C / C++ / MFC

void CMyCtrl::OnNcPaint()
{
    CWindowDC dc(this);
    // dc.SelectClipRgn(&invalidRgn) ???
    DoPaint(&dc);
    ...
}

dc.SelectClipRgn(&invalidRgn)

class A 
{ virtual bool method M() };

class B : public A { .... }

class C1 : public B
{ virtual bool method M() override };
class C2 : public B
{ virtual bool method M() override };

class D 
{
   static bool DoSomething( A* ptr ) { ptr -> M(); }  
}

C1::anymethod()
{ 
  D::DoSomething( this ); 
}

C1::anymethod()
{ 
  D::DoSomething( (A*)this ); 
}

class B { 
public 
//... some other methods
// 
   virtual void M1();    
   virtual void M2(); 
   // ...
   virtual void Mn(); 
}; 

class Ca1 : public B { .... };
class Ca2 : public B { .... };
//...
class Can : public B { .... };

class Cb1 : public Ca1 { .... };
class Cb2 : public Ca2 { .... };
//...
class Cbn : public Can { .... };

class Cc1 : public Cb1 { .... };
class Cc2 : public Cb2 { .... };
//...
class Ccn : public Cb3 { .... };

class Cc1 : public Cb1 {
virtual void M1() { /* code m1 */ } override;
virtual void M2() { /* code m2 */ } override;
...
virtual void M3() { /* code m3 */ } override;
};
class Cc2 : public Cb2 {
virtual void M1() { /* code m1 */ } override;
virtual void M2() { /* code m2 */ } override;
...
virtual void M3() { /* code m3 */ } override;
};

#define DRIVED_METHODS \
virtual void M1 { /* code m1 */ } \

class Cc1 : public Cb1, public CMpack
{};
class Mpack { void M1 {}; ... }; 

class Mcommon {
virtual void m_M1() { };
virtual void m_M2() {}; 
// ... etc 
}

class Cc1 : public Mcommon 
{ 
virtual void M1() { Mcommon::m_M1() ; } override 
// ... M2 and so on 
};