#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>
#include <iostream>
#include <fstream>
using namespace std;

//fstream output("data.txt",ios::out);

double dt = 0.05; // this is the time step
float coeF = 0.5;
float verysmall = 0.001;
float totaltime = 0.0;
float gravity = 0.1;
GLfloat near = 0.1,far = 20.0;
GLfloat startdispz = -1.0;

const float DEG2RAD = 3.14159/180;
        
class ball
{
	private:
		// ax acceleration in x, px position in x, vx velocity in x
		double ax,ay,az,px,py,pz,vx,vy,vz,size;

	public:
		ball()
		{
			px=0.0;py=0.0;
		}
		ball(double dummyvx, double dummyvy,double dummyvz)
		{
			px=0;	py=0.1;	pz=0;	size=0.1;
			vx=dummyvx;	vy=dummyvy;	vz=dummyvz;	ay=gravity;
		}
		double getpx(){return px;}  double getpy(){return py;}	double getpz(){return pz;}
		double getvx(){return vx;}  double getvy(){return vy;}	double getvz(){return vz;}
		double getballsize(){return size;}

		double getspeed(){return  sqrt(py*py + px*px + pz*pz);}

		void evolve()
		{
			//cout << "vy" << vy << "\n";
			vy += (-gravity*dt);							// equation for the y component of v
			px += vx*dt;	py += vy*dt;	pz += vz*dt;	// equations for all 3 components of p
			totaltime += dt;								// update total time
			//output << totaltime << " " << px << " "   << py << " "  << pz << "\n";
			//cout << totaltime << " " << py  << " " << pz << "\n";
			//terminate when we hit the ground i.e pz < 0
    
			if(py < size)  
			{			
				py = size;
				vy = -vy*coeF;

				//cout << "The ball has hit the ground\n";
				//vx=0;	vy=0;	vz=0;
				//output.close();
				//exit(0); 
			}
		}
};

// ball start at origin with velocity vector as in the constructor
ball golfball(0.0, 0.4, 0.8);

void init(void)
{
	glClearColor(1.0,1.0,1.0,0.0);
}

void drawCircle(float Radius, int numPoints)
{
	glBegin( GL_LINE_LOOP );
	for( int i=0; i<numPoints; i++ )
	{
		float Angle = i * (2.0*M_PI/numPoints);
		float X = cos( Angle )*Radius;
		float Y = sin( Angle )*Radius;
		glVertex2f( X, Y );
	}
	glEnd();
} 

void display(void)
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(40,1,near,far);
	
	glMatrixMode(GL_MODELVIEW);	
	glLoadIdentity();	
	gluLookAt(0.0, 2.0, -3.0, 0.0, 0.0, 10.0, 0.0, 1.0, 0.0);
		
	glClear(GL_COLOR_BUFFER_BIT);	

	glPushMatrix();		
		glColor3f (0.0, 0.0, 0.0);
		glTranslatef(golfball.getpx(),golfball.getpy(),startdispz - golfball.getpz());
		glutSolidSphere(golfball.getballsize(),20,20);
	glPopMatrix();	
	
	glPushMatrix();
		glColor3f (0.0, 1.0, 0.0);
		glTranslatef(0,0.0,-7.5);
		glRotatef(90, 1.0, 0.0, 0.0);
		drawCircle(0.1,24);
		glRotatef(-90, 1.0, 0.0, 0.0);
	glPopMatrix();
	
	glFlush();
	glutSwapBuffers();
}

void keyboard(unsigned char key, int x, int y)
{
	switch (key)
	{
		case 'q':
		exit(0);
	}
}
 
void evolve(int a)
{
    // evolve system here 
	golfball.evolve();
	glutPostRedisplay();   
	glutTimerFunc(20,evolve,20);
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
   glutInitWindowSize (800, 800);
   glutCreateWindow (argv[0]);   init();
   glutKeyboardFunc (keyboard);
   //  glutIdleFunc(evolve);
   glutTimerFunc(100,evolve,100);
   glutDisplayFunc (display);
   cout << "Hello All on CG6301\n";
   cout << "This program models projectile motion, the golf ball moves under gravity(no friction)\n";
   cout << "The file is closed and the program terminates when the ball is deemed to have hit the ground \n";
   cout << "The lab questions ask you to determine how accurately we have modelled the system\n";
 
   glutMainLoop();
   return 0;
}