// build like this:
//    c++ glxtest.cpp -o glxtest -ldl -lX11
// run like this:
//    ./glxtest
// Example output:
//   VENDOR
//   Tungsten Graphics, Inc
//   RENDERER
//   Mesa DRI Intel(R) Sandybridge Mobile
//   VERSION
//   3.0 Mesa 8.0.4
//   TFP
//   TRUE

#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <stdint.h>
#include <string.h>

#include "X11/Xlib.h"
#include "X11/Xutil.h"

// stuff from glx.h
typedef struct __GLXcontextRec *GLXContext;
typedef XID GLXPixmap;
typedef XID GLXDrawable;
/* GLX 1.3 and later */
typedef struct __GLXFBConfigRec *GLXFBConfig;
typedef XID GLXFBConfigID;
typedef XID GLXContextID;
typedef XID GLXWindow;
typedef XID GLXPbuffer;
#define GLX_RGBA        4
#define GLX_RED_SIZE    8
#define GLX_GREEN_SIZE  9
#define GLX_BLUE_SIZE   10

// stuff from gl.h
typedef uint8_t GLubyte;
typedef uint32_t GLenum;
#define GL_VENDOR       0x1F00
#define GL_RENDERER     0x1F01
#define GL_VERSION      0x1F02

// the write end of the pipe, which we're going to write to
// XXX for the standalone version, this is replaced by stderr (2)
static int write_end_of_the_pipe = 2;

// C++ standard collides with C standard in that it doesn't allow casting void* to function pointer types.
// So the work-around is to convert first to size_t.
// http://www.trilithium.com/johan/2004/12/problem-with-dlsym/
template<typename func_ptr_type>
static func_ptr_type cast(void *ptr)
{
  return reinterpret_cast<func_ptr_type>(
           reinterpret_cast<size_t>(ptr)
         );
}

static void fatal_error(const char *str)
{
  write(write_end_of_the_pipe, str, strlen(str));
  write(write_end_of_the_pipe, "\n", 1);
  exit(EXIT_FAILURE);
}

static int
x_error_handler(Display *, XErrorEvent *ev)
{
  enum { bufsize = 1024 };
  char buf[bufsize];
  int length = snprintf(buf, bufsize,
                        "X error occurred in GLX probe, error_code=%d, request_code=%d, minor_code=%d\n",
                        ev->error_code,
                        ev->request_code,
                        ev->minor_code);
  write(write_end_of_the_pipe, buf, length);
  exit(EXIT_FAILURE);
  return 0;
}

static void glxtest()
{
  ///// Open libGL and load needed symbols /////
#ifdef __OpenBSD__
  #define LIBGL_FILENAME "libGL.so"
#else
  #define LIBGL_FILENAME "libGL.so.1"
#endif
  void *libgl = dlopen(LIBGL_FILENAME, RTLD_LAZY);
  if (!libgl)
    fatal_error("Unable to load " LIBGL_FILENAME);

  typedef void* (* PFNGLXGETPROCADDRESS) (const char *);
  PFNGLXGETPROCADDRESS glXGetProcAddress = cast<PFNGLXGETPROCADDRESS>(dlsym(libgl, "glXGetProcAddress"));

  if (!glXGetProcAddress)
    fatal_error("Unable to find glXGetProcAddress in " LIBGL_FILENAME);

  typedef GLXFBConfig* (* PFNGLXQUERYEXTENSION) (Display *, int *, int *);
  PFNGLXQUERYEXTENSION glXQueryExtension = cast<PFNGLXQUERYEXTENSION>(glXGetProcAddress("glXQueryExtension"));

  typedef GLXFBConfig* (* PFNGLXQUERYVERSION) (Display *, int *, int *);
  PFNGLXQUERYVERSION glXQueryVersion = cast<PFNGLXQUERYVERSION>(dlsym(libgl, "glXQueryVersion"));

  typedef XVisualInfo* (* PFNGLXCHOOSEVISUAL) (Display *, int, int *);
  PFNGLXCHOOSEVISUAL glXChooseVisual = cast<PFNGLXCHOOSEVISUAL>(glXGetProcAddress("glXChooseVisual"));

  typedef GLXContext (* PFNGLXCREATECONTEXT) (Display *, XVisualInfo *, GLXContext, Bool);
  PFNGLXCREATECONTEXT glXCreateContext = cast<PFNGLXCREATECONTEXT>(glXGetProcAddress("glXCreateContext"));

  typedef Bool (* PFNGLXMAKECURRENT) (Display*, GLXDrawable, GLXContext);
  PFNGLXMAKECURRENT glXMakeCurrent = cast<PFNGLXMAKECURRENT>(glXGetProcAddress("glXMakeCurrent"));

  typedef void (* PFNGLXDESTROYCONTEXT) (Display*, GLXContext);
  PFNGLXDESTROYCONTEXT glXDestroyContext = cast<PFNGLXDESTROYCONTEXT>(glXGetProcAddress("glXDestroyContext"));

  typedef GLubyte* (* PFNGLGETSTRING) (GLenum);
  PFNGLGETSTRING glGetString = cast<PFNGLGETSTRING>(glXGetProcAddress("glGetString"));

  if (!glXQueryExtension ||
      !glXQueryVersion ||
      !glXChooseVisual ||
      !glXCreateContext ||
      !glXMakeCurrent ||
      !glXDestroyContext ||
      !glGetString)
  {
    fatal_error("glXGetProcAddress couldn't find required functions");
  }
  ///// Open a connection to the X server /////
  Display *dpy = XOpenDisplay(NULL);
  if (!dpy)
    fatal_error("Unable to open a connection to the X server");

  ///// Check that the GLX extension is present /////
  if (!glXQueryExtension(dpy, NULL, NULL))
    fatal_error("GLX extension missing");

  XSetErrorHandler(x_error_handler);

  ///// Get a visual /////
   int attribs[] = {
      GLX_RGBA,
      GLX_RED_SIZE, 1,
      GLX_GREEN_SIZE, 1,
      GLX_BLUE_SIZE, 1,
      None };
  XVisualInfo *vInfo = glXChooseVisual(dpy, DefaultScreen(dpy), attribs);
  if (!vInfo)
    fatal_error("No visuals found");

  // using a X11 Window instead of a GLXPixmap does not crash
  // fglrx in indirect rendering. bug 680644
  Window window;
  XSetWindowAttributes swa;
  swa.colormap = XCreateColormap(dpy, RootWindow(dpy, vInfo->screen),
                                 vInfo->visual, AllocNone);

  swa.border_pixel = 0;
  window = XCreateWindow(dpy, RootWindow(dpy, vInfo->screen),
                       0, 0, 16, 16,
                       0, vInfo->depth, InputOutput, vInfo->visual,
                       CWBorderPixel | CWColormap, &swa);

  ///// Get a GL context and make it current //////
  GLXContext context = glXCreateContext(dpy, vInfo, NULL, True);
  glXMakeCurrent(dpy, window, context);

  ///// Look for this symbol to determine texture_from_pixmap support /////
  void* glXBindTexImageEXT = glXGetProcAddress("glXBindTexImageEXT");

  ///// Get GL vendor/renderer/versions strings /////
  enum { bufsize = 1024 };
  char buf[bufsize];
  const GLubyte *vendorString = glGetString(GL_VENDOR);
  const GLubyte *rendererString = glGetString(GL_RENDERER);
  const GLubyte *versionString = glGetString(GL_VERSION);

  if (!vendorString || !rendererString || !versionString)
    fatal_error("glGetString returned null");

  int length = snprintf(buf, bufsize,
                        "VENDOR\n%s\nRENDERER\n%s\nVERSION\n%s\nTFP\n%s\n",
                        vendorString,
                        rendererString,
                        versionString,
                        glXBindTexImageEXT ? "TRUE" : "FALSE");
  if (length >= bufsize)
    fatal_error("GL strings length too large for buffer size");

  ///// Clean up. Indeed, the parent process might fail to kill us (e.g. if it doesn't need to check GL info)
  ///// so we might be staying alive for longer than expected, so it's important to consume as little memory as
  ///// possible. Also we want to check that we're able to do that too without generating X errors.
  glXMakeCurrent(dpy, None, NULL); // must release the GL context before destroying it
  glXDestroyContext(dpy, context);
  XDestroyWindow(dpy, window);
  XFreeColormap(dpy, swa.colormap);
  XCloseDisplay(dpy);
  dlclose(libgl);

  ///// Finally write data to the pipe
  write(write_end_of_the_pipe, buf, length);
}

int main(int argc, char **argv)
{
  glxtest();
  return 0;
}