#include <GL/glut.h>

GLfloat ctlarray[][3] = { { -0.9, -0.5,0.0 },
{ -0.7, 0.5, 0.0 },
{ -0.4, -0.5, 0.0 },
{ -0.1, 0.5, 0.0 },
{ 0.2, -0.5, 0.0 },
{ 0.5, 0.5, 0.0 } };


double N_i_k(int k, int i, GLfloat x[], double t) {
	if (k == 1)
	{
		if ((x[i] <= t) && (t <= x[i + 1]))
			return 1;
		else
			return 0;
	}
	else
	{
		double sum1, sum2;
		if (x[i + k -1] == x[i])
			sum1 = 0;
		else
			sum1 = ((t - x[i]) / (x[i + k - 1] - x[i]))*N_i_k(k - 1, i, x, t);
		if (x[i + k + 1] == x[i + 1])
			sum2 = 0;
		else
			sum2 = ((x[i + k ] - t) / (x[i + k ] - x[i + 1]))*N_i_k(k - 1, i + 1, x, t);
		return sum1 + sum2;
	}
}

void init(void) {
	glClearColor(1, 1, 1, 1);
}

void Display() {
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();
	int k = 4;
	int n = 6;
	GLfloat knot[] = { 0.0, 1.0, 2.0,3.0 ,4.0 ,5.0,6.0,7.0,8.0,9.0 };

	glScalef(0.3, 0.3, 1.0f);
	glTranslatef(-2, 0.0, 0.0);
	glColor3f(1, 0, 0);
	glPointSize(3);
	glBegin(GL_POINTS);
	for (int i = 0; i < n; i++) {
		glVertex3f(ctlarray[i][0], ctlarray[i][1], ctlarray[i][2]);
	}
	glEnd();


	double X = 0.0;
	double Y = 0.0;
	double basis = 0.0;
	for (double t = k-1; t <= n; t += 0.001) {
		for (int i = 0; i < n; i++) {
			basis = N_i_k(k, i, knot, t);

			glBegin(GL_POINTS);
			glColor3f(0, 0, 1);
			glVertex3f(t-2, basis-1, 0);
			X += ctlarray[i][0] * basis;
			Y += ctlarray[i][1] * basis;
		}
		glEnd();




		glBegin(GL_POINTS);
		glColor3f(0, 1, 1);
		glVertex3f(X, Y, 0);
		glEnd();
		X = 0.0;
		Y = 0.0;
	}

	glEnd();
	glFlush();
}

void main() {
	glutInitDisplayMode(GLUT_RGBA | GLUT_SINGLE);
	glutInitWindowSize(480, 480);
	glutInitWindowPosition(100, 100);
	glutCreateWindow(" ");
	init();
	glutDisplayFunc(Display);
	glutMainLoop();
}