Project a 3D Hexognal using perspective projection OpenGL in C++

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Figure 1
Perspective in the graphic arts, such as drawing, is an approximate representation, on a flat surface (such as paper), of an image as it is seen by the eye.(wikipedia)


Figure 2
Using these technique to generate an 3D object in 2D plane. The code is here :


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#include <windows.h>
#include <gl/Gl.h>
#include <gl/glut.h>
#include <cmath> 

typedef struct{float x;float y;}Point2D;
typedef struct{float x;float y;float z;}Point3D;
int d = 600;
GLfloat vlist[8][4];

void init(void)
{
 vlist[0][0] = 140;
 vlist[0][1] = 270;
 vlist[0][2] = 100;

 vlist[1][0] = 220;
 vlist[1][1] = 270;
 vlist[1][2] = 100;

 vlist[2][0] = 260;
 vlist[2][1] = 200;
 vlist[2][2] = 100;

 vlist[3][0] = 220;
 vlist[3][1] = 130;
 vlist[3][2] = 100;

 vlist[4][0] = 140;
 vlist[4][1] = 130;
 vlist[4][2] = 100;

 vlist[5][0] = 100;
 vlist[5][1] = 200;
 vlist[5][2] = 100;

 vlist[6][0] = 140;
 vlist[6][1] = 270;
 vlist[6][2] = 300;

 vlist[7][0] = 220;
 vlist[7][1] = 270;
 vlist[7][2] = 300;

 vlist[8][0] = 260;
 vlist[8][1] = 200;
 vlist[8][2] = 300;

 vlist[9][0] = 220;
 vlist[9][1] = 130;
 vlist[9][2] = 300;

 vlist[10][0] = 140;
 vlist[10][1] = 130;
 vlist[10][2] = 300;

 vlist[11][0] = 100;
 vlist[11][1] = 200;
 vlist[11][2] = 300;
  
}

void rotateObj_x(float deg_x){  // rotate the Object about a line which is parallel to X axis 
 float ang = deg_x * 3.14159265359 / 180.0;  //angle in radians 
 
 for(int i=0; i<12; i++){
  float tmpx = vlist[i][0];
  float tmpy = vlist[i][1];
  float tmpz = vlist[i][2];
  vlist[i][0] = tmpx;
  vlist[i][2] = tmpz*cos(ang) - tmpy*sin(ang);
  vlist[i][1] = tmpz*sin(ang) + tmpy*cos(ang);
 }
  
 
 glutPostRedisplay(); //this will call the function "myDisplay()" again
}

void rotateObj_y(float deg_y){  // rotate the Object about a line which is parallel to Y axis 
 float ang = deg_y * 3.14159265359 / 180.0;
 
 for(int i=0; i<12; i++){
  float tmpx = vlist[i][0];
  float tmpy = vlist[i][1];
  float tmpz = vlist[i][2];
  vlist[i][1] = tmpy;
  vlist[i][0] = tmpx*cos(ang) - tmpz*sin(ang);
  vlist[i][2] = tmpx*sin(ang) + tmpz*cos(ang);
 }


 glutPostRedisplay(); //this will call the function "myDisplay()" again
}

Point2D ProjectXY(float x, float y, float z){ //Perspective projection on XY plane with COP is at (180,200,-d) 
 Point2D p0;
 d= abs(d);
 p0.x = (x*d)/(d-z);
 p0.y = (y*d)/(d-z);

 return p0;
}

void drawObj(Point2D A,Point2D B,Point2D C,Point2D D, Point2D E,Point2D F, Point2D G,Point2D H, Point2D I,Point2D J,Point2D K, Point2D L)
{
 glPointSize(1.0);
 glLineWidth(2.0);
 //Draw front
 glBegin(GL_LINE_LOOP);
 
  glVertex2f(A.x,A.y);glVertex2f(B.x,B.y);glVertex2f(C.x,C.y);glVertex2f(D.x,D.y);glVertex2f(E.x,E.y);glVertex2f(F.x,F.y);
 glEnd();

 //Draw BACK
 
 glBegin(GL_LINE_LOOP);
 glVertex2f(G.x,G.y),glVertex2f(H.x,H.y);glVertex2f(I.x,I.y);glVertex2f(J.x,J.y);glVertex2f(K.x,K.y);glVertex2f(L.x,L.y);
 glEnd();

 //Connect Lines
 glBegin(GL_LINES);
 glVertex2f(A.x,A.y);glVertex2f(G.x,G.y);
 glVertex2f(B.x,B.y);glVertex2f(H.x,H.y);
 glVertex2f(C.x,C.y);glVertex2f(I.x,I.y);
 glVertex2f(D.x,D.y);glVertex2f(J.x,J.y);
 glVertex2f(E.x,E.y);glVertex2f(K.x,K.y);
 glVertex2f(F.x,F.y);glVertex2f(L.x,L.y);
 glEnd();
 glFlush();
}

void myDisplay()
{
 glClearColor(1.0f, 1.0f, 1.0f, 0.0f); 
 glClear(GL_COLOR_BUFFER_BIT);
 glColor3f(0.0f, 0.0f, 0.0f);

 Point2D pro_A = ProjectXY(vlist[0][0],vlist[0][1],vlist[0][2]);
 Point2D pro_B = ProjectXY(vlist[1][0],vlist[1][1],vlist[1][2]);
 Point2D pro_C = ProjectXY(vlist[2][0],vlist[2][1],vlist[2][2]);
 Point2D pro_D = ProjectXY(vlist[3][0],vlist[3][1],vlist[3][2]);
 Point2D pro_E = ProjectXY(vlist[4][0],vlist[4][1],vlist[4][2]);
 Point2D pro_F = ProjectXY(vlist[5][0],vlist[5][1],vlist[5][2]);
 Point2D pro_G = ProjectXY(vlist[6][0],vlist[6][1],vlist[6][2]);
 Point2D pro_H = ProjectXY(vlist[7][0],vlist[7][1],vlist[7][2]);
 Point2D pro_I = ProjectXY(vlist[8][0],vlist[8][1],vlist[8][2]);
 Point2D pro_J = ProjectXY(vlist[9][0],vlist[9][1],vlist[9][2]);
 Point2D pro_K = ProjectXY(vlist[10][0],vlist[10][1],vlist[10][2]);
 Point2D pro_L = ProjectXY(vlist[11][0],vlist[11][1],vlist[11][2]);
 drawObj(pro_A,pro_B,pro_C,pro_D,pro_E,pro_F,pro_G,pro_H,pro_I,pro_J,pro_K,pro_L);
}



void keyboard(unsigned char key, int x, int y)
{
 if (key == 'q' || key == 'Q')
  exit(EXIT_SUCCESS);
 if (key == '+')
 {
  if(d > 0 && d < 2000){
   d++;
   glutPostRedisplay();
  }
 }
 if (key == '-')
 {
  if(d > 0 && d < 2000){
   d--;
   glutPostRedisplay();
  }
 }
}

void special(int key, int, int) {
 switch (key) {
 case GLUT_KEY_LEFT: rotateObj_y(-1); break; // decreasing the angle by 1 degree
 case GLUT_KEY_RIGHT: rotateObj_y(1);break; // increasing the angle by 1 degree
 case GLUT_KEY_UP: rotateObj_x(-1);break; // decreasing the angle by 1 degree
 case GLUT_KEY_DOWN: rotateObj_x(1);break; // increasing the angle by 1 degree
 default: return;
 }
}

int main( int argc, char ** argv ) {
 glutInit( &argc, argv );
 glutInitWindowPosition( 0, 0 );
 glutInitWindowSize( 800, 600 );
 glutCreateWindow( "Hexagonal Prism " );

 glMatrixMode( GL_PROJECTION ); 
 glLoadIdentity();
 gluOrtho2D( 0, 800, 0, 600 );
 glViewport(0, 0, 800, 600);

 init();

 glutKeyboardFunc(keyboard); 
 glutSpecialFunc(special);
 glutDisplayFunc( myDisplay );
 glutMainLoop();

 return( 0 );
}


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