mutter/cogl/cogl-context.c

/*
 * Cogl
 *
 * An object oriented GL/GLES Abstraction/Utility Layer
 *
 * Copyright (C) 2007,2008,2009 Intel Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 *
 *
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "cogl-object.h"
#include "cogl-internal.h"
#include "cogl-private.h"
#include "cogl-winsys-private.h"
#include "winsys/cogl-winsys-stub-private.h"
#include "cogl-profile.h"
#include "cogl-util.h"
#include "cogl-context-private.h"
#include "cogl-display-private.h"
#include "cogl-renderer-private.h"
#include "cogl-journal-private.h"
#include "cogl-texture-private.h"
#include "cogl-texture-2d-private.h"
#include "cogl-texture-3d-private.h"
#include "cogl-texture-rectangle-private.h"
#include "cogl-pipeline-private.h"
#include "cogl-pipeline-opengl-private.h"
#include "cogl-framebuffer-private.h"
#include "cogl-onscreen-private.h"
#include "cogl2-path.h"
#include "cogl-attribute-private.h"
#include "cogl1-context.h"
#include "cogl-gpu-info-private.h"
#include "cogl-config-private.h"
#include "cogl-error-private.h"

#include <string.h>

#ifdef HAVE_COGL_GL
#include "cogl-pipeline-fragend-arbfp-private.h"
#endif

/* This isn't defined in the GLES headers */
#ifndef GL_POINT_SPRITE
#define GL_POINT_SPRITE 0x8861
#endif

static void _cogl_context_free (CoglContext *context);

COGL_OBJECT_DEFINE (Context, context);

extern void
_cogl_create_context_driver (CoglContext *context);

static CoglContext *_cogl_context = NULL;

static void
_cogl_init_feature_overrides (CoglContext *ctx)
{
  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_VBOS)))
    ctx->private_feature_flags &= ~COGL_PRIVATE_FEATURE_VBOS;

  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_PBOS)))
    ctx->private_feature_flags &= ~COGL_PRIVATE_FEATURE_PBOS;

  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_ARBFP)))
    {
      ctx->feature_flags &= ~COGL_FEATURE_SHADERS_ARBFP;
      COGL_FLAGS_SET (ctx->features, COGL_FEATURE_ID_ARBFP, FALSE);
    }

  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_GLSL)))
    {
      ctx->feature_flags &= ~COGL_FEATURE_SHADERS_GLSL;
      COGL_FLAGS_SET (ctx->features, COGL_FEATURE_ID_GLSL, FALSE);
    }

  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_NPOT_TEXTURES)))
    {
      ctx->feature_flags &= ~(COGL_FEATURE_TEXTURE_NPOT |
                              COGL_FEATURE_TEXTURE_NPOT_BASIC |
                              COGL_FEATURE_TEXTURE_NPOT_MIPMAP |
                              COGL_FEATURE_TEXTURE_NPOT_REPEAT);
      COGL_FLAGS_SET (ctx->features, COGL_FEATURE_ID_TEXTURE_NPOT, FALSE);
      COGL_FLAGS_SET (ctx->features,
                      COGL_FEATURE_ID_TEXTURE_NPOT_BASIC, FALSE);
      COGL_FLAGS_SET (ctx->features,
                      COGL_FEATURE_ID_TEXTURE_NPOT_MIPMAP, FALSE);
      COGL_FLAGS_SET (ctx->features,
                      COGL_FEATURE_ID_TEXTURE_NPOT_REPEAT, FALSE);
    }
}

const CoglWinsysVtable *
_cogl_context_get_winsys (CoglContext *context)
{
  return context->display->renderer->winsys_vtable;
}

/* For reference: There was some deliberation over whether to have a
 * constructor that could throw an exception but looking at standard
 * practices with several high level OO languages including python, C++,
 * C# Java and Ruby they all support exceptions in constructors and the
 * general consensus appears to be that throwing an exception is neater
 * than successfully constructing with an internal error status that
 * would then have to be explicitly checked via some form of ::is_ok()
 * method.
 */
CoglContext *
cogl_context_new (CoglDisplay *display,
                  CoglError **error)
{
  CoglContext *context;
  GLubyte default_texture_data[] = { 0xff, 0xff, 0xff, 0x0 };
  CoglBitmap *default_texture_bitmap;
  const CoglWinsysVtable *winsys;
  int i;
  CoglError *internal_error = NULL;

  _cogl_init ();

#ifdef COGL_ENABLE_PROFILE
  /* We need to be absolutely sure that uprof has been initialized
   * before calling _cogl_uprof_init. uprof_init (NULL, NULL)
   * will be a NOP if it has been initialized but it will also
   * mean subsequent parsing of the UProf GOptionGroup will have no
   * affect.
   *
   * Sadly GOptionGroup based library initialization is extremely
   * fragile by design because GOptionGroups have no notion of
   * dependencies and so the order things are initialized isn't
   * currently under tight control.
   */
  uprof_init (NULL, NULL);
  _cogl_uprof_init ();
#endif

  /* Allocate context memory */
  context = g_malloc0 (sizeof (CoglContext));

  /* Convert the context into an object immediately in case any of the
     code below wants to verify that the context pointer is a valid
     object */
  _cogl_context_object_new (context);

  /* XXX: Gross hack!
   * Currently everything in Cogl just assumes there is a default
   * context which it can access via _COGL_GET_CONTEXT() including
   * code used to construct a CoglContext. Until all of that code
   * has been updated to take an explicit context argument we have
   * to immediately make our pointer the default context.
   */
  _cogl_context = context;

  /* Init default values */
  memset (context->features, 0, sizeof (context->features));
  context->feature_flags = 0;
  context->private_feature_flags = 0;

  context->texture_types = NULL;
  context->buffer_types = NULL;

  context->rectangle_state = COGL_WINSYS_RECTANGLE_STATE_UNKNOWN;

  memset (context->winsys_features, 0, sizeof (context->winsys_features));

  if (!display)
    {
      CoglRenderer *renderer = cogl_renderer_new ();
      if (!cogl_renderer_connect (renderer, error))
        {
          g_free (context);
          return NULL;
        }

      display = cogl_display_new (renderer, NULL);
    }
  else
    cogl_object_ref (display);

  if (!cogl_display_setup (display, error))
    {
      cogl_object_unref (display);
      g_free (context);
      return NULL;
    }

  context->display = display;

  /* This is duplicated data, but it's much more convenient to have
     the driver attached to the context and the value is accessed a
     lot throughout Cogl */
  context->driver = display->renderer->driver;

  /* Again this is duplicated data, but it convenient to be able
   * access these from the context. */
  context->driver_vtable = display->renderer->driver_vtable;
  context->texture_driver = display->renderer->texture_driver;

  winsys = _cogl_context_get_winsys (context);
  if (!winsys->context_init (context, error))
    {
      cogl_object_unref (display);
      g_free (context);
      return NULL;
    }

  context->attribute_name_states_hash =
    g_hash_table_new_full (g_str_hash, g_str_equal, g_free, g_free);
  context->attribute_name_index_map = NULL;
  context->n_attribute_names = 0;

  /* The "cogl_color_in" attribute needs a deterministic name_index
   * so we make sure it's the first attribute name we register */
  _cogl_attribute_register_attribute_name (context, "cogl_color_in");


  context->uniform_names =
    g_ptr_array_new_with_free_func ((GDestroyNotify) g_free);
  context->uniform_name_hash = g_hash_table_new (g_str_hash, g_str_equal);
  context->n_uniform_names = 0;

  /* Initialise the driver specific state */
  _cogl_init_feature_overrides (context);

  context->sampler_cache = _cogl_sampler_cache_new (context);

  _cogl_pipeline_init_default_pipeline ();
  _cogl_pipeline_init_default_layers ();
  _cogl_pipeline_init_state_hash_functions ();
  _cogl_pipeline_init_layer_state_hash_functions ();

  context->current_clip_stack_valid = FALSE;
  context->current_clip_stack = NULL;

  context->legacy_backface_culling_enabled = FALSE;

  cogl_matrix_init_identity (&context->identity_matrix);
  cogl_matrix_init_identity (&context->y_flip_matrix);
  cogl_matrix_scale (&context->y_flip_matrix, 1, -1, 1);

  context->flushed_matrix_mode = COGL_MATRIX_MODELVIEW;

  context->texture_units =
    g_array_new (FALSE, FALSE, sizeof (CoglTextureUnit));

  /* See cogl-pipeline.c for more details about why we leave texture unit 1
   * active by default... */
  context->active_texture_unit = 1;
  GE (context, glActiveTexture (GL_TEXTURE1));

  context->legacy_fog_state.enabled = FALSE;

  context->opaque_color_pipeline = cogl_pipeline_new (context);
  context->blended_color_pipeline = cogl_pipeline_new (context);
  context->texture_pipeline = cogl_pipeline_new (context);
  context->codegen_header_buffer = g_string_new ("");
  context->codegen_source_buffer = g_string_new ("");
  context->source_stack = NULL;

  context->legacy_state_set = 0;

  context->default_gl_texture_2d_tex = NULL;
  context->default_gl_texture_3d_tex = NULL;
  context->default_gl_texture_rect_tex = NULL;

  context->framebuffers = NULL;
  context->current_draw_buffer = NULL;
  context->current_read_buffer = NULL;
  context->current_draw_buffer_state_flushed = 0;
  context->current_draw_buffer_changes = COGL_FRAMEBUFFER_STATE_ALL;

  g_queue_init (&context->gles2_context_stack);

  context->journal_flush_attributes_array =
    g_array_new (TRUE, FALSE, sizeof (CoglAttribute *));
  context->journal_clip_bounds = NULL;

  context->polygon_vertices = g_array_new (FALSE, FALSE, sizeof (float));

  context->current_pipeline = NULL;
  context->current_pipeline_changes_since_flush = 0;
  context->current_pipeline_skip_gl_color = FALSE;

  _cogl_bitmask_init (&context->enabled_builtin_attributes);
  _cogl_bitmask_init (&context->enable_builtin_attributes_tmp);
  _cogl_bitmask_init (&context->enabled_texcoord_attributes);
  _cogl_bitmask_init (&context->enable_texcoord_attributes_tmp);
  _cogl_bitmask_init (&context->enabled_custom_attributes);
  _cogl_bitmask_init (&context->enable_custom_attributes_tmp);
  _cogl_bitmask_init (&context->changed_bits_tmp);

  context->max_texture_units = -1;
  context->max_activateable_texture_units = -1;

  context->current_fragment_program_type = COGL_PIPELINE_PROGRAM_TYPE_FIXED;
  context->current_vertex_program_type = COGL_PIPELINE_PROGRAM_TYPE_FIXED;
  context->current_gl_program = 0;

  context->current_gl_dither_enabled = TRUE;
  context->current_gl_color_mask = COGL_COLOR_MASK_ALL;

  context->gl_blend_enable_cache = FALSE;

  context->depth_test_enabled_cache = FALSE;
  context->depth_test_function_cache = COGL_DEPTH_TEST_FUNCTION_LESS;
  context->depth_writing_enabled_cache = TRUE;
  context->depth_range_near_cache = 0;
  context->depth_range_far_cache = 1;

  context->legacy_depth_test_enabled = FALSE;

  context->pipeline_cache = cogl_pipeline_cache_new ();

  for (i = 0; i < COGL_BUFFER_BIND_TARGET_COUNT; i++)
    context->current_buffer[i] = NULL;

  context->window_buffer = NULL;
  context->framebuffer_stack = _cogl_create_framebuffer_stack ();

  /* XXX: In this case the Clutter backend is still responsible for
   * the OpenGL binding API and for creating onscreen framebuffers and
   * so we have to add a dummy framebuffer to represent the backend
   * owned window... */
  if (_cogl_context_get_winsys (context) == _cogl_winsys_stub_get_vtable ())
    {
      CoglOnscreen *window = _cogl_onscreen_new ();
      cogl_set_framebuffer (COGL_FRAMEBUFFER (window));
      cogl_object_unref (COGL_FRAMEBUFFER (window));
    }

  context->current_path = cogl2_path_new ();
  context->stencil_pipeline = cogl_pipeline_new (context);

  context->in_begin_gl_block = FALSE;

  context->quad_buffer_indices_byte = NULL;
  context->quad_buffer_indices = NULL;
  context->quad_buffer_indices_len = 0;

  context->rectangle_byte_indices = NULL;
  context->rectangle_short_indices = NULL;
  context->rectangle_short_indices_len = 0;

  context->texture_download_pipeline = NULL;
  context->blit_texture_pipeline = NULL;

#if defined (HAVE_COGL_GL) || defined (HAVE_COGL_GLES)
  if (context->driver != COGL_DRIVER_GLES2)
    /* The default for GL_ALPHA_TEST is to always pass which is equivalent to
     * the test being disabled therefore we assume that for all drivers there
     * will be no performance impact if we always leave the test enabled which
     * makes things a bit simpler for us. Under GLES2 the alpha test is
     * implemented in the fragment shader so there is no enable for it
     */
    GE (context, glEnable (GL_ALPHA_TEST));
#endif

  context->current_modelview_entry = NULL;
  context->current_projection_entry = NULL;
  _cogl_matrix_entry_identity_init (&context->identity_entry);
  _cogl_matrix_entry_cache_init (&context->builtin_flushed_projection);
  _cogl_matrix_entry_cache_init (&context->builtin_flushed_modelview);

  default_texture_bitmap =
    cogl_bitmap_new_for_data (context,
                              1, 1, /* width/height */
                              COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                              4, /* rowstride */
                              default_texture_data);

  /* Create default textures used for fall backs */
  context->default_gl_texture_2d_tex =
    cogl_texture_2d_new_from_bitmap (default_texture_bitmap,
                                     /* internal format */
                                     COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                                     NULL);

  /* If 3D or rectangle textures aren't supported then these will
   * return errors that we can simply ignore. */
  internal_error = NULL;
  context->default_gl_texture_3d_tex =
    cogl_texture_3d_new_from_bitmap (default_texture_bitmap,
                                     1, /* height */
                                     1, /* depth */
                                     COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                                     &internal_error);
  if (internal_error)
    cogl_error_free (internal_error);

  internal_error = NULL;
  context->default_gl_texture_rect_tex =
    cogl_texture_rectangle_new_from_bitmap (default_texture_bitmap,
                                            COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                                            &internal_error);
  if (internal_error)
    cogl_error_free (internal_error);

  cogl_object_unref (default_texture_bitmap);

  cogl_push_source (context->opaque_color_pipeline);

  context->atlases = NULL;
  g_hook_list_init (&context->atlas_reorganize_callbacks, sizeof (GHook));

  context->buffer_map_fallback_array = g_byte_array_new ();
  context->buffer_map_fallback_in_use = FALSE;

  /* As far as I can tell, GL_POINT_SPRITE doesn't have any effect
     unless GL_COORD_REPLACE is enabled for an individual
     layer. Therefore it seems like it should be ok to just leave it
     enabled all the time instead of having to have a set property on
     each pipeline to track whether any layers have point sprite
     coords enabled. We don't need to do this for GLES2 because point
     sprites are handled using a builtin varying in the shader. */
  if (context->driver != COGL_DRIVER_GLES2 &&
      cogl_has_feature (context, COGL_FEATURE_ID_POINT_SPRITE))
    GE (context, glEnable (GL_POINT_SPRITE));

  return context;
}

static void
_cogl_context_free (CoglContext *context)
{
  const CoglWinsysVtable *winsys = _cogl_context_get_winsys (context);

  winsys->context_deinit (context);

  _cogl_free_framebuffer_stack (context->framebuffer_stack);

  if (context->current_path)
    cogl_handle_unref (context->current_path);

  if (context->default_gl_texture_2d_tex)
    cogl_object_unref (context->default_gl_texture_2d_tex);
  if (context->default_gl_texture_3d_tex)
    cogl_object_unref (context->default_gl_texture_3d_tex);
  if (context->default_gl_texture_rect_tex)
    cogl_object_unref (context->default_gl_texture_rect_tex);

  if (context->opaque_color_pipeline)
    cogl_object_unref (context->opaque_color_pipeline);
  if (context->blended_color_pipeline)
    cogl_object_unref (context->blended_color_pipeline);
  if (context->texture_pipeline)
    cogl_object_unref (context->texture_pipeline);

  if (context->blit_texture_pipeline)
    cogl_object_unref (context->blit_texture_pipeline);

  g_warn_if_fail (context->gles2_context_stack.length == 0);

  if (context->journal_flush_attributes_array)
    g_array_free (context->journal_flush_attributes_array, TRUE);
  if (context->journal_clip_bounds)
    g_array_free (context->journal_clip_bounds, TRUE);

  if (context->polygon_vertices)
    g_array_free (context->polygon_vertices, TRUE);

  if (context->quad_buffer_indices_byte)
    cogl_object_unref (context->quad_buffer_indices_byte);
  if (context->quad_buffer_indices)
    cogl_object_unref (context->quad_buffer_indices);

  if (context->rectangle_byte_indices)
    cogl_object_unref (context->rectangle_byte_indices);
  if (context->rectangle_short_indices)
    cogl_object_unref (context->rectangle_short_indices);

  if (context->default_pipeline)
    cogl_object_unref (context->default_pipeline);

  if (context->dummy_layer_dependant)
    cogl_object_unref (context->dummy_layer_dependant);
  if (context->default_layer_n)
    cogl_object_unref (context->default_layer_n);
  if (context->default_layer_0)
    cogl_object_unref (context->default_layer_0);

  if (context->current_clip_stack_valid)
    _cogl_clip_stack_unref (context->current_clip_stack);

  g_slist_free (context->atlases);
  g_hook_list_clear (&context->atlas_reorganize_callbacks);

  _cogl_bitmask_destroy (&context->enabled_builtin_attributes);
  _cogl_bitmask_destroy (&context->enable_builtin_attributes_tmp);
  _cogl_bitmask_destroy (&context->enabled_texcoord_attributes);
  _cogl_bitmask_destroy (&context->enable_texcoord_attributes_tmp);
  _cogl_bitmask_destroy (&context->enabled_custom_attributes);
  _cogl_bitmask_destroy (&context->enable_custom_attributes_tmp);
  _cogl_bitmask_destroy (&context->changed_bits_tmp);

  g_slist_free (context->texture_types);
  g_slist_free (context->buffer_types);

  if (context->current_modelview_entry)
    _cogl_matrix_entry_unref (context->current_modelview_entry);
  if (context->current_projection_entry)
    _cogl_matrix_entry_unref (context->current_projection_entry);
  _cogl_matrix_entry_cache_destroy (&context->builtin_flushed_projection);
  _cogl_matrix_entry_cache_destroy (&context->builtin_flushed_modelview);

  cogl_pipeline_cache_free (context->pipeline_cache);

  _cogl_sampler_cache_free (context->sampler_cache);

  _cogl_destroy_texture_units ();

  g_ptr_array_free (context->uniform_names, TRUE);
  g_hash_table_destroy (context->uniform_name_hash);

  g_hash_table_destroy (context->attribute_name_states_hash);
  g_array_free (context->attribute_name_index_map, TRUE);

  g_byte_array_free (context->buffer_map_fallback_array, TRUE);

  cogl_object_unref (context->display);

  g_free (context);
}

CoglContext *
_cogl_context_get_default (void)
{
  CoglError *error = NULL;
  /* Create if doesn't exist yet */
  if (_cogl_context == NULL)
    {
      _cogl_context = cogl_context_new (NULL, &error);
      if (!_cogl_context)
        {
          g_warning ("Failed to create default context: %s",
                     error->message);
          cogl_error_free (error);
        }
    }

  return _cogl_context;
}

CoglDisplay *
cogl_context_get_display (CoglContext *context)
{
  return context->display;
}

#ifdef COGL_HAS_EGL_SUPPORT
EGLDisplay
cogl_egl_context_get_egl_display (CoglContext *context)
{
  const CoglWinsysVtable *winsys = _cogl_context_get_winsys (context);

  /* This should only be called for EGL contexts */
  _COGL_RETURN_VAL_IF_FAIL (winsys->context_egl_get_egl_display != NULL, NULL);

  return winsys->context_egl_get_egl_display (context);
}
#endif

CoglBool
_cogl_context_update_features (CoglContext *context,
                               CoglError **error)
{
  return context->driver_vtable->update_features (context, error);
}

void
_cogl_context_set_current_projection_entry (CoglContext *context,
                                            CoglMatrixEntry *entry)
{
  _cogl_matrix_entry_ref (entry);
  if (context->current_projection_entry)
    _cogl_matrix_entry_unref (context->current_projection_entry);
  context->current_projection_entry = entry;
}

void
_cogl_context_set_current_modelview_entry (CoglContext *context,
                                           CoglMatrixEntry *entry)
{
  _cogl_matrix_entry_ref (entry);
  if (context->current_modelview_entry)
    _cogl_matrix_entry_unref (context->current_modelview_entry);
  context->current_modelview_entry = entry;
}

const char *
_cogl_context_get_gl_extensions (CoglContext *context)
{
  const char *env_disabled_extensions;

  if ((env_disabled_extensions = g_getenv ("COGL_DISABLE_GL_EXTENSIONS"))
      || _cogl_config_disable_gl_extensions)
    {
      static CoglUserDataKey extensions_key;
      const char *enabled_extensions;
      char **split_enabled_extensions;
      char **split_env_disabled_extensions;
      char **split_conf_disabled_extensions;
      char **e;
      GString *result;

      /* We need to return a const string so we'll attach the results
       * to the CoglContext to avoid leaking the generated string.
       * This string is only used rarely so we are using
       * cogl_object_set_user_data instead of adding an explicit
       * member to CoglContext to avoid making the struct bigger */

      enabled_extensions =
        cogl_object_get_user_data (COGL_OBJECT (context), &extensions_key);
      if (enabled_extensions)
        return enabled_extensions;

      enabled_extensions = (const char *) context->glGetString (GL_EXTENSIONS);

      split_enabled_extensions = g_strsplit (enabled_extensions,
                                             " ",
                                             0 /* no max tokens */);

      if (env_disabled_extensions)
        split_env_disabled_extensions =
          g_strsplit (env_disabled_extensions,
                      ",",
                      0 /* no max tokens */);
      else
        split_env_disabled_extensions = NULL;

      if (_cogl_config_disable_gl_extensions)
        split_conf_disabled_extensions =
          g_strsplit (_cogl_config_disable_gl_extensions,
                      ",",
                      0 /* no max tokens */);
      else
        split_conf_disabled_extensions = NULL;

      result = g_string_new (NULL);

      for (e = split_enabled_extensions; *e; e++)
        {
          char **d;

          if (split_env_disabled_extensions)
            for (d = split_env_disabled_extensions; *d; d++)
              if (!strcmp (*e, *d))
                goto disabled;
          if (split_conf_disabled_extensions)
            for (d = split_conf_disabled_extensions; *d; d++)
              if (!strcmp (*e, *d))
                goto disabled;

          if (result->len > 0)
            g_string_append_c (result, ' ');
          g_string_append (result, *e);

        disabled:
          continue;
        }

      enabled_extensions = g_string_free (result, FALSE);

      g_strfreev (split_enabled_extensions);
      if (split_env_disabled_extensions)
        g_strfreev (split_env_disabled_extensions);
      if (split_conf_disabled_extensions)
        g_strfreev (split_conf_disabled_extensions);

      cogl_object_set_user_data (COGL_OBJECT (context),
                                 &extensions_key,
                                 (void *) enabled_extensions,
                                 (CoglUserDataDestroyCallback) g_free);

      return enabled_extensions;
    }
  else
    return (const char *) context->glGetString (GL_EXTENSIONS);
}

const char *
_cogl_context_get_gl_version (CoglContext *context)
{
  const char *version_override;

  if ((version_override = g_getenv ("COGL_OVERRIDE_GL_VERSION")))
    return version_override;
  else if (_cogl_config_override_gl_version)
    return _cogl_config_override_gl_version;
  else
    return (const char *) context->glGetString (GL_VERSION);
}