glPixelStore(3G)glPixelStore(3G)NAME
glPixelStore, glPixelStoref, glPixelStorei - set pixel storage modes
SYNOPSIS
void glPixelStoref(
GLenum pname,
GLfloat param ); void glPixelStorei(
GLenum pname,
GLint param );
PARAMETERS
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.
Specifies the value that pname is set to.
DESCRIPTIONglPixelStore() sets pixel storage modes that affect the operation of
subsequent glDrawPixels() and glReadPixels() as well as the unpacking
of polygon stipple patterns (see glPolygonStipple()), bitmaps (see
glBitmap()), texture patterns (see glTexImage1D(), glTexImage2D(),
glTexImage3D(), glTexSubImage1D(), glTexSubImage2D(), glTexSubIm‐
age3D()). Additionally, if the GL_ARB_imaging extension is supported,
pixle storage modes affect convlution filters (see glConvolutionFil‐
ter1D(), glConvolutionFilter2D(), and glSeparableFilter2D(), color ta‐
ble (see glColorTable(), and glColorSubTable(), and unpacking histogram
(See glHistogram()), and minmax (See glMinmax()) data.
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: 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 [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 compo‐
nents 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. 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. 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
n1 s >= a k =
a / s snl / 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 com‐
ponent (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 =
8a nl / 8a
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. If greater than 0, GL_PACK_IMAGE_HEIGHT
defines the number of pixels in an image three-dimensional tex‐
ture 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 n1h s
>= a k =
a / s snlh / 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
arguemnt 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. 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 glRead‐
Pixels(). 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 compo‐
nents 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. Specifies the alignment require‐
ments 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 glDrawPix‐
els(), glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubIm‐
age1D(), glTexSubImage2D(), glTexSubImage3D(), glBitmap(), and glPoly‐
gonStipple().
Additionally, if the GL_ARB_imaging extension is supported, glCol‐
orTable(), glColorSubTable(), glConvolutionFilter1D(), glConvolution‐
Filter2D(), and glSeparableFilter2D(). They are as follows: If true,
byte ordering for multibyte color components, depth components, color
indices, or stencil indices is reversed. That is, if a four-byte compo‐
nent 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. If true,
bits are ordered within a byte from least significant to most signifi‐
cant; otherwise, the first bit in each byte is the most significant
one. This is relevant only for bitmap data. 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 loca‐
tion of the first pixel of the next row is obtained by skipping
n1 s >= a k =
a / s snl / 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 argu‐
ment 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 skip‐
ping k = 8a nl / 8a
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. 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
n1h s >= a k =
a / s snlh / 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 argu‐
ment 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. 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(), glTexSubIm‐
age2D(), 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.
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 Range
Value
─────────────────────────────────────────────────────────────
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,Infin‐
ity)
GL_PACK_IMAGE_HEIGHT integer 0 [0, Infin‐
ity)
GL_PACK_SKIP_ROWS integer 0 [0,Infin‐
ity)
GL_PACK_SKIP_PIXELS integer 0 [0,Infin‐
ity)
GL_PACK_SKIP_IMAGES integer 0 [0,Infin‐
ity)
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,Infin‐
ity)
GL_UNPACK_IMAGE_HEIGHT integer 0 [0,Infin‐
ity)
GL_UNPACK_SKIP_ROWS integer 0 [0,Infin‐
ity)
GL_UNPACK_SKIP_PIXELS integer 0 [0,Infin‐
ity)
GL_UNPACK_SKIP_IMAGES integer 0 [0,Infin‐
ity)
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.
NOTES
The pixel storage modes in effect when glDrawPixels(), glReadPixels(),
glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubImage1D(),
glTexSubImage2D(), glTexSubImage3D(), glBitmap(), or glPolygonStipple()
is placed in a display list control the interpretation of memory data.
Likewise, if the GL_ARB_imaging extension is supported, the pixel stor‐
age modes in effect when glColorTable(), glColorSubTable(), glConvolu‐
tionFilter1D(), glConvolutionFilter2D(), of glSeparableFilter2D() is
placed in a display list control the intrepretation of memory data. The
pixel storage modes in effect when a display list is executed are not
significant.
Pixel storage modes are client state and must be pushed and restored
using glPushClientAttrib() and glPopClientAttrib().
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.
GL_INVALID_OPERATION is generated if glPixelStore() is executed between
the execution of glBegin() and the corresponding execution of glEnd().
ASSOCIATED GETSglGet() 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 ALSOglBitmap(3), glColorTable(3), glColorSubTable(3), glConvolutionFil‐
ter1D(3), glConvolutionFilter2D(3), glSeparableFilter2D(3), glDrawPix‐
els(3), glHistogram(3), glMinmax(3), glPixelMap(3), glPixelTransfer(3),
glPixelZoom(3), glPolygonStipple(3), glPushClientAttrib(3), glReadPix‐
els(3), glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glTexSubIm‐
age1D(3), glTexSubImage2D(3), glTexSubImage3D(3)glPixelStore(3G)