PlasmaCloud.java

/*************************************************************************
 *  Compilation:  javac PlasmaCloud.java 
 *  Execution:    java Plasma N
 *  Dependencies: StdDraw.java
 *
 *  Create an N-by-N plasma fractal using the midpoint displacement method.
 *  Also called a fractal cloud. Try different colors to get a cloud.
 *  Also used to generate random terrain where "color" becomes the
 *  altitude.
 *
 *  % java PlasmaCloud 500
 *
 * 
 *  Remarks
 *  -------
 *  - it's possible that the color c does not stay between 0 and 1;
 *    this is not disastorous since the HSB color routine uses only
 *    the fractional part
 *
 **************************************************************************/

public class PlasmaCloud { 

    // centered at (x, y), of given size, using given standard deviation for computing the
    // displacement, and with upper left, upper right, lower lower, and lower right hues
    // c1, c2, c3, c4
    public static void plasma(double x,  double y,  double size, double stddev,
                              double c1, double c2, double c3,   double c4) {

        // base case: draw one pixel in color which is average of 4 endpoints
        if (size <= 0.5) {
            double c = (c1 + c2 + c3 + c4) / 4.0;
            StdDraw.setColorHSB(c, 1.0, 1.0);
            StdDraw.go(x, y);
            StdDraw.spot();
            return;
        }

        // calculate new color of midpoint using random displacement
        double displacement = MyMath.gaussian(0, stddev);
        double cM = (c1 + c2 + c3 + c4) / 4.0 + displacement;

        double cT = (c1 + c2) / 2.0;    // top
        double cB = (c3 + c4) / 2.0;    // bottom
        double cL = (c1 + c3) / 2.0;    // left
        double cR = (c2 + c4) / 2.0;    // right

        plasma(x - size/2, y - size/2, size/2, stddev/2, cL, cM, c3, cB);
        plasma(x + size/2, y - size/2, size/2, stddev/2, cM, cR, cB, c4);
        plasma(x - size/2, y + size/2, size/2, stddev/2, c1, cT, cL, cM);
        plasma(x + size/2, y + size/2, size/2, stddev/2, cT, c2, cM, cR);
    }



    public static void main(String[] args) {
        int SIZE = Integer.parseInt(args[0]);
        StdDraw.create(SIZE, SIZE);

        // choose intial corner colors at random betwen 0 and 1
        double c1 = Math.random();
        double c2 = Math.random();
        double c3 = Math.random();
        double c4 = Math.random();

        // controls variation in color
        double stddev = 1.0;

        plasma(SIZE/2, SIZE/2, SIZE, stddev, c1, c2, c3, c4);
        StdDraw.show();
    }
}