Subclassing using DLL Injection

// dllmain.cpp : Defines the entry point for the DLL application.
#include "stdafx.h"
#include <windowsx.h>
#include <tchar.h>

LONG_PTR oldWindowProc;

//*******************************************************************************************************
void DrawRect(HDC hDC, int x, int y )
{
	::Rectangle(  hDC,x,y,(x+50),(y+50) );
}
//*******************************************************************************************************
void DrawText( HDC hDC, int x, int y )
{
	TCHAR str[] = TEXT("UR HACKED!!!!");
	RECT r;
	r.left = x;
	r.top = y;
	r.right = x+150;
	r.bottom = y+30;
	::DrawText( hDC,str,_tcslen(str),&r,DT_CENTER );
}
//*******************************************************************************************************
LRESULT CALLBACK HackingWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	switch( message ) 
	{
		case WM_LBUTTONDOWN:
			{
				int x = GET_X_LPARAM(lParam);
				int y = GET_Y_LPARAM(lParam);
				HDC hDC = ::GetDC( hWnd );
				//::Rectangle(  hDC,x,y,(x+50),(y+50) );
				DrawText( hDC,x,y);
				break;
			}
		case WM_RBUTTONDOWN:
			{
					int x = GET_X_LPARAM(lParam);
					int y = GET_Y_LPARAM(lParam);
					HDC hDC = ::GetDC( hWnd );
					::Ellipse( hDC,x,y,(x+50),(y+50));
					break;
			}
		case WM_DESTROY:
			{
				PostQuitMessage(0);
				break;
			}
		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return 0;
}
//*******************************************************************************************************
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
					 )
{
	
	switch (ul_reason_for_call)
	{
	case DLL_PROCESS_ATTACH:
		{
			//Get the main window of the client
			HWND hwnd = ::FindWindow(NULL,TEXT("Injectee") );

			//If the window found, then it's window proc
			if( hwnd )
			{
				oldWindowProc = ::SetWindowLongPtr( hwnd, GWL_WNDPROC, (LONG_PTR) HackingWndProc );
			}
			break;
		}
	case DLL_THREAD_ATTACH:
		{
			break;
		}
	case DLL_THREAD_DETACH:
		{
			break;
		}
	case DLL_PROCESS_DETACH:
		{
			break;
		}
	}
	return TRUE;
}
//*******************************************************************************************************