A basic lerp function for ExtendScript. amt is similar to t in the more conventional naming of lerp. This function is similar to the Linear function inside After-Effects expression, however it does not let you map the range to something else, and the argument list order is different. This function works with arrays of numbers as well (for exampl…

lerp.jsx

function lerp(start, end, amt) {
  if (start == undefined || end == undefined || amt == undefined) {
    // can't lerp, start end amount is missing
    if (start !== undefined) {
      return start;
    }
    return 0;
  }

  function oneDLerp(start, end, amt) {
    try {
      if (amt == undefined) {
        if (start !== undefined) {
          return start;
        }
        if (end !== undefined) {
          return end;
        }
        return 0;
      }
      amt = amt < 0 ? 0 : amt > 1 ? 1 : amt;
      return (1 - amt) * start + amt * end;
    } catch (e) {
      // error in oneDLerp, you can print or alert the error
    }
  }
  if (start.length >= 1) {
    var result = [];
    for (lrp = 0; lrp < start.length; lrp++) {
      result.push(oneDLerp(start[lrp], end[lrp], amt));
    }
    return result;
  } else {
    return oneDLerp(start, end, amt);
  }
};