add color saturation utility

src/org/oscim/utils/FastMath.java

@@ -54,10 +54,19 @@ public class FastMath {
 
 		return (pow > 0 ? (1 << pow) : (1.0f / (1 << -pow)));
 	}
+
 	public static int clamp(int value, int max, int min) {
 		return (value < min ? min : (value > max ? max : value));
 	}
 
+	public static float clamp(float value, float max, float min) {
+		return (value < min ? min : (value > max ? max : value));
+	}
+
+	public static float clampN(float value) {
+		return (value < 0f ? 0f : (value > 1f ? 1f : value));
+	}
+
 	public static byte clampToByte(int value) {
 		return (byte) (value < 0 ? 0 : (value > 255 ? 255 : value));
 	}

src/org/oscim/utils/GlUtils.java

@@ -257,6 +257,29 @@ public class GlUtils {
 		return c;
 	}
 
+	/**
+	 * public-domain function by Darel Rex Finley
+	 * from http://alienryderflex.com/saturation.html
+	 *
+	 * @param color
+	 *            The passed-in RGB values can be on any desired scale, such as
+	 *            0 to 1, or 0 to 255.
+	 * @param change
+	 *            0.0 creates a black-and-white image.
+	 *            0.5 reduces the color saturation by half.
+	 *            1.0 causes no change.
+	 *            2.0 doubles the color saturation.
+	 */
+	public static void changeSaturation(float color[], float change) {
+		float r = color[0];
+		float g = color[1];
+		float b = color[2];
+		double p = Math.sqrt(r * r * 0.299f + g * g * 0.587f + b * b * 0.114f);
+		color[0] = FastMath.clampN((float) (p + (r - p) * change));
+		color[1] = FastMath.clampN((float) (p + (g - p) * change));
+		color[2] = FastMath.clampN((float) (p + (b - p) * change));
+	}
+
 	private final static float[] mIdentity = {
 			1, 0, 0, 0,
 			0, 1, 0, 0,