Question

I am attempting to draw a quadrilateral (square) on the screen. I inserted this into a pre-existing program that drew a cylinder. This is in an orthographic modelview matrix, and I am almost positive the clipping volume is correct (It’s 200 in any direction from the origin). In the display function I’m using, I pushed a matrix, translated forward (0.0,0.0,-20.0), called quadriliteral, and then popped the matrix. Are the any common openGL settings people use that I’m unaware of that may make this not visible? Is there a way to get the current clipping volume and print it out in the console?

void quadrilateral() 
{
    glLoadIdentity();
    glColor3f(0.5f,0.0f,0.8f);
    glBegin(GL_QUADS);

    glVertex3f(-10.0f,-10.0f,0.0f);
    glVertex3f(-10.0f,10.0f,0.0f);
    glVertex3f(10.0f,10.0f,0.0f);
    glVertex3f(10.0f,-10.0f,0.0f);

    glEnd();
}


//This is called from a main function elsewhere
void draw(void)
{
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500); 
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Cylinder");
    glutReshapeFunc(CChangeSize);
    glutSpecialFunc(CSpecialKeys);
    glutKeyboardFunc(Ckeyboard);
    glutDisplayFunc(CRenderScene);
    CSetupRC();
    glPopMatrix();
}


void CSetupRC()
{
// Light values and coordinates
GLfloat  ambientLight[] = {0.4f, 0.4f, 0.4f, 1.0f };
GLfloat  diffuseLight[] = {0.7f, 0.7f, 0.7f, 1.0f };
GLfloat  specular[] = { 0.9f, 0.9f, 0.9f, 1.0f};
GLfloat  lightPos[] = { -50.0f, 200.0f, 200.0f, 1.0f };
GLfloat  specref[] =  { 0.6f, 0.6f, 0.6f, 1.0f };


glEnable(GL_DEPTH_TEST);    // Hidden surface removal
glEnable(GL_CULL_FACE);     // Do not calculate inside of solid object
glFrontFace(GL_CCW);

// Enable lighting
glEnable(GL_LIGHTING);

// Setup light 0
glLightModelfv(GL_LIGHT_MODEL_AMBIENT,ambientLight);
glLightfv(GL_LIGHT0,GL_AMBIENT,ambientLight);
glLightfv(GL_LIGHT0,GL_DIFFUSE,diffuseLight);
glLightfv(GL_LIGHT0,GL_SPECULAR,specular);

// Position and turn on the light
glLightfv(GL_LIGHT0,GL_POSITION,lightPos);
glEnable(GL_LIGHT0);

// Enable color tracking
glEnable(GL_COLOR_MATERIAL);

// Set Material properties to follow glColor values
glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);

// All materials hereafter have full specular reflectivity
// with a moderate shine
glMaterialfv(GL_FRONT, GL_SPECULAR,specref);
glMateriali(GL_FRONT,GL_SHININESS,64);

// Black background
glClearColor(0.0f, 0.0f, 0.0f, 0.0f );


glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glEnable(GL_TEXTURE_2D);

}


// Called to draw scene
void CRenderScene(void)
{
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// Save the matrix state
glMatrixMode(GL_MODELVIEW);
glPushMatrix();

// Rotate about x and y axes
glRotatef(CxRot, 1.0f, 0.0f, 0.0f);
glRotatef(CyRot, 0.0f, 1.0f, 0.0f);

// Draw the cylinder
cylinder();

glPopMatrix();

// CylinderTwo
glMatrixMode(GL_MODELVIEW);
glPushMatrix();

// Rotate about x and y axes
glRotatef(CxRot, 1.0f, 0.0f, 0.0f);
glRotatef(CyRot, 0.0f, 1.0f, 0.0f);

// Draw the cylinder
glRotatef(120.0f, 1.0f, 1.0f, 1.0f);
cylinderTwo();

glPopMatrix();

// Random square
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glTranslatef(-30.0f,20.0f,10.0f);
quadrilateral();
glPopMatrix();

// Swap buffers
glutSwapBuffers();

}

Answer 1

It looks like your winding order is incorrect:

glEnable(GL_CULL_FACE);

this line means it will cull back faces.

glFrontFace(GL_CCW);

and this sets the front face to counter clockwise.

    glVertex3f(-10.0f,-10.0f,0.0f);
    glVertex3f(-10.0f,10.0f,0.0f);
    glVertex3f(10.0f,10.0f,0.0f);
    glVertex3f(10.0f,-10.0f,0.0f);

Here you have clockwise ordering of your vertices meaning you are drawing with the back to camera. either disable culling:

    glDisable(GL_CULL_FACE);

make the front face clockwise:

    glFrontFace(GL_CW);

or change the order of your vertices to a counter clockwise order.