3D depth issues with OpenGL

I'm trying to make a cube in OpenGL and make it rotate, but when it rotates it won't keep the depth in order. It just draws the most recent quad on the previous ones. This is my code:
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/**************************
 * 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,
      400, 200, 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, 1.0f, 1.0f, 1.0f);
            
            glBegin (GL_QUADS);//back
            glColor4f (1.0f, 1.0f, 0.0f, 0.0f);//yellow
            glVertex3f (0.5f, -0.5f, -0.5f);
            glVertex3f (0.5f, 0.5f, -0.5f);
            glVertex3f (-0.5f, 0.5f, -0.5f);
            glVertex3f (-0.5f, -0.5f, -0.5f);
            glEnd ();
            glBegin (GL_QUADS);//bottom
            glColor3f (1.0f, 0.6f, 0.0f);//orange
            glVertex3f (-0.5f, -0.5f, -0.5f);
            glVertex3f (-0.5f, -0.5f, 0.5f);
            glVertex3f (0.5f, -0.5f, 0.5f);
            glVertex3f (0.5f, -0.5f, -0.5f);
            glEnd ();
            glBegin (GL_QUADS);//right
            glColor3f (0.0f, 1.0f, 0.0f);//green
            glVertex3f (0.5f, -0.5f, 0.5f);
            glVertex3f (0.5f, 0.5f, 0.5f);
            glVertex3f (0.5f, 0.5f, -0.5f);
            glVertex3f (0.5f, -0.5f, -0.5f);
            glEnd ();
            glBegin (GL_QUADS);//left
            glColor3f (0.0f, 0.0f, 1.0f);//blue
            glVertex3f (-0.5f, -0.5f, 0.5f);
            glVertex3f (-0.5f, 0.5f, 0.5f);
            glVertex3f (-0.5f, 0.5f, -0.5f);
            glVertex3f (-0.5f, -0.5f, -0.5f);
            glEnd ();
            glBegin (GL_QUADS);//top
            glColor3f (1.0f, 0.0f, 0.0f);//red
            glVertex3f (-0.5f, 0.5f, -0.5f);
            glVertex3f (-0.5f, 0.5f, 0.5f);
            glVertex3f (0.5f, 0.5f, 0.5f);
            glVertex3f (0.5f, 0.5f, -0.5f);
            glEnd ();
            glBegin (GL_QUADS);//front
            glColor4f (1.0f, 1.0f, 1.0f, 0.0f);//white
            glVertex3f (-0.5f, -0.5f, 0.5f);
            glVertex3f (-0.5f, 0.5f, 0.5f);
            glVertex3f (0.5f, 0.5f, 0.5f);
            glVertex3f (0.5f, -0.5f, 0.5f);
            glEnd ();
            
            glPopMatrix ();
            SwapBuffers (hDC);

            theta += 1.0f;
            Sleep (100);
        }
    }

    /* 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);
}

How can I fix this issue?
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glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
Where do I put that? When I added it, I got just a blank black window.
Put it in your initialization code.

Also, when you clear, you need to clear the depth buffer:

 
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
thanks, that worked!
Now I can see it, but everything is flipped. It is like what I should see the monitor sees and what should not be seen is actually seen. What's up with that? Is there a simple way to fix that?
Last edited on
I might have gotten the depth func backwards. try glDepthFunc(GL_GREATER);
That just makes a blank screen. When I switch the sign of all z values, it is now displayed properly. Apparently, I had all the z values flipped. now it works.
Last edited on
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