glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
glDrawPixels - write a block of pixels to the frame buffer
void glDrawPixels( GLsizei width,
GLsizei height,
GLenum format,
GLenum type,
const GLvoid *pixels )
width, height Specify the dimensions of the pixel rectangle to be written
into the frame buffer.
format Specifies the format of the pixel data. Symbolic constants
GL_COLOR_INDEX, GL_STENCIL_INDEX, GL_DEPTH_COMPONENT,
GL_RGB, GL_BGR, GL_RGBA, GL_BGRA, GL_ABGR_EXT, GL_RED,
GL_GREEN, GL_BLUE, GL_ALPHA, GL_LUMINANCE, and
GL_LUMINANCE_ALPHA are accepted.
type Specifies the data type for pixels. Symbolic constants
GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP, GL_UNSIGNED_SHORT,
GL_SHORT, GL_UNSIGNED_INT, GL_INT, GL_FLOAT,
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, and
GL_UNSIGNED_INT_2_10_10_10_REV are accepted.
pixels Specifies a pointer to the pixel data.
glDrawPixels reads pixel data from memory and writes it into the frame
buffer relative to the current raster position, provided that the raster
position is valid. Use glRasterPos to set the current raster position;
use glGet with argument GL_CURRENT_RASTER_POSITION_VALID to determine if
the specified raster position is valid, and glGet with argument
GL_CURRENT_RASTER_POSITION to query the raster position.
Several parameters define the encoding of pixel data in memory and
control the processing of the pixel data before it is placed in the frame
buffer. These parameters are set with four commands: glPixelStore,
glPixelTransfer, glPixelMap, and glPixelZoom. This reference page
describes the effects on glDrawPixels of many, but not all, of the
parameters specified by these four commands.
Page 1
glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
Data is read from pixels as a sequence of signed or unsigned bytes,
signed or unsigned shorts, signed or unsigned integers, or singleprecision
floating-point values, depending on type. When type is one of
GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT,
GL_INT, or GL_FLOAT each of these bytes, shorts, integers, or floatingpoint
values is interpreted as one color or depth component, or one
index, depending on format. When type is one of GL_UNSIGNED_BYTE_3_3_2,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_4_4_4_4,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_INT_8_8_8_8,
GL_UNSIGNED_INT_10_10_10_2, each unsigned value is interpreted as
containing all the components for a single pixel, with the color
components arranged according to format. When type is one of
GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_2_10_10_10_REV, each
unsigned value is interpreted as containing all color components,
specified by format, for a single pixel in a reversed order. Indices are
always treated individually. Color components are treated as groups of
one, two, three, or four values, again based on format. Both individual
indices and groups of components are referred to as pixels. If type is
GL_BITMAP, the data must be unsigned bytes, and format must be either
GL_COLOR_INDEX or GL_STENCIL_INDEX. Each unsigned byte is treated as
eight 1-bit pixels, with bit ordering determined by GL_UNPACK_LSB_FIRST
(see glPixelStore).
width x height pixels are read from memory, starting at location pixels.
By default, these pixels are taken from adjacent memory locations, except
that after all width pixels are read, the read pointer is advanced to the
next four-byte boundary. The four-byte row alignment is specified by
glPixelStore with argument GL_UNPACK_ALIGNMENT, and it can be set to one,
two, four, or eight bytes. Other pixel store parameters specify
different read pointer advancements, both before the first pixel is read
and after all width pixels are read. See the glPixelStore reference page
for details on these options.
The width x height pixels that are read from memory are each operated on
in the same way, based on the values of several parameters specified by
glPixelTransfer and glPixelMap. The details of these operations, as well
as the target buffer into which the pixels are drawn, are specific to the
format of the pixels, as specified by format. format can assume one of
13 symbolic values:
GL_COLOR_INDEX [Toc] [Back]
Each pixel is a single value, a color index. It is converted
to fixed-point format, with an unspecified number of bits to
the right of the binary point, regardless of the memory data
type. Floating-point values convert to true fixed-point
values. Signed and unsigned integer data is converted with all
fraction bits set to 0. Bitmap data convert to either 0 or 1.
Page 2
glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
Each fixed-point index is then shifted left by GL_INDEX_SHIFT
bits and added to GL_INDEX_OFFSET. If GL_INDEX_SHIFT is
negative, the shift is to the right. In either case, zero bits
fill otherwise unspecified bit locations in the result.
If the GL is in RGBA mode, the resulting index is converted to
an RGBA pixel with the help of the GL_PIXEL_MAP_I_TO_R,
GL_PIXEL_MAP_I_TO_G, GL_PIXEL_MAP_I_TO_B, and
GL_PIXEL_MAP_I_TO_A tables. If the GL is in color index mode,
and if GL_MAP_COLOR is true, the index is replaced with the
value that it references in lookup table GL_PIXEL_MAP_I_TO_I.
Whether the lookup replacement of the index is done or not, the
b
integer part of the index is then ANDed with 2 -1, where b is
the number of bits in a color index buffer.
The GL then converts the resulting indices or RGBA colors to
fragments by attaching the current raster position z coordinate
and texture coordinates to each pixel, then assigning x and y
window coordinates to the nth fragment such that
x = x + n mod width
n r
y = y + |n/width |
n r
where (x ,y ) is the current raster position. These pixel
r r
fragments are then treated just like the fragments generated by
rasterizing points, lines, or polygons. Texture mapping, fog,
and all the fragment operations are applied before the
fragments are written to the frame buffer.
GL_STENCIL_INDEX [Toc] [Back]
Each pixel is a single value, a stencil index. It is converted
to fixed-point format, with an unspecified number of bits to
the right of the binary point, regardless of the memory data
type. Floating-point values convert to true fixed-point
values. Signed and unsigned integer data is converted with all
fraction bits set to 0. Bitmap data convert to either 0 or 1.
Each fixed-point index is then shifted left by GL_INDEX_SHIFT
bits, and added to GL_INDEX_OFFSET. If GL_INDEX_SHIFT is
negative, the shift is to the right. In either case, zero bits
fill otherwise unspecified bit locations in the result. If
GL_MAP_STENCIL is true, the index is replaced with the value
that it references in lookup table GL_PIXEL_MAP_S_TO_S.
Whether the lookup replacement of the index is done or not, the
b
integer part of the index is then ANDed with 2 -1, where b is
the number of bits in the stencil buffer. The resulting
stencil indices are then written to the stencil buffer such
that the nth index is written to location
Page 3
glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
x = x + n mod width
n r
y = y + | n/width |
n r
where (x ,y ) is the current raster position. Only the pixel
r r
ownership test, the scissor test, and the stencil writemask affect
these write operations.
GL_DEPTH_COMPONENT [Toc] [Back]
Each pixel is a single-depth component. Floating-point data is
converted directly to an internal floating-point format with
unspecified precision. Signed integer data is mapped linearly to
the internal floating-point format such that the most positive
representable integer value maps to 1.0, and the most negative
representable value maps to -1.0. Unsigned integer data is mapped
similarly: the largest integer value maps to 1.0, and 0 maps to
0.0. The resulting floating-point depth value is then multiplied by
GL_DEPTH_SCALE and added to GL_DEPTH_BIAS. The result is clamped to
the range [0,1].
The GL then converts the resulting depth components to fragments by
attaching the current raster position color or color index and
texture coordinates to each pixel, then assigning x and y window
coordinates to the nth fragment such that
x = x + n mod width
n r
y = y + | n/width |
n r
where (x ,y ) is the current raster position. These pixel fragments
r r
are then treated just like the fragments generated by rasterizing
points, lines, or polygons. Texture mapping, fog, and all the
fragment operations are applied before the fragments are written to
the frame buffer.
GL_RGBA [Toc] [Back]
GL_BGRA [Toc] [Back]
GL_ABGR_EXT [Toc] [Back]
Each pixel is a four-component group: for GL_RGBA, the red component
is first, followed by green, followed by blue, followed by alpha;
for GL_BGRA the order is blue, green, red and then alpha; for
GL_ABGR_EXT the order is alpha, blue, green, and then red.
Floating-point values are converted directly to an internal
floating-point format with unspecified precision. Signed integer
values are mapped linearly to the internal floating-point format
such that the most positive representable integer value maps to 1.0,
and the most negative representable value maps to -1.0. (Note that
this mapping does not convert 0 precisely to 0.0.) Unsigned integer
Page 4
glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
data is mapped similarly: the largest integer value maps to 1.0,
and 0 maps to 0.0. The resulting floating-point color values are
then multiplied by GL_c_SCALE and added to GL_c_BIAS, where c is
RED, GREEN, BLUE, and ALPHA for the respective color components.
The results are clamped to the range [0,1].
If GL_MAP_COLOR is true, each color component is scaled by the size
of lookup table GL_PIXEL_MAP_c_TO_c, then replaced by the value that
it references in that table. c is R, G, B, or A respectively.
The GL then converts the resulting RGBA colors to fragments by
attaching the current raster position z coordinate and texture
coordinates to each pixel, then assigning x and y window coordinates
to the nth fragment such that
x = x + n mod width
n r
y = y + | n/width |
n r
where (x ,y ) is the current raster position. These pixel fragments
r r
are then treated just like the fragments generated by rasterizing
points, lines, or polygons. Texture mapping, fog, and all the
fragment operations are applied before the fragments are written to
the frame buffer.
GL_RED [Toc] [Back]
Each pixel is a single red component. This component is converted
to the internal floating-point format in the same way the red
component of an RGBA pixel is. It is then converted to an RGBA pixel
with green and blue set to 0, and alpha set to 1. After this
conversion, the pixel is treated as if it had been read as an RGBA
pixel.
GL_GREEN [Toc] [Back]
Each pixel is a single green component. This component is converted
to the internal floating-point format in the same way the green
component of an RGBA pixel is. It is then converted to an RGBA
pixel with red and blue set to 0, and alpha set to 1. After this
conversion, the pixel is treated as if it had been read as an RGBA
pixel.
GL_BLUE [Toc] [Back]
Each pixel is a single blue component. This component is converted
to the internal floating-point format in the same way the blue
component of an RGBA pixel is. It is then converted to an RGBA
pixel with red and green set to 0, and alpha set to 1. After this
conversion, the pixel is treated as if it had been read as an RGBA
pixel.
Page 5
glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
GL_ALPHA [Toc] [Back]
Each pixel is a single alpha component. This component is converted
to the internal floating-point format in the same way the alpha
component of an RGBA pixel is. It is then converted to an RGBA
pixel with red, green, and blue set to 0. After this conversion,
the pixel is treated as if it had been read as an RGBA pixel.
GL_RGB [Toc] [Back]
GL_BGR [Toc] [Back]
Each pixel is a three-component group: red first, followed by
green, followed by blue; for GL_BGR, the first component is blue,
followed by green and then red. Each component is converted to the
internal floating-point format in the same way the red, green, and
blue components of an RGBA pixel are. The color triple is converted
to an RGBA pixel with alpha set to 1. After this conversion, the
pixel is treated as if it had been read as an RGBA pixel.
GL_LUMINANCE [Toc] [Back]
Each pixel is a single luminance component. This component is
converted to the internal floating-point format in the same way the
red component of an RGBA pixel is. It is then converted to an RGBA
pixel with red, green, and blue set to the converted luminance
value, and alpha set to 1. After this conversion, the pixel is
treated as if it had been read as an RGBA pixel.
GL_LUMINANCE_ALPHA [Toc] [Back]
Each pixel is a two-component group: luminance first, followed by
alpha. The two components are converted to the internal floatingpoint
format in the same way the red component of an RGBA pixel is.
They are then converted to an RGBA pixel with red, green, and blue
set to the converted luminance value, and alpha set to the converted
alpha value. After this conversion, the pixel is treated as if it
had been read as an RGBA pixel.
The following table summarizes the meaning of the valid constants for the
type parameter:
_________________________________________________________________________________________
Type Corresponding Type
_________________________________________________________________________________________
GL_UNSIGNED_BYTE unsigned 8-bit integer
GL_BYTE signed 8-bit integer
GL_BITMAP single bits in unsigned 8-bit integers
GL_UNSIGNED_SHORT unsigned 16-bit integer
GL_SHORT signed 16-bit integer
GL_UNSIGNED_INT unsigned 32-bit integer
GL_INT 32-bit integer
GL_FLOAT single-precision floating-point
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glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
GL_UNSIGNED_BYTE_3_3_2 unsigned 8-bit integer
GL_UNSIGNED_BYTE_2_3_3_REV unsigned 8-bit integer with reversed component ordering
GL_UNSIGNED_SHORT_5_6_5 unsigned 16-bit integer
GL_UNSIGNED_SHORT_5_6_5_REV unsigned 16-bit integer with reversed component ordering
GL_UNSIGNED_SHORT_4_4_4_4 unsigned 16-bit integer
GL_UNSIGNED_SHORT_4_4_4_4_REV unsigned 16-bit integer with reversed component ordering
GL_UNSIGNED_SHORT_5_5_5_1 unsigned 16-bit integer
GL_UNSIGNED_SHORT_1_5_5_5_REV unsigned 16-bit integer with reversed component ordering
GL_UNSIGNED_INT_8_8_8_8 unsigned 32-bit integer
GL_UNSIGNED_INT_8_8_8_8_REV unsigned 32-bit integer with reversed component ordering
GL_UNSIGNED_INT_10_10_10_2 unsigned 32-bit integer
GL_UNSIGNED_INT_2_10_10_10_REV unsigned 32-bit integer with reversed component ordering
_________________________________________________________________________________________
The rasterization described so far assumes pixel zoom factors of 1. If
glPixelZoom is used to change the x and y pixel zoom factors, pixels are
converted to fragments as follows. If (x , y ) is the current raster
r r
position, and a given pixel is in the nth column and mth row of the pixel
rectangle, then fragments are generated for pixels whose centers are in
the rectangle with corners at
(x + zoom n, y + zoom m)
r x r y
(x + zoom (n + 1), y + zoom (m + 1))
r x r y
where zoom is the value of GL_ZOOM_X and zoom is the value of
x y
GL_ZOOM_Y.
When GL_INTERLACE_SGIX is enabled, every other row of the destination
pixel rectangle is modified. The height of the pixel rectangle is
equivalent to 2xGL_ZOOM_Yxheight. Only rows (y +0,y +2,...) are affected
r r
by the draw operation.
Normally glDrawPixels is synchronous: OpenGL executes a glDrawPixels
command in the order it is issued in the OpenGL command stream. Calling
glEnable with parameter GL_ASYNC_DRAW_PIXELS_SGIX causes subsequent
glDrawPixels commands to be asynchronous as defined by the SGIX_async
extension. An asynchronous glDrawPixels command samples the OpenGL state
vector at the point in the OpenGL command stream where the command is
issued, but the results of the command (e.g. updates to the frame buffer)
do not happen until some unspecified time in the future. In particular,
the order of the asynchronous command relative to other OpenGL commands
issued later in the command stream is undefined. An implementation may
choose to execute asynchronous commands in parallel with the normal
command stream or at some convenient time in the future.
Calling glDisable with parameter GL_ASYNC_DRAW_PIXELS_SGIX restores the
default synchronous behavior for subsequent glDrawPixels commands. It
does not affect any pending asynchronous glDrawPixels commands, or wait
for their completion.
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glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
When an asynchronous glDrawPixels command is issued, it is associated
with the current value of GL_ASYNC_MARKER_SGIX as defined by the
SGIX_async extension. A program can determine if an asynchronous
glDrawPixels command has completed by using the glFinishAsyncSGIX or
glPollAsyncSGIX commands.
There is a maximum number of asynchronous glDrawPixels commands that can
be outstanding at any one time, defined by the implementation. This
value can be queried with glGetIntegerv with argument
GL_MAX_ASYNC_DRAW_PIXELS_SGIX.
GL_BGR and GL_BGRA are only valid for format if the GL version is 1.2 or
greater.
GL_ABGR_EXT is valid only if the EXT_abgr extension is supported.
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, and GL_UNSIGNED_INT_2_10_10_10_REV are only
valid for type if the GL version is 1.2 or greater.
GL_INVALID_VALUE is generated if either width or height is negative.
GL_INVALID_ENUM is generated if format or type is not one of the accepted
values.
GL_INVALID_OPERATION is generated if format is GL_RED, GL_GREEN, GL_BLUE,
GL_ALPHA, GL_RGB, GL_RGBA, GL_BGR, GL_BGRA, GL_ABGR_EXT, GL_LUMINANCE, or
GL_LUMINANCE_ALPHA, and the GL is in color index mode.
GL_INVALID_ENUM is generated if type is GL_BITMAP and format is not
either GL_COLOR_INDEX or GL_STENCIL_INDEX.
GL_INVALID_OPERATION is generated if format is GL_STENCIL_INDEX and there
is no stencil buffer.
GL_INVALID_OPERATION is generated if glDrawPixels is executed between the
execution of glBegin and the corresponding execution of glEnd.
GL_INVALID_OPERATION is generated if format is one
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, of GL_UNSIGNED_SHORT_5_6_5_REV and format is not
GL_RGB.
GL_INVALID_OPERATION is generated if format is one of
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
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glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, or GL_UNSIGNED_INT_2_10_10_10_REV and format
is not GL_RGBA, GL_BGRA or GL_ABGR_EXT.
GL_INVALID_OPERATION is generated when the SGIX_subsample extension is
supported, and the pixel storage mode GL_UNPACK_SUBSAMPLE_RATE_SGIX is
not GL_PIXEL_SUBSAMPLE_4444_SGIX, and width is not a multiple of 2, or
format is not a 3 or 4 component format, or type is a packed pixels type.
GL_INVALID_OPERATION is generated if GL_ASYNC_DRAW_PIXELS_SGIX is enabled
and the number of asynchronous glDrawPixels commands that have been
issued but not queried (using glFinishAsyncSGIX or glPollAsyncSGIX)
exceeds GL_MAX_ASYNC_DRAW_PIXELS_SGIX.
glGet with argument GL_CURRENT_RASTER_POSITION
glGet with argument GL_CURRENT_RASTER_POSITION_VALID
glGet with argument GL_INTERLACE_SGIX
MACHINE DEPENDENCIES
The SGIX_async and SGIX_async_pixel extensions are implemented only on
Octane2 VPro systems.
On RealityEngine, RealityEngine2, and VTX systems convolution may not be
used in the following circumstances:
1. When rendering to pixmaps.
2. When fragment processing (texturing, depth buffering, alpha
testing, multisampling, fog) is enabled.
3. When histogramming or minmax is enabled.
4. When either of the pixel zoom factors has a value other than 1.0
or -1.0.
In these cases, glDrawPixels and glCopyPixels report a
GL_INVALID_OPERATION error and do not transfer any pixels.
Performance note for RealityEngine, RealityEngine2, and VTX systems:
Unsigned color types use the fastest pixel-drawing path. Smaller types
(e.g., GL_UNSIGNED_BYTE) require less host-to-graphics bandwidth, and are
therefore faster than larger types (e.g., GL_UNSIGNED_INT). Signed and
float types use the significantly slower floating-point pixel-drawing
path. The slower pixel-drawing path is also used when the format is
GL_DEPTH_COMPONENT and when fragment operations (i.e., depth or alpha
testing, texturing, fog, etc.) are enabled.
For best performance on XS, XZ, Elan, and Extreme systems set type to
GL_UNSIGNED_BYTE and, when drawing to the color buffer, set format to
GL_ABGR_EXT.
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glDrawPixels(3G) OpenGL Reference glDrawPixels(3G)
On InfiniteReality systems, signed color-index pixels written to
drawables with dual-personality (luminance + color-index) visuals will be
sign-extended into the high-order bits of the framebuffer. For example,
writing a signed byte value of 0x88 would yield 0xF88 in a 12-bit
drawable.
The SGIX_ycrcb extension is supported only on O2 systems. When using
GL_YCRCB_422_SGIX with glDrawPixels on O2 systems, an odd integer value
for GL_UNPACK_SKIP_PIXELS will be set to the next highest even integer
value to preserve color alignment.
On CRIME systems with a Crime Revision of 1.0-1.3, the SGIX_ycrcb
extension will generate incorrect RGB colors from video with highly
saturated blue or red values. Commonly, the blue of a very saturated sky
will be converted to a pale yellow. This problem is fixed with the CRIME
1.4 graphics.
On Octane2 VPro systems the format GL_DEPTH_COMPONENT24_SGIX can be used
to transfer depth pixel values to and from the depth buffer in their
internal eye-space range. There are performance advantages over
transfers that convert to screen-space values, particularly for
GL_UNSIGNED_INT type pixels.
The SGIX_interlace extension is supported only on InfiniteReality
systems, on RealityEngine, RealityEngine2, and VTX systems, on Octane2
VPro systems, and on O2 systems.
The EXT_packed_pixels extension is not supported on RealityEngine,
RealityEngine2, and VTX systems.
The SGIX_subsample and SGIX_resample extensions are supported only on
Octane2 VPro systems. Applying the GL_PIXEL_SUBSAMPLE_2424_SGIX
subsample rate is accelerated for direct immmediate mode transfers when
the format is GL_RGB or GL_RGBA, and the type is GL_UNSIGNED_BYTE or
GL_UNSIGNED_SHORT.
glAlphaFunc, glBlendFunc, glCopyPixels, glDepthFunc, glLogicOp,
glPixelMap, glPixelStore, glPixelTransfer, glPixelZoom, glRasterPos,
glReadPixels, glScissor, glStencilFunc, glAsyncMarkerSGIX,
glDeleteAsyncMarkersSGIX, glFinishAsyncSGIX, glGenAsyncMarkersSGIX,
glIsAsyncMarkerSGIX, glPollAsyncSGIX
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