#include <stdlib.h>
#include <math.h>
#include <stdio.h>
#include <GL/glut.h>

#define PI 3.141592654
#define g 9.8

float x_init, y_init, z_init;
float rho, theta;
float V;

void Dibujar_Grid(GLfloat GridScale, GLfloat XSteps, GLfloat ZSteps)
{
 GLfloat zExtent, xExtent;
 GLfloat xLocal, zLocal;
 int loopX, loopZ;

 glBegin( GL_LINES );
 zExtent = GridScale*ZSteps;
 for(loopX = -XSteps; loopX <=XSteps; loopX++ )
    {
    xLocal = GridScale*loopX;
    glVertex3f( xLocal, 0.0, -zExtent );
    glVertex3f( xLocal, 0.0,  zExtent );
    }
 xExtent = GridScale * XSteps ;
 for(loopZ = -ZSteps; loopZ <= ZSteps; loopZ++ )
    {
    zLocal = GridScale * loopZ;
    glVertex3f( -xExtent, 0.0, zLocal );
    glVertex3f(  xExtent, 0.0, zLocal );
    }
 glEnd();
}

void Dibujar_VectorTiro(void)
{
 float x, y, z;
 float l;

 l=1.0;
 x=l*sin(rho)*sin(theta);
 y=l*cos(rho);
 z=l*sin(rho)*cos(theta);
 x_init=x;
 y_init=y;
 z_init=z;
 glBegin(GL_LINES);
 glVertex3f(0.0, 0.0, 0.0);
 glVertex3f( x, y, z);
 glEnd();
}

void Dibujar_Ejes(void)
{
 glBegin(GL_LINES);
 //eje X
 glVertex3f(0.0, 0.0, 0.0);
 glVertex3f(1.0, 0.0, 0.0);
 //eje Y
 glVertex3f(0.0, 0.0, 0.0);
 glVertex3f(0.0, 1.0, 0.0);
 //eje Z
 glVertex3f(0.0, 0.0, 0.0);
 glVertex3f(0.0, 0.0, 1.0);
 glEnd();
}

void Dibujar_Trayectoria(void)
{
 float x_pos, y_pos, z_pos;
 float Vx, Vy, Vz;
 float t, dt;
 
 x_pos=x_init;
 y_pos=y_init;
 z_pos=z_init;
 Vx=V*sin(rho)*sin(theta);
 Vy=V*cos(rho);
 Vz=V*sin(rho)*cos(theta);
 t=0.0;
 dt=0.02;
 glBegin(GL_POINTS);
 while (y_pos>=0)
	{
	x_pos = Vx*t + x_init;
	y_pos = Vy*t-0.5*g*t*t + y_init;
	z_pos = Vz*t + z_init;
	glVertex3f(x_pos, y_pos, z_pos);
	t=t+dt;	
	};
 glEnd();
}

void iniciar(void)
{
 glClearColor(0.0, 0.0, 0.0, 0.0);
 glPointSize(2.0);
 rho=PI/4.0;
 theta=PI/8.0;
 V=10.0;
}

void display(void)
{
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 glPushMatrix();
 gluLookAt(2.0, 2.0, -3.0, 0.0, 0.0, 5.0, 0.0, 1.0, 0.0);

 glLineWidth(1.0);
 glColor3f(0.5, 0.5, 0.5);
 Dibujar_Grid(1.0, 20.0, 20.0);

 glColor3f (1.0, 1.0, 0.0);  
 Dibujar_Ejes();

 glLineWidth(2.0);
 glColor3f (1.0, 0.0, 0.0);  
 Dibujar_VectorTiro();

 glColor3f (1.0, 1.0, 1.0);  
 Dibujar_Trayectoria();

 glPopMatrix();
 glFlush();
}

void reshape(int w, int h)
{
 if (!h)
	return;
 glViewport(0, 0,  (GLsizei) w, (GLsizei) h);
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();
 gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 100.0);
 glMatrixMode(GL_MODELVIEW);
 glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
 switch (key)
   {
   case 27: exit(0);
             break;
   }
}

int main(int argc, char **argv)
{
 glutInit(&argc, argv);
 glutInitWindowSize(400, 400);
 glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
 glutCreateWindow("Tiro en 3D");
 iniciar();
 glutDisplayFunc(display);
 glutReshapeFunc(reshape);
 glutKeyboardFunc(keyboard);
 glutMainLoop();
 return 0;
}