#include<iostream.h>
#include<dos.h>
#include<conio.h>
#include<math.h>
#include<graphics.h>

// Function to plot points based on ellipse symmetry
void display(int xs1, int ys1, int x, int y);

// Function to implement the Midpoint Ellipse Algorithm
void ellips1(int xs1, int ys1, int rx, int ry)
{
    int x, y;
    float d1, d2, dx, dy;
    x = 0;
    y = ry;
    
    // Initial decision parameter for region 1
    d1 = pow(ry, 2) - (pow(rx, 2) * ry) + (0.25 * pow(rx, 2));
    dx = 2 * pow(ry, 2) * x;
    dy = 2 * pow(rx, 2) * y;

    // Region 1 (Slope < 1)
    do
    {
        display(xs1, ys1, x, y); // Plot the calculated points
        if (d1 < 0) // Choose the next pixel based on decision parameter
        {
            x++;
            dx += 2 * pow(ry, 2);
            d1 += dx + pow(ry, 2);
        }
        else
        {
            x++;
            y--;
            dx += 2 * pow(ry, 2);
            dy -= 2 * pow(rx, 2);
            d1 += dx - dy + pow(ry, 2);
        }
    } while (dx < dy); // Continue until slope becomes greater than 1

    // Initial decision parameter for region 2
    d2 = pow(ry, 2) * pow((x + 0.5), 2) + pow(rx, 2) * pow((y - 1), 2) - pow(rx, 2) * pow(ry, 2);
    
    // Region 2 (Slope > 1)
    do
    {
        display(xs1, ys1, x, y); // Plot the calculated points
        if (d2 > 0) // Choose the next pixel based on decision parameter
        {
            y--;
            dy -= 2 * pow(rx, 2);
            d2 -= dy + pow(rx, 2);
        }
        else
        {
            x++;
            y--;
            dx += 2 * pow(ry, 2);
            dy -= 2 * pow(rx, 2);
            d2 += dx - dy + pow(rx, 2);
        }
    } while (y > 0); // Continue until reaching the x-axis
}

// Function to plot ellipse points using 4-way symmetry
void display(int xs, int ys, int x, int y)
{
    putpixel(xs + x, ys + y, WHITE); // First quadrant
    putpixel(xs - x, ys - y, WHITE); // Third quadrant
    putpixel(xs + x, ys - y, WHITE); // Fourth quadrant
    putpixel(xs - x, ys + y, WHITE); // Second quadrant
}

// Main function
int main(void)
{
    int xs1, ys1;
    float rx1, ry1;
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "c:\\tc\\bgi"); // Initialize graphics mode

    // User input for center and radii
    cout << "\t\tMidpoint Ellipse Drawing Algorithm\n";
    cout << "Enter the Center Coordinates\n";
    cout << "xc = \t";
    cin >> xs1;
    cout << "yc = \t";
    cin >> ys1;
    cout << "Enter the X Radius\t";
    cin >> rx1;
    cout << "Enter the Y Radius\t";
    cin >> ry1;

    // Call function to draw the ellipse
    ellips1(xs1, ys1, rx1, ry1);
    getch();
    closegraph(); // Close the graphics window
    return 0;
}