Questions on wxWidgets Understanding

1. How is the wxWidgets app instantiated?

#include <wx/wx.h>
class MyApp : public wxApp
{
public:
    virtual bool OnInit();
};

wxIMPLEMENT_APP(MyApp); //calls MyApp declared above

class MyFrame : public wxFrame
{
public:
    MyFrame(const wxString &title, const wxPoint &pos, const wxSize &size);
}
bool MyApp::OnInit()
{
    MyFrame *frame = new MyFrame("Hello World", wxDefaultPosition, wxDefaultSize);
    frame->Show(true);
    return true;
}
MyFrame::MyFrame(const wxString &title, const wxPoint &pos, const wxSize &size)
    : wxFrame(nullptr, wxID_ANY, title, pos, size)
{
}

Following is the callstack:

1 MyFrame::MyFrame main.cpp, MyFrame::MyFrame

2 MyApp::OnInit main.cpp, bool MyApp::OnInit()

3 wxAppConsoleBase::CallOnInit app.h, virtual bool CallOnInit() {return OnInit();}

4 wxEntry init.cpp

5 wxEntry init.cpp

6 main main.cpp,wxIMPLEMENT_APP(MyApp);