// Offers very precise sRGB encoding and decoding.

// The actual values defining sRGB are alpha = 0.055 and gamma = 2.4.

// This class works directly from that definition to take advantage of all
// available precision, unlike pre-rounded constants like 12.92 that cause a
// comparatively humongous discontinuity at a point that should be of
// differentiability class C^1.

// Stored values are chosen to speed up bulk conversion somewhat.

package example.jonathan2520;

public class SRGBCalculator {
	private double decode_threshold,
	               decode_slope,
	               decode_multiplier,
	               decode_addend,
	               decode_exponent,
	               encode_threshold,
	               encode_slope,
	               encode_multiplier,
	               encode_addend,
	               encode_exponent;
	
	public SRGBCalculator(double gamma, double alpha) {
		encode_multiplier = alpha + 1.0;
		decode_multiplier = 1.0 / encode_multiplier;
		encode_addend = -alpha;
		decode_addend = decode_multiplier * alpha;
		encode_exponent = 1.0 / gamma;
		decode_exponent = gamma;
		decode_threshold = alpha / (gamma - 1.0);
		encode_threshold = Math.pow(gamma * decode_threshold * decode_multiplier, gamma);
		encode_slope = decode_threshold / encode_threshold;
		decode_slope = encode_threshold / decode_threshold;
	}
	
	public SRGBCalculator() {
		this(2.4, 0.055);
	}
	
	public double decode(double x) {
		if (x < decode_threshold)
			return decode_slope * x;
		else
			return Math.pow(x * decode_multiplier + decode_addend, decode_exponent);
	}
	
	public double encode(double x) {
		if (x < encode_threshold)
			return encode_slope * x;
		else
			return Math.pow(x, encode_exponent) * encode_multiplier + encode_addend;
	}
}