Interactive Line drawing in openGL

This is simple program based on the mouse inputs.
Using mouse inputs user can draw the lines in the opengl window.
Since the world space is same as that of the device space we dont have to worry about the
convertion here and that makes this program simple.

Still in the 2D world. :-)

// This program is for line drawing using opengl 
// User cn draw the lines by clicking the points in the opengl window
// User can remove the lines by pressing the right mouse button 

#include "stdafx.h"

#include <string.h>
#include <GL/glut.h>
#include "math.h"

float rotate =0.0;
float start = 0.0;
float z_dep = 0.0;

int poi_size = 0;
int poi_arr[100][2];
int m_x = 0;
int m_y = 0;

int rubber_band_on = 0;

int down_flag = 0;
void *font = GLUT_BITMAP_TIMES_ROMAN_24;
void *fonts[] =
{
  GLUT_BITMAP_9_BY_15,
  GLUT_BITMAP_TIMES_ROMAN_10,
  GLUT_BITMAP_TIMES_ROMAN_24
};

void selectFont(int newfont)
{
  font = fonts[newfont];
  glutPostRedisplay();
}

void drawCircle(float radius, float x1, float y1)
{
    float angle = 0;
    float x2,y2,cx,cy,fx,fy;
    int cache = 0;
    glBegin(GL_LINES);
    for (angle = 0; angle < 360; angle+=1.0) {
        float rad_angle = angle * 3.14 / 180;
        x2 = x1+radius * sin((double)rad_angle);
        y2 = y1+radius * cos((double)rad_angle);
        if (cache) {
            glVertex2f(cx,cy);
            glVertex2f(x2,y2);
        } else {
            fx = x2;
            fy = y2;
        }
        cache = 1;
        cx = x2;
        cy = y2;
    }
    glVertex2f(x2,y2);
    glVertex2f(fx,fy);

    glEnd();
}


void tick(void)
{
  glutPostRedisplay();
}

void output(int x, int y, char *string)
{
  int len, i;

  glRasterPos2f(x, y);
  len = (int) strlen(string);
  for (i = 0; i < len; i++) {
    glutBitmapCharacter(font, string[i]);
  }
}

void display(void)
{
    // Show the X and Y coordinate location of the mouse 
  glClear(GL_COLOR_BUFFER_BIT);
  char x_coord[10];
  sprintf(x_coord,"X:%d",m_x);
  char y_coord[10];
  sprintf(y_coord,"Y:%d",m_y);
  output(0, 24, x_coord);
  output(100, 24, y_coord);
  
  // Draw the lines created by user 
   glBegin(GL_LINES);
   for(int i=0; i<poi_size; i++) {
      glVertex2f(poi_arr[i][0],poi_arr[i][1]);
   }
   if (rubber_band_on && (poi_size%2==1)) {
     glVertex2f(m_x,m_y);
   }

   glEnd();

   // Draw small circles at the line start ane end point 
   for(int i=0; i<poi_size; i++) {
    drawCircle(2,poi_arr[i][0],poi_arr[i][1]);
   }
  glutSwapBuffers();
}

void handleKeypress(unsigned char key, int x, int y) {
    switch (key) {
        case 27: //Escape key
            exit(0);
    }
}

void reshape(int w, int h)
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0, w, h, 0);
  glMatrixMode(GL_MODELVIEW);
}

// the mouse callback function:
void mouse_move(int x, int y)
{
    m_x = x;
    m_y = y;
    display();
}

// the mouse callback function:
void mouse(int button, int state, int x, int y)
{
    m_x = x;
    m_y = y;

    switch (button) {
    case GLUT_RIGHT_BUTTON:
        if (state == GLUT_DOWN) {
        //    glutIdleFunc(spinDisplay);
        }
        if (state == GLUT_UP) {
            if (poi_size>0) {
              poi_size-=2;
            }
            rubber_band_on = 0;
            glutIdleFunc(NULL);
        }
        break;
    case GLUT_LEFT_BUTTON:
        rubber_band_on = 1;
        if (state == GLUT_DOWN) {
            down_flag = 1;
        }
        if (state == GLUT_UP) {
            if(down_flag) {
                poi_arr[poi_size][0]=x;
                poi_arr[poi_size][1]=y;
                poi_size++;
                down_flag = 0;
            }
            glutIdleFunc(NULL);
        }
        break;

    default:
        break;
    }
    display();
}

int main(int argc, char **argv)
{
  int i, msg_submenu, color_submenu;

  glutInit(&argc, argv);
  for (i = 1; i < argc; i++) {
    if (!strcmp(argv[i], "-mono")) {
      font = GLUT_BITMAP_9_BY_15;
    }
  }
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowSize(1000, 800);
  glutCreateWindow("OPENGL LINE DRAWING");
  glClearColor(0.0, 0.0, 0.0, 1.0);
  
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutIdleFunc(tick);
  glutKeyboardFunc(handleKeypress);
  glutMouseFunc(mouse);
  glutMotionFunc(mouse_move);
  glutPassiveMotionFunc(mouse_move);

  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}