Drawing a ball and two cones in OpenGL C++ - c++

Question

I have a code where I want to draw a bowl and two cones at a time.
But, it is showing only those cones, not showing the ball.
#include <GL/glut.h>
#include <stdlib.h>
#include <Math.h> // Needed for sin, cos
#define PI 3.14159265f
GLfloat ballRadius = 0.5f; // Radius of the bouncing ball
GLfloat ballX = 0.0f; // Ball's center (x, y) position
GLfloat ballY = 0.0f;
GLfloat ballXMax, ballXMin, ballYMax, ballYMin; // Ball's center (x, y) bounds
GLfloat xSpeed = 0.02f; // Ball's speed in x and y directions
GLfloat ySpeed = 0.007f;
int refreshMillis = 30; // Refresh period in milliseconds
static void resize(int width, int height)
{
const float ar = (float) width / (float) height;
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-ar, ar, -1.0, 1.0, 2.0, 100.0);
}
static void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// This is ball's code that is not being drawn.
***glTranslatef(ballX, ballY, 0.0f); // Translate to (xPos, yPos)
// Use triangular segments to form a circle
glBegin(GL_TRIANGLE_FAN);
glColor3f(1.0f, 0.0f, 0.0f); // Blue
glVertex2f(0.0f, 0.0f); // Center of circle
int numSegments = 100;
GLfloat angle;
for (int i = 0; i <= numSegments; i++) { // Last vertex same as first vertex
angle = i * 2.0f * PI / numSegments; // 360 deg for all segments
glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
}
glEnd();***
//End of ball code
glColor3d(0,1,0);
glPushMatrix();
glTranslated(-1.0,0.5,-6);
glRotated(65, -1.0, 0.0, 0.0);
glutSolidCone(1, 2, 70, 50);
glPopMatrix();
glPushMatrix();
glTranslated(0.0,-1.5,-6);
glRotated(65, -1.0, 3.0, 0.0);
glutWireCone(1,2, 16, 16);
glPopMatrix();
glutSwapBuffers();
}
/* Program entry point */
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitWindowSize(740,580);
glutInitWindowPosition(10,10);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Programming Techniques - 3D Cones");
glutReshapeFunc(resize);
glutDisplayFunc(display);
glClearColor(1,1,1,1);
glutMainLoop();
return EXIT_SUCCESS;
}

Answer 1

The reason you don't see the circle is that it's clipped against the near plane. With glFrustum(-ar, ar, -1.0, 1.0, 2.0, 100.0); you specify that the near plane is at z = -2, and the far plane at z = -100. Anything outside these values are clipped. But by using glVertex2, your z values for the circle vertices are 0, so all of them are clipped. You can fix it by calling glTranslatef(ballX, ballY, -10.0f); instead.
A couple more pointers:
Always reset the matrix mode to GL_MODELVIEW (e.g. in your resize() function). You don't have to, but it's a good convention.
Always glPush/PopMatrix() before modifying the matrix stack (e.g. when translating the circle).
glColor3f(1.0f, 0.0f, 0.0f); // Blue? ;)