Polygon Won't Show Up In The Screen - c

Question

I am trying to draw a 6 sided obelisk using opengl.
Below is the code I use to model the bottom surface of the obelisk:
void drawObelisk() {
glColor3f(1.0,1.0,0.0);
glBegin(GL_POLYGON);
for ( x=0.0; x<2.0*pi/3; x=x+inc )
{
glVertex3f(0.3*cos(x),0.3*sin(x),0.0);
}
glEnd();
}
This code is used to render the model:
void myDisplay(void)
{
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glPushMatrix();
drawObelisk();
glPopMatrix();
glFlush();
}
void SetupRC(void)
{
glClearColor(0.0, 0.0, 1.0, 1.0);
glOrtho(-6.0,6.0,-6.0,6.0,-6.0,6.0);
}
void main(void)
{
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(640,480);
glutInitWindowPosition(10,15);
glutCreateWindow("Test");
glutDisplayFunc(myDisplay);
SetupRC();
glutIdleFunc(idle);
glutMainLoop();
}
For certain reasons the polygon surface that I drew didn't show up on the screen once the model is rendered.

Answer 1

Give this a shot:
#include <GL/glut.h>
#include <math.h>
void drawObelisk()
{
double pi = 3.14159;
double inc = (2*pi) / 6;
glColor3f(1.0,1.0,0.0);
glBegin(GL_POLYGON);
for( double theta = 0.0; theta < 2*pi; theta += inc )
{
double scale = 2.0;
double x = scale * cos( theta );
double y = scale * sin( theta );
glVertex3d(x,y,0.0);
}
glEnd();
}
void myDisplay(void)
{
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glClearColor(0.0, 0.0, 1.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-6.0,6.0,-6.0,6.0,-6.0,6.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
drawObelisk();
glPopMatrix();
glFlush();
}
void main( int argc, char** argv )
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(640,480);
glutInitWindowPosition(10,15);
glutCreateWindow("Test");
glutDisplayFunc(myDisplay);
glutMainLoop();
}
Things that were wonky:
Missing glutInit() call.
glClear()ing the depth buffer without requesting one via GLUT_DEPTH.
Not switching to GL_MODELVIEW after setting your projection matrix.
Original drawObelisk() for-loop only generated two vertices. GL_POLYGON needs a minimum of three.