/**
   * This constructor is called by {@link GLRenderPanel}.
   *
   * @param drawable the OpenGL rendering context. All OpenGL calls are directed to this object.
   */
  public GLRenderContext(GLAutoDrawable drawable) {

    // Some OpenGL initialization
    gl = drawable.getGL().getGL3();
    gl.glEnable(GL3.GL_DEPTH_TEST);
    gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

    // Load and use the default shader
    defaultShader = (GLShader) makeShader();
    try {
      defaultShader.load("../jrtr/shaders/default.vert", "../jrtr/shaders/default.frag");
    } catch (Exception e) {
      System.out.print("Problem with shader:\n");
      System.out.print(e.getMessage());
    }
    useDefaultShader();
  }