GLPIXELSTORE(3G) UNIX Programmer's Manual GLPIXELSTORE(3G)
glPixelStoref, glPixelStorei - 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 opera-
tion 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, glTexSubImage3D). Addi-
tionally, if the GL_ARB_imaging extension is supported,
pixle storage modes affect convlution filters (see
glConvolutionFilter1D, glConvolutionFilter2D, and
glSeparableFilter2D, color table (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:
GL_PACK_SWAP_BYTES
If true, byte ordering for multibyte color com-
ponents, depth components, color indices, or sten-
cil indices is reversed. That is, if a four-byte
component consists of bytes b0, b1, b2, b3, it is
stored in memory as b3, b2, b1, b0 if
GL_PACK_SWAP_BYTES is true. GL_PACK_SWAP_BYTES has
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no effect on the memory order of components within
a pixel, only on the order of bytes within com-
ponents or indices. For example, the three com-
ponents of a GL_RGB pixel are always stored with
red first, green second, and blue third, regard-
less 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. This parameter is significant for bitmap data
only.
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
|
|nl s ≥ a
k = |_|_n__| 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 = 8a|_l_|
|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.
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
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the next row is obtained by skipping
|
| nlh s ≥ a
k = | _|_n__h_| 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 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 incre-
menting the pointer by in 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 jm com-
ponents or indices, where m is the number of com-
ponents or indices per row, as just computed in
the GL_PACK_ROW_LENGTH section. Setting
GL_PACK_SKIP_IMAGES to k is equivalent to incre-
menting the pointer by kp, 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 sig-
nificant for glDrawPixels, glTexImage1D, glTexImage2D,
glTexImage3D, glTexSubImage1D, glTexSubImage2D,
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glTexSubImage3D, glBitmap, and glPolygonStipple.
Additionally, if the GL_ARB_imaging extension is supported,
glColorTable, glColorSubTable, glConvolutionFilter1D,
glConvolutionFilter2D, and glSeparableFilter2D. They are as
follows:
GL_UNPACK_SWAP_BYTES
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 b0, b1, b2, b3, it is taken from memory as b3,
b2, b1, b0 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, regard-
less of the value of GL_UNPACK_SWAP_BYTES.
GL_UNPACK_LSB_FIRST
If true, bits are ordered within a byte from least sig-
nificant to most significant; otherwise, the first bit
in each byte is the most significant one. This is
relevant only for bitmap data.
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
|
| nl s ≥ a
k = | _|_n__| s < a
| s| a |
|
components or indices, where n is the number of com-
ponents or indices in a pixel, l is the number of pix-
els in a row (GL_UNPACK_ROW_LENGTH if it is greater
than 0, the width argument to the pixel routine other-
wise), 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 = 8a|_l_|
|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
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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
|
| nlh s ≥ a
k = | _|_n__h_| s < a
| s| a |
|
components or indices, where n is the number of com-
ponents or indices in a pixel, l is the number of pix-
els 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 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 pro-
grammer; they provide no functionality that cannot be
duplicated by incrementing the pointer passed to
glDrawPixels, glTexImage1D, glTexImage2D,
glTexSubImage1D, glTexSubImage2D, glBitmap, or
glPolygonStipple. Setting GL_UNPACK_SKIP_PIXELS to i is
equivalent to incrementing the pointer by in 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 jk com-
ponents 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).
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The following table gives the type, initial value, and range
of valid values for each storage parameter that can be set
with glPixelStore.
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