function scaleAndAdd(out, a, b, scale) {
    out[0] = a[0] + b[0] * scale;
    out[1] = a[1] + b[1] * scale;
    return out;
  }
Adds two vec2's after scaling the second operand by a scalar value

@param {vec2} out the receiving vector
@param {ReadonlyVec2} a the first operand
@param {ReadonlyVec2} b the second operand
@param {Number} scale the amount to scale b by before adding
@returns {vec2} out