brl/mutter
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Add a public cogl_framebuffer_read_pixels_into_bitmap

Browse Source 
This adds a public function to read pixels from a framebuffer into a
CoglBitmap. This replaces the internal function
_cogl_read_pixels_with_rowstride because a CoglBitmap contains a
rowstride so it can be used for the same purpose. A CoglBitmap already
has public API to make one that points to a CoglPixelBuffer so this
function can be used to read pixels into a PBO. It also avoids the
need to push the framebuffer on to the context's stack so it provides
a function which can be used in the 2.0 API after the stack is
removed.

Reviewed-by: Robert Bragg <robert@linux.intel.com>
This commit is contained in:
Neil Roberts 2012-02-25 19:23:51 +00:00
parent 2501899044
commit 10a38bb14f
9 changed files with 328 additions and 226 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
cogl/cogl-framebuffer-private.h
View File

@ -244,14 +244,6 @@ _cogl_framebuffer_flush_journal (CoglFramebuffer *framebuffer);
void
_cogl_framebuffer_flush_dependency_journals (CoglFramebuffer *framebuffer);
gboolean
_cogl_framebuffer_try_fast_read_pixel (CoglFramebuffer *framebuffer,
int x,
int y,
CoglReadPixelsFlags source,
CoglPixelFormat format,
guint8 *pixel);
void
_cogl_framebuffer_flush_state (CoglFramebuffer *draw_buffer,
CoglFramebuffer *read_buffer,

258
cogl/cogl-framebuffer.c
View File

@ -25,6 +25,8 @@
#include "config.h"
#endif
#include <string.h>
#include "cogl-debug.h"
#include "cogl-internal.h"
#include "cogl-context-private.h"
@ -43,6 +45,7 @@
#include "cogl-primitive-private.h"
#include "cogl-offscreen.h"
#include "cogl1-context.h"
#include "cogl-private.h"
#ifndef GL_FRAMEBUFFER
#define GL_FRAMEBUFFER 0x8D40
@ -1860,15 +1863,15 @@ cogl_framebuffer_get_context (CoglFramebuffer *framebuffer)
return framebuffer->context;
}
gboolean
static gboolean
_cogl_framebuffer_try_fast_read_pixel (CoglFramebuffer *framebuffer,
int x,
int y,
CoglReadPixelsFlags source,
CoglPixelFormat format,
guint8 *pixel)
CoglBitmap *bitmap)
{
gboolean found_intersection;
CoglPixelFormat format;
if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_FAST_READ_PIXEL)))
return FALSE;
@ -1876,12 +1879,14 @@ _cogl_framebuffer_try_fast_read_pixel (CoglFramebuffer *framebuffer,
if (source != COGL_READ_PIXELS_COLOR_BUFFER)
return FALSE;
format = _cogl_bitmap_get_format (bitmap);
if (format != COGL_PIXEL_FORMAT_RGBA_8888_PRE &&
format != COGL_PIXEL_FORMAT_RGBA_8888)
return FALSE;
if (!_cogl_journal_try_read_pixel (framebuffer->journal,
x, y, format, pixel,
x, y, bitmap,
&found_intersection))
return FALSE;
@ -1906,23 +1911,268 @@ _cogl_framebuffer_try_fast_read_pixel (CoglFramebuffer *framebuffer,
y >= framebuffer->clear_clip_y0 &&
y < framebuffer->clear_clip_y1)
{
guint8 *pixel;
/* we currently only care about cases where the premultiplied or
* unpremultipled colors are equivalent... */
if (framebuffer->clear_color_alpha != 1.0)
return FALSE;
pixel = _cogl_bitmap_map (bitmap,
COGL_BUFFER_ACCESS_WRITE,
COGL_BUFFER_MAP_HINT_DISCARD);
if (pixel == NULL)
return FALSE;
pixel[0] = framebuffer->clear_color_red * 255.0;
pixel[1] = framebuffer->clear_color_green * 255.0;
pixel[2] = framebuffer->clear_color_blue * 255.0;
pixel[3] = framebuffer->clear_color_alpha * 255.0;
_cogl_bitmap_unmap (bitmap);
return TRUE;
}
return FALSE;
}
gboolean
cogl_framebuffer_read_pixels_into_bitmap (CoglFramebuffer *framebuffer,
int x,
int y,
CoglReadPixelsFlags source,
CoglBitmap *bitmap)
{
CoglContext *ctx;
int framebuffer_height;
CoglPixelFormat format;
CoglPixelFormat required_format;
GLenum gl_intformat;
GLenum gl_format;
GLenum gl_type;
gboolean pack_invert_set;
int width;
int height;
_COGL_RETURN_VAL_IF_FAIL (source == COGL_READ_PIXELS_COLOR_BUFFER, FALSE);
_COGL_RETURN_VAL_IF_FAIL (_cogl_is_framebuffer (framebuffer), FALSE);
ctx = cogl_framebuffer_get_context (framebuffer);
width = _cogl_bitmap_get_width (bitmap);
height = _cogl_bitmap_get_height (bitmap);
if (width == 1 && height == 1 && !framebuffer->clear_clip_dirty)
{
/* If everything drawn so far for this frame is still in the
* Journal then if all of the rectangles only have a flat
* opaque color we have a fast-path for reading a single pixel
* that avoids the relatively high cost of flushing primitives
* to be drawn on the GPU (considering how simple the geometry
* is in this case) and then blocking on the long GPU pipelines
* for the result.
*/
if (_cogl_framebuffer_try_fast_read_pixel (framebuffer,
x, y, source, bitmap))
return TRUE;
}
/* make sure any batched primitives get emitted to the GL driver
* before issuing our read pixels...
*/
_cogl_framebuffer_flush_journal (framebuffer);
_cogl_framebuffer_flush_state (framebuffer,
framebuffer,
COGL_FRAMEBUFFER_STATE_BIND);
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;
format = _cogl_bitmap_get_format (bitmap);
required_format = ctx->texture_driver->pixel_format_to_gl (format,
&gl_intformat,
&gl_format,
&gl_type);
/* NB: All offscreen rendering is done upside down so there is no need
* to flip in this case... */
if ((ctx->private_feature_flags & COGL_PRIVATE_FEATURE_MESA_PACK_INVERT) &&
!cogl_is_offscreen (framebuffer))
{
GE (ctx, glPixelStorei (GL_PACK_INVERT_MESA, TRUE));
pack_invert_set = TRUE;
}
else
pack_invert_set = FALSE;
/* 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. We also need
to use this intermediate buffer if the rowstride has padding
because GLES does not support setting GL_ROW_LENGTH */
if ((ctx->driver != COGL_DRIVER_GL &&
(gl_format != GL_RGBA || gl_type != GL_UNSIGNED_BYTE ||
_cogl_bitmap_get_rowstride (bitmap) != 4 * width)) ||
(required_format & ~COGL_PREMULT_BIT) != (format & ~COGL_PREMULT_BIT))
{
CoglBitmap *tmp_bmp;
guint8 *tmp_data;
CoglPixelFormat read_format;
int bpp, rowstride;
int succeeded;
if (ctx->driver == COGL_DRIVER_GL)
read_format = required_format;
else
{
read_format = COGL_PIXEL_FORMAT_RGBA_8888;
gl_format = GL_RGBA;
gl_type = GL_UNSIGNED_BYTE;
}
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (read_format))
read_format = ((read_format & ~COGL_PREMULT_BIT) |
(framebuffer->format & COGL_PREMULT_BIT));
bpp = _cogl_pixel_format_get_bytes_per_pixel (read_format);
rowstride = (width * bpp + 3) & ~3;
tmp_data = g_malloc (rowstride * height);
tmp_bmp = _cogl_bitmap_new_from_data (tmp_data,
read_format,
width, height, rowstride,
(CoglBitmapDestroyNotify) g_free,
NULL);
ctx->texture_driver->prep_gl_for_pixels_download (rowstride, bpp);
GE( ctx, glReadPixels (x, y, width, height,
gl_format, gl_type,
tmp_data) );
succeeded = _cogl_bitmap_convert_into_bitmap (tmp_bmp, bitmap);
cogl_object_unref (tmp_bmp);
if (!succeeded)
return FALSE;
}
else
{
CoglBitmap *shared_bmp;
CoglPixelFormat bmp_format;
int bpp, rowstride;
gboolean succeeded = FALSE;
guint8 *pixels;
rowstride = _cogl_bitmap_get_rowstride (bitmap);
/* We match the premultiplied state of the target buffer to the
* premultiplied state of the framebuffer so that it will get
* converted to the right format below */
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (format))
bmp_format = ((format & ~COGL_PREMULT_BIT) |
(framebuffer->format & COGL_PREMULT_BIT));
else
bmp_format = format;
if (bmp_format != format)
shared_bmp = _cogl_bitmap_new_shared (bitmap,
bmp_format,
width, height,
rowstride);
else
shared_bmp = cogl_object_ref (bitmap);
bpp = _cogl_pixel_format_get_bytes_per_pixel (bmp_format);
ctx->texture_driver->prep_gl_for_pixels_download (rowstride, bpp);
pixels = _cogl_bitmap_bind (shared_bmp,
COGL_BUFFER_ACCESS_WRITE,
0 /* hints */);
GE( ctx, glReadPixels (x, y,
width, height,
gl_format, gl_type,
pixels) );
_cogl_bitmap_unbind (shared_bmp);
/* Convert to the premult format specified by the caller
in-place. This will do nothing if the premult status is already
correct. */
if (_cogl_bitmap_convert_premult_status (shared_bmp, format))
succeeded = TRUE;
cogl_object_unref (shared_bmp);
if (!succeeded)
return FALSE;
}
/* Currently this function owns the pack_invert state and we don't want this
* to interfere with other Cogl components so all other code can assume that
* we leave the pack_invert state off. */
if (pack_invert_set)
GE (ctx, glPixelStorei (GL_PACK_INVERT_MESA, FALSE));
/* NB: All offscreen rendering is done upside down so there is no need
* to flip in this case... */
if (!cogl_is_offscreen (framebuffer) && !pack_invert_set)
{
guint8 *temprow;
int rowstride;
guint8 *pixels;
rowstride = _cogl_bitmap_get_rowstride (bitmap);
pixels = _cogl_bitmap_map (bitmap,
COGL_BUFFER_ACCESS_READ |
COGL_BUFFER_ACCESS_WRITE,
0 /* hints */);
if (pixels == NULL)
return FALSE;
temprow = g_alloca (rowstride * sizeof (guint8));
/* 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 * rowstride, rowstride);
memcpy (pixels + y * rowstride,
pixels + (height - y - 1) * rowstride, rowstride);
memcpy (pixels + (height - y - 1) * rowstride,
temprow,
rowstride);
}
}
_cogl_bitmap_unmap (bitmap);
}
return TRUE;
}
void
_cogl_blit_framebuffer (unsigned int src_x,
unsigned int src_y,

34
cogl/cogl-framebuffer.h
View File

@ -46,6 +46,7 @@
#include <cogl/cogl-pipeline.h>
#include <cogl/cogl-indices.h>
#include <cogl/cogl-bitmap.h>
G_BEGIN_DECLS
@ -1245,6 +1246,39 @@ cogl_framebuffer_discard_buffers (CoglFramebuffer *framebuffer,
void
cogl_framebuffer_finish (CoglFramebuffer *framebuffer);
/**
* cogl_framebuffer_read_pixels_into_bitmap:
* @framebuffer: A #CoglFramebuffer
* @x: The x position to read from
* @y: The y position to read from
* @source: Identifies which auxillary buffer you want to read
* (only COGL_READ_PIXELS_COLOR_BUFFER supported currently)
* @bitmap: The bitmap to store the results in.
*
* This reads a rectangle of pixels from the given framebuffer where
* position (0, 0) is the top left. The pixel at (x, y) is the first
* read, and a rectangle of pixels with the same size as the bitmap is
* read right and downwards from that point.
*
* Currently Cogl assumes that the framebuffer is in a premultiplied
* format so if the format of @bitmap is non-premultiplied it will
* convert it. To read the pixel values without any conversion you
* should either specify a format that doesn't use an alpha channel or
* use one of the formats ending in PRE.
*
* Return value: %TRUE if the read succeeded or %FALSE otherwise. The
* function is only likely to fail if the bitmap points to a pixel
* buffer and it could not be mapped.
* Since: 1.10
* Stability: unstable
*/
gboolean
cogl_framebuffer_read_pixels_into_bitmap (CoglFramebuffer *framebuffer,
int x,
int y,
CoglReadPixelsFlags source,
CoglBitmap *bitmap);
/**
* cogl_get_draw_framebuffer:
*

3
cogl/cogl-journal-private.h
View File

@ -105,8 +105,7 @@ gboolean
_cogl_journal_try_read_pixel (CoglJournal *journal,
int x,
int y,
CoglPixelFormat format,
guint8 *pixel,
CoglBitmap *bitmap,
gboolean *found_intersection);
#endif /* __COGL_JOURNAL_PRIVATE_H */

15
cogl/cogl-journal.c
View File

@ -1791,10 +1791,10 @@ gboolean
_cogl_journal_try_read_pixel (CoglJournal *journal,
int x,
int y,
CoglPixelFormat format,
guint8 *pixel,
CoglBitmap *bitmap,
gboolean *found_intersection)
{
CoglPixelFormat format;
int i;
_COGL_GET_CONTEXT (ctx, FALSE);
@ -1810,6 +1810,8 @@ _cogl_journal_try_read_pixel (CoglJournal *journal,
if (journal->fast_read_pixel_count > 50)
return FALSE;
format = _cogl_bitmap_get_format (bitmap);
if (format != COGL_PIXEL_FORMAT_RGBA_8888_PRE &&
format != COGL_PIXEL_FORMAT_RGBA_8888)
return FALSE;
@ -1832,6 +1834,7 @@ _cogl_journal_try_read_pixel (CoglJournal *journal,
float *vertices = (float *)color + 1;
float poly[16];
CoglFramebuffer *framebuffer = journal->framebuffer;
guint8 *pixel;
entry_to_screen_polygon (framebuffer, entry, vertices, poly);
@ -1870,11 +1873,19 @@ _cogl_journal_try_read_pixel (CoglJournal *journal,
if (color[3] != 0xff)
return FALSE;
pixel = _cogl_bitmap_map (bitmap,
COGL_BUFFER_ACCESS_WRITE,
COGL_BUFFER_MAP_HINT_DISCARD);
if (pixel == NULL)
return FALSE;
pixel[0] = color[0];
pixel[1] = color[1];
pixel[2] = color[2];
pixel[3] = color[3];
_cogl_bitmap_unmap (bitmap);
goto success;
}

10
cogl/cogl-private.h
View File

@ -44,16 +44,6 @@ _cogl_check_extension (const char *name, const char *ext);
void
_cogl_clear (const CoglColor *color, unsigned long buffers);
void
_cogl_read_pixels_with_rowstride (int x,
int y,
int width,
int height,
CoglReadPixelsFlags source,
CoglPixelFormat format,
guint8 *pixels,
int rowstride);
void
_cogl_init (void);

23
cogl/cogl-texture.c
View File

@ -1015,6 +1015,7 @@ get_texture_bits_via_offscreen (CoglTexture *texture,
{
CoglOffscreen *offscreen;
CoglFramebuffer *framebuffer;
CoglBitmap *bitmap;
_COGL_GET_CONTEXT (ctx, FALSE);
@ -1031,19 +1032,17 @@ get_texture_bits_via_offscreen (CoglTexture *texture,
framebuffer = COGL_FRAMEBUFFER (offscreen);
if (!cogl_framebuffer_allocate (framebuffer, NULL))
{
cogl_object_unref (framebuffer);
return FALSE;
}
cogl_push_framebuffer (framebuffer);
_cogl_read_pixels_with_rowstride (x, y, width, height,
bitmap = _cogl_bitmap_new_from_data (dst_bits,
dst_format,
width, height,
dst_rowstride,
NULL, /* destroy_fn */
NULL /* destroy_fn_data */);
cogl_framebuffer_read_pixels_into_bitmap (framebuffer,
x, y,
COGL_READ_PIXELS_COLOR_BUFFER,
dst_format, dst_bits, dst_rowstride);
cogl_pop_framebuffer ();
bitmap);
cogl_object_unref (bitmap);
cogl_object_unref (framebuffer);

200
cogl/cogl.c
View File

@ -368,189 +368,6 @@ cogl_flush (void)
_cogl_framebuffer_flush_journal (l->data);
}
void
_cogl_read_pixels_with_rowstride (int x,
int y,
int width,
int height,
CoglReadPixelsFlags source,
CoglPixelFormat format,
guint8 *pixels,
int rowstride)
{
CoglFramebuffer *framebuffer = _cogl_get_read_framebuffer ();
int framebuffer_height;
int bpp;
CoglBitmap *bmp;
GLenum gl_intformat;
GLenum gl_format;
GLenum gl_type;
CoglPixelFormat bmp_format;
gboolean pack_invert_set;
_COGL_GET_CONTEXT (ctx, NO_RETVAL);
_COGL_RETURN_IF_FAIL (source == COGL_READ_PIXELS_COLOR_BUFFER);
if (width == 1 && height == 1 && !framebuffer->clear_clip_dirty)
{
/* If everything drawn so far for this frame is still in the
* Journal then if all of the rectangles only have a flat
* opaque color we have a fast-path for reading a single pixel
* that avoids the relatively high cost of flushing primitives
* to be drawn on the GPU (considering how simple the geometry
* is in this case) and then blocking on the long GPU pipelines
* for the result.
*/
if (_cogl_framebuffer_try_fast_read_pixel (framebuffer,
x, y, source, format,
pixels))
return;
}
/* make sure any batched primitives get emitted to the GL driver
* before issuing our read pixels...
*
* XXX: Note we currently use cogl_flush to ensure *all* journals
* are flushed here and not _cogl_journal_flush because we don't
* track the dependencies between framebuffers so we don't know if
* the current framebuffer depends on the contents of other
* framebuffers which could also have associated journal entries.
*/
cogl_flush ();
_cogl_framebuffer_flush_state (cogl_get_draw_framebuffer (),
framebuffer,
COGL_FRAMEBUFFER_STATE_BIND);
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_pixel_format_get_bytes_per_pixel (format);
bmp_format = format;
if (COGL_PIXEL_FORMAT_CAN_HAVE_PREMULT (format & COGL_A_BIT))
{
/* We match the premultiplied state of the target buffer to the
* premultiplied state of the framebuffer so that it will get
* converted to the right format below */
if ((framebuffer->format & COGL_PREMULT_BIT))
bmp_format |= COGL_PREMULT_BIT;
else
bmp_format &= ~COGL_PREMULT_BIT;
}
bmp = _cogl_bitmap_new_from_data (pixels,
bmp_format, width, height, rowstride,
NULL, NULL);
ctx->texture_driver->pixel_format_to_gl (format,
&gl_intformat,
&gl_format,
&gl_type);
/* NB: All offscreen rendering is done upside down so there is no need
* to flip in this case... */
if ((ctx->private_feature_flags & COGL_PRIVATE_FEATURE_MESA_PACK_INVERT) &&
!cogl_is_offscreen (framebuffer))
{
GE (ctx, glPixelStorei (GL_PACK_INVERT_MESA, TRUE));
pack_invert_set = TRUE;
}
else
pack_invert_set = FALSE;
/* 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. We also need
to use this intermediate buffer if the rowstride has padding
because GLES does not support setting GL_ROW_LENGTH */
if (ctx->driver != COGL_DRIVER_GL &&
(gl_format != GL_RGBA || gl_type != GL_UNSIGNED_BYTE ||
rowstride != 4 * width))
{
CoglBitmap *tmp_bmp;
guint8 *tmp_data = g_malloc (width * height * 4);
tmp_bmp = _cogl_bitmap_new_from_data (tmp_data,
COGL_PIXEL_FORMAT_RGBA_8888 |
(bmp_format & COGL_PREMULT_BIT),
width, height, 4 * width,
(CoglBitmapDestroyNotify) g_free,
NULL);
ctx->texture_driver->prep_gl_for_pixels_download (4 * width, 4);
GE( ctx, glReadPixels (x, y, width, height,
GL_RGBA, GL_UNSIGNED_BYTE,
tmp_data) );
if (!_cogl_bitmap_convert_into_bitmap (tmp_bmp, bmp))
{
/* FIXME: there's no way to report an error here so we'll
just have to leave the data initialised */
}
cogl_object_unref (tmp_bmp);
}
else
{
ctx->texture_driver->prep_gl_for_pixels_download (rowstride, bpp);
GE( ctx, 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);
}
/* Currently this function owns the pack_invert state and we don't want this
* to interfere with other Cogl components so all other code can assume that
* we leave the pack_invert state off. */
if (pack_invert_set)
GE (ctx, glPixelStorei (GL_PACK_INVERT_MESA, FALSE));
/* NB: All offscreen rendering is done upside down so there is no need
* to flip in this case... */
if (!cogl_is_offscreen (framebuffer) && !pack_invert_set)
{
guint8 *temprow = g_alloca (rowstride * sizeof (guint8));
/* 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 * rowstride, rowstride);
memcpy (pixels + y * rowstride,
pixels + (height - y - 1) * rowstride, rowstride);
memcpy (pixels + (height - y - 1) * rowstride,
temprow,
rowstride);
}
}
}
cogl_object_unref (bmp);
}
void
cogl_read_pixels (int x,
int y,
@ -561,10 +378,19 @@ cogl_read_pixels (int x,
guint8 *pixels)
{
int bpp = _cogl_pixel_format_get_bytes_per_pixel (format);
_cogl_read_pixels_with_rowstride (x, y, width, height,
source, format, pixels,
/* rowstride */
bpp * width);
CoglBitmap *bitmap;
bitmap = _cogl_bitmap_new_from_data (pixels,
format,
width, height,
bpp * width, /* rowstride */
NULL, /* destroy_fn */
NULL /* destroy_fn_data */);
cogl_framebuffer_read_pixels_into_bitmap (_cogl_get_read_framebuffer (),
x, y,
source,
bitmap);
cogl_object_unref (bitmap);
}
void

1
doc/reference/cogl-2.0-experimental/cogl-2.0-experimental-sections.txt
View File

@ -406,6 +406,7 @@ cogl_framebuffer_set_point_samples_per_pixel
cogl_framebuffer_get_context
cogl_framebuffer_clear
cogl_framebuffer_clear4f
cogl_framebuffer_read_pixels_into_bitmap
<SUBSECTION>
cogl_framebuffer_draw_primitive