OpenGL program to make simple Triangle and bouncing Ball

This source code is for making a simple triangle and bouncing ball.

OpenGL program:

#if __APPLE__
#include<GLUT/glut.h>
#else
#include<GL/glut.h>
#endif

static int flag=0;
float tx=0.0,ty=0.0,tz=0.0;
float ball_x=0.5,ball_y=0.0,ball_z=0.0;
//placing the ball 0.5 unit right to origin

void glutInitRendering()
{
    glEnable(GL_DEPTH_TEST);
   
}

void reshaped(int w,int h)
{
    glViewport(0,0,w,h);
   
    glMatrixMode(GL_PROJECTION);
   
    glLoadIdentity();
   
    gluPerspective(45,0,1,200);
}

void updateBall()
{
    if(!flag)
    {
        ball_y+=0.05;
        if(ball_y>1.0)
            flag=1;
    }
    if(flag)
    {
        ball_y-=0.05;
        if(ball_y<-1)
            flag=0;
    }
}
void display()
{
        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
        
        glClearColor(0,0,1,0);
        
        glPushMatrix();
        
        glBegin(GL_POLYGON);
            glColor3f(1,0,0);
            
            glVertex3f(-0.25,0,-1);

            glVertex3f(0.25,0,-1);

            glVertex3f(0,0.25,-1);
        glEnd();
        glPopMatrix();
   

        glPushMatrix();
            glColor3f(0,1,1);
            glTranslatef(ball_x,ball_y,ball_z);
            glutSolidSphere(0.1,23,23);
        glPopMatrix();

        //update functin, will be called after every microsecond
        updateBall();


        glutSwapBuffers();
}

void keyPressed(int key,int x,int y){}

        
int main(int argc,char **argv)
{
    glutInit(&argc,argv);
   
    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
   
    glutInitWindowSize(400,500);
   
    glutCreateWindow("Bouncing Ball");
   
    glutInitRendering();
   
    glutDisplayFunc(display);
   
    glutIdleFunc(display);
   
    glutSpecialFunc(keyPressed);
   
    glutReshapeFunc(reshaped);
   
    glutMainLoop();
   
}  

//Output of the above Program:-