CODEWITHSUNDEEP
openglgraphicsglut
Lara
Lara

Reputation: 81

gluLookAt with cone not showing expected result

I am trying to look at a cone in 3D, for which I used gluLookAt. I draw a cone in the middle of the screen at pos (250, 250, 0) and then look at it with a camera above the origin looking at the middle. The output is a circle, contrary to the cone I expected to see. It seems the camera is instead at point (250,250,0) also, but it is specified in gluLookAt it should be above the origin. What am I overlooking here?

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glTranslatef(250, 250, 0);
    glutSolidCone(30, 10, 20, 20);
    glTranslatef(-250, -250, 0);

    gluLookAt(0, 0, 100, 250, 250, 0, 0, 0, 1);

    glFlush();
    glutSwapBuffers();

}


int main(int argc, char **argv)
{
    float x, y;
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    glutCreateWindow("Cone");
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMotionFunc(drag);
    glutMouseFunc(click);
    glutSpecialFunc(catchKey);



    glEnable(GL_DEPTH_TEST);

    glutMainLoop();         //calls do_one_simulation_step, keyboard, display, drag, reshape
    return 0;
}

Upvotes: 1

Views: 88

Answers (1)

genpfault
genpfault

Reputation: 52094

A few issues:

  • Set your camera matrix, then draw. The way you have it now your gluLookAt() does nothing useful.
  • The default identity projection matrix probably isn't what you want. Set a real perspective transform using gluPerspective() or glFrustum().
  • Your gluLookAt() eye/center coords were a bit wonky; I've put the eye at (50, 50, 50) and set it to look at the origin.

All together:

cone screenshot 

#include <GL/glut.h>
#include <GL/GLU.h>

void display( void )
{
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    double w = glutGet( GLUT_WINDOW_WIDTH );
    double h = glutGet( GLUT_WINDOW_HEIGHT );
    gluPerspective( 60.0, w / h, 1.0, 1000.0 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
    gluLookAt( 50, 50, 50, 0, 0, 0, 0, 0, 1 );

    glutWireCone( 10, 30, 20, 20 );

    glutSwapBuffers();
}

int main( int argc, char **argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH );
    glutInitWindowSize( 500, 500 );
    glutCreateWindow( "Cone" );
    glutDisplayFunc( display );
    glEnable( GL_DEPTH_TEST );
    glutMainLoop();
    return 0;
}

Upvotes: 2

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