#include<windows.h>
#include<stdio.h>
#include<string>
#include"glut.h"

const int n = 5;
const int k = 4;
GLfloat pp[n][2] = {
	-0.4, -0.4,
	-0.2, 0.4,
	0, -0.4,
	0.2, 0.4,
	0.4, -0.4
};
GLfloat x[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 }; //period
//GLfloat x[] = { -1, 0, 0, 0, 0, 1, 2, 3, 4, 5, 5, 5, 5 };  //открытый В сплайн

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

double N(int i, int k, double t) {
	if (k == 1) {
		if (t < x[i] || t > x[i + 1])
			return 0;
		return 1;
	}
	double a = 0, b = 0;
	if ((x[i + k - 1] - x[i]) != 0) a = (t - x[i])*N(i, k - 1, t) / (x[i + k - 1] - x[i]);
	if ((x[i + k] - x[i + 1]) != 0) b = (x[i + k] - t)*N(i + 1, k - 1, t) / (x[i + k] - x[i + 1]);
	return a + b;

}

void Display() {
	//glColor3f(0, 0, 0);
	glBegin(GL_POINTS);
	for (double i = 3; i <= 5; i += 0.001) { // (k-1) < < (n+1)
		double x = 0;
		double y = 0;
		for (int j = 1; j <= n; ++j) {
			double n = N(j, k, i);
			x += pp[j - 1][0] * n;
			y += pp[j - 1][1] * n;
			glColor3f(0.01*j, j % 7 * 0.1, j % 2);
			//glVertex2d(0.3*(i - 3), 0.3*n - 0.8); //внизу кривые
		}
		glColor3f(0, 0, 0);
		glVertex2d(x - 0.3, y); // splain
	}
	for (int i = 0; i < n; ++i) {
		glVertex2d(pp[i][0] - 0.3, pp[i][1]); // to4ki
	}
	glEnd();
	glutSwapBuffers();
	glutPostRedisplay();
}

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