CODEWITHSUNDEEP
javamandelbrot
Syzorr
Syzorr

Reputation: 607

Representing Mandelbrot and Julia Sets Graphically in Java

I'm working on a problem where I'm needing to represent the Mandelbrot set graphically using OpenCL and working on my sequential code first. However, the image it is producing isn't very good and I'm unsure if I've missed something somewhere or if this is merely an issue with a lack of resolution (so to speak). I've posted the code below along with a screenshot of what it produces - is this what I should be expecting or have I messed this up somewhere?

public class SequentialMandelbrot {

    private static int[] colorMap;
    private static int xSize = 200, ySize = 200;
    private static float yMin = -2f, yMax = 2f;
    private static float xMin = -2f, xMax = 2f;
    private static float xStep =  (xMax - xMin) / (float)xSize;
    private static float yStep =  (yMax - yMin) / (float)ySize;
    private static final int maxIter = 250;
    private static BufferedImage image;
    private static JComponent imageComponent;   

    public static void main(String[] args) {

        // Create the image and the component that will paint the image
        initColorMap(32, Color.RED, Color.GREEN, Color.BLUE);
        image = new BufferedImage(xSize, ySize, BufferedImage.TYPE_INT_RGB);
        imageComponent = new JPanel()
        {
            private static final long serialVersionUID = 1L;
            public void paintComponent(Graphics g)
            {
                super.paintComponent(g);
                g.drawImage(image, 0,0,this);
            }   
        };

        for (int j = 0; j < xSize; j++) {
            for (int k = 0; k < ySize; k++) {
                int iter = mandelbrot(j, k);
                if (iter == maxIter) {
                    image.setRGB(j, k, 0);                  
                } else {
                    int local_rgb = colorMap[iter%64];
                    image.setRGB(j, k, local_rgb);
                }
            }
        }

        JFrame frame = new JFrame("JOCL Simple Mandelbrot");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        imageComponent.setPreferredSize(new Dimension(xSize, ySize));
        frame.add(imageComponent, BorderLayout.CENTER);
        frame.pack();

        frame.setVisible(true);
    }

    private static int mandelbrot(float j, float k) {
        int t = 0;
        float norm = 0;
        float x = 0;
        float y = 0;
        float r = xMin + (j * xStep);
        float i = yMin + (k * yStep);
        while (t < maxIter && norm < 4) {
            x = (x*x) - (y*y) + r;
            y = (2*x*y) + i;
            norm = (x*x) + (y*y);
            t++;
        }
        return t;
    }

Mandelbrot Set

I have also altered the code for the Julia set (from the number 0.45 + 0.1428i) and it produces something equally questionable:
Julia Set

Upvotes: 1

Views: 129

Answers (1)

Weather Vane
Weather Vane

Reputation: 34585

This is your iteration loop, which is incorrect.

while (t < maxIter && norm < 4) {
    x = (x*x) - (y*y) + r;
    y = (2*x*y) + i;
    norm = (x*x) + (y*y);
    t++;
}

You are overwriting x before re-using it to calculate y. I suggest using a temporary variable, such as

while (t < maxIter && norm < 4) {
    tempx = (x*x) - (y*y) + r;
    y = (2*x*y) + i;
    x = tempx;
    norm = (x*x) + (y*y);
    t++;
}

Aside: there is room for some efficiency too, as you are calculating x*x and y*y twice.

Upvotes: 2

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