add basic java classes needed for core image -> ascii conversion

copied from another project of mine

src/java/clj_image2ascii/java/ImageToAscii.java

@@ -0,0 +1,64 @@
+package clj_image2ascii.java;
+
+import java.awt.image.BufferedImage;
+
+// This method of converting an image to ascii representation is based on the method used in
+// Claskii (https://github.com/LauJensen/Claskii). Some improvements have been made, such as
+// a better way of calculating pixel brightness and little tweaks to how the right ASCII
+// character is selected, as well as obviously a conversion to Java purely for performance.
+
+public class ImageToAscii {
+	static final char[] asciiChars = {'#', 'A', '@', '%', '$', '+', '=', '*', ':', ',', '.', ' '};
+	static final int numAsciiChars = asciiChars.length - 1;
+	static final int spanLength = "<span style=\"color:#112233;\">X</span>".length();
+	static final int lineTerminatorLength = "<br>".length();
+
+	public static String convert(BufferedImage image, boolean useColor) {
+		final int width = image.getWidth();
+		final int height = image.getHeight();
+
+		final int maxLength = (useColor ?
+		                       (width * height * spanLength) + (height * lineTerminatorLength) :
+		                       (width * height) + height);
+
+		final MicroStringBuilder sb = new MicroStringBuilder(maxLength);
+
+		final int[] pixels = image.getRGB(0, 0, width, height, null, 0, width);
+
+		for (int y = 0; y < height; ++y) {
+			for (int x = 0; x < width; ++x) {
+				final int argb = pixels[(y * width) + x];
+				final int r = (0x00ff0000 & argb) >> 16;
+				final int g = (0x0000ff00 & argb) >> 8;
+				final int b = (0x000000ff & argb);
+				final double brightness = Math.sqrt((r * r * 0.241f) +
+				                                    (g * g * 0.691f) +
+				                                    (b * b * 0.068f));
+				int charIndex;
+				if (brightness == 0.0f)
+					charIndex = numAsciiChars;
+				else
+					charIndex = (int)((brightness / 255.0f) * numAsciiChars);
+
+				final char pixelChar = asciiChars[charIndex > 0 ? charIndex : 0];
+
+				if (useColor) {
+					sb.append("<span style=\"color:#");
+					sb.appendAsHex(r);
+					sb.appendAsHex(g);
+					sb.appendAsHex(b);
+					sb.append(";\">");
+					sb.append(pixelChar);
+					sb.append("</span>");
+				} else
+					sb.append(pixelChar);
+			}
+			if (useColor)
+				sb.append("<br>");
+			else
+				sb.append('\n');
+		}
+
+		return sb.toString();
+	}
+}

src/java/clj_image2ascii/java/MicroStringBuilder.java

@@ -0,0 +1,58 @@
+package clj_image2ascii.java;
+
+// I wanted a StringBuilder that had an append() method which allowed appending unsigned byte values
+// as a 2-char hex representation (e.g. 255 => "FF") in a way that did not allocate any extra memory
+// and could be done "in-place" with the StringBuilder's internal character array. This kind of evolved
+// into this class being added since I was only using 2 append() methods from java.lang.StringBuilder
+// anyway. Except for the appendAsHex(), this class does not perform noticeably faster then
+// java.lang.StringBuilder does.
+
+public class MicroStringBuilder {
+	// copied from java.lang.Integer.digits (which is private so we can't just reference it, boourns)
+	static final char[] digits = {
+		'0' , '1' , '2' , '3' , '4' , '5' ,
+		'6' , '7' , '8' , '9' , 'a' , 'b' ,
+		'c' , 'd' , 'e' , 'f' , 'g' , 'h' ,
+		'i' , 'j' , 'k' , 'l' , 'm' , 'n' ,
+		'o' , 'p' , 'q' , 'r' , 's' , 't' ,
+		'u' , 'v' , 'w' , 'x' , 'y' , 'z'
+	};
+
+	final char[] chars;
+	int length;
+
+	public MicroStringBuilder(int capacity) {
+		chars = new char[capacity];
+		length = 0;
+	}
+
+	public void append(final String s) {
+		final int srcLength = s.length();
+		s.getChars(0, srcLength, chars, length);
+		length += srcLength;
+	}
+
+	public void append(final char c) {
+		chars[length] = c;
+		++length;
+	}
+
+	// modification of java.lang.Integer.toUnsignedString -- no garbage generated, but limited to max value
+	// of 255 ...hence the 'unsigned byte' thing :)
+	public void appendAsHex(int unsignedByte) {
+		for (int i = 0; i < 2; ++i) {
+			final int index = length + 1 - i;
+			if (unsignedByte != 0) {
+				chars[index] = digits[unsignedByte & 15];
+				unsignedByte >>>= 4;
+			} else
+				chars[index] = '0';
+		}
+		length += 2;
+	}
+
+	@Override
+	public String toString() {
+		return new String(chars, 0, length);
+	}
+}