Add Transform1 and use it for ChartTransform, see phetsims/bamboo#27

js/Transform1.js

@@ -0,0 +1,68 @@
+// Copyright 2021, University of Colorado Boulder
+
+/**
+ * One dimensional (scalar) transforms, which are invertible.
+ *
+ * @author Sam Reid (PhET Interactive Simulations)
+ */
+
+import merge from '../../phet-core/js/merge.js';
+import Range from './Range.js';
+import dot from './dot.js';
+
+const TOLERANCE = 1E-6;
+const approxEquals = ( a, b ) => Math.abs( a - b ) <= TOLERANCE;
+
+class Transform1 {
+
+  /**
+   * @param {function(number):number} evaluationFunction
+   * @param {function(number):number} inverseFunction
+   * @param {Object} [options]
+   */
+  constructor( evaluationFunction, inverseFunction, options ) {
+
+    options = merge( {
+
+      // Used for asserting the inverse is correct, and that inputs are valid
+      domain: new Range( Number.NEGATIVE_INFINITY, Number.POSITIVE_INFINITY ),
+      range: new Range( Number.NEGATIVE_INFINITY, Number.POSITIVE_INFINITY )
+    }, options );
+
+    // @private
+    this.evaluationFunction = evaluationFunction;
+    this.inverseFunction = inverseFunction;
+    this.domain = options.domain;
+    this.range = options.range;
+  }
+
+  /**
+   * Evaluate the transform at the specified scalar.
+   * @param {number} x
+   * @returns {number}
+   * @public
+   */
+  evaluate( x ) {
+    assert && assert( this.domain.contains( x ), 'Value out of domain' );
+    const result = this.evaluationFunction( x );
+    assert && assert( approxEquals( this.inverseFunction( result ), x ) );
+    return result;
+  }
+
+  /**
+   * Evaluate the inverse at the specified scalar.
+   * @param {number} x
+   * @returns {number}
+   * @public
+   */
+  inverse( x ) {
+    assert && assert( this.range.contains( x ), 'Value out of range' );
+    const result = this.inverseFunction( x );
+    assert && assert( approxEquals( this.evaluationFunction( result ), x ) );
+    return result;
+  }
+}
+
+dot.register( 'Transform1', Transform1 );
+
+export default Transform1;