Exposing a C object from an external C library from C++ to R and back again using Rcpp

Question

This is a follow-up question on this one: Exposing a C struct with Rcpp?

@DirkEddelbuettel justly criticized that aforementioned question as being too broad in scope so I am here trying to be more specific in my goals, while providing some actual code exemplifying my attempt at this problem.

Description of the problem

First thing: please note that I use (somewhat unfortunately, I will change it eventually) two similar names in my code: GLuint and Gluint.

I'm trying to wrap this C OpenGL functionality in R (taken from here: OpenGL Textures objects and parameters):

GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);

Approach

I am using Rcpp to achieve these goals:

1. Provide a way of allocating the Gluint object from R; perhaps by instantiating an S4 object that wraps the C object (GLuint tex) inside?
2. Then, have an R exposed function named gl_gen_textures that takes an integer and that object mentioned in 1. Internally, this function gl_gen_textures accesses the memory address of the GLuint C object and passes it on to glGenTextures (C library function).
3. Eventually provide a way of destroying the Gluint object created in R and along with it the internal GLuint C object.

Actual code

#include <Rcpp.h>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
using namespace Rcpp;


class Gluint {
public:
  Gluint() {}
  GLuint obj;
};

RCPP_MODULE(gluint_module) {
  class_<Gluint>("Gluint")
  .constructor()
  .field("obj", &Gluint::obj)
  ;
}

//' @export
// [[Rcpp::export]]
void gl_gen_textures(unsigned int n, Gluint& tex) {

  uint32_t _n;
  _n = (uint32_t) n; // Convert unsigned int to uint32_t.
  glGenTextures((GLsizei) _n, &(tex.obj));

}

Errors

Currently this code does not compile. I'm getting these errors:

And here's a snippet of the function gl_gen_textures as generated in Rcpp::Exports.cpp lines 136-146:

// gl_gen_textures
void gl_gen_textures(unsigned int n, Gluint& tex);
RcppExport SEXP _glfw_gl_gen_textures(SEXP nSEXP, SEXP texSEXP) {
BEGIN_RCPP
    Rcpp::RNGScope rcpp_rngScope_gen;
    Rcpp::traits::input_parameter< unsigned int >::type n(nSEXP);
    Rcpp::traits::input_parameter< Gluint& >::type tex(texSEXP);
    gl_gen_textures(n, tex);
    return R_NilValue;
END_RCPP
}