Add code, README, and examples

Author: intrepidcoder

README.md

@@ -1,2 +1,30 @@
 # RgbRandomWalk
 Creates fractal-like images with three 2D random walks in red, green, and blue.
+
+The intensity of a pixel is proportional (until it reaches the brightest value) to the number of times it is visited. See [Wikipedia](https://en.wikipedia.org/wiki/Random_walk) for more info on random walks.
+
+Made just for fun.
+
+
+## Usage
+`java RgbRandomWalk <imagefilepath> <width> <height> <steps>`
+
+`imagefilepath` is the image file to write. Output in in PNG format regardless of specified extension. This can be changed in source file. **Note: will overwrite any existing file. Use caution.**
+
+`width` and `height` are the size of image.
+
+`steps` is the number of steps to take for each random walk.
+
+## Examples
+
+![Example 1](example1.png?raw=true)
+
+Width: 600, height: 400, steps: 500000
+
+![Example 2](example2.png?raw=true)
+
+Width: 600, height: 400, steps: 1000000
+
+![Example 3](example3.png?raw=true)
+
+Width: 1920, height: 1080, steps: 6000000

RgbRandomWalk.java

@@ -0,0 +1,104 @@
+import java.awt.*;
+import java.io.*;
+import javax.imageio.*;
+import java.awt.image.*;
+import java.util.Random;
+
+public class RgbRandomWalk {
+	private static Random prng = new Random();
+
+	private static int step(int pos, int upperBound) {
+		if (pos <= 0) {
+			return prng.nextInt(2);
+		} else if (pos >= upperBound - 1) {
+			return upperBound - 1 - prng.nextInt(2);
+		} else {
+			return pos - 1 + prng.nextInt(3);
+		}
+	}
+
+	public static void main(String[] args) {
+		long start = System.currentTimeMillis();
+		String fileName = "";
+		int width = 1920, height = 1080;
+		int increment = 8;
+		int steps = 6000000;
+		String imgFormat = "png";
+
+		if (args.length != 4) {
+			System.out.println("Usage: java RgbRandomWalk <imagefilepath> <width> <height> <steps>");
+			System.exit(0);
+		} else {
+			try {
+				fileName = args[0];
+				width = Integer.parseInt(args[1], 10);
+				height = Integer.parseInt(args[2], 10);
+				steps = Integer.parseInt(args[3], 10);
+
+			} catch (NumberFormatException e) {
+				System.out.println("Usage: java RgbRandomWalk <imagefilepath> <width> <height> <steps>");
+				System.out.println("Error: Invalid number.");
+				System.exit(0);
+			}
+			
+			if (width <= 0 || height <= 0 || steps <= 0) {
+				System.out.println("Usage: java RgbRandomWalk <imagefilepath> <width> <height> <steps>");
+				System.out.println("Error: Negative number.");
+				System.exit(0);
+			}
+		}
+
+		BufferedImage img;
+		Color c;
+		// Good parameters are 1920 x 1080, intensity increment 8, and steps = 6000000.
+
+		int rX = width / 2, rY = height / 2;
+		int gX = width / 2, gY = height / 2;
+		int bX = width / 2, bY = height / 2;
+		int r = 0, g = 0, b = 0;
+		// int sRGB, other;
+
+
+		img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
+
+		rX = width / 2;
+		rY = height / 2;
+		gX = width / 2;
+		gY = height / 2;
+		bX = width / 2;
+		bY = height / 2;
+
+		for (int j = 0; j < steps; j++) {
+
+
+			rX = step(rX, width);
+			rY = step(rY, height);
+			gX = step(gX, width);
+			gY = step(gY, height);
+			bX = step(bX, width);
+			bY = step(bY, height);
+
+			c = new Color(img.getRGB(rX, rY));
+			img.setRGB(rX, rY, (c.getRGB() & 0xff00ffff) | (Math.min(c.getRed() + increment, 255) << 16));
+
+			c = new Color(img.getRGB(gX, gY));
+			img.setRGB(gX, gY, (c.getRGB() & 0xffff00ff) | (Math.min(c.getGreen() + increment, 255) << 8));
+
+			c = new Color(img.getRGB(bX, bY));
+			img.setRGB(bX, bY, (c.getRGB() & 0xffffff00) | (Math.min(c.getBlue() + increment, 255)));
+		}
+
+		try {
+			File outputfile = new File(fileName);
+			ImageIO.write(img, imgFormat, outputfile);
+		} catch (Exception e) {
+			System.out.println("Error: cannot open the file.");
+			System.exit(0);
+		}
+
+
+		long time = System.currentTimeMillis()-start;
+		System.out.printf("Time used: %dm, %ds, %dms.%n", time / 60000, (time / 1000) % 60, time % 1000);
+	}
+
+}