1 /* 2 * Copyright 2017 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.sample.oboe.manualtest; 18 19 /** 20 * Maps integer range info to a double value along an exponential scale. 21 * 22 * <pre> 23 * 24 * x = ival / mResolution 25 * f(x) = a*(root**bx) 26 * f(0.0) = dmin 27 * f(1.0) = dmax 28 * 29 * f(0.0) = a * 1.0 => a = dmin 30 * f(1.0) = dmin * root**b = dmax 31 * b = log(dmax / dmin) / log(root) 32 * 33 * </pre> 34 */ 35 36 public class ExponentialTaper { 37 private double offset = 0.0; 38 private double a = 1.0; 39 private double b = 2.0; 40 private static final double ROOT = 10.0; // because we are using log10 41 ExponentialTaper(double dmin, double dmax)42 public ExponentialTaper(double dmin, double dmax) { 43 this(dmin, dmax, 10000.0); 44 } 45 ExponentialTaper(double dmin, double dmax, double maxRatio)46 public ExponentialTaper(double dmin, double dmax, double maxRatio) { 47 a = dmax; 48 double curvature; 49 if (dmax > dmin * maxRatio) { 50 offset = dmax / maxRatio; 51 a = offset; 52 curvature = (dmax + offset) / offset; 53 } else { 54 curvature = dmax / dmin; 55 a = dmin; 56 } 57 b = Math.log10(curvature); 58 } 59 linearToExponential(double linear)60 public double linearToExponential(double linear) { 61 return a * Math.pow(ROOT, b * linear) - offset; 62 } 63 exponentialToLinear(double exponential)64 public double exponentialToLinear(double exponential) { 65 return Math.log((exponential + offset) / a) / (b * Math.log(ROOT)); 66 } 67 } 68