code: public Layer setAlpha(float alpha) {
      this.alpha = alpha;
      int ialpha = (int)(0xFF * MathUtil.clamp(alpha, 0, 1));
      this.tint = (ialpha << 24) | (tint & 0xFFFFFF);
      return this;
    }
docs: Sets the alpha component of this layer's current tint. Note that this value will be quantized
  to an integer between 0 and 255. Also see {@link #setTint}.
  
  <p> Values outside the range [0,1] will be clamped to the range [0,1]. </p>
  
  @param alpha alpha value in range [0,1] where 0 is transparent and 1 is opaque.
  
  @return a reference to this layer for call chaining.