mutter/cogl/cogl/cogl-context.c

/*
 * Cogl
 *
 * A Low Level GPU Graphics and Utilities API
 *
 * Copyright (C) 2007,2008,2009,2013 Intel Corporation.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 *
 */

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

#include "cogl-object.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-util-gl-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 "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 "cogl-gtype-private.h"

#include "cogl/deprecated/cogl-framebuffer-deprecated.h"

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

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

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

#ifndef GL_NUM_EXTENSIONS
#define GL_NUM_EXTENSIONS 0x821D
#endif

/* This is a relatively new extension */
#ifndef GL_PURGED_CONTEXT_RESET_NV
#define GL_PURGED_CONTEXT_RESET_NV 0x92BB
#endif

/* These aren't defined in the GLES2 headers */
#ifndef GL_GUILTY_CONTEXT_RESET_ARB
#define GL_GUILTY_CONTEXT_RESET_ARB 0x8253
#endif

#ifndef GL_INNOCENT_CONTEXT_RESET_ARB
#define GL_INNOCENT_CONTEXT_RESET_ARB 0x8254
#endif

#ifndef GL_UNKNOWN_CONTEXT_RESET_ARB
#define GL_UNKNOWN_CONTEXT_RESET_ARB 0x8255
#endif

static void _cogl_context_free (CoglContext *context);

COGL_OBJECT_DEFINE (Context, context);
COGL_GTYPE_DEFINE_CLASS (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)))
    COGL_FLAGS_SET (ctx->private_features, COGL_PRIVATE_FEATURE_VBOS, FALSE);

  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_PBOS)))
    COGL_FLAGS_SET (ctx->private_features, COGL_PRIVATE_FEATURE_PBOS, FALSE);

  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);
      COGL_FLAGS_SET (ctx->features,
                      COGL_FEATURE_ID_PER_VERTEX_POINT_SIZE,
                      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;
  uint8_t white_pixel[] = { 0xff, 0xff, 0xff, 0xff };
  CoglBitmap *white_pixel_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;
  memset (context->private_features, 0, sizeof (context->private_features));

  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);
      cogl_object_unref(renderer);
    }
  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;

  for (i = 0; i < G_N_ELEMENTS (context->private_features); i++)
    context->private_features[i] |= display->renderer->private_features[i];

  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);

  /* XXX: ONGOING BUG: Intel viewport scissor
   *
   * Intel gen6 drivers don't currently correctly handle offset
   * viewports, since primitives aren't clipped within the bounds of
   * the viewport.  To workaround this we push our own clip for the
   * viewport that will use scissoring to ensure we clip as expected.
   *
   * TODO: file a bug upstream!
   */
  if (context->gpu.driver_package == COGL_GPU_INFO_DRIVER_PACKAGE_MESA &&
      context->gpu.architecture == COGL_GPU_INFO_ARCHITECTURE_SANDYBRIDGE &&
      !getenv ("COGL_DISABLE_INTEL_VIEWPORT_SCISSORT_WORKAROUND"))
    context->needs_viewport_scissor_workaround = TRUE;
  else
    context->needs_viewport_scissor_workaround = FALSE;

  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));

  if (_cogl_has_private_feature (context, COGL_PRIVATE_FEATURE_ANY_GL))
    {
      /* 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->codegen_boilerplate_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;

  context->swap_callback_closures =
    g_hash_table_new (g_direct_hash, g_direct_equal);

  _cogl_list_init (&context->onscreen_events_queue);
  _cogl_list_init (&context->onscreen_dirty_queue);

  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_with_color_attrib = 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 = NULL;
  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 (_cogl_has_private_feature (context, COGL_PRIVATE_FEATURE_ALPHA_TEST))
    /* 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

#if defined (HAVE_COGL_GL)
  if ((context->driver == COGL_DRIVER_GL3))
    {
      GLuint vertex_array;

      /* In a forward compatible context, GL 3 doesn't support rendering
       * using the default vertex array object. Cogl doesn't use vertex
       * array objects yet so for now we just create a dummy array
       * object that we will use as our own default object. Eventually
       * it could be good to attach the vertex array objects to
       * CoglPrimitives */
      context->glGenVertexArrays (1, &vertex_array);
      context->glBindVertexArray (vertex_array);
    }
#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);

  /* Create default textures used for fall backs */
  context->default_gl_texture_2d_tex =
    cogl_texture_2d_new_from_data (context,
                                   1, 1,
                                   COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                                   0, /* rowstride */
                                   white_pixel,
                                   NULL); /* abort on error */

  /* 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_data (context,
                                   1, 1, 1, /* width, height, depth */
                                   COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                                   0, /* rowstride */
                                   0, /* image stride */
                                   white_pixel,
                                   &internal_error);
  if (internal_error)
    cogl_error_free (internal_error);

  /* TODO: add cogl_texture_rectangle_new_from_data() */
  white_pixel_bitmap =
    cogl_bitmap_new_for_data (context,
                              1, 1, /* width/height */
                              COGL_PIXEL_FORMAT_RGBA_8888_PRE,
                              4, /* rowstride */
                              white_pixel);

  internal_error = NULL;
  context->default_gl_texture_rect_tex =
    cogl_texture_rectangle_new_from_bitmap (white_pixel_bitmap);

  /* XXX: we need to allocate the texture now because the white_pixel
   * data is on the stack */
  cogl_texture_allocate (COGL_TEXTURE (context->default_gl_texture_rect_tex),
                         &internal_error);
  if (internal_error)
    cogl_error_free (internal_error);

  cogl_object_unref (white_pixel_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 GL3 or GLES2 because point
     sprites are handled using a builtin varying in the shader. */
  if (_cogl_has_private_feature (context, COGL_PRIVATE_FEATURE_GL_FIXED) &&
      cogl_has_feature (context, COGL_FEATURE_ID_POINT_SPRITE))
    GE (context, glEnable (GL_POINT_SPRITE));

  _cogl_list_init (&context->fences);

  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);

  if (context->swap_callback_closures)
    g_hash_table_destroy (context->swap_callback_closures);

  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);

  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;
}

CoglRenderer *
cogl_context_get_renderer (CoglContext *context)
{
  return context->display->renderer;
}

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;
}

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

  /* In GL 3, querying GL_EXTENSIONS is deprecated so we have to build
   * the array using glGetStringi instead */
#ifdef HAVE_COGL_GL
  if (context->driver == COGL_DRIVER_GL3)
    {
      int num_extensions, i;

      context->glGetIntegerv (GL_NUM_EXTENSIONS, &num_extensions);

      ret = g_malloc (sizeof (char *) * (num_extensions + 1));

      for (i = 0; i < num_extensions; i++)
        {
          const char *ext =
            (const char *) context->glGetStringi (GL_EXTENSIONS, i);
          ret[i] = g_strdup (ext);
        }

      ret[num_extensions] = NULL;
    }
  else
#endif
    {
      const char *all_extensions =
        (const char *) context->glGetString (GL_EXTENSIONS);

      ret = g_strsplit (all_extensions, " ", 0 /* max tokens */);
    }

  if ((env_disabled_extensions = g_getenv ("COGL_DISABLE_GL_EXTENSIONS"))
      || _cogl_config_disable_gl_extensions)
    {
      char **split_env_disabled_extensions;
      char **split_conf_disabled_extensions;
      char **src, **dst;

      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;

      for (dst = ret, src = ret;
           *src;
           src++)
        {
          char **d;

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

          *(dst++) = *src;
          continue;

        disabled:
          g_free (*src);
          continue;
        }

      *dst = NULL;

      if (split_env_disabled_extensions)
        g_strfreev (split_env_disabled_extensions);
      if (split_conf_disabled_extensions)
        g_strfreev (split_conf_disabled_extensions);
    }

  return ret;
}

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);

}

int64_t
cogl_get_clock_time (CoglContext *context)
{
  const CoglWinsysVtable *winsys = _cogl_context_get_winsys (context);

  if (winsys->context_get_clock_time)
    return winsys->context_get_clock_time (context);
  else
    return 0;
}

CoglGraphicsResetStatus
cogl_get_graphics_reset_status (CoglContext *context)
{
  if (!context->glGetGraphicsResetStatus)
    return COGL_GRAPHICS_RESET_STATUS_NO_ERROR;

  switch (context->glGetGraphicsResetStatus ())
    {
    case GL_GUILTY_CONTEXT_RESET_ARB:
      return COGL_GRAPHICS_RESET_STATUS_GUILTY_CONTEXT_RESET;

    case GL_INNOCENT_CONTEXT_RESET_ARB:
      return COGL_GRAPHICS_RESET_STATUS_INNOCENT_CONTEXT_RESET;

    case GL_UNKNOWN_CONTEXT_RESET_ARB:
      return COGL_GRAPHICS_RESET_STATUS_UNKNOWN_CONTEXT_RESET;

    case GL_PURGED_CONTEXT_RESET_NV:
      return COGL_GRAPHICS_RESET_STATUS_PURGED_CONTEXT_RESET;

    default:
      return COGL_GRAPHICS_RESET_STATUS_NO_ERROR;
    }
}