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GLPIXELSTORE(3G) OpenGL 3.3 GLPIXELSTORE(3G)
NAME
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()).
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 | Valid |
| | | Value | 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()
COPYRIGHT
Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software
B License. For details, see http://oss.sgi.com/projects/FreeB/.
OpenGL 3.3 03/08/2011 GLPIXELSTORE(3G)
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