GL how to look at the center of the viewport

Question

I'm using GLFW3 and OpenGL to visualize measurements from an IMU that I have. I've gotten the simple cube example working and I can rotate it successfully with quaternions that I've input.

However since I'm visualizing an IMU, it is important that I know which way I am looking at it. I would prefer to look at it from a top down view.

Hence I want to keep the cube at the center of the world (0, 0, 0) and look down at it from a corresponding height (0, 0, z) which is where I want my camera to be at. I've the following code, can someone please guide me on how to set up my glLookAt function? All the values that I input make my cube disappear.

void display( GLFWwindow* window )
{
  while(!glfwWindowShouldClose(window))
  {
    // Scale to window size
    GLint windowWidth, windowHeight;
    glfwGetWindowSize(window, &windowWidth, &windowHeight);
    glViewport(0, 0, windowWidth, windowHeight);

    // Draw stuff
    glClearColor(0.2, 0.2, 0.2, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION_MATRIX);
    glLoadIdentity();
    gluPerspective( 60, (double)windowWidth / (double)windowHeight, 0.1, 100 );

    glMatrixMode(GL_MODELVIEW_MATRIX);
    glTranslatef(0,0,-5);

    drawCube();

    // Update Screen
    glfwSwapBuffers(window);

    // Check for any input, or window movement
    glfwPollEvents();
  }

Answer 1

Let's look at the declaration of gluLookAt:

void gluLookAt(GLdouble eyeX,
               GLdouble eyeY,
               GLdouble eyeZ,
               GLdouble centerX,
               GLdouble centerY,
               GLdouble centerZ,
               GLdouble upX,
               GLdouble upY,
               GLdouble upZ);

eyeX, eyeY and eyeZ are (obviously) the camera position (which you should have already).

center X, Y and Z are the positions of the object you want to focus on.

upX, upY and upZ are the up vector's coordinates (I seriously have no idea why OpenGL needs this, but I won't argue). This should be 0, 1 and 0 respectively.

Although, you mentioned that you wanted to visualize some data without messing with vbos or even vaos, but this is one of the reasons engines are implemented.