怎么把BMP做成DIALOG的背景？

怎么把BMP做成DIALOG的背景？并且背景随我的DIALOG的放大而放大，缩小而缩小！
怎么来实现呢？
我有一段SDI的程序：参看：
#define STRICT
#define WIN32_LEAN_AND_MEAN#include <windows.h>
#include <tchar.h>#include "resource.h"LRESULT CALLBACK FrameWndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK SubClassProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam);WNDPROC g_fnOldProc = NULL;
HINSTANCE g_hInstance = NULL;
_TCHAR szFrameClass[] = _T("VnMdiFrame");
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
   PSTR szCommandList, int iCmdShow)
{
HWND hWndFrame;
MSG msg; WNDCLASSEX wc;
ZeroMemory(&wc, sizeof(WNDCLASSEX)); g_hInstance = hInstance; if (!hPrevInstance)
{
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = FrameWndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = NULL;
wc.hCursor = NULL;
wc.hbrBackground = (HBRUSH) (COLOR_APPWORKSPACE + 1);
wc.lpszMenuName = NULL;
wc.lpszClassName = szFrameClass;
wc.hIconSm = NULL; RegisterClassEx(&wc); hWndFrame = CreateWindow(szFrameClass, _T("MDI Bitmap Background"),
WS_VISIBLE | WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN,
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
NULL, NULL, hInstance, NULL); UpdateWindow(hWndFrame); while(GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
} return msg.wParam;
} return 0;
}
LRESULT CALLBACK FrameWndProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam)
{
static HWND hwndClient = NULL; CLIENTCREATESTRUCT ccs; switch(nMsg)
{
case WM_CREATE :
ZeroMemory(&ccs, sizeof(CLIENTCREATESTRUCT));
ccs.hWindowMenu = NULL;
hwndClient = CreateWindow(_T("MDICLIENT"), NULL, WS_CHILD | WS_CLIPCHILDREN | WS_VISIBLE,
0, 0, 0, 0, hWnd, (HMENU) NULL, g_hInstance, (LPSTR) &ccs);
g_fnOldProc = (WNDPROC) SetWindowLong(hwndClient, GWL_WNDPROC, (LONG) SubClassProc);
return 0;
break; case WM_QUERYENDSESSION :
case WM_CLOSE :
if (NULL != GetWindow(hwndClient, GW_CHILD))
return 0;
break; case WM_DESTROY :
PostQuitMessage(0);
return 0;
break;
} return DefFrameProc(hWnd, hwndClient, nMsg, wParam, lParam);
}
LRESULT CALLBACK SubClassProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam)
{
static HBITMAP hBitmap = NULL;
static BITMAP bm; switch (nMsg)
{
case WM_ERASEBKGND:
if (!hBitmap)
{
hBitmap = LoadBitmap(g_hInstance, MAKEINTRESOURCE(IDB_MDIBKGND));
ZeroMemory(&bm, sizeof(BITMAP));
GetObject(hBitmap, sizeof(BITMAP), (LPVOID)&bm);
} if (hBitmap != NULL)
{
HDC hDC = (HDC) wParam; RECT rect;
GetClientRect(hWnd, &rect); HDC hMemDC = CreateCompatibleDC(NULL);
HBITMAP hOldBitmap = NULL; UINT nWidth = rect.right - rect.left;
UINT nHeight = rect.bottom - rect.top; hOldBitmap = (HBITMAP) SelectObject(hMemDC, hBitmap); UINT nX;
UINT nY; for (nX = 0; nX < nWidth; nX += bm.bmWidth)
for (nY = 0; nY < nHeight; nY += bm.bmHeight)
BitBlt(hDC, nX, nY, bm.bmWidth, bm.bmHeight, hMemDC, 0, 0, SRCCOPY); SelectObject(hMemDC, hOldBitmap); return 1;
} break; case WM_DESTROY:
if (hBitmap)
{
DeleteObject(hBitmap);
hBitmap = NULL;
ZeroMemory(&bm, sizeof(BITMAP));
} break;
} return CallWindowProc(g_fnOldProc, hWnd, nMsg, wParam, lParam);
}