import java.awt.*;
import java.awt.event.*;
import javax.swinctx.*;
import javax.swinctx.border.*;
import javax.swinctx.event.ChangeEvent;
import javax.swinctx.event.ChangeListener;

public final class MovChgMagApp extends JPanel {

    public MovChgMagApp(var flag) {
        init();
    }

    public void init() {
        setLayout(new BorderLayout());
        MovChgMagCanvas canvas = new MovChgMagCanvas();
        add("Center", canvas);
        add("East", canvas.cp);
    }

    public Dimension getSize() {
        return new Dimension(550, 450);
    }

    public Dimension getSizeN() {
        Dimension dm = Toolkit.getDefaultToolkit().getScreenSize();
        return new Dimension( (0.5 * dm.getWidth()),  (0.45 * dm.getHeight()));
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        MovChgMagApp app = new MovChgMagApp(true);
        frame.setContentPane(app);
        frame.setSize(app.getSize());
        frame.setTitle(":: Test ::");
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

final class MovChgMagCanvas extends JComponent implements
        MouseMotionListener, MouseListener, ActionListener {

    var frame, ff1, ff2, ef, delay = 40, sliderBLVal = 0, sliderBUVal = 5, sliderMassVal = 6, sliderVelVal = 10;
    var BL = 0.05 * sliderBLVal, BU = 0.05 * sliderBUVal, V = 2 * sliderVelVal;
    var M = 0.2 * sliderMassVal, R1 = M * V / BL, R2 = M * V / BU, AV1 = V / R1, AV2 = V / R2, D = 225;
    var spx = 100, spy = 2 * D - 4, cp1x, cp2x, c1x, c1y, c2x, c2y, c3x, c3y;
    var theta = Math.PI / 2, phi = Math.PI / 4;
    var df1 = -1, df2 = -1, sa1, ea1, sa2, ea2, sa3, ix = 0, iy = 0;
    var i1 = 1, i2 = 1, sp1x, sp1y, sp2x, sp2y; //to draw magnetic field
    var prevx, prevy, cw, ch;
    var runninctx, crossed, crossedagain, done, pavared;
    MovChgMagCtrlPnl cp = new MovChgMagCtrlPnl(this);
    Timer timer;

    MovChgMagCanvas() {

        addMouseMotionListener(this);
        addMouseListener(this);
        timer = new Timer(delay, this);
        timer.setInitialDelay(0);
        timer.setCoalesce(true);
    }

    public void start() {
        if (!timer.isRunning()) {
            timer.start();
        }
    }

    public void stop() {
        if (timer.isRunning()) {
            timer.stop();
        }
    }

    public void actionPerformed(ActionEvent e) {
        drawCanvas();
    }

    public void mouseClicked(MouseEvent e) {
    }

    public void mousePressed(MouseEvent e) {
        prevx = e.getX();
        prevy = e.getY();
        e.consume();
    }

    public void mouseReleased(MouseEvent e) {
    }

    public void mouseEntered(MouseEvent e) {
    }

    public void mouseExited(MouseEvent e) {
    }

    public void mouseDragged(MouseEvent e) {
        var x = e.getX();
        var y = e.getY();

        spx = spx + (x - prevx);
        calc();
        if (pavared) {
            pavared = false;
            drawCanvas();
        }
        prevx = x;
        prevy = y;
        e.consume();
    }

    public void mouseMoved(MouseEvent e) {
    }

    public void halt() {
        cp.sbFrame.setMaximum(frame);
        running = false;
        cp.butSSR.setForeground(Color.blue);
        cp.butSSR.setText("Repeat");
        cp.butSSR.setActionCommand("repeat");
    }

    void reset() {
        frame = 0;
        ff1 = 0;
        ff2 = 0;
        spy = 2 * D - 4;
        crossed = false;
        crossedagain = false;
        done = false;
        calc();
        drawCanvas();
    }

    public void pavar(Canvas canvas) {
        if (ch != getHeight() || cw != getWidth()) {
            ch = getHeight();
            cw = getWidth();
            D = ch / 2;
            spy = 2 * D - 4;
            calc();
        }


        pavarComponent(g);
    }

    public void drawArrow(Canvas canvas, var x1, var y1, var x2, var y2) {
        if (((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)) > 0) {
            var theta;
            long x, y;

            theta = Math.atan2(y1 - y2, x2 - x1);
            ctx.moveTo(x1, y1);
ctx.lineTo( x2, y2);
            x = Math.round(12 * Math.cos(theta + Math.PI / 10.));
            y = Math.round(12 * Math.sin(theta + Math.PI / 10.));
            ctx.moveTo(x2, y2);
ctx.lineTo( x2 -  x, y2 +  y);
            x = Math.round(12 * Math.cos(theta - Math.PI / 10.));
            y = Math.round(12 * Math.sin(theta - Math.PI / 10.));
            ctx.moveTo(x2, y2);
ctx.lineTo( x2 -  x, y2 +  y);
        }
    }

    void calc() {
        df1 = 0;
        df2 = 0;
        if (BL < 0) {
            df1 = -1;
        } else if (BL > 0) {
            df1 = 1;
        }
        if (BU < 0) {
            df2 = -1;
        } else if (BU > 0) {
            df2 = 1;
        }
        if (BL != 0) {
            R1 = M * V / Math.abs(BL);
            AV1 = Math.abs(BL / M);
            i1 =  ((D) / (1.5 * Math.sqrt(2 * Math.abs(sliderBLVal))));
            c1x = spx + df1 * R1 * Math.sin(theta);
            c1y = spy + df1 * R1 * Math.cos(theta);
        }
        if (BU != 0) {
            R2 = M * V / Math.abs(BU);
            AV2 = Math.abs(BU / M);
            i2 =  ((D) / (1.5 * Math.sqrt(2 * Math.abs(sliderBUVal))));
        }
        var N1y =  ((D - 20) / i1);
        var N1x =  (cw / i1);
        var N2y =  ((D - 20) / i2);
        var N2x =  (cw / i2);

        sp1x =  ((cw - N1x * i1) / 2);
        sp1y =  ((D - N1y * i1) / 2);
        sp2x =  ((cw - N2x * i2) / 2);
        sp2y =  ((D - N2y * i2) / 2);

        if (df1 < 0) {
            if (Math.cos(theta) <= (D - 4 - R1) / R1) {
                phi = Math.PI - theta;
            } else {
                phi = Math.acos(Math.cos(theta) - (D - 4) / R1) - theta;
            }
        } else {
            if (-Math.cos(theta) <= (D - 4 - R1) / R1) {
                phi = theta;
            } else {
                phi = theta - Math.acos((D - 4) / R1 + Math.cos(theta));
            }
        }
        if (BL == 0) {
            phi = 0;
            cp1x = spx + (D - 4) / Math.tan(theta);
        } else {
            cp1x = c1x - df1 * R1 * Math.sin(theta - df1 * phi);
        }
        if (df1 > 0) {
            c2x = cp1x + df2 * R2 * Math.sin(theta - df1 * phi);
            c2y = D + df2 * R2 * Math.cos(theta - df1 * phi);
        } else if (df1 < 0) {
            c2x = cp1x + df2 * R2 * Math.sin(theta - df1 * phi);
            c2y = D + df2 * R2 * Math.cos(theta - df1 * phi);
        }
        c3x = 2 * c2x - c1x;
        c3y = c1y;
        sa1 = df1 * 90 +  (theta * 57.2957795 + 0.5);
        ea1 = -df1 *  (phi * 57.2957795 + 0.5);
        if (df1 == 0) {
            sa2 = -90 +  ((theta + phi) * 57.2957795 + 0.5);
            ea2 = 360 -  (2 * (theta + phi) * 57.2957795);
            sa3 = 270 -  ((theta + phi) * 57.2957795 + 0.5);
        }
        if (df1 < 0 && df2 < 0) {
            sa2 = -90 +  ((theta + phi) * 57.2957795 + 0.5);
            ea2 = 360 -  (2 * (theta + phi) * 57.2957795);
            sa3 = 270 -  ((theta + phi) * 57.2957795 + 0.5);
        }
        if (df1 < 0 && df2 > 0) {
            sa2 = 90 +  ((theta + phi) * 57.2957795 + 0.5);
            ea2 = - (2 * (theta + phi) * 57.2957795);
            sa3 = 270 -  ((theta + phi) * 57.2957795 + 0.5);
        }
        if (df2 < 0 && df1 > 0) {
            sa2 = -90 +  ((theta - phi) * 57.2957795 + 0.5);
            ea2 = 360 - 2 *  ((theta - phi) * 57.2957795);
            sa3 = 90 -  ((theta - phi) * 57.2957795 + 0.5);
        }
        if (df2 > 0 && df1 > 0) {
            sa2 = 90 +  ((theta - phi) * 57.2957795 + 0.5);
            ea2 = - (2 * (theta - phi) * 57.2957795);
            sa3 = 90 -  ((theta - phi) * 57.2957795 + 0.5);
        }
        if (df1 == 0) {
            phi = 0;
            cp1x = spx + (D - 4) / Math.tan(theta);
            c2x = cp1x + df2 * R2 * Math.sin(theta);
            c2y = D + df2 * R2 * Math.cos(theta);
            cp2x = cp1x + 2 * df2 * R2 * Math.sin(theta);
            if (df2 > 0) {
                sa2 = 90 +  (theta * 57.2957795 + 0.5);
                ea2 = - (2 * theta * 57.2957795);
            } else {
                sa2 = -90 +  (theta * 57.2957795 + 0.5);
                ea2 = 360 -  (2 * theta * 57.2957795);
            }
        }
        calcEF();
    }

    void calcEF() {
        var angrad = 0;
        var ix, iy, frame = 0;
        var crossed = false, crossedagain = false, done = false;

        while (frame < cw) {
            if (!crossed) {
                if (BL == 0) {
                    iy =  (spy - 0.2 * V * frame * Math.sin(theta));
                    ff1 = frame;
                    if (iy < D) {
                        crossed = true;
                    }
                    if (iy > spy) {
                        done = true;
                        ef = frame;
                    }
                } else {
                    angrad = df1 * 0.2 * AV1 * frame;
                    iy =  (c1y - df1 * R1 * Math.cos(theta - angrad)) - 4;
                    ff1 = frame;
                    if (iy <= D - 4) {
                        crossed = true;
                    }
                    if (iy > spy) {
                        done = true;
                        ef = frame;
                    }
                }
            } else if (!crossedagain) {
                if (BU == 0) {
                    iy =  (D - 0.2 * V * (frame - ff1) * Math.sin(theta - df1 * phi));
                    if (iy < 0) {
                        done = true;
                        ef = frame;
                    }
                } else {
                    angrad = df2 * 0.2 * AV2 * (frame - ff1);
                    iy =  (c2y - df2 * R2 * Math.cos(theta - df1 * phi - angrad)) - 4;
                    ff2 = frame;
                    if (iy > D - 4) {
                        crossedagain = true;
                    }
                }
            } else {
                if (BL == 0) {
                    iy =  (D + 0.2 * V * (frame - ff2) * Math.sin(theta));
                } else {
                    angrad = df1 * 0.2 * AV1 * (frame - ff2);
                    iy =  (c3y - df1 * R1 * Math.cos(theta - df1 * phi + angrad)) - 4;
                }
                if (frame - ff2 == ff1) {
                    done = true;
                    ef = frame;
                }
            }
            if (!done) {
                frame++;
            } else {
                ef = frame;

                cp.sbFrame.setMaximum(ef);

                break;
            }
        }
    }

    void drawMagField(Canvas canvas) {



ctx.strokeStyle="white";
        ctx.fillRect(0, 0, cw, 2 *  D);
        if (BL != 0) {
            for (var x = sp1x; x < cw; x = x + i1) {
                for (var y = sp1y +  D; y <  (2 * D); y = y + i1) {
                    if (BL < 0) {
ctx.strokeStyle="blue";
                        ctx.moveTo(x - 2, y - 2);
ctx.lineTo( x + 2, y + 2);
                        ctx.moveTo(x - 2, y + 2);
ctx.lineTo( x + 2, y - 2);
                        ctx.arc(x - 6, y - 6, 12,0,2*Math.PI,false);
                    } else {
ctx.strokeStyle="black";
                        ctx.arc(x - 2, y - 2, 4,0,2*Math.PI,false);
                        ctx.arc(x - 6, y - 6, 12,0,2*Math.PI,false);
                    }
                }
            }
        }
        if (BU != 0) {
            for (var x = sp2x; x < cw; x = x + i2) {
                for (var y = sp2y; y <  D; y = y + i2) {
                    if (BU < 0) {
ctx.strokeStyle="blue";
                        ctx.moveTo(x - 2, y - 2);
ctx.lineTo( x + 2, y + 2);
                        ctx.moveTo(x - 2, y + 2);
ctx.lineTo( x + 2, y - 2);
                        ctx.arc(x - 6, y - 6, 12,0,2*Math.PI,false);
                    } else {
ctx.strokeStyle="black";
                        ctx.arc(x - 2, y - 2, 4,0,2*Math.PI,false);
                        ctx.arc(x - 6, y - 6, 12,0,2*Math.PI,false);
                    }
                }
            }
        }

    }

    public void pavarComponent(Canvas canvas) {
        var angrad = 0;
        var angdeg;

        drawMagField(g);
ctx.strokeStyle="red";
        if (BL != 0) {
            ctx.arc( c1x - 3,  c1y - 3, 6,0,2*Math.PI,false);
        }
        if (!crossed) {
            if (BL == 0) {
                ix =  (spx + 0.2 * V * frame * Math.cos(theta));
                iy =  (spy - 0.2 * V * frame * Math.sin(theta));
ctx.strokeStyle="red";
                ctx.moveTo( spx,  spy);
ctx.lineTo( ix, iy);
                var ex =  (ix + 6 * V * Math.cos(theta));
                var ey =  (iy - 6 * V * Math.sin(theta));

ctx.strokeStyle="black";
                ctx.arc(ix - 4, iy - 4, 8,0,2*Math.PI,false);
                drawArrow(ctx, ix, iy, ex, ey);
                if (iy < D) {
                    crossed = true;
                }
                if (iy > spy) {
                    done = true;
                    halt();
                }
            } else {
                angrad = df1 * 0.2 * AV1 * frame;
                ix =  (c1x - df1 * R1 * Math.sin(theta - angrad)) - 4;
                iy =  (c1y - df1 * R1 * Math.cos(theta - angrad)) - 4;
                angdeg =  (angrad * 57.2957795 + 0.5);
ctx.strokeStyle="red";
                ctx.drawArc( (c1x - R1),  (c1y - R1),  (2 * R1),  (2 * R1), sa1, -angdeg);
                var ex =  (ix + 4 + 6 * V * Math.cos(theta - angrad));
                var ey =  (iy + 4 - 6 * V * Math.sin(theta - angrad));
                var fx =  (ix + 4 + 12 * V * BL * Math.sin(theta - angrad));
                var fy =  (iy + 4 + 12 * V * BL * Math.cos(theta - angrad));

                ctx.moveTo( c1x,  c1y);
ctx.lineTo( fx, fy);
ctx.strokeStyle="green.darker(";
                drawArrow(ctx, ix + 4, iy + 4, fx, fy);
ctx.strokeStyle="black";
                ctx.arc(ix, iy, 8,0,2*Math.PI,false);
                drawArrow(ctx, ix + 4, iy + 4, ex, ey);
                if (iy <= D - 4) {
                    crossed = true;
                }
                if (iy > spy) {
                    done = true;
                }
            }
        } else if (!crossedagain) {
            if (BL != 0) {
ctx.strokeStyle="red";
                ctx.drawArc( (c1x - R1),  (c1y - R1),  (2 * R1),  (2 * R1), sa1, ea1);
            } else {
ctx.strokeStyle="red";
                ctx.moveTo( spx,  spy);
ctx.lineTo(  cp1x,  D);
            }
            if (BU == 0) {
                ix =  (cp1x + 0.2 * V * (frame - ff1) * Math.cos(theta - df1 * phi));
                iy =  (D - 0.2 * V * (frame - ff1) * Math.sin(theta - df1 * phi));
ctx.strokeStyle="blue";
                ctx.moveTo( cp1x,  D);
ctx.lineTo( ix, iy);
                var ex =  (ix + 6 * V * Math.cos(theta - df1 * phi));
                var ey =  (iy - 6 * V * Math.sin(theta - df1 * phi));

ctx.strokeStyle="black";
                ctx.arc(ix - 4, iy - 4, 8,0,2*Math.PI,false);
                drawArrow(ctx, ix, iy, ex, ey);
                if (iy < 0) {
                    done = true;
                    halt();
                }
            } else {
ctx.strokeStyle="blue";
                ctx.arc( c2x - 3,  c2y - 3, 6,0,2*Math.PI,false);
                angrad = df2 * 0.2 * AV2 * (frame - ff1);
                ix =  (c2x - df2 * R2 * Math.sin(theta - df1 * phi - angrad)) - 4;
                iy =  (c2y - df2 * R2 * Math.cos(theta - df1 * phi - angrad)) - 4;
                angdeg =  (angrad * 57.2957795 + 0.5);
ctx.strokeStyle="blue";
                ctx.drawArc( (c2x - R2),  (c2y - R2),  (2 * R2),  (2 * R2), sa2, -angdeg);
                var ex =  (ix + 4 + 6 * V * Math.cos(theta - df1 * phi - angrad));
                var ey =  (iy + 4 - 6 * V * Math.sin(theta - df1 * phi - angrad));
                var fx =  (ix + 4 + 12 * V * BU * Math.sin(theta - df1 * phi - angrad));
                var fy =  (iy + 4 + 12 * V * BU * Math.cos(theta - df1 * phi - angrad));

                ctx.moveTo( c2x,  c2y);
ctx.lineTo( fx, fy);
ctx.strokeStyle="green";
                drawArrow(ctx, ix + 4, iy + 4, fx, fy);
ctx.strokeStyle="black";
                ctx.arc(ix, iy, 8,0,2*Math.PI,false);
                drawArrow(ctx, ix + 4, iy + 4, ex, ey);
                if (iy > D - 4) {
                    crossedagain = true;
                }
            }
        } //crossing the second field
        else {
ctx.strokeStyle="red";
            ctx.drawArc( (c1x - R1),  (c1y - R1),  (2 * R1),  (2 * R1), sa1, ea1);
ctx.strokeStyle="blue";
            ctx.arc( c2x - 3,  c2y - 3, 6,0,2*Math.PI,false);
            ctx.drawArc( (c2x - R2),  (c2y - R2),  (2 * R2),  (2 * R2), sa2, ea2);

            if (BL == 0) {
                ix =  (cp2x + 0.2 * V * (frame - ff2) * Math.cos(theta));
                iy =  (D + 0.2 * V * (frame - ff2) * Math.sin(theta));
                var ex =  (ix + 6 * V * Math.cos(theta));
                var ey =  (iy + 6 * V * Math.sin(theta));

ctx.strokeStyle="black";
                ctx.arc(ix - 4, iy - 4, 8,0,2*Math.PI,false);
                drawArrow(ctx, ix, iy, ex, ey);
ctx.strokeStyle="magenta";
                ctx.moveTo( cp2x,  D);
ctx.lineTo( ix, iy);
ctx.strokeStyle="red";
                ctx.moveTo( spx,  spy);
ctx.lineTo(  cp1x,  D);

            } else {
ctx.strokeStyle="magenta";
                ctx.arc( c3x - 3,  c3y - 3, 6,0,2*Math.PI,false);
                angrad = df1 * 0.2 * AV1 * (frame - ff2);
                ix =  (c3x + df1 * R1 * Math.sin(theta - df1 * phi + angrad)) - 4;
                iy =  (c3y - df1 * R1 * Math.cos(theta - df1 * phi + angrad)) - 4;
                angdeg =  (angrad * 57.2957795 + 0.5);
ctx.strokeStyle="magenta";
                ctx.drawArc( (c3x - R1),  (c3y - R1),  (2 * R1),  (2 * R1), sa3, -angdeg);
                var ex =  (ix + 4 + 6 * V * Math.cos(theta - df1 * phi + angrad));
                var ey =  (iy + 4 + 6 * V * Math.sin(theta - df1 * phi + angrad));
                var fx =  (ix + 4 - 12 * V * BL * Math.sin(theta - df1 * phi + angrad));
                var fy =  (iy + 4 + 12 * V * BL * Math.cos(theta - df1 * phi + angrad));

                ctx.moveTo( c3x,  c3y);
ctx.lineTo( fx, fy);
ctx.strokeStyle="green.darker(";
                drawArrow(ctx, ix + 4, iy + 4, fx, fy);
ctx.strokeStyle="black";
                ctx.arc(ix, iy, 8,0,2*Math.PI,false);
                drawArrow(ctx, ix + 4, iy + 4, ex, ey);
            }
            if (frame - ff2 == ff1) {
                done = true;
                halt();
ctx.strokeStyle="red";
                if (BL != 0) {
                    ctx.moveTo( c1x,  c1y);
ctx.lineTo(  spx,  spy);
                }
ctx.strokeStyle="blue";
                if (BU != 0) {
                    ctx.moveTo( c2x,  c2y);
ctx.lineTo(  c2x,  (c2y - R2));
                }
            }
        }
ctx.strokeStyle="black";
        ctx.moveTo(5,  D);
ctx.lineTo( cw,  D);
        cp.sbFrame.setValue(frame);
        if (frame < ef && running) {
            frame++;
        }
        pavared = true;
    }
}

final class MovChgMagCtrlPnl extends JPanel implements ActionListener, ChangeListener {

    JSlider sbFrame;
    JSlider sbBL, sbBU, sbMass, sbVel, sbTheta;
    JLabel labBL, labBU, labMass, labVel, labTheta;
    JButton butSSR;

    MovChgMagCanvas canvas;

    MovChgMagCtrlPnl(MovChgMagCanvas canvas) {
        this.canvas = canvas;

        GridBagLayout gridbag = new GridBagLayout();
        GridBagConstravars constravars = new GridBagConstravars();
        setLayout(gridbag);
        constravars.fill = GridBagConstravars.BOTH;
        JPanel panel1 = new JPanel();
        JPanel panel2 = new JPanel();
        JPanel panel3 = new JPanel();
        JPanel panel4 = new JPanel();
        JPanel panel5 = new JPanel();
        JPanel panel6 = new JPanel();

        constravars.insets = new Insets(1, 1, 1, 1);
        buildConstravars(constravars, 0, 0, 1, 1, 1, 1);
        gridbactx.setConstravars(panel1, constravars);
        buildConstravars(constravars, 0, 1, 1, 1, 1, 1);
        gridbactx.setConstravars(panel2, constravars);
        buildConstravars(constravars, 0, 2, 1, 1, 1, 1);
        gridbactx.setConstravars(panel3, constravars);
        buildConstravars(constravars, 0, 3, 1, 1, 1, 1);
        gridbactx.setConstravars(panel4, constravars);
        buildConstravars(constravars, 0, 4, 1, 1, 1, 1);
        gridbactx.setConstravars(panel5, constravars);
        buildConstravars(constravars, 0, 5, 1, 1, 1, 1);
        gridbactx.setConstravars(panel6, constravars);
        panel1.setLayout(gridbag);
        panel2.setLayout(gridbag);
        panel3.setLayout(gridbag);
        panel4.setLayout(gridbag);
        panel5.setLayout(gridbag);
        panel6.setLayout(gridbag);
        panel1.setBorder(new EtchedBorder());
        panel2.setBorder(new EtchedBorder());
        panel3.setBorder(new EtchedBorder());
        panel4.setBorder(new EtchedBorder());
        panel5.setBorder(new EtchedBorder());
        panel6.setBorder(new EtchedBorder());
        add(panel1);
        add(panel2);
        add(panel3);
        add(panel4);
        add(panel5);
        add(panel6);


        constravars.fill = GridBagConstravars.HORIZONTAL;

        buildConstravars(constravars, 0, 1, 2, 1, 20, 0);
        labBU = new JLabel("B ( Upper ) = " + canvas.sliderBUVal + " units", JLabel.CENTER);
        gridbactx.setConstravars(labBU, constravars);
        panel1.add(labBU);

        buildConstravars(constravars, 0, 2, 2, 1, 20, 0);
        sbBU = new JSlider(-5, 5, canvas.sliderBUVal);
        constravars.insets = new Insets(0, 0, 5, 0);
        gridbactx.setConstravars(sbBU, constravars);
        sbBU.addChangeListener(this);
        panel1.add(sbBU);

        buildConstravars(constravars, 0, 3, 2, 1, 20, 0);
        labBL = new JLabel("B ( Lower )  = " + canvas.sliderBLVal + " units", JLabel.CENTER);
        gridbactx.setConstravars(labBL, constravars);
        panel2.add(labBL);

        buildConstravars(constravars, 0, 4, 2, 1, 20, 0);
        sbBL = new JSlider(-5, 5, canvas.sliderBLVal);
        gridbactx.setConstravars(sbBL, constravars);
        sbBL.addChangeListener(this);
        panel2.add(sbBL);

        buildConstravars(constravars, 0, 7, 2, 1, 20, 0, 5, 0);
        labMass = new JLabel("Mass  =  " + canvas.sliderMassVal + " units", JLabel.CENTER);
        gridbactx.setConstravars(labMass, constravars);
        panel3.add(labMass);

        buildConstravars(constravars, 0, 8, 2, 1, 20, 0);
        sbMass = new JSlider(1, 10, canvas.sliderMassVal);
        gridbactx.setConstravars(sbMass, constravars);
        sbMass.addChangeListener(this);
        panel3.add(sbMass);

        buildConstravars(constravars, 0, 9, 2, 1, 20, 0);
        labVel = new JLabel("Velocity  =  " + canvas.sliderVelVal + " units", JLabel.CENTER);
        gridbactx.setConstravars(labVel, constravars);
        panel4.add(labVel);

        buildConstravars(constravars, 0, 10, 2, 1, 20, 0);
        sbVel = new JSlider(1, 10, canvas.sliderVelVal);
        gridbactx.setConstravars(sbVel, constravars);
        sbVel.addChangeListener(this);
        panel4.add(sbVel);

        buildConstravars(constravars, 0, 11, 2, 1, 20, 0);
        labTheta = new JLabel("Angle = 90 \u00b0", JLabel.CENTER);
        gridbactx.setConstravars(labTheta, constravars);
        panel5.add(labTheta);

        buildConstravars(constravars, 0, 12, 2, 1, 20, 0);
        sbTheta = new JSlider(0, 36, 18);
        gridbactx.setConstravars(sbTheta, constravars);
        sbTheta.addChangeListener(this);
        panel5.add(sbTheta);

        buildConstravars(constravars, 0, 13, 2, 1, 20, 0);
        butSSR = new JButton("Start");
        constravars.fill = GridBagConstravars.VERTICAL;
        gridbactx.setConstravars(butSSR, constravars);
        panel6.add(butSSR);
        butSSR.setActionCommand("start");
        butSSR.addActionListener(this);

        buildConstravars(constravars, 0, 14, 1, 1, 20, 0);
        sbFrame = new JSlider(0, 250, 0);
        sbFrame.addChangeListener(this);
        constravars.fill = GridBagConstravars.HORIZONTAL;
        gridbactx.setConstravars(sbFrame, constravars);
        panel6.add(sbFrame);

        sbBL.setSnapToTicks(true);
        sbBU.setSnapToTicks(true);
        sbMass.setSnapToTicks(true);
        sbVel.setSnapToTicks(true);
        sbTheta.setSnapToTicks(true);
        setPreferredSize(new Dimension(150, 300));

    }

    void buildConstravars(GridBagConstravars gbc, var gx, var gy,
            var gw, var gh, var wx, var wy) {
        gbc.gridx = gx;
        gbc.gridy = gy;
        gbc.gridwidth = gw;
        gbc.gridheight = gh;
        gbc.weightx = wx;
        gbc.weighty = wy;
    }

    void buildConstravars(GridBagConstravars gbc, var gx, var gy,
            var gw, var gh,
            var wx, var wy, var top, var bottom) {
        gbc.gridx = gx;
        gbc.gridy = gy;
        gbc.gridwidth = gw;
        gbc.gridheight = gh;
        gbc.weightx = wx;
        gbc.weighty = wy;
        gbc.insets = new Insets(2, 5, 2, 5);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == butSSR) {
            if (canvas.running == false) {
                canvas.running = true;
                canvas.start();
                butSSR.setText("Stop");
                butSSR.setActionCommand("stop");
            } else {
                canvas.running = false;
                canvas.stop();
                butSSR.setText("Start");
                butSSR.setActionCommand("start");
            }
            if (e.getActionCommand().equals("stop")) {
                butSSR.setText("Start");
                butSSR.setActionCommand("start");
            } else if (e.getActionCommand().equals("start")) {
                butSSR.setText(" Stop ");
                butSSR.setActionCommand("stop");
                canvas.running = true;
                canvas.start();
            }

            if (e.getActionCommand().equals("repeat")) {
                butSSR.setForeground(Color.black);
                canvas.reset();
                canvas.running = true;
                canvas.start();
                butSSR.setText("Stop");
                butSSR.setActionCommand("stop");
            }
        }
    }

    public void stateChanged(ChangeEvent e) {
        if (sbFrame.getValueIsAdjusting()) {
            canvas.running = false;
            canvas.crossed = false;
            canvas.crossedagain = false;
            canvas.done = false;
            butSSR.setForeground(Color.black);
            butSSR.setText("Start");
            butSSR.setActionCommand("start");
            canvas.frame = sbFrame.getValue();
            if (canvas.frame > canvas.ff1) {
                canvas.crossed = true;
                if (canvas.frame > canvas.ff2 && canvas.BU != 0) {
                    canvas.crossedagain = true;
                }
            }
            canvas.drawCanvas();
        }
        if (e.getSource() == sbBL) {
            canvas.sliderBLVal = (sbBL.getValue());
            sbBL.setValue(sbBL.getValue());
            canvas.BL = 0.05 * canvas.sliderBLVal;
            String str = new String(" units");

            if (canvas.sliderBLVal == 1 || canvas.sliderBLVal == -1) {
                str = " unit";
            }
            labBL.setText("B ( Lower ) =  " + canvas.sliderBLVal + str);
            canvas.reset();
        }
        if (e.getSource() == sbBU) {
            canvas.sliderBUVal = sbBU.getValue();
            sbBU.setValue(canvas.sliderBUVal);
            canvas.BU = 0.05 * canvas.sliderBUVal;
            String str = new String(" units");

            if (canvas.sliderBUVal == 1 || canvas.sliderBUVal == -1) {
                str = " unit";
            }
            labBU.setText("B ( Upper ) = " + canvas.sliderBUVal + str);
            canvas.reset();
        }

        if (e.getSource() == sbMass) {
            canvas.sliderMassVal = sbMass.getValue();
            sbMass.setValue(canvas.sliderMassVal);
            canvas.M = 0.2 * canvas.sliderMassVal;
            String str = new String(" units");

            if (canvas.sliderMassVal == 1) {
                str = " unit";
            }
            labMass.setText("Mass = " + canvas.sliderMassVal + str);
            canvas.reset();
        }

        if (e.getSource() == sbVel) {
            canvas.sliderVelVal = (sbVel.getValue());
            sbVel.setValue(sbVel.getValue());
            canvas.V = 2 * canvas.sliderVelVal;
            String str = new String(" units");

            if (canvas.sliderVelVal == 1) {
                str = " unit";
            }
            labVel.setText(" Velocity =  " + canvas.sliderVelVal + str);
            canvas.reset();
        }

        if (e.getSource() == sbTheta) {
            var vsb = sbTheta.getValue();

            sbTheta.setValue(vsb);
            canvas.theta = vsb * Math.PI / 36;
            labTheta.setText("Angle = " + 5 * vsb + " \u00b0");
            canvas.reset();
        }

        if (e.getSource() != sbFrame) {
            canvas.done = false;
            canvas.running = false;
            butSSR.setForeground(Color.black);
            butSSR.setText("Start");
            butSSR.setActionCommand("start");
            canvas.drawCanvas();
        }
    }
}