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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()),
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
VERSION SUPPORT
┌──────────────┬───────────────────────────────────────────────────────────────────────┐
│ │ OpenGL Version │
├──────────────┼─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┤
│Function │ 2.0 │ 2.1 │ 3.0 │ 3.1 │ 3.2 │ 3.3 │ 4.0 │ 4.1 │ 4.2 │ 4.3 │ 4.4 │ 4.5 │
│/ │ │ │ │ │ │ │ │ │ │ │ │ │
│Feature │ │ │ │ │ │ │ │ │ │ │ │ │
│Name │ │ │ │ │ │ │ │ │ │ │ │ │
├──────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
│glPixelStoref │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │
├──────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
│glPixelStorei │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │ ✔ │
└──────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘
SEE ALSO
glReadPixels(), glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubImage1D(),
glTexSubImage2D(), glTexSubImage3D(), glCompressedTexImage1D(), glCompressedTexImage2D(),
glCompressedTexImage3D(), glCompressedTexSubImage1D(), glCompressedTexSubImage2D(),
glCompressedTexSubImage1D().
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group. This
document is licensed under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc.
Copyright © 2010-2014 Khronos Group
[FIXME: source] 01/03/2018 GLPIXELSTORE(3G)