/* Copyright (c) Mark J. Kilgard, 1996. */

/* This program is freely distributable without licensing fees 
   and is provided without guarantee or warrantee expressed or 
   implied. This program is -not- in the public domain. */

#include <stdlib.h>
#include <string.h>
#include "glutint.h"

int __glutMesaSwapHackSupport = 0;  /* Not supported until
                                       proven otherwise. */

/* Use the "Mesa swap hack" if reasonable if and only if
   MESA_SWAP_HACK is set to something whose first character is
   not "N" or "n" AND "Brian Paul" is the vendor string AND
   "Mesa X11"* (or "Mesa" for backward compatibility)  is the
   renderer string.

   Anyone who modifies Mesa so that glXSwapBuffers does not
   simply blit the previously rendered back buffer should
   change either their vendor or renderer string to avoid
   confusing GLUT. */

void
__glutDetermineMesaSwapHackSupport(void)
{
  static int doneAlready = 0;
  char *env, *vendor, *renderer;

  if (doneAlready)
    return;
  env = getenv("MESA_SWAP_HACK");
  if (env) {
    if ((env[0] != 'n') && (env[0] != 'N')) {
      vendor = (char *) glGetString(GL_VENDOR);
      renderer = (char *) glGetString(GL_RENDERER);

      /* Old versions of X11 Mesa uses the renderer string
         "Mesa"; Brian plans to start using "Mesa X11" to
         distinguish the X version of Mesa from other flavor
         such as Windows or 3Dfx. */

#define MESA_X11 "Mesa X11"

      /* XXX At some point in the future, eliminate the
         backward compatibility for the old "Mesa" renderer
         string. */

      if (!strcmp(vendor, "Brian Paul") && (!strcmp(renderer, "Mesa") ||
          !strncmp(renderer, MESA_X11, sizeof(MESA_X11) - 1)))
        __glutMesaSwapHackSupport = 1;
    }
  }
  doneAlready = 1;
}