#include <GL/glut.h>
#define MAX_CPTS 25

GLfloat cpts[MAX_CPTS][3];
int ncpts = 0;

static int width = 500, height = 500;

void drawCurves()
{
   int i;

   for(i=0; i<ncpts-3; i+= 3) {
      glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, 4, cpts[i]);
      glMapGrid1f(30, 0.0, 1.0);
      glEvalMesh1(GL_LINE, 0, 30);
      }
   glFlush();
}

static void display()
{
   int i;
   glClear(GL_COLOR_BUFFER_BIT);
   glBegin(GL_POINTS);
   for(i=0; i<ncpts; i++) glVertex3fv(cpts[i]);
   glEnd();
   glFlush();
   }

static void mouse(int button, int state, int x, int y)
{
   float wx, wy;
   if (button != GLUT_LEFT_BUTTON || state != GLUT_DOWN) return;
   wx = (2.0 * x) / (float)(width-1) - 1.0;
   wy = (2.0 * (height - 1 - y)) / (float)(height - 1) - 1.0;
   if (ncpts == MAX_CPTS) return;

   cpts[ncpts][0] = wx;
   cpts[ncpts][1] = wy;
   cpts[ncpts][2] = 0.0;
   ncpts++;

   glColor3f(0.0, 0.0, 0.0);
   glPointSize(5.0);
   glBegin(GL_POINTS);
   glVertex3f(wx, wy, 0.0);
   glEnd();
   glFlush();
   }

void keyboard(unsigned char key, int x, int y)
{
switch(key) {
 case 'q': case 'Q':  exit(); break;
 case 'c': case 'C': ncpts = 0;
 case 'e': case 'E': glutPostRedisplay(); break;
 case 'b': case 'B': drawCurves(); break;
   }
}

void reshape(int w, int h)
{
   width = w;
   height = h;
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
   glViewport(0,0,w,h);
}

int main(int argc, char **argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_RGB);
   glutInitWindowSize(width, height);
   glutCreateWindow("Bezier Curve");
   glutDisplayFunc(display);
   glutMouseFunc(mouse);
   glutKeyboardFunc(keyboard);
   glutReshapeFunc(reshape);
   glClearColor(1.0,1.0,1.0,1.0);
   glColor3f(0.0, 0.0, 0.0);
   glPointSize(5.0);
   glEnable(GL_MAP1_VERTEX_3);
   glutMainLoop();
}