glPixelStorei — set pixel storage modes
void glPixelStorei(
|
GLenum pname, |
GLint param) ; |
pname
Specifies the symbolic name of the parameter to be set.
Four values affect the packing of pixel data into memory:
GL_PACK_ROW_LENGTH
,
GL_PACK_SKIP_PIXELS
,
GL_PACK_SKIP_ROWS
, and
GL_PACK_ALIGNMENT
.
Six more affect the unpacking of pixel data from memory:
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.
glPixelStorei
sets pixel storage modes that affect the operation of subsequent
glReadPixels as well as the unpacking of
texture patterns (see glTexImage2D,
glTexImage3D,
glTexSubImage2D,
glTexSubImage3D).
pname
is a symbolic constant indicating the parameter to be set, and
param
is the new value. Four of the ten storage parameters affect
how pixel data is returned to client memory.
They are as follows:
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
in memory,
then the location of the first pixel of the next row is obtained by skipping
components or indices,
where
is the number of components or indices in a pixel,
is the number of pixels in a row
(GL_PACK_ROW_LENGTH
if it is greater than 0,
the
argument to the pixel routine otherwise),
is the value of GL_PACK_ALIGNMENT
, and
is the size, in bytes, of a single component
(if
,
then it is as if
).
In the case of 1-bit values,
the location of the next row is obtained by skipping
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_SKIP_PIXELS
and GL_PACK_SKIP_ROWS
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
is equivalent to incrementing
the pointer by
components or indices,
where
is the number of components or indices in each pixel.
Setting GL_PACK_SKIP_ROWS
to
is equivalent to incrementing
the pointer by
components or indices,
where
is the number of components or indices per row,
as just computed in the GL_PACK_ROW_LENGTH
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 ten storage parameters affect how pixel data is read from client memory. These values are significant for glTexImage2D, glTexImage3D, glTexSubImage2D, and glTexSubImage3D
They are as follows:
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
in memory,
then the location of the first pixel of the next row is obtained by skipping
components or indices,
where
is the number of components or indices in a pixel,
is the number of pixels in a row
(GL_UNPACK_ROW_LENGTH
if it is greater than 0,
the
argument to the pixel routine otherwise),
is the value of GL_UNPACK_ALIGNMENT
, and
is the size, in bytes, of a single component
(if
,
then it is as if
).
In the case of 1-bit values,
the location of the next row is obtained by skipping
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
in memory,
then the location of the first pixel of the next row is obtained by skipping
components or indices,
where
is the number of components or indices in a pixel,
is the number of pixels in a row
(GL_UNPACK_ROW_LENGTH
if it is greater than 0,
the
argument to glTexImage3D otherwise),
is the number of rows in an image (GL_UNPACK_IMAGE_HEIGHT
if
it is greater than 0, the
argument to glTexImage3D otherwise),
is the value of GL_UNPACK_ALIGNMENT
, and
is the size, in bytes, of a single component
(if
,
then it is as if
).
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
, GL_UNPACK_SKIP_ROWS
and GL_UNPACK_SKIP_IMAGES
These values are provided as a convenience to the programmer;
they provide no functionality that cannot be duplicated by
incrementing the pointer passed to
glTexImage2D or
glTexSubImage2D.
Setting GL_UNPACK_SKIP_PIXELS
to
is equivalent to incrementing
the pointer by
components or indices,
where
is the number of components or indices in each pixel.
Setting GL_UNPACK_SKIP_ROWS
to
is equivalent to incrementing
the pointer by
components or indices,
where
is the number of components or indices per row,
as just computed in the GL_UNPACK_ROW_LENGTH
section.
Setting GL_UNPACK_SKIP_IMAGES
to
is equivalent to incrementing
the pointer by
,
where
is the number of components or indices
per image, as computed in the GL_UNPACK_IMAGE_HEIGHT
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 glPixelStorei
.
pname
|
Type | Initial Value | Valid Range |
---|---|---|---|
GL_PACK_ROW_LENGTH
|
integer | 0 | |
GL_PACK_SKIP_ROWS
|
integer | 0 | |
GL_PACK_SKIP_PIXELS
|
integer | 0 | |
GL_PACK_ALIGNMENT
|
integer | 4 | 1, 2, 4, or 8 |
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 |
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_ROW_LENGTH
glGet with argument GL_PACK_SKIP_ROWS
glGet with argument GL_PACK_SKIP_PIXELS
glGet with argument GL_PACK_ALIGNMENT
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
OpenGL ES API Version | |||
---|---|---|---|
Function Name | 2.0 | 3.0 | 3.1 |
glPixelStorei | ✔ | ✔ | ✔ |
glReadPixels, glTexImage2D, glTexImage3D, glTexSubImage2D, glTexSubImage3D
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