inscribed_circle.cpp

#include <stdio.h>
#include <math.h>
#include <GL/glut.h>
#include<iostream>
#define PI 3.14159
// Center of the cicle = (320, 240)
int xc = 320, yc = 240;

// Plot eight points using circle's symmetrical property
float round_value(float v)
{
  return floor(v + 0.5);
}

void LineDDA(double X1, double Y1, double X2, double Y2)
{
  double dx=(X2-X1);
  double dy=(Y2-Y1);
  double steps;
  float xInc,yInc,x=X1,y=Y1;
  steps=(abs(dx)>abs(dy))?(abs(dx)):(abs(dy));
  xInc=dx/(float)steps;
  yInc=dy/(float)steps;

  glBegin(GL_POINTS);

  glVertex2d(x,y);
  int k;

  for(k=0;k<steps;k++)
  {
    x+=xInc;
    y+=yInc;

    glVertex2d(round_value(x), round_value(y));
  }
  glEnd();
}

void plot_point(int x, int y)
{
  glBegin(GL_POINTS);
  glVertex2i(xc+x, yc+y);
  glVertex2i(xc+x, yc-y);
  glVertex2i(xc+y, yc+x);
  glVertex2i(xc+y, yc-x);
  glVertex2i(xc-x, yc-y);
  glVertex2i(xc-y, yc-x);
  glVertex2i(xc-x, yc+y);
  glVertex2i(xc-y, yc+x);
  glEnd();
}

// Function to draw a circle using bresenham's
// circle drawing algorithm
void bresenham_circle(int r)
{
  int x=0,y=r;
  float pk=(5.0/4.0)-r;

  /* Plot the points */
  /* Plot the first point */
  plot_point(x,y);

  /* Find all vertices till x=y */
  while(x < y)
  {
    x = x + 1;
    if(pk < 0)
      pk = pk + 2*x+1;
    else
    {
      y = y - 1;
      pk = pk + 2*(x - y) + 1;
    }
    plot_point(x,y);
  }
  glFlush();
}

void draw_triangle(int r){
float length_x = r*cos(PI/6);
float length_y = r*sin(PI/6);
/*glBegin(GL_TRIANGLES);
glVertex2d((xc - length_x),(yc - length_y));
glVertex2d((xc + length_x), (yc - length_y));
glVertex2d(xc, (yc + r));
glEnd();*/

LineDDA((xc - length_x),(yc - length_y),(xc + length_x),(yc - length_y));
LineDDA((xc + length_x),(yc - length_y),(xc),(yc + r));
LineDDA((xc ),(yc + r),(xc - length_x),(yc - length_y));
}
// Function to draw two concentric circles
void concentric_circles(void)
{
  /* Clears buffers to preset values */
  glClear(GL_COLOR_BUFFER_BIT);
  int radius1 = 100, radius2 = 200;
  bresenham_circle(radius1);
  draw_triangle(radius1);
  draw_triangle(radius2);
  bresenham_circle(radius2);

}

void Init()
{
  /* Set clear color to white */
  glClearColor(1.0,1.0,0.0,0);
  /* Set fill color to black */
  glColor3f(1.0,0.0,0.0);
  gluOrtho2D(0 , 640 , 0 , 480);
}

int main(int argc, char **argv)
{
  /* Initialise GLUT library */
  glutInit(&argc,argv);
  /* Set the initial display mode */
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  /* Set the initial window position and size */
  glutInitWindowPosition(0,0);
  glutInitWindowSize(640,480);
  /* Create the window with title "DDA_Line" */
  glutCreateWindow("bresenham_circle");
  /* Initialize drawing colors */
  Init();
  /* Call the displaying function */
  glutDisplayFunc(concentric_circles);
  /* Keep displaying untill the program is closed */
  glutMainLoop();
}