task1

import javax.swing.*;
import java.awt.*;
import java.util.Vector;

/**
 * Created by Helen on 12.04.2016.
 */
public class Main extends JPanel {
    // x = (a+t)^2+b
    // y = ct+d
    static int width = 800;
    static int height = 600;

    public int A = 1;
    public int B = 1;
    public int C = 10;
    public int D = 1;

    class DoublePoint{
        public double x;
        public double y;

        DoublePoint(double x, double y){
            this.x = x;
            this.y = y;
        }

        public double getDistToIntPoint(IntPoint point)
        {
            return Math.sqrt((point.x - x)*(point.x - x) + (point.y - y)*(point.y - y));
        }
    }

    class IntPoint {
        public int x;
        public int y;

        IntPoint(int x, int y){
            this.x = x;
            this.y = y;
        }

        public double getDistToLine(Line ab)
        {
            DoublePoint a = ab.a;
            DoublePoint b = ab.b;
            double A = b.y - a.y;
            double B = -b.x + a.x;
            double C = a.y*(b.x - a.x) - a.x*(b.y - a.y);
            return Math.abs(A*x + B*y + C) / Math.sqrt(A*A + B*B);
        }
    }

    class Line{
        DoublePoint a;
        DoublePoint b;
        public Line(DoublePoint a, DoublePoint b)
        {
            this.a = a;
            this.b = b;
        }
    }

    private class Parabola{

        DoublePoint focus;
        IntPoint point0;
        double p;

        Line direct;

        public Parabola()
        {
            if (C == 0)
            {
                return;
            }

            p = C / 2.0;
            point0 = new IntPoint(0, 0);
            focus = new DoublePoint(p/2.0, 0);
            direct = new Line(new DoublePoint(-p/2.0, 10),
                    new DoublePoint(-p/2, -10));
        }
    }

    public double getDelta(Parabola parabola, IntPoint point)
    {
        double distToFocus = parabola.focus.getDistToIntPoint(point);
        double distToDirect = point.getDistToLine(parabola.direct);
        return distToDirect - distToFocus;
    }

    public IntPoint dVSc(Parabola parabola, IntPoint curPoint, double deltaC) {
        IntPoint pD = new IntPoint(curPoint.x, curPoint.y + 1);
        double deltaD = getDelta(parabola, pD);
        if (Math.abs(deltaD) < Math.abs(deltaC))
            return pD;
        return new IntPoint(curPoint.x + 1, curPoint.y + 1);
    }

    public IntPoint bVSc(Parabola parabola, IntPoint curPoint, double deltaC) {
        IntPoint pB = new IntPoint(curPoint.x + 1, curPoint.y);
        double deltaB = getDelta(parabola, pB);
        if (Math.abs(deltaB) < Math.abs(deltaC))
            return pB;
        return new IntPoint(curPoint.x + 1, curPoint.y + 1);
    }

    public Vector<IntPoint> calculate(Graphics g)
    {
        Vector<IntPoint> resPoints = new Vector<>();
        Parabola parabola = new Parabola();
        IntPoint sP = parabola.point0;
        resPoints.add(sP);

        while(sP.x < width / 2) {
            IntPoint pointC = new IntPoint(sP.x + 1, sP.y + 1);
            double deltaC = getDelta(parabola, pointC);
            IntPoint pB = new IntPoint(sP.x + 1, sP.y);
            double deltaB = getDelta(parabola, pB);
            IntPoint pD = new IntPoint(sP.x, sP.y + 1);
            double deltaD = getDelta(parabola, pD);
            if (deltaC > 0) {
                sP = dVSc(parabola, sP, deltaC);
            } else {
                sP = bVSc(parabola, sP, deltaC);
            }
            resPoints.add(sP);
        }
        return resPoints;
    }

    public void drawPoints(Graphics g, Vector<IntPoint> points)
    {
        int shiftX = width / 2 - A + B;
        int shiftY = height / 2 + D;
        for(IntPoint point : points) {
            g.drawLine(point.x + shiftX, point.y + shiftY,
                    point.x + shiftX, point.y + shiftY);

            g.drawLine(point.x + shiftX, -point.y + shiftY,
                    point.x + shiftX, -point.y + shiftY);
        }
    }

    @Override
    public void paint(Graphics g)
    {
        super.paint(g);

        Vector<IntPoint> points = calculate(g);
        drawPoints(g, points);
        super.repaint();
    }

    public static void main(String[] args) {
        Main canv = new Main();
        canv.setPreferredSize(new Dimension(width, height));

        JFrame w=new JFrame("Function");
        w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        w.getContentPane().add(canv);
        w.pack();

        w.setLocationRelativeTo(null);
        w.setVisible(true);
    }
}