How do I call wndproc on WNDCLASSEX from a class in C++ - c++

Question

I'm trying to make an ImGui DX9 Window. However I get an error when I try to reference the wndproc function on the WNDCLASSEX structure.
When I try to pre-define the wndproc function as static I get an error: cannot overload static and non-static member functions with the same parameter types.
I already tried to call the function directly like so: menu::wnd_proc.
When I try to call the function without static I get this error on the function: a value of type "LRESULT (__stdcall menu::*)(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)" cannot be used to initialize an entity of type "WNDPROC".
Here's my function
#include "ui.hpp"
bool menu::render( )
{
WNDCLASSEX wc = {
sizeof( WNDCLASSEX ),
CS_CLASSDC,
menu::wnd_proc,
0L,
0L,
GetModuleHandle( NULL ),
NULL,
NULL,
NULL,
NULL,
_T( "ImGui Example" ),
NULL
};
...
}
Here's the ui.hpp header file
#pragma once
class menu
{
public:
bool render( );
private:
LPDIRECT3D9 g_pD3D = NULL;
LPDIRECT3DDEVICE9 g_pd3dDevice = NULL;
D3DPRESENT_PARAMETERS g_d3dpp = {};
static LRESULT WINAPI wnd_proc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam );
private:
...
LRESULT WINAPI wnd_proc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
if ( ImGui_ImplWin32_WndProcHandler( hWnd, msg, wParam, lParam ) )
return true;
switch ( msg )
{
case WM_SIZE:
if ( g_pd3dDevice != NULL && wParam != SIZE_MINIMIZED )
{
g_d3dpp.BackBufferWidth = LOWORD( lParam );
g_d3dpp.BackBufferHeight = HIWORD( lParam );
menu::reset_device( );
}
return 0;
case WM_SYSCOMMAND:
if ( ( wParam & 0xfff0 ) == SC_KEYMENU )
return 0;
break;
case WM_DESTROY:
::PostQuitMessage( 0 );
return 0;
}
return ::DefWindowProc( hWnd, msg, wParam, lParam );
}
};
extern IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam );