObject(pDC, BLACK_PEN);

    pDC->LineTo(100, 100);
}

// Example to draw a line using a custom pen
void DrawLinesWithPen(CDC* pDC)
{                                                         // Current Pen Selected
    CPen thePen(PS_SOLID, 3, RGB(100, 200, 2));

    CGDIObject<CPen> theObject(pDC, &thePen);                  // thePen Selected

    pDC->LineTo(100, 100);

    // Use brackets to nest calls
    {
        CPen theOtherPen(PS_SOLID, 3, RGB(200, 10, 2));         

        CGDIObject<CPen> theOtherObject(pDC, &theOtherPen);    // theOtherPen Selected

        pDC->LineTo(200, 200);
    }                                                     // thePen Selected

    pDC->LineTo(300, 300);
}                                                         // Current Pen Selected




// helper template function for unused parameters
template <class T>
void Unused(T rT)
{
    static_cast<void>(rT);
};


class CGDI
{
protected:
    CDC* m_pDC;

    CGDI(CDC* pDC) : 
      m_pDC(pDC)
    {
    }

    virtual ~CGDI()
    {
        m_pDC = NULL;
    }
};

// Class to select a stock object
class CGDIStockObject : public CGDI
{
    CGdiObject* m_pLastObject;

public:
    CGDIStockObject(CDC* pDC, int nIndex) : CGDI(pDC),
      m_pLastObject(NULL)
    {
        m_pLastObject = m_pDC->SelectStockObject(nIndex);
    }

    virtual ~CGDIStockObject()
    {
        if (m_pLastObject)
        {
            Unused(m_pDC->SelectObject(m_pLastObject));

            m_pLastObject = NULL;
        }
    }
};


class CGDITextColor : public CGDI
{
    COLORREF m_LastColor;

public:
    CGDITextColor(CDC* pDC, COLORREF theColor) : CGDI(pDC),
      m_LastColor(RGB(0,0,0))
    {
        m_LastColor = m_pDC->SetTextColor(theColor);
    }

    virtual ~CGDITextColor()
    {
        Unused(m_pDC->SetTextColor(m_LastColor));
    }

};

class CGDIBackColor : public CGDI
{
    COLORREF m_LastColor;

public:
    CGDIBackColor(CDC* pDC, COLORREF theColor) : CGDI(pDC),
      m_LastColor(RGB(0,0,0))
    {
        m_LastColor = m_pDC->SetBkColor(theColor);
    }

    virtual ~CGDIBackColor()
    {
        Unused(m_pDC->SetBkColor(m_LastColor));
    }

};

class CGDIBackMode : public CGDI
{
    int m_LastMode;

public:
    CGDIBackMode(CDC* pDC, int theMode) : CGDI(pDC),
	  m_LastMode(0)
    {
        m_LastMode = m_pDC->SetBkMode(theMode);
    }

    virtual ~CGDIBackMode()
    {
        Unused(m_pDC->SetBkMode(m_LastMode));
    }

};

// This class can be used like this:
// CGDIObject<CFont>(pDC, pFont);
// CGDIObject<CPen>(pDC, pPen);

template <class T>
class CGDIObject : public CGDI
{
T* m_pLast;

public:
    CGDIObject(CDC* pDC, T* pObject) : CGDI(pDC), 
	  m_pLast(NULL)
    {
        if (pObject)
        {
            m_pLast = pDC->SelectObject(pObject);
        }
    }

    virtual ~CGDIObject()
    {
        if (m_pLast)
        {
            Unused(m_pDC->SelectObject(m_pLast));

            m_pLast = NULL;
        }
    }
};

class CGDITextAlign : public CGDI
{
UINT m_Last;

public:
    CGDITextAlign(CDC* pDC, UINT nTextAlign) : CGDI(pDC),
	  m_Last(0)
    {
        m_Last = pDC->SetTextAlign(nTextAlign);
    }

    virtual ~CGDITextAlign()
    {
        Unused(m_pDC->SetTextAlign(m_Last));
    }
};


class CGDIROP : public CGDI
{
int m_Last;

public:
    CGDIROP(CDC* pDC, int nROP) : CGDI(pDC),
	  m_Last(0)
    {
        m_Last = pDC->SetROP2(nROP);
    }

    virtual ~CGDIROP()
    {
        Unused(m_pDC->SetROP2(m_Last));
    }
};

class CGDIMapMode : public CGDI
{
int m_Last;

public:
    CGDIMapMode(CDC* pDC, int nMapMode) : CGDI(pDC),
	  m_Last(0)
    {
        m_Last = pDC->SetMapMode(nMapMode);
    }

    virtual ~CGDIMapMode()
    {
        Unused(m_pDC->SetMapMode(m_Last));
    }
};

Last updated: 8 June 1998



Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Are you truly leading your team or simply managing them? Organizations need leaders and your team needs someone to follow. With some ongoing development, you could become that leader. Learn the top leadership qualities that inspire others to want to follow you and the direction of your company.

  • On-demand Event Event Date: March 19, 2015 The 2015 Enterprise Mobile Application Survey asked 250 mobility professionals what their biggest mobile challenges are, how many employees they are equipping with mobile apps, and their methods for driving value with mobility. Join Dan Woods, Editor and CTO of CITO Research, and Alan Murray, SVP of Products at Apperian, as they break down the results of this survey and discuss how enterprises are using mobile application management and private app stores to …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date