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glPixelStore(3G)
NAME
glPixelStore, glPixelStoref, glPixelStorei - set pixel storage modes
SYNOPSIS
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 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()).
Additionally, 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 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 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_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
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 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 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.
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
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.
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 glDrawPixels(),
glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubImage1D(),
glTexSubImage2D(), 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 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.
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. 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
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 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 = 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.
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
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 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 programmer; 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 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 Valid Range
Initial
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,Infinity)
GL_PACK_IMAGE_HEIGHT integer 0
[0,
Infinity)
GL_PACK_SKIP_ROWS integer 0
[0,Infinity)
GL_PACK_SKIP_PIXELS integer 0
[0,Infinity)
GL_PACK_SKIP_IMAGES integer 0
[0,Infinity)
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,Infinity)
GL_UNPACK_IMAGE_HEIGHT integer 0
[0,Infinity)
GL_UNPACK_SKIP_ROWS integer 0
[0,Infinity)
GL_UNPACK_SKIP_PIXELS integer 0
[0,Infinity)
GL_UNPACK_SKIP_IMAGES integer 0
[0,Infinity)
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 storage
modes in effect when glColorTable(), glColorSubTable(),
glConvolutionFilter1D(), 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 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
SEE ALSO
glBitmap(3), glColorTable(3), glColorSubTable(3), glConvolutionFilter1D(3),
glConvolutionFilter2D(3), glSeparableFilter2D(3), glDrawPixels(3),
glHistogram(3), glMinmax(3), glPixelMap(3), glPixelTransfer(3),
glPixelZoom(3), glPolygonStipple(3), glPushClientAttrib(3),
glReadPixels(3), glTexImage1D(3), glTexImage2D(3), glTexImage3D(3),
glTexSubImage1D(3), glTexSubImage2D(3), glTexSubImage3D(3)
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Index for
Section 3G |
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Alphabetical
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Top of
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