I used IScreenElement interface from the GameCode download and I am getting
a strange error that I am trying to instantiate an abstract class (error C2259:
'IScreenElement' : cannot instantiate abstract class). I made a list which I
want to use to iterate through for drawing to the screen and I am currently
stuck. The following is a partial class I wrote that inherits from
IScreenElement.

<code>
#include "UIControl.h"
#include "../interfaces.h"

class Button : public UIControl , public IScreenElement
{
public:
Button();
~Button();

// IScreenElement Implementation
HRESULT VOnRestore();
HRESULT VOnRender(); // double fTime, float fElapsedTime
void VOnUpdate(int deltaMilliseconds);
int VGetZOrder();
void VSetZOrder(int const zOrder);
bool VIsVisible();
void VSetVisible(bool visible);
bool const operator <(IScreenElement const &other) { return VGetZOrder() <
other.VGetZOrder(); }
static void CALLBACK OnGUIEvent( UINT nEvent, int nControlID, UIControl*
pControl, void *pUserContext );
LRESULT CALLBACK VOnMsgProc( AppMsg msg );
// End of IScreenElement Implementation

// UIControl Implementation
bool OnRender(void);
void OnMouseDown(int i_Button, int X, int Y); // what does i_Button mean in
this context
void OnMouseMove(int X, int Y);
void OnMouseUp(int i_Button, int X, int Y); // what does i_Button mean in this
context
void OnSetFocus();
void OnLostFocus();
void OnKeyDown(WPARAM Key, LPARAM Extended);
void OnKeyUp(WPARAM Key, LPARAM Extended);
void OnSysKey(WPARAM Key, LPARAM Extended);
// end of Control Implementation

protected:
ControlRect* m_Billboard;
D3DXVECTOR3 position[4];
D3DXVECTOR3 m_TopLeft;
D3DXVECTOR3 m_TopRight;
D3DXVECTOR3 m_BottomLeft;
D3DXVECTOR3 m_BottomRight;
</code>

The compiler is telling me that HRESULT IScreenElement::VOnRestore(void)' : is
abstract however I have created this method in the Button class (HRESULT
VOnRestore();). I am not sure why this error is showing up when I clearly
implemented all the virtual functions in my subclass.