- GL_PACK_SWAP_BYTES
-
If true,
byte ordering for multibyte color components,
depth components,
color indices,
or stencil indices
is reversed.
That is,
if a four-byte component consists of bytes
$b sub 0$,
$b sub 1$,
$b sub 2$,
$b sub 3$,
it is stored in memory as
$b sub 3$,
$b sub 2$,
$b sub 1$,
$b sub 0$
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 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.
This parameter is significant for bitmap data only.
- 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
$k ~=~~ left { ^ lpile { n l above {a over s left ceiling { s n l } over a right ceiling}} ~~ lpile {s ~>=~ a above s ~<~ a }$
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
$k ~=~ 8 a left ceiling { n l } over { 8 a } ^ right ceiling$
components or indices.
-
The word component in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage 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
$k ~=~~ left { ~ lpile { n l h above {a over s left ceiling { s n l h }
over a ^ right ceiling}} ~~ lpile {s ~>=~ a above s ~<~ a }$
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 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 glDrawPixels,
glTexImage1D,
glTexImage2D,
glTexImage3D,
glTexSubImage1D,
glTexSubImage2D,
glTexSubImage3D,
glBitmap, and
glPolygonStipple.
Additionally, if the GL_ARB_imaging extension is supported,
glColorTable,
glColorSubTable,
glConvolutionFilter1D,
glConvolutionFilter2D, and
glSeparableFilter2D.
They are as follows:
- GL_UNPACK_SWAP_BYTES
-
If true,
byte ordering for multibyte color components,
depth components,
color indices,
or stencil indices
is reversed.
That is,
if a four-byte component consists of bytes
$b sub 0$,
$b sub 1$,
$b sub 2$,
$b sub 3$,
it is taken from memory as
$b sub 3$,
$b sub 2$,
$b sub 1$,
$b sub 0$
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 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.
This is relevant only for bitmap data.
- 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
$k ~=~~ left { ~ lpile { n l above {a over s left ceiling { s n l }
over a ^ right ceiling}} ~~ lpile {s ~>=~ a above s ~<~ a }$
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
$k ~=~ 8 a left ceiling { n l } over { 8 a } right ceiling$
components or indices.
-
The word component in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage 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
$k ~=~~ left {~ lpile { n l h above {a over s left ceiling { s n l h }
over a ^ right ceiling}} ~~ lpile {s ~ >=~ a above s ~<~ a }$
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 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
glDrawPixels,
glTexImage1D,
glTexImage2D,
glTexSubImage1D,
glTexSubImage2D,
glBitmap, or
glPolygonStipple.
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,Infinity)
|
| GL_PACK_IMAGE_HEIGHT | integer | 0 | [0, Infinity)
|
| GL_PACK_SKIP_ROWS | integer | 0 | [0,Infinity)
|
| GL_PACK_SKIP_PIXELS | integer | 0 | [0,Infinity)
|
| GL_PACK_SKIP_IMAGES | integer | 0 | [0,Infinity)
|
| 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,Infinity)
|
| GL_UNPACK_IMAGE_HEIGHT | integer | 0 | [0,Infinity)
|
| GL_UNPACK_SKIP_ROWS | integer | 0 | [0,Infinity)
|
| GL_UNPACK_SKIP_PIXELS | integer | 0 | [0,Infinity)
|
| GL_UNPACK_SKIP_IMAGES | integer | 0 | [0,Infinity)
|
| 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.
