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

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 
#include
#include
#include

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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