All in one OpenGL program examples

This code contains source code of rotation of triangle, moving ball, collision detection and other related codes.

OpenGL program:-

#include<stdio.h>
#include<stdlib.h>

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

float size_x=0.5;
float size_y=0.5;
float rot_ang=0.0;
float ball_x=-1.0;
float ball_y=0.0;
static int flag=0;
float bb_x=0.5;
float bb_y=-0.25;
static int flag_bb=0;
float bg_b=0.1;

void reshape(int w,int h)
{
    glViewport(0,0,w,h);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    gluPerspective(45,w/h,1,200);
}

void keyPressed(int key,int x,int y)
{
    if(key==GLUT_KEY_UP)
    {size_x+=0.05;size_y+=0.05;}

    if(key==GLUT_KEY_DOWN)
    {size_x-=0.05;size_y-=0.05;}

    if(key==GLUT_KEY_RIGHT)
        rot_ang+=5;
    if(key==GLUT_KEY_LEFT)
        rot_ang-=5;

    //glutPostRedisplay();
}

void drawBall()
{
    glColor3f(1,0.5,0.1);

    glPushMatrix();

        glTranslatef(ball_x,ball_y,-1);
        glutSolidSphere(0.1,20,20);

    glPopMatrix();
}

void update()
{
   
    if(!flag)
    {
        if(ball_x>-0.25)
        {
            ball_x+=0.005;
            ball_y+=0.005;
        }
        else
            ball_x+=0.005;
        if(ball_x>0)
            flag=1;
    }

    if(flag)
    {
        if(ball_y>0.025)
        {
            ball_x+=0.005;
            ball_y-=0.005;
        }
        else
            ball_x+=0.005;
        //if(ball_x>0)
            //flag=1;
    }

    if(ball_x>1)
    {
        ball_x=-1;
        ball_y=0;
        flag=0;
    }
}

void bouncingBall()
{
    glPushMatrix();

        glColor3f(1,0,0);
        glTranslatef(bb_x,bb_y,0);
        glutSolidSphere(0.1,30,30);

    glPopMatrix();
}

void updateBB(){

    if(!flag_bb)
    {
        bb_y-=0.008;
        if(bb_y<-0.9)
            flag_bb=1;
    }
    if(flag_bb)
    {
        bb_y+=0.005;
        if(bb_y>-0.25)
            flag_bb=0;
    }
}

void updateBg()
{
    bg_b+=0.005;
    if(bg_b>1)
        bg_b=0.1;
}


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

    glClearColor(0,0.1,bg_b,0);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

/***************************triangle centred*********************************/
    glPushMatrix();

    //glTranslatef(0.5,0.5,0);

    //glRotatef(rot_ang,0,1,-1);

    glScalef(0.5,0.5,0.5);

    glBegin(GL_POLYGON);
       
        glColor3f(1,0.1,0.1);
   
        glVertex3f(-0.25,0,-1);

        glVertex3f(0.25,0,-1);

        glVertex3f(0,0.25,-1);

    glEnd();

    glPopMatrix();
   
/***********************triangle right upper corner*****************************/

    glPushMatrix();
   
    //glScalef(0.5,0.5,0.5);
    glScalef(size_x,size_y,0.5);
    glTranslatef(1,1,0);

    //glRotatef(rot_ang,0,1,-1);

    glBegin(GL_POLYGON);
       
        glColor3f(0,1,0);
   
        glVertex3f(-1,0,-1);

        glVertex3f(1,0,-1);

        glVertex3f(0,1,-1);

    glEnd();

    glPopMatrix();

    //rot_ang+=5;

/********************left upper corner**************************************/
    glPushMatrix();

    //glTranslatef(0.5,0.5,-0.5);

    glRotatef(rot_ang,-0.75,1,-1);

    glBegin(GL_TRIANGLES);

        glColor3f(1.5,1,0.05);
   
        glVertex3f(-1.0,0.5,-1);

        glVertex3f(-0.5,0.5,-1);

        glVertex3f(-0.75,1,-1);

    glEnd();
    glPopMatrix();
    rot_ang+=5;
/*********************************sphere**************************************/

    drawBall();

    update();

/***********************bouncing ball****************************************/
    bouncingBall();

    updateBB();

    updateBg();

    glutSwapBuffers();

}


void glutInitRendering()
{
    glEnable(GL_DEPTH_TEST);

}

int main(int argc,char **argv)
{
    glutInit(&argc,argv);

    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);

    glutInitWindowSize(500,600);

    glutCreateWindow("simple_to_advanced");

    glutInitRendering();

    glutDisplayFunc(display);

    glutIdleFunc(display);

    glutSpecialFunc(keyPressed);

    glutReshapeFunc(reshape);

    glutMainLoop();

}