glPixelStore — set pixel storage modes
void glPixelStoref( | GLenum pname, |
GLfloat param) ; |
void glPixelStorei( | GLenum pname, |
GLint param) ; |
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.
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
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
components or indices,
where
GL_PACK_ROW_LENGTH
if it is greater than 0,
the
GL_PACK_ALIGNMENT
, and
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
components or indices, where
GL_PACK_ROW_LENGTH
if it is greater than 0, the
GL_PACK_IMAGE_HEIGHT
if it is greater than
0, the
GL_PACK_ALIGNMENT
, and
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
GL_PACK_SKIP_ROWS
to
GL_PACK_ROW_LENGTH
section.
Setting GL_PACK_SKIP_IMAGES
to
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
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
components or indices,
where
GL_UNPACK_ROW_LENGTH
if it is greater than 0,
the
GL_UNPACK_ALIGNMENT
, and
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
components or indices,
where
GL_UNPACK_ROW_LENGTH
if it is greater than 0,
the
GL_UNPACK_IMAGE_HEIGHT
if
it is greater than 0, the
GL_UNPACK_ALIGNMENT
, and
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
GL_UNPACK_SKIP_ROWS
to
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 |
|
GL_PACK_IMAGE_HEIGHT
| integer | 0 |
|
GL_PACK_SKIP_ROWS
| integer | 0 |
|
GL_PACK_SKIP_PIXELS
| integer | 0 |
|
GL_PACK_SKIP_IMAGES
| integer | 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 |
|
GL_UNPACK_IMAGE_HEIGHT
| integer | 0 |
|
GL_UNPACK_SKIP_ROWS
| integer | 0 |
|
GL_UNPACK_SKIP_PIXELS
| integer | 0 |
|
GL_UNPACK_SKIP_IMAGES
| integer | 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.
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.
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
glReadPixels, glTexImage1D, glTexImage2D, glTexImage3D, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D, glCompressedTexImage1D, glCompressedTexImage2D, glCompressedTexImage3D, glCompressedTexSubImage1D, glCompressedTexSubImage2D, glCompressedTexSubImage1D.
Copyright © 1991-2006 Silicon Graphics, Inc. © 2011 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.