mutter/cogl/cogl-texture.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/>.
 *
 *
 *
 * Authors:
 *  Matthew Allum  <mallum@openedhand.com>
 *  Neil Roberts   <neil@linux.intel.com>
 *  Robert Bragg   <robert@linux.intel.com>
 */

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

#include "cogl.h"
#include "cogl-internal.h"
#include "cogl-util.h"
#include "cogl-bitmap.h"
#include "cogl-bitmap-private.h"
#include "cogl-buffer-private.h"
#include "cogl-pixel-buffer-private.h"
#include "cogl-texture-private.h"
#include "cogl-texture-driver.h"
#include "cogl-texture-2d-sliced-private.h"
#include "cogl-texture-2d-private.h"
#include "cogl-sub-texture-private.h"
#include "cogl-atlas-texture-private.h"
#include "cogl-material.h"
#include "cogl-context.h"
#include "cogl-handle.h"
#include "cogl-primitives.h"
#include "cogl-framebuffer-private.h"

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

/* XXX:
 * The CoglHandle macros don't support any form of inheritance, so for
 * now we implement the CoglHandle support for the CoglTexture
 * abstract class manually.
 */

gboolean
cogl_is_texture (CoglHandle handle)
{
  CoglHandleObject *obj = (CoglHandleObject *)handle;

  if (handle == COGL_INVALID_HANDLE)
    return FALSE;

  return (obj->klass->type == _cogl_handle_texture_2d_get_type () ||
          obj->klass->type == _cogl_handle_atlas_texture_get_type () ||
          obj->klass->type == _cogl_handle_texture_2d_sliced_get_type () ||
          obj->klass->type == _cogl_handle_sub_texture_get_type ());
}

CoglHandle
cogl_texture_ref (CoglHandle handle)
{
  if (!cogl_is_texture (handle))
    return COGL_INVALID_HANDLE;

  _COGL_HANDLE_DEBUG_REF (CoglTexture, handle);

  cogl_handle_ref (handle);

  return handle;
}

void
cogl_texture_unref (CoglHandle handle)
{
  if (!cogl_is_texture (handle))
    {
      g_warning (G_STRINGIFY (cogl_texture_unref)
                 ": Ignoring unref of Cogl handle "
                 "due to type mismatch");
      return;
    }

  _COGL_HANDLE_DEBUG_UNREF (CoglTexture, handle);

  cogl_handle_unref (handle);
}

void
_cogl_texture_free (CoglTexture *texture)
{
  g_free (texture);
}

static gboolean
_cogl_texture_needs_premult_conversion (CoglPixelFormat src_format,
                                        CoglPixelFormat dst_format)
{
  return ((src_format & COGL_A_BIT) &&
          src_format != COGL_PIXEL_FORMAT_A_8 &&
          (src_format & COGL_PREMULT_BIT) !=
          (dst_format & COGL_PREMULT_BIT));
}

CoglPixelFormat
_cogl_texture_determine_internal_format (CoglPixelFormat src_format,
                                         CoglPixelFormat dst_format)
{
  /* If the application hasn't specified a specific format then we'll
   * pick the most appropriate. By default Cogl will use a
   * premultiplied internal format. Later we will add control over
   * this. */
  if (dst_format == COGL_PIXEL_FORMAT_ANY)
    {
      if ((src_format & COGL_A_BIT) &&
          src_format != COGL_PIXEL_FORMAT_A_8)
        return src_format | COGL_PREMULT_BIT;
      else
        return src_format;
    }
  else
    return dst_format;
}

gboolean
_cogl_texture_prepare_for_upload (CoglBitmap      *src_bmp,
                                  CoglPixelFormat  dst_format,
                                  CoglPixelFormat *dst_format_out,
                                  CoglBitmap      *dst_bmp,
                                  gboolean        *copied_bitmap,
                                  GLenum          *out_glintformat,
                                  GLenum          *out_glformat,
                                  GLenum          *out_gltype)
{
  dst_format = _cogl_texture_determine_internal_format (src_bmp->format,
                                                        dst_format);

  *copied_bitmap = FALSE;
  *dst_bmp = *src_bmp;

  /* OpenGL supports specifying a different format for the internal
     format when uploading texture data. We should use this to convert
     formats because it is likely to be faster and support more types
     than the Cogl bitmap code. However under GLES the internal format
     must be the same as the bitmap format and it only supports a
     limited number of formats so we must convert using the Cogl
     bitmap code instead */

#ifdef HAVE_COGL_GL

  /* If the source format does not have the same premult flag as the
     dst format then we need to copy and convert it */
  if (_cogl_texture_needs_premult_conversion (src_bmp->format,
                                              dst_format))
    {
      dst_bmp->data = g_memdup (dst_bmp->data,
                                dst_bmp->height * dst_bmp->rowstride);
      *copied_bitmap = TRUE;

      if (!_cogl_bitmap_convert_premult_status (dst_bmp,
                                                src_bmp->format ^
                                                COGL_PREMULT_BIT))
        {
          g_free (dst_bmp->data);
          return FALSE;
        }
    }

  /* Use the source format from the src bitmap type and the internal
     format from the dst format type so that GL can do the
     conversion */
  _cogl_pixel_format_to_gl (src_bmp->format,
                            NULL, /* internal format */
                            out_glformat,
                            out_gltype);
  _cogl_pixel_format_to_gl (dst_format,
                            out_glintformat,
                            NULL,
                            NULL);

#else /* HAVE_COGL_GL */
  {
    CoglPixelFormat closest_format;

    closest_format = _cogl_pixel_format_to_gl (dst_bmp->format,
                                               out_glintformat,
                                               out_glformat,
                                               out_gltype);


    if (closest_format != src_bmp->format)
      {
        if (!_cogl_bitmap_convert_format_and_premult (src_bmp,
                                                      dst_bmp,
                                                      closest_format))
          return FALSE;

        *copied_bitmap = TRUE;
      }
  }
#endif /* HAVE_COGL_GL */

  if (dst_format_out)
    *dst_format_out = dst_format;

  return TRUE;
}

void
_cogl_texture_prep_gl_alignment_for_pixels_upload (int pixels_rowstride)
{
  if (!(pixels_rowstride & 0x7))
    GE( glPixelStorei (GL_UNPACK_ALIGNMENT, 8) );
  else if (!(pixels_rowstride & 0x3))
    GE( glPixelStorei (GL_UNPACK_ALIGNMENT, 4) );
  else if (!(pixels_rowstride & 0x1))
    GE( glPixelStorei (GL_UNPACK_ALIGNMENT, 2) );
  else
    GE( glPixelStorei (GL_UNPACK_ALIGNMENT, 1) );
}

void
_cogl_texture_prep_gl_alignment_for_pixels_download (int pixels_rowstride)
{
  if (!(pixels_rowstride & 0x7))
    GE( glPixelStorei (GL_PACK_ALIGNMENT, 8) );
  else if (!(pixels_rowstride & 0x3))
    GE( glPixelStorei (GL_PACK_ALIGNMENT, 4) );
  else if (!(pixels_rowstride & 0x1))
    GE( glPixelStorei (GL_PACK_ALIGNMENT, 2) );
  else
    GE( glPixelStorei (GL_PACK_ALIGNMENT, 1) );
}

/* FIXME: wrap modes should be set on materials not textures */
void
_cogl_texture_set_wrap_mode_parameters (CoglHandle handle,
                                        GLenum wrap_mode_s,
                                        GLenum wrap_mode_t,
                                        GLenum wrap_mode_r)
{
  CoglTexture *tex = COGL_TEXTURE (handle);

  tex->vtable->set_wrap_mode_parameters (tex,
                                         wrap_mode_s,
                                         wrap_mode_t,
                                         wrap_mode_r);
}

/* This is like CoglSpanIter except it deals with floats and it
   effectively assumes there is only one span from 0.0 to 1.0 */
typedef struct _CoglTextureIter
{
  float pos, end, next_pos;
  gboolean flipped;
  float t_1, t_2;
} CoglTextureIter;

static void
_cogl_texture_iter_update (CoglTextureIter *iter)
{
  float t_2;
  float frac_part;

  frac_part = modff (iter->pos, &iter->next_pos);

  /* modff rounds the int part towards zero so we need to add one if
     we're meant to be heading away from zero */
  if (iter->pos >= 0.0f || frac_part == 0.0f)
    iter->next_pos += 1.0f;

  if (iter->next_pos > iter->end)
    t_2 = iter->end;
  else
    t_2 = iter->next_pos;

  if (iter->flipped)
    {
      iter->t_1 = t_2;
      iter->t_2 = iter->pos;
    }
  else
    {
      iter->t_1 = iter->pos;
      iter->t_2 = t_2;
    }
}

static void
_cogl_texture_iter_begin (CoglTextureIter *iter,
                          float t_1, float t_2)
{
  if (t_1 <= t_2)
    {
      iter->pos = t_1;
      iter->end = t_2;
      iter->flipped = FALSE;
    }
  else
    {
      iter->pos = t_2;
      iter->end = t_1;
      iter->flipped = TRUE;
    }

  _cogl_texture_iter_update (iter);
}

static void
_cogl_texture_iter_next (CoglTextureIter *iter)
{
  iter->pos = iter->next_pos;
  _cogl_texture_iter_update (iter);
}

static gboolean
_cogl_texture_iter_end (CoglTextureIter *iter)
{
  return iter->pos >= iter->end;
}

/* This invokes the callback with enough quads to cover the manually
   repeated range specified by the virtual texture coordinates without
   emitting coordinates outside the range [0,1] */
void
_cogl_texture_iterate_manual_repeats (CoglTextureManualRepeatCallback callback,
                                      float tx_1, float ty_1,
                                      float tx_2, float ty_2,
                                      void *user_data)
{
  CoglTextureIter x_iter, y_iter;

  for (_cogl_texture_iter_begin (&y_iter, ty_1, ty_2);
       !_cogl_texture_iter_end (&y_iter);
       _cogl_texture_iter_next (&y_iter))
    for (_cogl_texture_iter_begin (&x_iter, tx_1, tx_2);
         !_cogl_texture_iter_end (&x_iter);
         _cogl_texture_iter_next (&x_iter))
      {
        float coords[4] = { x_iter.t_1, y_iter.t_1, x_iter.t_2, y_iter.t_2 };
        callback (coords, user_data);
      }
}

CoglHandle
cogl_texture_new_with_size (unsigned int     width,
			    unsigned int     height,
                            CoglTextureFlags flags,
			    CoglPixelFormat  internal_format)
{
  CoglHandle tex;

  /* First try creating a fast-path non-sliced texture */
  tex = _cogl_texture_2d_new_with_size (width, height, flags, internal_format);

  /* If it fails resort to sliced textures */
  if (tex == COGL_INVALID_HANDLE)
    tex = _cogl_texture_2d_sliced_new_with_size (width,
                                                 height,
                                                 flags,
                                                 internal_format);

  return tex;
}

CoglHandle
cogl_texture_new_from_data (unsigned int      width,
			    unsigned int      height,
                            CoglTextureFlags  flags,
			    CoglPixelFormat   format,
			    CoglPixelFormat   internal_format,
			    unsigned int      rowstride,
			    const guint8     *data)
{
  CoglBitmap bitmap;

  if (format == COGL_PIXEL_FORMAT_ANY)
    return COGL_INVALID_HANDLE;

  if (data == NULL)
    return COGL_INVALID_HANDLE;

  /* Rowstride from width if not given */
  if (rowstride == 0)
    rowstride = width * _cogl_get_format_bpp (format);

  /* Wrap the data into a bitmap */
  bitmap.width = width;
  bitmap.height = height;
  bitmap.data = (guint8 *) data;
  bitmap.format = format;
  bitmap.rowstride = rowstride;

  return cogl_texture_new_from_bitmap (&bitmap, flags, internal_format);
}

CoglHandle
cogl_texture_new_from_bitmap (CoglHandle       bmp_handle,
                              CoglTextureFlags flags,
                              CoglPixelFormat  internal_format)
{
  CoglHandle tex;

  /* First try putting the texture in the atlas */
  if ((tex = _cogl_atlas_texture_new_from_bitmap (bmp_handle,
                                                  flags,
                                                  internal_format)))
    return tex;

  /* If that doesn't work try a fast path 2D texture */
  if ((tex = _cogl_texture_2d_new_from_bitmap (bmp_handle,
                                               flags,
                                               internal_format)))
    return tex;

  /* Otherwise create a sliced texture */
  return _cogl_texture_2d_sliced_new_from_bitmap (bmp_handle,
                                                  flags,
                                                  internal_format);
}

CoglHandle
cogl_texture_new_from_file (const char        *filename,
                            CoglTextureFlags   flags,
                            CoglPixelFormat    internal_format,
                            GError           **error)
{
  CoglHandle bmp_handle;
  CoglBitmap *bmp;
  CoglHandle handle = COGL_INVALID_HANDLE;

  g_return_val_if_fail (error == NULL || *error == NULL, COGL_INVALID_HANDLE);

  bmp_handle = cogl_bitmap_new_from_file (filename, error);
  if (bmp_handle == COGL_INVALID_HANDLE)
    return COGL_INVALID_HANDLE;

  bmp = (CoglBitmap *) bmp_handle;

  /* We know that the bitmap data is solely owned by this function so
     we can do the premult conversion in place. This avoids having to
     copy the bitmap which will otherwise happen in
     _cogl_texture_prepare_for_upload */
  internal_format = _cogl_texture_determine_internal_format (bmp->format,
                                                             internal_format);
  if (!_cogl_texture_needs_premult_conversion (bmp->format, internal_format) ||
      _cogl_bitmap_convert_premult_status (bmp, bmp->format ^ COGL_PREMULT_BIT))
    handle = cogl_texture_new_from_bitmap (bmp, flags, internal_format);

  cogl_handle_unref (bmp);

  return handle;
}

CoglHandle
cogl_texture_new_from_foreign (GLuint           gl_handle,
			       GLenum           gl_target,
			       GLuint           width,
			       GLuint           height,
			       GLuint           x_pot_waste,
			       GLuint           y_pot_waste,
			       CoglPixelFormat  format)
{
  /* FIXME: only create a sliced texture if x or y waste was specified
   */
  return _cogl_texture_2d_sliced_new_from_foreign (gl_handle,
                                                   gl_target,
                                                   width,
                                                   height,
                                                   x_pot_waste,
                                                   y_pot_waste,
                                                   format);
}

gboolean
_cogl_texture_is_foreign (CoglHandle handle)
{
  CoglTexture *tex;

  g_return_val_if_fail (cogl_is_texture (handle), FALSE);

  tex = COGL_TEXTURE (handle);

  if (tex->vtable->is_foreign)
    return tex->vtable->is_foreign (tex);
  else
    return FALSE;
}

CoglHandle
cogl_texture_new_from_sub_texture (CoglHandle full_texture,
                                   int        sub_x,
                                   int        sub_y,
                                   int        sub_width,
                                   int        sub_height)
{
  return _cogl_sub_texture_new (full_texture, sub_x, sub_y,
                                sub_width, sub_height);
}

CoglHandle
cogl_texture_new_from_buffer_EXP (CoglHandle          buffer,
                                  unsigned int        width,
                                  unsigned int        height,
                                  CoglTextureFlags    flags,
                                  CoglPixelFormat     format,
                                  CoglPixelFormat     internal_format,
                                  unsigned int        rowstride,
                                  const unsigned int  offset)
{
  CoglHandle texture;
  CoglBuffer *cogl_buffer;
  CoglPixelBuffer *pixel_buffer;

  g_return_val_if_fail (cogl_is_buffer (buffer), COGL_INVALID_HANDLE);

  if (format == COGL_PIXEL_FORMAT_ANY)
    return COGL_INVALID_HANDLE;

  cogl_buffer = COGL_BUFFER (buffer);
  pixel_buffer = COGL_PIXEL_BUFFER (buffer);

  /* Rowstride from CoglBuffer or even width * bpp if not given */
  if (rowstride == 0)
    rowstride = pixel_buffer->stride;
  if (rowstride == 0)
    rowstride = width * _cogl_get_format_bpp (format);

  /* use the CoglBuffer height and width as last resort */
  if (width == 0)
    width = pixel_buffer->width;
  if (height == 0)
    height = pixel_buffer->height;
  if (width == 0 || height == 0)
    {
      /* no width or height specified, neither at creation time (because the
       * buffer was created by cogl_pixel_buffer_new()) nor when calling this
       * function */
      return COGL_INVALID_HANDLE;
    }

#if !defined (COGL_HAS_GLES)
  if (cogl_features_available (COGL_FEATURE_PBOS))
    {
      CoglBitmap bitmap;

      /* Wrap the data into a bitmap */
      bitmap.width = width;
      bitmap.height = height;
      bitmap.data = GUINT_TO_POINTER (offset);
      bitmap.format = format;
      bitmap.rowstride = rowstride;

      _cogl_buffer_bind (cogl_buffer, GL_PIXEL_UNPACK_BUFFER);
      texture =  cogl_texture_new_from_bitmap (&bitmap, flags, internal_format);
      _cogl_buffer_bind (NULL, GL_PIXEL_UNPACK_BUFFER);
    }
  else
#endif
    {
      texture = cogl_texture_new_from_data (width,
			                    height,
                                            flags,
                                            format,
                                            internal_format,
                                            rowstride,
                                            cogl_buffer->data);
    }

  return texture;
}

unsigned int
cogl_texture_get_width (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return 0;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->get_width (tex);
}

unsigned int
cogl_texture_get_height (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return 0;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->get_height (tex);
}

CoglPixelFormat
cogl_texture_get_format (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return COGL_PIXEL_FORMAT_ANY;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->get_format (tex);
}

unsigned int
cogl_texture_get_rowstride (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return 0;

  /* FIXME: This function should go away. It previously just returned
     the rowstride that was used to upload the data as far as I can
     tell. This is not helpful */

  tex = COGL_TEXTURE (handle);

  /* Just guess at a suitable rowstride */
  return (_cogl_get_format_bpp (cogl_texture_get_format (tex))
          * cogl_texture_get_width (tex));
}

int
cogl_texture_get_max_waste (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return 0;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->get_max_waste (tex);
}

gboolean
cogl_texture_is_sliced (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return FALSE;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->is_sliced (tex);
}

/* Some CoglTextures, notably sliced textures or atlas textures when repeating
 * is used, will need to divide the coordinate space into multiple GL textures
 * (or rather; in the case of atlases duplicate a single texture in multiple
 * positions to handle repeating)
 *
 * This function helps you implement primitives using such textures by
 * invoking a callback once for each sub texture that intersects a given
 * region specified in texture coordinates.
 */
void
_cogl_texture_foreach_sub_texture_in_region (CoglHandle handle,
                                             float virtual_tx_1,
                                             float virtual_ty_1,
                                             float virtual_tx_2,
                                             float virtual_ty_2,
                                             CoglTextureSliceCallback callback,
                                             void *user_data)
{
  CoglTexture *tex = COGL_TEXTURE (handle);

  tex->vtable->foreach_sub_texture_in_region (tex,
                                              virtual_tx_1,
                                              virtual_ty_1,
                                              virtual_tx_2,
                                              virtual_ty_2,
                                              callback,
                                              user_data);
}

/* If this returns FALSE, that implies _foreach_sub_texture_in_region
 * will be needed to iterate over multiple sub textures for regions whos
 * texture coordinates extend out of the range [0,1]
 */
gboolean
_cogl_texture_can_hardware_repeat (CoglHandle handle)
{
  CoglTexture *tex = (CoglTexture *)handle;

  return tex->vtable->can_hardware_repeat (tex);
}

/* NB: You can't use this with textures comprised of multiple sub textures (use
 * cogl_texture_is_sliced() to check) since coordinate transformation for such
 * textures will be different for each slice. */
void
_cogl_texture_transform_coords_to_gl (CoglHandle handle,
                                      float *s,
                                      float *t)
{
  CoglTexture *tex = COGL_TEXTURE (handle);

  tex->vtable->transform_coords_to_gl (tex, s, t);
}

CoglTransformResult
_cogl_texture_transform_quad_coords_to_gl (CoglHandle handle,
                                           float *coords)
{
  CoglTexture *tex = COGL_TEXTURE (handle);

  return tex->vtable->transform_quad_coords_to_gl (tex, coords);
}

GLenum
_cogl_texture_get_gl_format (CoglHandle handle)
{
  CoglTexture *tex = COGL_TEXTURE (handle);

  return tex->vtable->get_gl_format (tex);
}

gboolean
cogl_texture_get_gl_texture (CoglHandle handle,
			     GLuint *out_gl_handle,
			     GLenum *out_gl_target)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return FALSE;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->get_gl_texture (tex, out_gl_handle, out_gl_target);
}

void
_cogl_texture_set_filters (CoglHandle handle,
                           GLenum min_filter,
                           GLenum mag_filter)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return;

  tex = COGL_TEXTURE (handle);

  tex->vtable->set_filters (tex, min_filter, mag_filter);
}

void
_cogl_texture_ensure_mipmaps (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return;

  tex = COGL_TEXTURE (handle);

  tex->vtable->ensure_mipmaps (tex);
}

void
_cogl_texture_ensure_non_quad_rendering (CoglHandle handle)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return;

  tex = COGL_TEXTURE (handle);

  tex->vtable->ensure_non_quad_rendering (tex);
}

gboolean
cogl_texture_set_region (CoglHandle       handle,
			 int              src_x,
			 int              src_y,
			 int              dst_x,
			 int              dst_y,
			 unsigned int     dst_width,
			 unsigned int     dst_height,
			 int              width,
			 int              height,
			 CoglPixelFormat  format,
			 unsigned int     rowstride,
			 const guint8    *data)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return FALSE;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->set_region (tex,
                                  src_x, src_y,
                                  dst_x, dst_y,
                                  dst_width, dst_height,
                                  width, height,
                                  format,
                                  rowstride,
                                  data);
}

/* Reads back the contents of a texture by rendering it to the framebuffer
 * and reading back the resulting pixels.
 *
 * It will perform multiple renders if the texture is larger than the
 * current glViewport.
 *
 * It assumes the projection and modelview have already been setup so
 * that rendering to 0,0 with the same width and height of the viewport
 * will exactly cover the viewport.
 *
 * NB: Normally this approach isn't normally used since we can just use
 * glGetTexImage, but may be used as a fallback in some circumstances.
 */
static void
do_texture_draw_and_read (CoglHandle   handle,
                          CoglBitmap  *target_bmp,
                          GLint       *viewport)
{
  int         bpp;
  float       rx1, ry1;
  float       rx2, ry2;
  float       tx1, ty1;
  float       tx2, ty2;
  int         bw,  bh;
  CoglBitmap  rect_bmp;
  unsigned int  tex_width, tex_height;

  bpp = _cogl_get_format_bpp (COGL_PIXEL_FORMAT_RGBA_8888);

  tex_width = cogl_texture_get_width (handle);
  tex_height = cogl_texture_get_height (handle);

  ry2 = 0;
  ty2 = 0;

  /* Walk Y axis until whole bitmap height consumed */
  for (bh = tex_height; bh > 0; bh -= viewport[3])
    {
      /* Rectangle Y coords */
      ry1 = ry2;
      ry2 += (bh < viewport[3]) ? bh : viewport[3];

      /* Normalized texture Y coords */
      ty1 = ty2;
      ty2 = (ry2 / (float) tex_height);

      rx2 = 0;
      tx2 = 0;

      /* Walk X axis until whole bitmap width consumed */
      for (bw = tex_width; bw > 0; bw-=viewport[2])
        {
          /* Rectangle X coords */
          rx1 = rx2;
          rx2 += (bw < viewport[2]) ? bw : viewport[2];

          /* Normalized texture X coords */
          tx1 = tx2;
          tx2 = (rx2 / (float) tex_width);

          /* Draw a portion of texture */
          cogl_rectangle_with_texture_coords (0, 0,
                                              rx2 - rx1,
                                              ry2 - ry1,
                                              tx1, ty1,
                                              tx2, ty2);

          /* Read into a temporary bitmap */
          rect_bmp.format = COGL_PIXEL_FORMAT_RGBA_8888;
          rect_bmp.width = rx2 - rx1;
          rect_bmp.height = ry2 - ry1;
          rect_bmp.rowstride = bpp * rect_bmp.width;
          rect_bmp.data = g_malloc (rect_bmp.rowstride *
                                    rect_bmp.height);

          _cogl_texture_driver_prep_gl_for_pixels_download (rect_bmp.rowstride,
                                                            bpp);
          GE( glReadPixels (viewport[0], viewport[1],
                            rect_bmp.width,
                            rect_bmp.height,
                            GL_RGBA, GL_UNSIGNED_BYTE,
                            rect_bmp.data) );

          /* Copy to target bitmap */
          _cogl_bitmap_copy_subregion (&rect_bmp,
                                       target_bmp,
                                       0,0,
                                       rx1,ry1,
                                       rect_bmp.width,
                                       rect_bmp.height);

          /* Free temp bitmap */
          g_free (rect_bmp.data);
        }
    }
}

/* Reads back the contents of a texture by rendering it to the framebuffer
 * and reading back the resulting pixels.
 *
 * NB: Normally this approach isn't normally used since we can just use
 * glGetTexImage, but may be used as a fallback in some circumstances.
 */
gboolean
_cogl_texture_draw_and_read (CoglHandle   handle,
                             CoglBitmap  *target_bmp,
                             GLuint       target_gl_format,
                             GLuint       target_gl_type)
{
  int        bpp;
  CoglHandle framebuffer;
  int        viewport[4];
  CoglBitmap alpha_bmp;
  CoglHandle prev_source;
  CoglMatrixStack *projection_stack;
  CoglMatrixStack *modelview_stack;

  _COGL_GET_CONTEXT (ctx, FALSE);

  bpp = _cogl_get_format_bpp (COGL_PIXEL_FORMAT_RGBA_8888);

  framebuffer = _cogl_get_framebuffer ();
  /* Viewport needs to have some size and be inside the window for this */
  _cogl_framebuffer_get_viewport4fv (framebuffer, viewport);
  if (viewport[0] <  0 || viewport[1] <  0 ||
      viewport[2] <= 0 || viewport[3] <= 0)
    return FALSE;

  /* Setup orthographic projection into current viewport (0,0 in bottom-left
   * corner to draw the texture upside-down so we match the way glReadPixels
   * works)
   */

  projection_stack = _cogl_framebuffer_get_projection_stack (framebuffer);
  _cogl_matrix_stack_push (projection_stack);
  _cogl_matrix_stack_load_identity (projection_stack);
  _cogl_matrix_stack_ortho (projection_stack,
                            0, (float)(viewport[2]),
                            0, (float)(viewport[3]),
                            (float)(0),
                            (float)(100));

  modelview_stack = _cogl_framebuffer_get_modelview_stack (framebuffer);
  _cogl_matrix_stack_push (modelview_stack);
  _cogl_matrix_stack_load_identity (modelview_stack);

  /* Direct copy operation */

  if (ctx->texture_download_material == COGL_INVALID_HANDLE)
    {
      ctx->texture_download_material = cogl_material_new ();
      cogl_material_set_blend (ctx->texture_download_material,
                               "RGBA = ADD (SRC_COLOR, 0)",
                               NULL);
    }

  prev_source = cogl_handle_ref (ctx->source_material);
  cogl_set_source (ctx->texture_download_material);

  cogl_material_set_layer (ctx->texture_download_material, 0, handle);

  cogl_material_set_layer_combine (ctx->texture_download_material,
                                   0, /* layer */
                                   "RGBA = REPLACE (TEXTURE)",
                                   NULL);

  do_texture_draw_and_read (handle, target_bmp, viewport);

  /* Check whether texture has alpha and framebuffer not */
  /* FIXME: For some reason even if ALPHA_BITS is 8, the framebuffer
     still doesn't seem to have an alpha buffer. This might be just
     a PowerVR issue.
  GLint r_bits, g_bits, b_bits, a_bits;
  GE( glGetIntegerv (GL_ALPHA_BITS, &a_bits) );
  GE( glGetIntegerv (GL_RED_BITS, &r_bits) );
  GE( glGetIntegerv (GL_GREEN_BITS, &g_bits) );
  GE( glGetIntegerv (GL_BLUE_BITS, &b_bits) );
  printf ("R bits: %d\n", r_bits);
  printf ("G bits: %d\n", g_bits);
  printf ("B bits: %d\n", b_bits);
  printf ("A bits: %d\n", a_bits); */
  if ((cogl_texture_get_format (handle) & COGL_A_BIT)/* && a_bits == 0*/)
    {
      guint8 *srcdata;
      guint8 *dstdata;
      guint8 *srcpixel;
      guint8 *dstpixel;
      int     x,y;

      /* Create temp bitmap for alpha values */
      alpha_bmp.format = COGL_PIXEL_FORMAT_RGBA_8888;
      alpha_bmp.width = target_bmp->width;
      alpha_bmp.height = target_bmp->height;
      alpha_bmp.rowstride = bpp * alpha_bmp.width;
      alpha_bmp.data = g_malloc (alpha_bmp.rowstride *
                                 alpha_bmp.height);

      /* Draw alpha values into RGB channels */
      cogl_material_set_layer_combine (ctx->texture_download_material,
                                       0, /* layer */
                                       "RGBA = REPLACE (TEXTURE[A])",
                                       NULL);

      do_texture_draw_and_read (handle, &alpha_bmp, viewport);

      /* Copy temp R to target A */
      srcdata = alpha_bmp.data;
      dstdata = target_bmp->data;

      for (y=0; y<target_bmp->height; ++y)
        {
          for (x=0; x<target_bmp->width; ++x)
            {
              srcpixel = srcdata + x*bpp;
              dstpixel = dstdata + x*bpp;
              dstpixel[3] = srcpixel[0];
            }
          srcdata += alpha_bmp.rowstride;
          dstdata += target_bmp->rowstride;
        }

      g_free (alpha_bmp.data);
    }

  /* Restore old state */
  _cogl_matrix_stack_pop (modelview_stack);
  _cogl_matrix_stack_pop (projection_stack);

  /* restore the original material */
  cogl_set_source (prev_source);
  cogl_handle_unref (prev_source);

  return TRUE;
}

int
cogl_texture_get_data (CoglHandle       handle,
		       CoglPixelFormat  format,
		       unsigned int     rowstride,
		       guint8          *data)
{
  CoglTexture *tex;

  if (!cogl_is_texture (handle))
    return FALSE;

  tex = COGL_TEXTURE (handle);

  return tex->vtable->get_data (handle, format, rowstride, data);
}