1991-2006
Silicon Graphics, Inc.
2010-2013
Khronos Group
glPixelStore
3G
glPixelStore
set pixel storage modes
C Specification
void glPixelStoref
GLenum pname
GLfloat param
void glPixelStorei
GLenum pname
GLint param
Parameters
pname
Specifies the symbolic name of the parameter to be set.
Six values affect the packing of pixel data into memory:
GL_PACK_SWAP_BYTES,
GL_PACK_LSB_FIRST,
GL_PACK_ROW_LENGTH,
GL_PACK_IMAGE_HEIGHT,
GL_PACK_SKIP_PIXELS,
GL_PACK_SKIP_ROWS,
GL_PACK_SKIP_IMAGES, and
GL_PACK_ALIGNMENT.
Six more affect the unpacking of pixel data from memory:
GL_UNPACK_SWAP_BYTES,
GL_UNPACK_LSB_FIRST,
GL_UNPACK_ROW_LENGTH,
GL_UNPACK_IMAGE_HEIGHT,
GL_UNPACK_SKIP_PIXELS,
GL_UNPACK_SKIP_ROWS,
GL_UNPACK_SKIP_IMAGES, and
GL_UNPACK_ALIGNMENT.
param
Specifies the value that pname is set to.
Description
glPixelStore sets pixel storage modes that affect the operation of subsequent
glReadPixels as well as the unpacking of
texture patterns (see glTexImage1D,
glTexImage2D, glTexImage3D, glTexSubImage1D,
glTexSubImage2D, glTexSubImage3D),
glCompressedTexImage1D, glCompressedTexImage2D,
glCompressedTexImage3D, glCompressedTexSubImage1D,
glCompressedTexSubImage2D or glCompressedTexSubImage1D.
pname is a symbolic constant indicating the parameter to be set, and
param is the new value. Six of the twelve storage parameters affect
how pixel data is returned to client memory.
They are as follows:
GL_PACK_SWAP_BYTES
If true,
byte ordering for multibyte color components,
depth components,
or stencil indices
is reversed.
That is,
if a four-byte component consists of bytes
b
0
,
b
1
,
b
2
,
b
3
,
it is stored in memory as
b
3
,
b
2
,
b
1
,
b
0
if GL_PACK_SWAP_BYTES is true.
GL_PACK_SWAP_BYTES has no effect on the memory order of components
within a pixel,
only on the order of bytes within components or indices.
For example,
the three components of a GL_RGB format pixel are always stored with
red first,
green second,
and blue third,
regardless of the value of GL_PACK_SWAP_BYTES.
GL_PACK_LSB_FIRST
If true,
bits are ordered within a byte from least significant to most significant;
otherwise,
the first bit in each byte is the most significant one.
GL_PACK_ROW_LENGTH
If greater than 0,
GL_PACK_ROW_LENGTH defines the number of pixels in a row.
If the first pixel of a row is placed at location
p
in memory,
then the location of the first pixel of the next row is obtained by skipping
k
=
n
l
a
s
s
n
l
a
s
>=
a
s
<
a
components or indices,
where
n
is the number of components or indices in a pixel,
l
is the number of pixels in a row
(GL_PACK_ROW_LENGTH if it is greater than 0,
the
width
argument to the pixel routine otherwise),
a
is the value of GL_PACK_ALIGNMENT, and
s
is the size, in bytes, of a single component
(if
a
<
s
,
then it is as if
a
=
s
).
In the case of 1-bit values,
the location of the next row is obtained by skipping
k
=
8
a
n
l
8
a
components or indices.
The word component in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage format GL_RGB,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
GL_PACK_IMAGE_HEIGHT
If greater than 0,
GL_PACK_IMAGE_HEIGHT defines the number of pixels in an image
three-dimensional texture volume, where ``image'' is defined by all pixels
sharing the same third dimension index.
If the first pixel of a row is placed at location
p
in memory,
then the location of the first pixel of the next row is obtained by skipping
k
=
n
l
h
a
s
s
n
l
h
a
s
>=
a
s
<
a
components or indices, where
n
is the number of components or indices
in a pixel,
l
is the number of pixels in a row
(GL_PACK_ROW_LENGTH if it is greater than 0, the
width
argument to glTexImage3D otherwise),
h
is the number of
rows in a pixel image (GL_PACK_IMAGE_HEIGHT if it is greater than
0, the
height
argument to the glTexImage3D routine otherwise),
a
is the value of
GL_PACK_ALIGNMENT, and
s
is the size, in bytes, of a single
component (if
a
<
s
,
then it is as if
a
=
s
).
The word component in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage format GL_RGB,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
GL_PACK_SKIP_PIXELS, GL_PACK_SKIP_ROWS, and GL_PACK_SKIP_IMAGES
These values are provided as a convenience to the programmer;
they provide no functionality that cannot be duplicated simply by
incrementing the pointer passed to glReadPixels.
Setting GL_PACK_SKIP_PIXELS to
i
is equivalent to incrementing
the pointer by
i
n
components or indices,
where
n
is the number of components or indices in each pixel.
Setting GL_PACK_SKIP_ROWS to
j
is equivalent to incrementing
the pointer by
j
m
components or indices,
where
m
is the number of components or indices per row,
as just computed in the GL_PACK_ROW_LENGTH section.
Setting GL_PACK_SKIP_IMAGES to
k
is equivalent to incrementing
the pointer by
k
p
,
where
p
is the number of components or indices
per image, as computed in the GL_PACK_IMAGE_HEIGHT section.
GL_PACK_ALIGNMENT
Specifies the alignment requirements for the start of each pixel row in memory.
The allowable values are
1 (byte-alignment),
2 (rows aligned to even-numbered bytes),
4 (word-alignment), and
8 (rows start on double-word boundaries).
The other six of the twelve storage parameters affect how pixel data is
read from client memory.
These values are significant for
glTexImage1D,
glTexImage2D,
glTexImage3D,
glTexSubImage1D,
glTexSubImage2D, and
glTexSubImage3D
They are as follows:
GL_UNPACK_SWAP_BYTES
If true,
byte ordering for multibyte color components,
depth components,
or stencil indices
is reversed.
That is,
if a four-byte component consists of bytes
b
0
,
b
1
,
b
2
,
b
3
,
it is taken from memory as
b
3
,
b
2
,
b
1
,
b
0
if GL_UNPACK_SWAP_BYTES is true.
GL_UNPACK_SWAP_BYTES has no effect on the memory order of components
within a pixel,
only on the order of bytes within components or indices.
For example,
the three components of a GL_RGB format pixel are always stored with
red first,
green second,
and blue third,
regardless of the value of GL_UNPACK_SWAP_BYTES.
GL_UNPACK_LSB_FIRST
If true,
bits are ordered within a byte from least significant to most significant;
otherwise,
the first bit in each byte is the most significant one.
GL_UNPACK_ROW_LENGTH
If greater than 0,
GL_UNPACK_ROW_LENGTH defines the number of pixels in a row.
If the first pixel of a row is placed at location
p
in memory,
then the location of the first pixel of the next row is obtained by skipping
k
=
n
l
a
s
s
n
l
a
s
>=
a
s
<
a
components or indices,
where
n
is the number of components or indices in a pixel,
l
is the number of pixels in a row
(GL_UNPACK_ROW_LENGTH if it is greater than 0,
the
width
argument to the pixel routine otherwise),
a
is the value of GL_UNPACK_ALIGNMENT, and
s
is the size, in bytes, of a single component
(if
a
<
s
,
then it is as if
a
=
s
).
In the case of 1-bit values,
the location of the next row is obtained by skipping
k
=
8
a
n
l
8
a
components or indices.
The word component in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage format GL_RGB,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
GL_UNPACK_IMAGE_HEIGHT
If greater than 0,
GL_UNPACK_IMAGE_HEIGHT defines the number of pixels in an image of
a three-dimensional texture volume. Where ``image'' is defined by all
pixel sharing the same third dimension index.
If the first pixel of a row is placed at location
p
in memory,
then the location of the first pixel of the next row is obtained by skipping
k
=
n
l
h
a
s
s
n
l
h
a
s
>=
a
s
<
a
components or indices,
where
n
is the number of components or indices in a pixel,
l
is the number of pixels in a row
(GL_UNPACK_ROW_LENGTH if it is greater than 0,
the
width
argument to glTexImage3D otherwise),
h
is the number of rows in an image (GL_UNPACK_IMAGE_HEIGHT if
it is greater than 0, the
height
argument to glTexImage3D otherwise),
a
is the value of GL_UNPACK_ALIGNMENT, and
s
is the size, in bytes, of a single component
(if
a
<
s
,
then it is as if
a
=
s
).
The word component in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage format GL_RGB,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
GL_UNPACK_SKIP_PIXELS and GL_UNPACK_SKIP_ROWS
These values are provided as a convenience to the programmer;
they provide no functionality that cannot be duplicated by
incrementing the pointer passed to
glTexImage1D,
glTexImage2D,
glTexSubImage1D or
glTexSubImage2D.
Setting GL_UNPACK_SKIP_PIXELS to
i
is equivalent to incrementing
the pointer by
i
n
components or indices,
where
n
is the number of components or indices in each pixel.
Setting GL_UNPACK_SKIP_ROWS to
j
is equivalent to incrementing
the pointer by
j
k
components or indices,
where
k
is the number of components or indices per row,
as just computed in the GL_UNPACK_ROW_LENGTH section.
GL_UNPACK_ALIGNMENT
Specifies the alignment requirements for the start of each pixel row in memory.
The allowable values are
1 (byte-alignment),
2 (rows aligned to even-numbered bytes),
4 (word-alignment), and
8 (rows start on double-word boundaries).
The following table gives the type,
initial value,
and range of valid values for each storage parameter
that can be set with glPixelStore.
pname
Type
Initial Value
Valid Range
GL_PACK_SWAP_BYTES
boolean
false
true or false
GL_PACK_LSB_FIRST
boolean
false
true or false
GL_PACK_ROW_LENGTH
integer
0
0
GL_PACK_IMAGE_HEIGHT
integer
0
0
GL_PACK_SKIP_ROWS
integer
0
0
GL_PACK_SKIP_PIXELS
integer
0
0
GL_PACK_SKIP_IMAGES
integer
0
0
GL_PACK_ALIGNMENT
integer
4
1, 2, 4, or 8
GL_UNPACK_SWAP_BYTES
boolean
false
true or false
GL_UNPACK_LSB_FIRST
boolean
false
true or false
GL_UNPACK_ROW_LENGTH
integer
0
0
GL_UNPACK_IMAGE_HEIGHT
integer
0
0
GL_UNPACK_SKIP_ROWS
integer
0
0
GL_UNPACK_SKIP_PIXELS
integer
0
0
GL_UNPACK_SKIP_IMAGES
integer
0
0
GL_UNPACK_ALIGNMENT
integer
4
1, 2, 4, or 8
glPixelStoref can be used to set any pixel store parameter.
If the parameter type is boolean,
then if param is 0,
the parameter is false;
otherwise it is set to true.
If pname is a integer type parameter,
param is rounded to the nearest integer.
Likewise, glPixelStorei can also be used to set any of the
pixel store parameters.
Boolean parameters are set to false if param is 0 and true otherwise.
Errors
GL_INVALID_ENUM is generated if pname is not an accepted value.
GL_INVALID_VALUE is generated if a negative row length,
pixel skip,
or row skip value is specified,
or if alignment is specified as other than 1, 2, 4, or 8.
Associated Gets
glGet with argument GL_PACK_SWAP_BYTES
glGet with argument GL_PACK_LSB_FIRST
glGet with argument GL_PACK_ROW_LENGTH
glGet with argument GL_PACK_IMAGE_HEIGHT
glGet with argument GL_PACK_SKIP_ROWS
glGet with argument GL_PACK_SKIP_PIXELS
glGet with argument GL_PACK_SKIP_IMAGES
glGet with argument GL_PACK_ALIGNMENT
glGet with argument GL_UNPACK_SWAP_BYTES
glGet with argument GL_UNPACK_LSB_FIRST
glGet with argument GL_UNPACK_ROW_LENGTH
glGet with argument GL_UNPACK_IMAGE_HEIGHT
glGet with argument GL_UNPACK_SKIP_ROWS
glGet with argument GL_UNPACK_SKIP_PIXELS
glGet with argument GL_UNPACK_SKIP_IMAGES
glGet with argument GL_UNPACK_ALIGNMENT
See Also
glReadPixels,
glTexImage1D,
glTexImage2D,
glTexImage3D,
glTexSubImage1D,
glTexSubImage2D,
glTexSubImage3D,
glCompressedTexImage1D,
glCompressedTexImage2D,
glCompressedTexImage3D,
glCompressedTexSubImage1D,
glCompressedTexSubImage2D,
glCompressedTexSubImage1D.
Copyright
Copyright 1991-2006 Silicon Graphics, Inc.
Copyright 2010-2013 Khronos Group.
This document is licensed under the SGI
Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.