   Minimalist setting for using Z-axis and the cost of it in OpenGL?
  I don't know how to set minimalist code to use depth ability of OpenGL, and will my program get more performance if I don't use it?I know I don't need use glMatrixMode, glOrtho, glViewport and such function if I don't use depth. As a example:/************************** * Includes * **************************/#include <windows.h>#include <gl/gl.h>/************************** * Function Declarations * **************************/LRESULT CALLBACK WndProc (HWND hWnd, UINT message,WPARAM wParam, LPARAM lParam);void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC);void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC);/************************** * WinMain * **************************/int WINAPI WinMain (HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int iCmdShow){    WNDCLASS wc;    HWND hWnd;    HDC hDC;    HGLRC hRC;  MSG msg;    BOOL bQuit = FALSE;    float theta = 0.0f;    /* register window class */    wc.style = CS_OWNDC;    wc.lpfnWndProc = WndProc;    wc.cbClsExtra = 0;    wc.cbWndExtra = 0;    wc.hInstance = hInstance;    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);    wc.hCursor = LoadCursor (NULL, IDC_ARROW);    wc.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH);    wc.lpszMenuName = NULL;    wc.lpszClassName = "GLSample";    RegisterClass (&wc);    /* create main window */    hWnd = CreateWindow ( "GLSample", "OpenGL Sample",  WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE, 0, 0, 256, 256, NULL, NULL, hInstance, NULL);    /* enable OpenGL for the window */    EnableOpenGL (hWnd, &hDC, &hRC);    /* program main loop */    while (!bQuit)    {   /* check for messages */   if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE))   {  /* handle or dispatch messages */  if (msg.message == WM_QUIT)  { bQuit = TRUE;  }  else  { TranslateMessage (&msg); DispatchMessage (&msg);  }   }   else   {  /* OpenGL animation code goes here */  glClearColor (0.0f, 0.0f, 0.0f, 0.0f);  glClear (GL_COLOR_BUFFER_BIT);  glPushMatrix ();  glRotatef (theta, 0.0f, 0.0f, 1.0f);  glBegin (GL_TRIANGLES);  glColor3f (1.0f, 0.0f, 0.0f);   glVertex2f (0.0f, 1.0f);  glColor3f (0.0f, 1.0f, 0.0f);   glVertex2f (0.87f, -0.5f);  glColor3f (0.0f, 0.0f, 1.0f);   glVertex2f (-0.87f, -0.5f);  glEnd ();  glPopMatrix ();  SwapBuffers (hDC);  theta += 1.0f;  Sleep (1);   }    }    /* shutdown OpenGL */    DisableOpenGL (hWnd, hDC, hRC);    /* destroy the window explicitly */    DestroyWindow (hWnd);    return msg.wParam;}/******************** * Window Procedure * ********************/LRESULT CALLBACK WndProc (HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam){    switch (message)    {    case WM_CREATE:   return 0;    case WM_CLOSE:   PostQuitMessage (0);   return 0;    case WM_DESTROY:   return 0;    case WM_KEYDOWN:   switch (wParam)   {   case VK_ESCAPE:  PostQuitMessage(0);  return 0;   }   return 0;    default:   return DefWindowProc (hWnd, message, wParam, lParam);    }}/******************* * Enable OpenGL * *******************/void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC){    PIXELFORMATDESCRIPTOR pfd;    int iFormat;    /* get the device context (DC) */    *hDC = GetDC (hWnd);    /* set the pixel format for the DC */    ZeroMemory (&pfd, sizeof (pfd));    pfd.nSize = sizeof (pfd);    pfd.nVersion = 1;    pfd.dwFlags = PFD_DRAW_TO_WINDOW |  PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;    pfd.iPixelType = PFD_TYPE_RGBA;    pfd.cColorBits = 24;    pfd.cDepthBits = 16;    pfd.iLayerType = PFD_MAIN_PLANE;    iFormat = ChoosePixelFormat (*hDC, &pfd);    SetPixelFormat (*hDC, iFormat, &pfd);    /* create and enable the render context (RC) */    *hRC = wglCreateContext( *hDC );    wglMakeCurrent( *hDC, *hRC );}/****************** * Disable OpenGL * ******************/void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC){    wglMakeCurrent (NULL, NULL);    wglDeleteContext (hRC);    ReleaseDC (hWnd, hDC);}I'm new to use OpenGL, and I haven't find information about that so far.Thanks!   
  And, can I use depth if I don't use matrix and don't do any matrix operation(as I don't need it).Will it be faster if there is no matrix process?   