mutter/cogl/cogl.c

/*
 * Cogl
 *
 * An object oriented GL/GLES Abstraction/Utility Layer
 *
 * Copyright (C) 2007,2008,2009,2010 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.h"

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

#include "cogl-debug.h"
#include "cogl-internal.h"
#include "cogl-util.h"
#include "cogl-context.h"
#include "cogl-material-private.h"
#include "cogl-winsys.h"
#include "cogl-framebuffer-private.h"
#include "cogl-matrix-private.h"
#include "cogl-journal-private.h"
#include "cogl-bitmap-private.h"
#include "cogl-texture-private.h"
#include "cogl-texture-driver.h"

#if defined (HAVE_COGL_GLES2) || defined (HAVE_COGL_GLES)
#include "cogl-gles2-wrapper.h"
#endif

#ifdef HAVE_COGL_GL
#define glClientActiveTexture ctx->drv.pf_glClientActiveTexture
#endif

#ifdef COGL_GL_DEBUG
/* GL error to string conversion */
static const struct {
  GLuint error_code;
  const char *error_string;
} gl_errors[] = {
  { GL_NO_ERROR,          "No error" },
  { GL_INVALID_ENUM,      "Invalid enumeration value" },
  { GL_INVALID_VALUE,     "Invalid value" },
  { GL_INVALID_OPERATION, "Invalid operation" },
  { GL_STACK_OVERFLOW,    "Stack overflow" },
  { GL_STACK_UNDERFLOW,   "Stack underflow" },
  { GL_OUT_OF_MEMORY,     "Out of memory" },

#ifdef GL_INVALID_FRAMEBUFFER_OPERATION_EXT
  { GL_INVALID_FRAMEBUFFER_OPERATION_EXT, "Invalid framebuffer operation" }
#endif
};

static const unsigned int n_gl_errors = G_N_ELEMENTS (gl_errors);

const char *
cogl_gl_error_to_string (GLenum error_code)
{
  int i;

  for (i = 0; i < n_gl_errors; i++)
    {
      if (gl_errors[i].error_code == error_code)
        return gl_errors[i].error_string;
    }

  return "Unknown GL error";
}
#endif /* COGL_GL_DEBUG */

CoglFuncPtr
cogl_get_proc_address (const char* name)
{
  void *address;
  static GModule *module = NULL;

  address = _cogl_winsys_get_proc_address (name);
  if (address)
    return address;

  /* this should find the right function if the program is linked against a
   * library providing it */
  if (G_UNLIKELY (module == NULL))
    module = g_module_open (NULL, 0);

  if (module)
    {
      gpointer symbol;

      if (g_module_symbol (module, name, &symbol))
        return symbol;
    }

  return NULL;
}

gboolean
_cogl_check_extension (const char *name, const gchar *ext)
{
  char *end;
  int name_len, n;

  if (name == NULL || ext == NULL)
    return FALSE;

  end = (char*)(ext + strlen(ext));

  name_len = strlen(name);

  while (ext < end)
    {
      n = strcspn(ext, " ");

      if ((name_len == n) && (!strncmp(name, ext, n)))
	return TRUE;
      ext += (n + 1);
    }

  return FALSE;
}

/* XXX: This has been deprecated as public API */
gboolean
cogl_check_extension (const char *name, const char *ext)
{
  return _cogl_check_extension (name, ext);
}

void
cogl_clear (const CoglColor *color, unsigned long buffers)
{
  GLbitfield gl_buffers = 0;

  COGL_NOTE (DRAW, "Clear begin");

  _cogl_journal_flush ();

  /* NB: _cogl_framebuffer_flush_state may disrupt various state (such
   * as the material state) when flushing the clip stack, so should
   * always be done first when preparing to draw. */
  _cogl_framebuffer_flush_state (_cogl_get_framebuffer (), 0);

  if (buffers & COGL_BUFFER_BIT_COLOR)
    {
      GE( glClearColor (cogl_color_get_red_float (color),
			cogl_color_get_green_float (color),
			cogl_color_get_blue_float (color),
			cogl_color_get_alpha_float (color)) );
      gl_buffers |= GL_COLOR_BUFFER_BIT;
    }

  if (buffers & COGL_BUFFER_BIT_DEPTH)
    gl_buffers |= GL_DEPTH_BUFFER_BIT;

  if (buffers & COGL_BUFFER_BIT_STENCIL)
    gl_buffers |= GL_STENCIL_BUFFER_BIT;

  if (!gl_buffers)
    {
      static gboolean shown = FALSE;

      if (!shown)
        {
	  g_warning ("You should specify at least one auxiliary buffer "
                     "when calling cogl_clear");
        }

      return;
    }

  GE (glClear (gl_buffers));

  /* This is a debugging variable used to visually display the quad
     batches from the journal. It is reset here to increase the
     chances of getting the same colours for each frame during an
     animation */
  if (G_UNLIKELY (cogl_debug_flags & COGL_DEBUG_RECTANGLES))
    {
      _COGL_GET_CONTEXT (ctxt, NO_RETVAL);
      ctxt->journal_rectangles_color = 1;
    }

  COGL_NOTE (DRAW, "Clear end");
}

static gboolean
toggle_flag (CoglContext *ctx,
	     unsigned long new_flags,
	     unsigned long flag,
	     GLenum gl_flag)
{
  /* Toggles and caches a single enable flag on or off
   * by comparing to current state
   */
  if (new_flags & flag)
    {
      if (!(ctx->enable_flags & flag))
	{
	  GE( glEnable (gl_flag) );
	  ctx->enable_flags |= flag;
	  return TRUE;
	}
    }
  else if (ctx->enable_flags & flag)
    {
      GE( glDisable (gl_flag) );
      ctx->enable_flags &= ~flag;
    }

  return FALSE;
}

static gboolean
toggle_client_flag (CoglContext *ctx,
		    unsigned long new_flags,
		    unsigned long flag,
		    GLenum gl_flag)
{
  /* Toggles and caches a single client-side enable flag
   * on or off by comparing to current state
   */
  if (new_flags & flag)
    {
      if (!(ctx->enable_flags & flag))
	{
	  GE( glEnableClientState (gl_flag) );
	  ctx->enable_flags |= flag;
	  return TRUE;
	}
    }
  else if (ctx->enable_flags & flag)
    {
      GE( glDisableClientState (gl_flag) );
      ctx->enable_flags &= ~flag;
    }

  return FALSE;
}

void
_cogl_enable (unsigned long flags)
{
  /* This function essentially caches glEnable state() in the
   * hope of lessening number GL traffic.
  */
  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  toggle_flag (ctx, flags,
               COGL_ENABLE_BLEND,
               GL_BLEND);

  toggle_flag (ctx, flags,
               COGL_ENABLE_BACKFACE_CULLING,
               GL_CULL_FACE);

  toggle_client_flag (ctx, flags,
		      COGL_ENABLE_VERTEX_ARRAY,
		      GL_VERTEX_ARRAY);

  toggle_client_flag (ctx, flags,
		      COGL_ENABLE_COLOR_ARRAY,
		      GL_COLOR_ARRAY);
}

unsigned long
_cogl_get_enable (void)
{
  _COGL_GET_CONTEXT (ctx, 0);

  return ctx->enable_flags;
}

void
cogl_set_depth_test_enabled (gboolean setting)
{
  /* Currently the journal can't track changes to depth state... */
  _cogl_journal_flush ();

  if (setting)
    {
      glEnable (GL_DEPTH_TEST);
      glDepthFunc (GL_LEQUAL);
    }
  else
    glDisable (GL_DEPTH_TEST);
}

gboolean
cogl_get_depth_test_enabled (void)
{
  return glIsEnabled (GL_DEPTH_TEST) == GL_TRUE ? TRUE : FALSE;
}

void
cogl_set_backface_culling_enabled (gboolean setting)
{
  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  if (ctx->enable_backface_culling == setting)
    return;

  /* Currently the journal can't track changes to backface culling state... */
  _cogl_journal_flush ();

  ctx->enable_backface_culling = setting;
}

gboolean
cogl_get_backface_culling_enabled (void)
{
  _COGL_GET_CONTEXT (ctx, FALSE);

  return ctx->enable_backface_culling;
}

void
_cogl_flush_face_winding (void)
{
  CoglFrontWinding winding;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  /* The front face winding doesn't matter if we aren't performing any
   * backface culling... */
  if (!ctx->enable_backface_culling)
    return;

  /* NB: We use a clockwise face winding order when drawing offscreen because
   * all offscreen rendering is done upside down resulting in reversed winding
   * for all triangles.
   */
  if (cogl_is_offscreen (_cogl_get_framebuffer ()))
    winding = COGL_FRONT_WINDING_CLOCKWISE;
  else
    winding = COGL_FRONT_WINDING_COUNTER_CLOCKWISE;

  if (winding != ctx->flushed_front_winding)
    {

      if (winding == COGL_FRONT_WINDING_CLOCKWISE)
        GE (glFrontFace (GL_CW));
      else
        GE (glFrontFace (GL_CCW));
      ctx->flushed_front_winding = winding;
    }
}

void
cogl_set_source_color (const CoglColor *color)
{
  CoglColor premultiplied;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  /* In case cogl_set_source_texture was previously used... */
  cogl_material_remove_layer (ctx->simple_material, 0);

  premultiplied = *color;
  cogl_color_premultiply (&premultiplied);
  cogl_material_set_color (ctx->simple_material, &premultiplied);

  cogl_set_source (ctx->simple_material);
}

void
cogl_set_viewport (int x,
                   int y,
                   int width,
                   int height)
{
  CoglHandle framebuffer;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  framebuffer = _cogl_get_framebuffer ();

  _cogl_framebuffer_set_viewport (framebuffer,
                                  x,
                                  y,
                                  width,
                                  height);
}

/* XXX: This should be deprecated, and we should expose a way to also
 * specify an x and y viewport offset */
void
cogl_viewport (unsigned int width,
	       unsigned int height)
{
  cogl_set_viewport (0, 0, width, height);
}

void
_cogl_setup_viewport (unsigned int width,
                      unsigned int height,
                      float fovy,
                      float aspect,
                      float z_near,
                      float z_far)
{
  float z_camera;
  CoglMatrix projection_matrix;
  CoglMatrixStack *modelview_stack;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  cogl_set_viewport (0, 0, width, height);

  /* For Ortho projection.
   * _cogl_matrix_stack_ortho (projection_stack, 0, width, 0,  height, -1, 1);
   */

  cogl_perspective (fovy, aspect, z_near, z_far);

  /*
   * In theory, we can compute the camera distance from screen as:
   *
   *   0.5 * tan (FOV)
   *
   * However, it's better to compute the z_camera from our projection
   * matrix so that we get a 1:1 mapping at the screen distance. Consider
   * the upper-left corner of the screen. It has object coordinates
   * (0,0,0), so by the transform below, ends up with eye coordinate
   *
   *   x_eye = x_object / width - 0.5 = - 0.5
   *   y_eye = (height - y_object) / width - 0.5 = 0.5
   *   z_eye = z_object / width - z_camera = - z_camera
   *
   * From cogl_perspective(), we know that the projection matrix has
   * the form:
   *
   *  (x, 0,  0, 0)
   *  (0, y,  0, 0)
   *  (0, 0,  c, d)
   *  (0, 0, -1, 0)
   *
   * Applied to the above, we get clip coordinates of
   *
   *  x_clip = x * (- 0.5)
   *  y_clip = y * 0.5
   *  w_clip = - 1 * (- z_camera) = z_camera
   *
   * Dividing through by w to get normalized device coordinates, we
   * have, x_nd = x * 0.5 / z_camera, y_nd = - y * 0.5 / z_camera.
   * The upper left corner of the screen has normalized device coordinates,
   * (-1, 1), so to have the correct 1:1 mapping, we have to have:
   *
   *   z_camera = 0.5 * x = 0.5 * y
   *
   * If x != y, then we have a non-uniform aspect ration, and a 1:1 mapping
   * doesn't make sense.
   */

  cogl_get_projection_matrix (&projection_matrix);
  z_camera = 0.5 * projection_matrix.xx;

  modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_load_identity (modelview_stack);
  _cogl_matrix_stack_translate (modelview_stack, -0.5f, -0.5f, -z_camera);
  _cogl_matrix_stack_scale (modelview_stack,
                            1.0f / width, -1.0f / height, 1.0f / width);
  _cogl_matrix_stack_translate (modelview_stack,
                                0.0f, -1.0 * height, 0.0f);
}

CoglFeatureFlags
cogl_get_features (void)
{
  _COGL_GET_CONTEXT (ctx, 0);

  if (G_UNLIKELY (cogl_debug_flags & COGL_DEBUG_DISABLE_VBOS))
    ctx->feature_flags &= ~COGL_FEATURE_VBOS;

  return ctx->feature_flags;
}

gboolean
cogl_features_available (CoglFeatureFlags features)
{
  _COGL_GET_CONTEXT (ctx, 0);

  if (!ctx->features_cached)
    _cogl_features_init ();

  return (ctx->feature_flags & features) == features;
}

/* XXX: This function should either be replaced with one returning
 * integers, or removed/deprecated and make the
 * _cogl_framebuffer_get_viewport* functions public.
 */
void
cogl_get_viewport (float v[4])
{
  CoglHandle framebuffer;
  int viewport[4];
  int i;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  framebuffer = _cogl_get_framebuffer ();
  _cogl_framebuffer_get_viewport4fv (framebuffer, viewport);

  for (i = 0; i < 4; i++)
    v[i] = viewport[i];
}

void
cogl_get_bitmasks (int *red,
                   int *green,
                   int *blue,
                   int *alpha)
{
  CoglHandle framebuffer;

  framebuffer = _cogl_get_framebuffer ();

  if (red)
    *red = cogl_framebuffer_get_red_bits (framebuffer);

  if (green)
    *green = cogl_framebuffer_get_green_bits (framebuffer);

  if (blue)
    *blue = cogl_framebuffer_get_blue_bits (framebuffer);

  if (alpha)
    *alpha = cogl_framebuffer_get_alpha_bits (framebuffer);
}

void
cogl_set_fog (const CoglColor *fog_color,
              CoglFogMode      mode,
              float            density,
              float            z_near,
              float            z_far)
{
  GLfloat fogColor[4];
  GLenum gl_mode = GL_LINEAR;

  /* The cogl journal doesn't currently track fog state changes */
  _cogl_journal_flush ();

  fogColor[0] = cogl_color_get_red_float (fog_color);
  fogColor[1] = cogl_color_get_green_float (fog_color);
  fogColor[2] = cogl_color_get_blue_float (fog_color);
  fogColor[3] = cogl_color_get_alpha_float (fog_color);

  glEnable (GL_FOG);

  glFogfv (GL_FOG_COLOR, fogColor);

#if HAVE_COGL_GLES
  switch (mode)
    {
    case COGL_FOG_MODE_LINEAR:
      gl_mode = GL_LINEAR;
      break;
    case COGL_FOG_MODE_EXPONENTIAL:
      gl_mode = GL_EXP;
      break;
    case COGL_FOG_MODE_EXPONENTIAL_SQUARED:
      gl_mode = GL_EXP2;
      break;
    }
#endif
  /* TODO: support other modes for GLES2 */

  /* NB: GLES doesn't have glFogi */
  glFogf (GL_FOG_MODE, gl_mode);
  glHint (GL_FOG_HINT, GL_NICEST);

  glFogf (GL_FOG_DENSITY, (GLfloat) density);
  glFogf (GL_FOG_START, (GLfloat) z_near);
  glFogf (GL_FOG_END, (GLfloat) z_far);
}

void
cogl_disable_fog (void)
{
  /* Currently the journal can't track changes to fog state... */
  _cogl_journal_flush ();

  glDisable (GL_FOG);
}

void
cogl_flush (void)
{
  _cogl_journal_flush ();
}

void
cogl_read_pixels (int x,
                  int y,
                  int width,
                  int height,
                  CoglReadPixelsFlags source,
                  CoglPixelFormat format,
                  guint8 *pixels)
{
  CoglHandle framebuffer;
  int        framebuffer_height;
  int        bpp;
  CoglBitmap bmp;
  GLenum     gl_intformat;
  GLenum     gl_format;
  GLenum     gl_type;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  g_return_if_fail (source == COGL_READ_PIXELS_COLOR_BUFFER);

  /* make sure any batched primitives get emitted to the GL driver before
   * issuing our read pixels... */
  cogl_flush ();

  framebuffer = _cogl_get_framebuffer ();

  _cogl_framebuffer_flush_state (framebuffer, 0);

  framebuffer_height = _cogl_framebuffer_get_height (framebuffer);

  /* The y co-ordinate should be given in OpenGL's coordinate system
   * so 0 is the bottom row
   *
   * NB: all offscreen rendering is done upside down so no conversion
   * is necissary in this case.
   */
  if (!cogl_is_offscreen (framebuffer))
    y = framebuffer_height - y - height;

  /* Initialise the CoglBitmap */
  bpp = _cogl_get_format_bpp (format);
  bmp.format = format;
  bmp.data = pixels;
  bmp.width = width;
  bmp.height = height;
  bmp.rowstride = bpp * width;

  if ((format & COGL_A_BIT))
    {
      /* FIXME: We are assuming glReadPixels will always give us
         premultiplied data so we'll set the premult flag on the
         bitmap format. This will usually be correct because the
         result of the default blending operations for Cogl ends up
         with premultiplied data in the framebuffer. However it is
         possible for the framebuffer to be in whatever format
         depending on what CoglMaterial is used to render to
         it. Eventually we may want to add a way for an application to
         inform Cogl that the framebuffer is not premultiplied in case
         it is being used for some special purpose. */
      bmp.format |= COGL_PREMULT_BIT;
    }

  _cogl_pixel_format_to_gl (format, &gl_intformat, &gl_format, &gl_type);

  /* Under GLES only GL_RGBA with GL_UNSIGNED_BYTE as well as an
     implementation specific format under
     GL_IMPLEMENTATION_COLOR_READ_FORMAT_OES and
     GL_IMPLEMENTATION_COLOR_READ_TYPE_OES is supported. We could try
     to be more clever and check if the requested type matches that
     but we would need some reliable functions to convert from GL
     types to Cogl types. For now, lets just always read in
     GL_RGBA/GL_UNSIGNED_BYTE and convert if necessary */
#ifndef COGL_HAS_GL
  if (gl_format != GL_RGBA || gl_type != GL_UNSIGNED_BYTE)
    {
      CoglBitmap tmp_bmp, dst_bmp;

      tmp_bmp.format = COGL_PIXEL_FORMAT_RGBA_8888_PRE;
      tmp_bmp.data = g_malloc (width * height * 4);
      tmp_bmp.width = width;
      tmp_bmp.height = height;
      tmp_bmp.rowstride = 4 * width;

      _cogl_texture_driver_prep_gl_for_pixels_download (tmp_bmp.rowstride, 4);

      GE( glReadPixels (x, y, width, height,
                        GL_RGBA, GL_UNSIGNED_BYTE,
                        tmp_bmp.data) );

      /* CoglBitmap doesn't currently have a way to convert without
         allocating its own buffer so we have to copy the data
         again */
      if (_cogl_bitmap_convert_format_and_premult (&tmp_bmp,
                                                   &dst_bmp,
                                                   bmp.format))
        {
          _cogl_bitmap_copy_subregion (&dst_bmp,
                                       &bmp,
                                       0, 0,
                                       0, 0,
                                       bmp.width, bmp.height);
          g_free (dst_bmp.data);
        }
      else
        {
          /* FIXME: there's no way to report an error here so we'll
             just have to leave the data initialised */
        }

      g_free (tmp_bmp.data);
    }
  else
#endif
    {
      _cogl_texture_driver_prep_gl_for_pixels_download (bmp.rowstride, bpp);

      GE( glReadPixels (x, y, width, height, gl_format, gl_type, pixels) );

      /* Convert to the premult format specified by the caller
         in-place. This will do nothing if the premult status is already
         correct. */
      _cogl_bitmap_convert_premult_status (&bmp, format);
    }

  /* NB: All offscreen rendering is done upside down so there is no need
   * to flip in this case... */
  if (!cogl_is_offscreen (framebuffer))
    {
      guint8 *temprow = g_alloca (bmp.rowstride * sizeof (guint8));

      /* TODO: consider using the GL_MESA_pack_invert extension in the future
       * to avoid this flip... */

      /* vertically flip the buffer in-place */
      for (y = 0; y < height / 2; y++)
        {
          if (y != height - y - 1) /* skip center row */
            {
              memcpy (temprow,
                      pixels + y * bmp.rowstride, bmp.rowstride);
              memcpy (pixels + y * bmp.rowstride,
                      pixels + (height - y - 1) * bmp.rowstride, bmp.rowstride);
              memcpy (pixels + (height - y - 1) * bmp.rowstride,
                      temprow,
                      bmp.rowstride);
            }
        }
    }
}

void
_cogl_disable_texcoord_arrays (unsigned int mask)
{
  int i = 0;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  /* Update the mask of arrays that are enabled */
  ctx->texcoord_arrays_enabled &= ~mask;

  /* Disable all of the texture coord arrays that have a 1 in the bit
     position in mask */
  while (mask)
    {
      if ((mask & 1))
        {
          GE (glClientActiveTexture (GL_TEXTURE0 + i));
          GE (glDisableClientState (GL_TEXTURE_COORD_ARRAY));
        }

      i++;
      mask >>= 1;
    }
}

void
cogl_begin_gl (void)
{
  CoglMaterialFlushOptions options;
  unsigned long enable_flags = 0;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  if (ctx->in_begin_gl_block)
    {
      static gboolean shown = FALSE;
      if (!shown)
        g_warning ("You should not nest cogl_begin_gl/cogl_end_gl blocks");
      shown = TRUE;
      return;
    }
  ctx->in_begin_gl_block = TRUE;

  /* Flush all batched primitives */
  cogl_flush ();

  /* Flush framebuffer state, including clip state, modelview and
   * projection matrix state
   *
   * NB: _cogl_framebuffer_flush_state may disrupt various state (such
   * as the material state) when flushing the clip stack, so should
   * always be done first when preparing to draw. */
  _cogl_framebuffer_flush_state (_cogl_get_framebuffer (), 0);

  /* Setup the state for the current material */

  /* We considered flushing a specific, minimal material here to try and
   * simplify the GL state, but decided to avoid special cases and second
   * guessing what would be actually helpful.
   *
   * A user should instead call cogl_set_source_color4ub() before
   * cogl_begin_gl() to simplify the state flushed.
   */
  options.flags = 0;
  _cogl_material_flush_gl_state (ctx->source_material, &options);

  /* FIXME: This api is a bit yukky, ideally it will be removed if we
   * re-work the _cogl_enable mechanism */
  enable_flags |= _cogl_material_get_cogl_enable_flags (ctx->source_material);

  if (ctx->enable_backface_culling)
    enable_flags |= COGL_ENABLE_BACKFACE_CULLING;

  _cogl_enable (enable_flags);
  _cogl_flush_face_winding ();

  /* Disable all client texture coordinate arrays */
  _cogl_disable_texcoord_arrays (ctx->texcoord_arrays_enabled);
}

void
cogl_end_gl (void)
{
  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  if (!ctx->in_begin_gl_block)
    {
      static gboolean shown = FALSE;
      if (!shown)
        g_warning ("cogl_end_gl is being called before cogl_begin_gl");
      shown = TRUE;
      return;
    }
  ctx->in_begin_gl_block = FALSE;
}

static CoglTextureUnit *
_cogl_texture_unit_new (int index_)
{
  CoglTextureUnit *unit = g_new0 (CoglTextureUnit, 1);
  unit->matrix_stack = _cogl_matrix_stack_new ();
  unit->index = index_;
  return unit;
}

static void
_cogl_texture_unit_free (CoglTextureUnit *unit)
{
  _cogl_matrix_stack_destroy (unit->matrix_stack);
  g_free (unit);
}

CoglTextureUnit *
_cogl_get_texture_unit (int index_)
{
  GList *l;
  CoglTextureUnit *unit;

  _COGL_GET_CONTEXT (ctx, NULL);

  for (l = ctx->texture_units; l; l = l->next)
    {
      unit = l->data;

      if (unit->index == index_)
        return unit;

      /* The units are always sorted, so at this point we know this unit
       * doesn't exist */
      if (unit->index > index_)
        break;
    }
  /* NB: if we now insert a new layer before l, that will maintain order.
   */

  unit = _cogl_texture_unit_new (index_);

  /* Note: see comment after for() loop above */
  ctx->texture_units =
    g_list_insert_before (ctx->texture_units, l, unit);

  return unit;
}

void
_cogl_destroy_texture_units (void)
{
  GList *l;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  for (l = ctx->texture_units; l; l = l->next)
    _cogl_texture_unit_free (l->data);
  g_list_free (ctx->texture_units);
}

/*
 * This is more complicated than that, another pass needs to be done when
 * cogl have a neat way of saying if we are using the fixed function pipeline
 * or not (for the GL case):
 * MAX_TEXTURE_UNITS: fixed function pipeline, a texture unit has both a
 *                    sampler and a set of texture coordinates
 * MAX_TEXTURE_IMAGE_UNITS: number of samplers one can use from a fragment
 *                          program/shader (ARBfp1.0 asm/GLSL)
 * MAX_VERTEX_TEXTURE_UNITS: number of samplers one can use from a vertex
 *                           program/shader (can be 0)
 * MAX_COMBINED_TEXTURE_IMAGE_UNITS: Maximum samplers one can use, counting both
 *                                   the vertex and fragment shaders
 *
 * If both the vertex shader and the fragment processing stage access the same
 * texture image unit, then that counts as using two texture image units
 * against the latter limit: http://www.opengl.org/sdk/docs/man/xhtml/glGet.xml
 *
 * Note that, for now, we use GL_MAX_TEXTURE_UNITS as we are exposing the
 * fixed function pipeline.
 */
unsigned int
_cogl_get_max_texture_image_units (void)
{
  _COGL_GET_CONTEXT (ctx, 0);

  /* This function is called quite often so we cache the value to
     avoid too many GL calls */
  if (ctx->max_texture_units == -1)
    {
      ctx->max_texture_units = 1;
      GE( glGetIntegerv (GL_MAX_TEXTURE_UNITS, &ctx->max_texture_units) );
    }

  return ctx->max_texture_units;
}

void
cogl_push_matrix (void)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_push (modelview_stack);
}

void
cogl_pop_matrix (void)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_pop (modelview_stack);
}

void
cogl_scale (float x, float y, float z)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_scale (modelview_stack, x, y, z);
}

void
cogl_translate (float x, float y, float z)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_translate (modelview_stack, x, y, z);
}

void
cogl_rotate (float angle, float x, float y, float z)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_rotate (modelview_stack, angle, x, y, z);
}

void
cogl_transform (const CoglMatrix *matrix)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_multiply (modelview_stack, matrix);
}

void
cogl_perspective (float fov_y,
		  float aspect,
		  float z_near,
		  float z_far)
{
  float ymax = z_near * tanf (fov_y * G_PI / 360.0);

  cogl_frustum (-ymax * aspect,  /* left */
                ymax * aspect,   /* right */
                -ymax,           /* bottom */
                ymax,            /* top */
                z_near,
                z_far);
}

void
cogl_frustum (float        left,
	      float        right,
	      float        bottom,
	      float        top,
	      float        z_near,
	      float        z_far)
{
  CoglMatrixStack *projection_stack =
    _cogl_framebuffer_get_projection_stack (_cogl_get_framebuffer ());

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  _cogl_matrix_stack_load_identity (projection_stack);

  _cogl_matrix_stack_frustum (projection_stack,
                              left,
                              right,
                              bottom,
                              top,
                              z_near,
                              z_far);
}

void
cogl_ortho (float left,
	    float right,
	    float bottom,
	    float top,
	    float z_near,
	    float z_far)
{
  CoglMatrix ortho;
  CoglMatrixStack *projection_stack =
    _cogl_framebuffer_get_projection_stack (_cogl_get_framebuffer ());

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  cogl_matrix_init_identity (&ortho);
  cogl_matrix_ortho (&ortho, left, right, bottom, top, z_near, z_far);
  _cogl_matrix_stack_set (projection_stack, &ortho);
}

void
cogl_get_modelview_matrix (CoglMatrix *matrix)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_get (modelview_stack, matrix);
  _COGL_MATRIX_DEBUG_PRINT (matrix);
}

void
cogl_set_modelview_matrix (CoglMatrix *matrix)
{
  CoglMatrixStack *modelview_stack =
    _cogl_framebuffer_get_modelview_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_set (modelview_stack, matrix);
  _COGL_MATRIX_DEBUG_PRINT (matrix);
}

void
cogl_get_projection_matrix (CoglMatrix *matrix)
{
  CoglMatrixStack *projection_stack =
    _cogl_framebuffer_get_projection_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_get (projection_stack, matrix);
  _COGL_MATRIX_DEBUG_PRINT (matrix);
}

void
cogl_set_projection_matrix (CoglMatrix *matrix)
{
  CoglMatrixStack *projection_stack =
    _cogl_framebuffer_get_projection_stack (_cogl_get_framebuffer ());
  _cogl_matrix_stack_set (projection_stack, matrix);

  /* FIXME: Update the inverse projection matrix!! Presumably use
   * of clip planes must currently be broken if this API is used. */
  _COGL_MATRIX_DEBUG_PRINT (matrix);
}

CoglClipState *
_cogl_get_clip_state (void)
{
  CoglHandle framebuffer;

  framebuffer = _cogl_get_framebuffer ();
  return _cogl_framebuffer_get_clip_state (framebuffer);
}

GQuark
_cogl_driver_error_quark (void)
{
  return g_quark_from_static_string ("cogl-driver-error-quark");
}

void
cogl_set_source (CoglHandle material_handle)
{
  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  g_return_if_fail (cogl_is_material (material_handle));

  if (ctx->source_material == material_handle)
    return;

  cogl_handle_ref (material_handle);

  if (ctx->source_material)
    cogl_handle_unref (ctx->source_material);

  ctx->source_material = material_handle;
}

void
cogl_set_source_texture (CoglHandle texture_handle)
{
  CoglColor white;

  _COGL_GET_CONTEXT (ctx, NO_RETVAL);

  g_return_if_fail (texture_handle != COGL_INVALID_HANDLE);

  cogl_material_set_layer (ctx->simple_material, 0, texture_handle);
  cogl_color_set_from_4ub (&white, 0xff, 0xff, 0xff, 0xff);
  cogl_material_set_color (ctx->simple_material, &white);
  cogl_set_source (ctx->simple_material);
}

void
cogl_set_source_color4ub (guint8 red,
                          guint8 green,
                          guint8 blue,
                          guint8 alpha)
{
  CoglColor c = { 0, };

  cogl_color_set_from_4ub (&c, red, green, blue, alpha);
  cogl_set_source_color (&c);
}

void
cogl_set_source_color4f (float red,
                         float green,
                         float blue,
                         float alpha)
{
  CoglColor c = { 0, };

  cogl_color_set_from_4f (&c, red, green, blue, alpha);
  cogl_set_source_color (&c);
}