########################################################################
##
## Copyright (C) 2016-2021 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################

## -*- texinfo -*-
## @deftypefn  {} {} __opengl_info__
## @deftypefnx {} {@var{retval} =} __opengl_info__ ()
##
## Get OpenGL driver information.
##
## If no output values are requested, display information about the
## OpenGL subsystem.  If an output is requested, return the information
## in a structure.
##
## Fields in the structure are:
##
## @table @asis
## @item version
## OpenGL Driver version string
##
## @item vendor
## OpenGL Driver vendor string
##
## @item renderer
## OpenGL renderer string
##
## @item extensions
## List of enabled extensions for the OpenGL driver.
## @end table
##
## Example Code:
##
## @example
## glinfo = __opengl_info__ ();
## @end example
##
## @end deftypefn

function retval = __opengl_info__ ()

  if (nargin != 0)
    print_usage ();
  endif

  [info, msg] = gl_info ();

  if (! isempty (msg))
    warning (msg);
  else
    if (nargout == 0)
      printf ("   version: %s\n", info.version);
      printf ("    vendor: %s\n", info.vendor);
      printf ("  renderer: %s\n", info.renderer);
      printf ("extensions:\n");
      printf ("  %s\n", info.extensions{:});
    else
      retval = info;
    endif
  endif

endfunction

function info = fig_gl_info (h)

  info = [];

  if (ishghandle (h) && strcmp (get (h, "renderer"), "opengl"))
    vend = get (h, "__gl_vendor__");
    if (isempty (vend))
      return;
    endif
    info.vendor   = vend;
    info.version  = get (h, "__gl_version__");
    info.renderer = get (h, "__gl_renderer__");
    info.extensions = strsplit (strtrim (get (h, "__gl_extensions__")));
  endif

endfunction

function [info, msg] = gl_info ()

  info = [];
  msg = "";

  ## If we have any open figures, take a look there for OpenGL info.
  figs = findall (0, "type", "figure");

  for hf = figs.'
    info = fig_gl_info (hf);
    if (! isempty (info))
      break;
    endif
  endfor

  ## If no info yet, try open a figure to get the info.
  attempts = 1;
  while (isempty (info) && attempts++ <= 3)
    ## Need to create a figure, place an OpenGL object, and force drawing.
    hf = figure ("position", [0,0,1,1], "toolbar", "none", "menubar", "none");
    hax = axes ();
    ## FIXME: Race condition means this delay may not always work.
    pause (0.1 * attempts);
    refresh (hf);
    info = fig_gl_info (hf);
    close (hf);
  endwhile

  if (isempty (info))
    msg = "__opengl_info__: can not obtain OpenGL information";
  endif

endfunction


## FIXME: This is really an internal function as indicated by the leading and
## trailing underscores.  As such, it doesn't require tests.  In addition,
## during the running of the test suite this function will throw up a figure
## which is undesirable.  The tests have been commented out, but are still
## available in case someone wants to hand-test the function by executing the
## code.

%!#testif HAVE_OPENGL, HAVE_FLTK; have_window_system () && any (strcmp ("fltk", available_graphics_toolkits ()))
%! old_toolkit = graphics_toolkit ();
%! unwind_protect
%!   graphics_toolkit ("fltk");
%!   a = __opengl_info__ ();
%! unwind_protect_cleanup
%!   graphics_toolkit (old_toolkit);
%! end_unwind_protect
%! assert (! isempty (a));
%! assert (isfield (a, "version"));

%!#testif HAVE_OPENGL, HAVE_QT; have_window_system () && any (strcmp ("qt", available_graphics_toolkits ()))
%! old_toolkit = graphics_toolkit ();
%! unwind_protect
%!   graphics_toolkit ("qt");
%!   a = __opengl_info__ ();
%! unwind_protect_cleanup
%!   graphics_toolkit (old_toolkit);
%! end_unwind_protect
%! assert (! isempty (a));
%! assert (isfield (a, "version"));

%!error __opengl_info ("foobar")
