/*  
 *  bezier_curve.cpp, based on bezcurve.c from OpenGL Red Book.			
 *  This program uses evaluators to draw a cubic Bezier curve.
 *  Draws the curve by evaluating individual vertex coordinates
 *  or by evaluating a uniform one-dimensional grid.
 */
#include <GL/glut.h>
#include <iostream>

GLfloat ctrlpoints[4][3] = {
	{ -4.0, -4.0, 0.0}, { -2.0, 4.0, 0.0}, 
	{2.0, -4.0, 0.0}, {4.0, 4.0, 0.0}};

int coord;

void init(void)
{
   glClearColor(0.0, 0.0, 0.0, 0.0);
   glShadeModel(GL_FLAT);
   coord = 1;
}

void display(void)
{
   int i;
   int num_steps = 30; // number of steps to generate curve

   glClear(GL_COLOR_BUFFER_BIT);
   
   // generate individual vertex coords to draw curve
   if(coord){
     glColor3f(1.0, 1.0, 1.0);
     glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, 4, &ctrlpoints[0][0]);
     glEnable(GL_MAP1_VERTEX_3);
     glBegin(GL_LINE_STRIP);
     // step uniformly along u
     for (i = 0; i <= num_steps; i++) 
       glEvalCoord1f((GLfloat) i/ (float) num_steps);
     glEnd();
   }
   // or (equivalently) generate uniform grid to draw curve
   else {
     glColor3f(1.0, 0.0, 0.0);
     glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, 4, &ctrlpoints[0][0]);
     glEnable(GL_MAP1_VERTEX_3);
     glMapGrid1f(num_steps, 0.0, 1.0);
     glEvalMesh1(GL_LINE, 0, num_steps); // replace GL_LINE with GL_POINT
                                        // to see evaluated grid points
   }
   /* The following code displays the control points as dots. */
   glPointSize(5.0);
   glColor3f(1.0, 1.0, 0.0);
   glBegin(GL_POINTS);
   for (i = 0; i < 4; i++) 
     glVertex3fv(&ctrlpoints[i][0]);
   glEnd();
   glFlush();
}

void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (w <= h)
      glOrtho(-5.0, 5.0, -5.0*(GLfloat)h/(GLfloat)w, 
               5.0*(GLfloat)h/(GLfloat)w, -5.0, 5.0);
   else
      glOrtho(-5.0*(GLfloat)w/(GLfloat)h, 
               5.0*(GLfloat)w/(GLfloat)h, -5.0, 5.0, -5.0, 5.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
  if (key == 'q' || key == 'Q')
    exit(0);
  else if (key == 'c'){ // vertex coords
    coord = 1;
    glutPostRedisplay();
  }
  else if (key == 'g'){ // uniform grid
    coord = 0;
    glutPostRedisplay();
  }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutKeyboardFunc (keyboard);
   glutMainLoop();
   return 0;
}