Question about vuserdraw

Hello,

i have read the source code of vuserdraw command in ViewerTest_OpenGlCommands.cxx.  I want to draw something using the Render() function, which means i need to create a OpenGl_Workspace as the parameter of the Render() function.  So i create a OpenGl_Workspace using a WNT_Window which is created by a dialog item in MFC. The problem is that i cannot see the view while the program runs successfully. Here is my code.

//create a window in a Dialog 

CWnd* cpwnd = GetDlgItem(IDC_STATIC_CP);

Handle(WNT_Window) cp_wnt_wnd = new WNT_Window(cpwnd->m_hWnd);

//create a OpenGl_Workspace

Handle(OpenGl_GraphicDriver) myglGraphicDriver = theApp.GetGraphicDriver();

Handle(OpenGl_Window) myglWindow = myglGraphicDriver->CreateRenderWindow(cp_wnt_wnd, (Aspect_RenderingContext)0);

Handle(OpenGl_Caps) myglCaps = &myglGraphicDriver->ChangeOptions();

Handle(Graphic3d_StructureManager) myG3dStructureCanager = new Graphic3d_StructureManager(myglGraphicDriver);

OpenGl_StateCounter* myglStateCounter = new OpenGl_StateCounter();

Handle(OpenGl_View) myglView = new OpenGl_View(myG3dStructureCanager, myglGraphicDriver, myglCaps, myglStateCounter);

Handle(OpenGl_Workspace) myglWorkSpace = new OpenGl_Workspace(myglView, myglWindow);

// the code below is the same as the code in Render().

Handle(OpenGl_Context) myglContext myglContext = myglWorkSpace->GetGlContext();

const OpenGl_AspectMarker* aMA = myglWorkSpace->AspectMarker();

aMA->Aspect()->Type();

const OpenGl_AspectText* aTA = myglWorkSpace->AspectText();

aTA->Aspect()->Font();

OpenGl_Vec4 aColor=myglWorkSpace->LineColor();

myglContext->ShaderManager()->BindLineProgram(Handle(OpenGl_TextureSet)(), Aspect_TOL_SOLID, Graphic3d_TOSM_UNLIT, Graphic3d_AlphaMode_Opaque, false, Handle(OpenGl_ShaderProgram)());

myglContext->SetColor4fv(aColor);

const OpenGl_Vec3 aVertArray[4] =

{

OpenGl_Vec3(-10.0,-20.0,-30.0),

OpenGl_Vec3(10.0, 20.0, -30.0),

OpenGl_Vec3(10.0, 20.0, 30.0),

OpenGl_Vec3(-10.0,-20.0,30.0),

};

Handle(OpenGl_VertexBuffer) aVertBuffer = new OpenGl_VertexBuffer();

aVertBuffer->Init(myglContext, 3, 4, aVertArray[0].GetData());

aVertBuffer->BindAttribute(myglContext, Graphic3d_TOA_POS);

glDrawArrays(GL_LINE_LOOP, 0, aVertBuffer->GetElemsNb());

aVertBuffer->UnbindAttribute(myglContext, Graphic3d_TOA_POS);

aVertBuffer->Release(myglContext.get());

Thanks in advance.