#include <stdio.h>
#include <math.h>

void MidPoint_Ellipse(double Xc, double Yc, double Rx, double Ry);
void Draw_Ellipse (double P, double Xc, double Yc, double X, double Y);

int main () {
	double Xc, Yc, Rx, Ry;
	printf("Please Enter an ellipse center point coordinates, x-axis radius, y-axis radius\n");
	scanf ("%lf %lf %lf %lf\n", &Xc, &Yc, &Rx, &Ry);
	printf ("Calculating Ellipse border points for center (%lf, %lf) and x-axis radius %lf, y-axis radius %lf\n", Xc, Yc, Rx, Ry);
	MidPoint_Ellipse (Xc, Yc, Rx, Ry);
	return 0;
} 

void MidPoint_Ellipse(double Xc, double Yc, double Rx, double Ry) {

	/* Xc and Yc here denotes the x coordinate and y coordinate of the center of the ellipse and Rx and Ry are the x-radius and y-radius of the ellipse respectively */
	double Sx = Rx * Rx;
	double Sy = Ry * Ry;
	double X = 0;
	double Y = Ry;
	double Px = 0;
	double Py = 2 * Sx * Y;
	double P = Sy - (Sx * Ry) + (0.25 * Sx);	/* First Region*/ 
	Draw_Ellipse (P, Xc, Yc, X, Y);
	while (Px<Py) {
		X = X + 1;
		Px = Px + 2 * Sy; 
		if (P < 0) {
			P = P + Sy + Px;
		} 
		else {
			Y = Y - 1;
			Py = Py - 2 * Sx;
			P = P + Sy + Px - Py; 
		}
		Draw_Ellipse (P, Xc, Yc, X, Y); 
	}
	P= Sy * pow((X+0.5), 2) +Sx * pow ((Y-1), 2) - Sx * Sy; 		/*Second Region*/
	
	while (Y > 0) {
		Y = Y - 1;
		Py = Py - 2 * Sx; 
		if (P > 0) {
			P = P + Sx - Py;
		} 
		else {
			X = X + 1;
			Px = Px + 2 * Sy;
			P = P + Sx - Py + Px; 
		}
		Draw_Ellipse (P, Xc, Yc, X, Y); 
	}
}


void Draw_Ellipse (double P, double Xc, double Yc, double X, double Y) {
	printf ("Decision Parameter P %lf\n", P);
	printf ("%lf  %lf\n", Xc + X, Yc + Y); 
	printf ("%lf  %lf\n", Xc - X, Yc + Y); 
	printf ("%lf  %lf\n", Xc + X, Yc - Y); 
	printf ("%lf  %lf\n\n", Xc - X, Yc - Y);
}