dx9 游戏终极开发 例子问题

bool InitializeD3D(HWND hWnd, bool fullscreen)
{
D3DDISPLAYMODE displayMode;
g_D3D = Direct3DCreate9(D3D_SDK_VERSION);
if(g_D3D == NULL) return false;
if(FAILED(g_D3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT,
&displayMode))) return false;

D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory(&d3dpp, sizeof(d3dpp));


if(fullscreen)
{
d3dpp.Windowed = FALSE;
d3dpp.BackBufferWidth = 640;
d3dpp.BackBufferHeight = 480;
}
else
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
d3dpp.BackBufferFormat = displayMode.Format;

if(FAILED(g_D3D->CreateDevice(D3DADAPTER_DEFAULT,
D3DDEVTYPE_HAL, hWnd, D3DCREATE_HARDWARE_VERTEXPROCESSING,
&d3dpp, &g_D3DDevice))) return false;

if(!InitializeObjects()) return false;

return true;
}


bool InitializeObjects()
{
unsigned long col = D3DCOLOR_XRGB(255, 255, 255);

stD3DVertex objData[] =
{
{ 420.0f, 150.0f, 0.5f, 1.0f, col, },
{ 420.0f, 350.0f, 0.5f, 1.0f, col, },
{ 220.0f, 150.0f, 0.5f, 1.0f, col, },
{ 220.0f, 350.0f, 0.5f, 1.0f, col, },
};

if(FAILED(g_D3DDevice->CreateVertexBuffer(sizeof(objData), 0,
D3DFVF_VERTEX, D3DPOOL_DEFAULT, &g_VertexBuffer,
NULL))) return false;

void *ptr;

if(FAILED(g_VertexBuffer->Lock(0, sizeof(objData),
(void**)&ptr, 0))) return false;
memcpy(ptr, objData, sizeof(objData));
g_VertexBuffer->Unlock();
return true;
}
void RenderScene()
{
g_D3DDevice->Clear(0, NULL, D3DCLEAR_TARGET,
D3DCOLOR_XRGB(0,0,0), 1.0f, 0);
g_D3DDevice->BeginScene();
g_D3DDevice->SetStreamSource(0, g_VertexBuffer, 0, sizeof(stD3DVertex));
g_D3DDevice->SetFVF(D3DFVF_VERTEX);
g_D3DDevice->DrawPrimitive(D3DPT_LINELIST, 0, 2);
g_D3DDevice->EndScene();
g_D3DDevice->Present(NULL, NULL, NULL, NULL);
}


void Shutdown()
{
if(g_D3DDevice != NULL) g_D3DDevice->Release();
if(g_D3D != NULL) g_D3D->Release();
if(g_VertexBuffer != NULL) g_VertexBuffer->Release();
g_D3DDevice = NULL;
g_D3D = NULL;
g_VertexBuffer = NULL;
}[/code]

为什么去掉这个memcpy 就不会显示三角形了呢？ （lock 和unlock之间的）
有没有大神愿意告诉我？