I'm creating GDIMario but I meet some problems. I create this thread to ask question about gdi and how to make an action game in Win32 API. Here's my main.cpp

Code:
#include "stdafx.h"

// Mario Headers
#include "GameMain.h"

#define MAX_LOADSTRING 100

// Global Variables:
HINSTANCE hInst;								// current instance
TCHAR szTitle[MAX_LOADSTRING];					// The title bar text
TCHAR szWindowClass[MAX_LOADSTRING];			// the main window class name

// Mario global variables =================
CGameMain* gGameMain;
HWND hWnd;
PAINTSTRUCT ps;
// ========================================



// Forward declarations of functions included in this code module:
ATOM				MyRegisterClass(HINSTANCE hInstance);
BOOL				InitInstance(HINSTANCE, int);
LRESULT CALLBACK	WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK	About(HWND, UINT, WPARAM, LPARAM);

// My unprocess function =====================================
void OnCreate(HWND hWnd)
{
}
void OnKeyUp(WPARAM wParam)
{
	switch (wParam) {
				case VK_LEFT:
					gGameMain->KeyReleased(LEFT);
					break;
				case VK_UP:
					gGameMain->KeyReleased(UP);
					break;
				case VK_RIGHT:
					gGameMain->KeyReleased(RIGHT);
					break;
				case VK_DOWN:
					gGameMain->KeyReleased(DOWN);
					break;
	}
}
void OnKeyDown(HWND hWnd,WPARAM wParam)
{
	switch (wParam) {
				case VK_LEFT:
					gGameMain->KeyPressed(LEFT);
					break;
				case VK_UP:
					gGameMain->KeyPressed(UP);
					break;
				case VK_RIGHT:
					gGameMain->KeyPressed(RIGHT);
					break;
				case VK_DOWN:
					gGameMain->KeyPressed(DOWN);
					break;
			}
}
void OnPaint(HWND hWnd)
{
   HDC hdc = BeginPaint(hWnd,&ps);

   RECT	rect;
   GetClientRect(hWnd,&rect);

   HDC hdcDouble		= CreateCompatibleDC(hdc);
   HBITMAP hdcBitmap	= CreateCompatibleBitmap(hdc,rect.right,rect.bottom);
   HBITMAP bmOld		= (HBITMAP)SelectObject(hdcDouble, hdcBitmap);

   gGameMain->SetHDC(&hdcDouble);
   gGameMain->SendMessage(MESSAGE_PAINT);

   BitBlt(hdc,0,0,rect.right,rect.bottom,hdcDouble,0,0,SRCCOPY);
   SelectObject(hdcDouble,bmOld);
   DeleteDC(hdcDouble);
   DeleteObject(hdcBitmap);
   DeleteDC(hdc);
}

void OnDestroy() 
{
	gGameMain->isPlaying = false;
	EndPaint(hWnd,&ps);
}
// My unprocess function =====================================

ATOM MyRegisterClass(HINSTANCE hInstance)
{
	WNDCLASSEX wcex;

	wcex.cbSize = sizeof(WNDCLASSEX);

	wcex.style			= CS_HREDRAW | CS_VREDRAW;
	wcex.lpfnWndProc	= WndProc;
	wcex.cbClsExtra		= 0;
	wcex.cbWndExtra		= 0;
	wcex.hInstance		= hInstance;
	wcex.hIcon			= LoadIcon(hInstance, MAKEINTRESOURCE(IDI_GDIMARIO));
	wcex.hCursor		= LoadCursor(NULL, IDC_ARROW);
	wcex.hbrBackground	= (HBRUSH)(COLOR_WINDOW+1);
	wcex.lpszMenuName	= MAKEINTRESOURCE(IDC_GDIMARIO);
	wcex.lpszClassName	= szWindowClass;
	wcex.hIconSm		= LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

	return RegisterClassEx(&wcex);
}

BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{

   hInst = hInstance; // Store instance handle in our global variable

   hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, CW_USEDEFAULT, WIDTH, HEIGHT, 0, NULL, hInstance, NULL);
   if (!hWnd)
   {
      return FALSE;
   }

   // ---------------- Start gdiplus ------------------
   GdiplusStartup(&gdiToken,&gdiStartInput,NULL);
   // -------------------------------------------------

   // Init GameMain
   gGameMain = new CGameMain();
   
   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	int wmId, wmEvent;
	switch (message)
	{
	case WM_COMMAND:
		wmId    = LOWORD(wParam);
		wmEvent = HIWORD(wParam);
		// Parse the menu selections:
		switch (wmId)
		{
		case IDM_ABOUT:
			DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
			break;

		case IDM_EXIT:
			DestroyWindow(hWnd);
			break;

		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
		}
		break;
	case WM_KEYDOWN: 
		OnKeyDown(hWnd,wParam);
		break;
	case WM_KEYUP: 
		OnKeyUp(wParam);	
		break;
	case WM_CREATE:
		OnCreate(hWnd);
		break;
	case WM_PAINT:			
		OnPaint(hWnd);
		break;
	case WM_DESTROY:
		OnDestroy();
		PostQuitMessage(0);
		break;
	default:
		return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)

{
	UNREFERENCED_PARAMETER(lParam);
	switch (message)
	{
	case WM_INITDIALOG:
		return (INT_PTR)TRUE;

	case WM_COMMAND:
		if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
		{
			EndDialog(hDlg, LOWORD(wParam));
			return (INT_PTR)TRUE;
		}
		break;
	}
	return (INT_PTR)FALSE;
}
int APIENTRY _tWinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPTSTR lpCmdLine,int nCmdShow)
{
	UNREFERENCED_PARAMETER(hPrevInstance);
	UNREFERENCED_PARAMETER(lpCmdLine);

 	// TODO: Place code here.
	MSG msg;
	HACCEL hAccelTable;

	// Initialize global strings
	LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
	LoadString(hInstance, IDC_GDIMARIO, szWindowClass, MAX_LOADSTRING);
	MyRegisterClass(hInstance);

	// Perform application initialization:
	if (!InitInstance (hInstance, nCmdShow))
	{
		return FALSE;
	}

	hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_GDIMARIO));

	// Main message loop:
	// GameLoop

	PeekMessage(&msg,NULL,0,0,PM_NOREMOVE);

	while (gGameMain->isPlaying)
	{
		while (PeekMessage(&msg,NULL,0,0,PM_REMOVE)) {
			if (msg.message == WM_QUIT) 
				break;

			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
		if (gGameMain->enterNextState) {
			gGameMain->SendMessage(MESSAGE_ENTER);
			gGameMain->enterNextState = false;
		}

		gGameMain->SendMessage(MESSAGE_UPDATE);
		InvalidateRect(hWnd,NULL,FALSE);
		/*if (gGameMain->exitCurrentState) {
			gGameMain->SendMessage(MESSAGE_EXIT);
			gGameMain->enterNextState = true;
			gGameMain->exitCurrentState = false;
		}*/
		::Sleep(gGameMain->timer);
			// Do your game stuff here
	}

	GdiplusShutdown(gdiToken); // Shut down gdiplus token

	return (int) msg.wParam;
}
The problem is : I really don't know why when I call InvalidateRect(hWnd,NULL,FALSE); to redraw windows. I draw a dark one instead therefore there's no change in info set by gGameMain->SendMessage(MESSAGE_ENTER);