CODEWITHSUNDEEP
openglglut
HRLTY
HRLTY

Reputation: 74

Why doesn't the teapot display? OpenGL

Here is my code that set a perspective view volume. The rectangle is displayed correctly.

I want to add a teapot to my scene now, so I add a line drawing a teapot after drawing the rectangle. But no teapot was displayed.

What params did I set wrong? What's the problem with my view and teapot?

GLint winWidth = 600, winHeight = 600;   //  Initial display-window size.

GLfloat x0 = 50.0, y0 = 50.0, z0 = 50.0;  //  Viewing-coordinate origin.
GLfloat xref = 50.0, yref = 50.0, zref = 0.0;  //  Look-at point.
GLfloat Vx = 0.0, Vy = 1.0, Vz = 0.0;          //  View-up vector.

/*  Set coordinate limits for the clipping window:  */
//GLfloat xwMin = -40.0, ywMin = -60.0, xwMax = 40.0, ywMax = 60.0;
GLfloat xwMin = -100.0, ywMin = -100.0, xwMax = 100.0, ywMax = 100.0;

/*  Set positions for near and far clipping planes:  */
GLfloat dnear = 25.0, dfar = 125.0;

void init (void)
{
    glClearColor (1.0, 1.0, 1.0, 0.0);

    glMatrixMode (GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (x0, y0, z0, xref, yref, zref, Vx, Vy, Vz);
    printf("look at orign:%.0f %.0f %.0f, pref: %.0f %.0f %.0f\n",x0, y0, z0, xref, yref, zref );

    glMatrixMode (GL_PROJECTION);
    glLoadIdentity();
    glFrustum (xwMin, xwMax, ywMin, ywMax, dnear, dfar);
}

void displayFcn (void)
{
    init ( );
    glClear (GL_COLOR_BUFFER_BIT);

    /*  Set parameters for a square fill area.  */
    glColor3f (0.0, 1.0, 0.0);         //  Set fill color to green.
    //glPolygonMode (GL_FRONT, GL_FILL);
    glPolygonMode(GL_FRONT, GL_LINE);
    glPolygonMode (GL_BACK, GL_LINE);  //  Wire-frame back face.
    glBegin (GL_QUADS);
    glVertex3f (0.0, 0.0, 0.0);
    glVertex3f (100.0, 0.0, 0.0);
    glVertex3f (100.0, 100.0, 0.0);
    glVertex3f (0.0, 100.0, 0.0);
    glEnd ( );
    glutSolidTeapot(50.9);

    glFlush ( );
}

void reshapeFcn (GLint newWidth, GLint newHeight)
{
    glViewport (0, 0, newWidth, newHeight);

    winWidth = newWidth;
    winHeight = newHeight;
}
void keyboard(unsigned char key, int x, int y);
int main (int argc, char** argv)
{
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowPosition (50, 50);
    glutInitWindowSize (winWidth, winHeight);
    glutCreateWindow ("Perspective View of A Square");
    glutKeyboardFunc(keyboard);
    glutDisplayFunc (displayFcn);
    glutReshapeFunc (reshapeFcn);
    glutMainLoop ( );
}

Upvotes: 0

Views: 1031

Answers (1)

derhass
derhass

Reputation: 45332

Your teapot is just totally off view.

You could place it inside the viewing volume like this:

glMatrixMode(GL_MODELVIEW);
glTranslatef(50.f, 50.f, 0.f);
glutSolidTeapot(50.9);

Also note that the field of view angle is insanely high for any normal viewing condition. Consider using the function gluPerspective instead of glFrustum to easily specify the angle, instead of manually having to specify the tangens of that angle scaled by the near plane distance as with glFrustum.

Also note that all of that is deprecated GL. Most of the functions you are using are removed from modern core profile contexts. If you start learning GL now, my advise is learning the new (well, 10 year old) way of using the programmable pipeline instead of the old (20 years) fixed-function pipeline with the builtin matrix stack.

Upvotes: 1

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