#include<GL/glut.h>
#include <cstdlib>
#include <iostream>

#include <vector>

using namespace std;

const float d = 8;

struct point {
    int x, y, z;
};

struct line {
    point start, end;
};

vector<line> figure;

// a utility routine to stick a line into the vector.
void makeLine(int x1, int y1, int z1, int x2, int y2, int z2) {
    point p1,p2;
    line l; 

    p1.x = x1;
    p1.y = y1; 
    p1.z = z1;
    p2.x = x2;
    p2.y = y2;
    p2.z = z2;
    l.start = p1;
    l.end= p2;
    figure.push_back(l);
}


// this builds the scene 
void makeShape() {

    // a simple cube

    // make the front of the cube
    makeLine(-10,-10,10,-10, 10,10);
    makeLine(-10,-10,10, 10,-10,10);
    makeLine(-10, 10,10, 10, 10,10);
    makeLine( 10,-10,10, 10, 10,10);
    // make the back of the cube
    makeLine(-10,-10,30,-10, 10,30);
    makeLine(-10,-10,30, 10,-10,30);
    makeLine(-10, 10,30, 10, 10,30);
    makeLine( 10,-10,30, 10, 10,30);
    // make the sides of the cube
    makeLine(-10,-10,30,-10,-10,10);
    makeLine( 10,-10,30, 10,-10,10);
    makeLine(-10, 10,30,-10, 10,10);
    makeLine( 10, 10,30, 10, 10,10);

    // put an x on the right side
    makeLine(10, -8, 12, 10, 8, 28);
    makeLine(10, -8, 28, 10, 8, 12);

    // and put a T on the Top
    makeLine(-8,10, 28, 8, 10,28);
    makeLine( 0,10, 12, 0, 10, 28);

    // finally a triangle on the back wall.
    makeLine( 0, 8, 28, -8, -8, 28);
    makeLine( 0, 8, 28,  8, -8, 28);
    makeLine(-8,-8, 28,  8, -8, 28);
}

void drawLine(line l) {
   float x1, y1, x2, y2;

   // do the projection (from the book)
   x1 = -float(l.start.x)/(float(l.start.z)/d);
   x2 = -float(l.end.x)  /(float(l.end.z)  /d);
   y1 = -float(l.start.y)/(float(l.start.z)/d);
   y2 = -float(l.end.y)  /(float(l.end.z)  /d);

   // this is how you draw a 2d line
   glBegin(GL_LINES);
     glVertex2f(x1, y1);
     glVertex2f(x2, y2);
   glEnd();
}


void display() {
    int i;

    // clear the scene
    glClear(GL_COLOR_BUFFER_BIT);

    // set the drawing color
    glColor3f(1.0,0,0);

    // actually draw the figure
    for(i=0;i<figure.size();i++) {
      drawLine(figure[i]);  
    }

    // tell gl to execute the commands
    glFlush();
}

void myinit() {

    // this builds my scene.
    makeShape();

    // we will discuss this later.
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // grab a frame that is 40x40 centered on the origin
    gluOrtho2D(-20.0,20.0,-20.0,20.0);

    glMatrixMode(GL_MODELVIEW);
    // when the screen in cleared, clear it to white
    glClearColor(1.0,1.0,1.0,1.0);
    // the drawing color is set to black.
    glColor3f(0.0,0.0,0.0);
}


// this is sort of a standard main routine.  It will become more complex
// as we go along.
int main (int argc, char ** argv) {

    // initialize openGL, and GLUT
    glutInit(&argc, argv);
    // This asks for a  single frame frame buffer, with RGB colors
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    // this asks for a window 500 pixels by 500 pixels
    glutInitWindowSize(500,500);
    // this makes a window with the title "Pinhole Camera"
    glutCreateWindow("Pinhole Camera");
    // this tells it what to call when it needs to redisplay
    glutDisplayFunc(display);
    // this is my function to initialize things
    myinit();
    // call the main loop.
    glutMainLoop();
}