linear interpolation

javascript lerp

/*handy arrow function definitions*/
/*
const lerp = (a,b,x) => a+x*(b-a);
const qarp = (a,b,c,x) => lerp(lerp(a,b,x),lerp(b,c,x),x);
const unlerp = (a,b,y) => (y-a)/(b-a);
const lerpUnlerp = (a, b, c, d, x) => a+((x-c)/(d-c))*(b-a);
*/

/**
 * Linear interpolation
 * 
 * Example:
 * lerp(0,10,0.5) => 5
 * lerp(65,84,0.5) => 74.5
 * 
 * @param {Number} min The "minimum" output value
 * @param {Number} max The "maximum" output value
 * @param {Number} x The input value to interpolate
 */
export function lerp(min,max,x){
  return x*(max-min)+min;
}

/**
 * Reversed linear interpolation
 * 
 * Example:
 * unlerp(0,10,5) => 0.5
 * unlerp(87,167,127) => 0.5
 * 
 * @param {Number} min The "minimum" input value
 * @param {Number} max The "maximum" input value
 * @param {Number} x The input value to unlerp
 */
export function unlerp(min,max,x){
  return (x-min)/(max-min);
}

/**
 * This is essentially the same as calling `lerp(minOutput, maxOutput, unler(minInput, maxInput, x))`, but requires one less function call.
 * @param {Number} minOutput The "minimum" output value
 * @param {Number} maxOutput The "maximum" output value
 * @param {Number} minInput The lower result (unlerp) value
 * @param {Number} maxInput The upper result (unlerp) value
 * @param {Number} x The input value
 */
export function lerpUnlerp(minOutput, maxOutput, minInput, maxInput, x) {
  return minOutput+((x-minInput)/(maxInput-minInput))*(maxOutput-minOutput);
}