getFragmentShader(args) {
    if (this.compiledFragmentShader !== null) {
      return this.compiledFragmentShader;
    }
    return this.compiledFragmentShader = this.replaceArtifacts(this.constructor.fragmentShader, this._getFragShaderArtifactMap(args));
  }
@desc Get the fragment shader String.
If the String hasn't been compiled yet,
then this method compiles it as well

@param {Array} args - The actual parameters sent to the Kernel
@returns {string} Fragment Shader string