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glPixelStore(3G)
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glPixelStore, glPixelStoref, glPixelStorei - set pixel
storage modes
void glPixelStoref(
GLenum pname,
GLfloat param ); void glPixelStorei(
GLenum pname,
GLint param );
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.
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: 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. 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 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. 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. 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. Specifies the
alignment requirements for the start of each pixel
row in memory. The allowable values are 1 (bytealignment),
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: 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. 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. 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. 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. 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. Specifies the
alignment requirements for the start of each pixel
row in memory. The allowable values are 1 (bytealignment),
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,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.
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().
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().
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
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)
glPixelStore(3G)
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