(tutorial) d3d hacking mit c++

#include <Windows.h>
#include <cstdio>
#include <d3d9.h>
#include <d3dx9.h>

void InitHook(void);
void *DetourFunc(BYTE *src, const BYTE *dst, const int len);
void DrawRect (LPDIRECT3DDEVICE9 Device_t, int X, int Y, int L, int H, D3DCOLOR color);
HRESULT __stdcall hkEndScene(LPDIRECT3DDEVICE9 pDevice);

const D3DCOLOR txtPink = D3DCOLOR_ARGB(255, 255, 0, 255);
typedef HRESULT(__stdcall* EndScene_t)(LPDIRECT3DDEVICE9);
EndScene_t pEndScene;

int WINAPI DllMain(HINSTANCE hInst,DWORD reason,LPVOID reserved)
{
	switch(reason)
	{
	case DLL_PROCESS_ATTACH:
		{
			CreateThread(0, 0, (LPTHREAD_START_ROUTINE) InitHook, 0, 0, 0);
			break;
		}
	}

	return true;
}

HRESULT __stdcall hkEndScene(LPDIRECT3DDEVICE9 pDevice)
{
	MessageBoxA(0, "hkEndScene", 0, 0);
	DrawRect (pDevice, 10, 10, 200, 200, txtPink);
	return pEndScene(pDevice);
}

void InitHook()
{
	HMODULE hModule = NULL;
	while( !hModule )
	{
		hModule = GetModuleHandleA( "d3d9.dll" );
		Sleep( 100 );
	}
	MessageBoxA(0, "InitHook", 0, 0);

	pEndScene = ( EndScene_t )DetourFunc((PBYTE) 0x7542CE09,(PBYTE)hkEndScene, 5);
}

void *DetourFunc(BYTE *src, const BYTE *dst, const int len)
{
	BYTE *jmp = (BYTE*)malloc(len+5);
	DWORD dwback;
	VirtualProtect(src, len, PAGE_READWRITE, &dwback);
	memcpy(jmp, src, len); jmp += len;
	jmp[0] = 0xE9;
	*(DWORD*)(jmp+1) = (DWORD)(src+len - jmp) - 5;
	src[0] = 0xE9;
	*(DWORD*)(src+1) = (DWORD)(dst - src) - 5;
	VirtualProtect(src, len, dwback, &dwback);

	return (jmp-len);
}

void DrawRect (LPDIRECT3DDEVICE9 Device_t, int X, int Y, int L, int H, D3DCOLOR color)
{
	MessageBoxA(0, "DrawRect", 0, 0);
	D3DRECT rect = {X, Y, X+L, Y+H};
	Device_t->Clear(1, &rect, D3DCLEAR_TARGET, color, 0, 0);
}