GLPIXELSTORE(3G) GLPIXELSTORE(3G)
NAME
glPixelStoref, glPixelStorei - 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 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, pixel
storage modes affect convolution 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 fol-lows: follows:
lows:
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 b0, b1,
b2, b2 it is stored in memory as b3, b2, b1, b0 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; other-wise, otherwise,
wise, the first bit in each byte is the most significant one. This parameter is signifi-cant significant
cant 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
k = nl for s>=a, (a/s)(snl/a) for 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 val-
ues, 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 threedimensional
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 = nlh for s>=a, (a/s)(snlh/a) for 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. Set-
ting 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 allow-able allowable
able values are 1 (byte-alignment), 2 (rows aligned to even-numbered bytes), 4 (word-align-ment), (word-alignment),
ment), 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 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, 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
k = nl for s>=a, (a/s)(snl/a) for 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 val-
ues, 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 threedimensional
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 = nlh for s>=a, (a/s)(snlh/a) for 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 parame-
ter that can be set with glPixelStore.
pname Type Initial Valid
Value 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,inf]
GL_PACK_IMAGE_HEIGHT integer 0 [0,inf]
GL_PACK_SKIP_ROWS integer 0 [0,inf]
GL_PACK_SKIP_PIXELS integer 0 [0,inf]
GL_PACK_SKIP_IMAGES integer 0 [0,inf]
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,inf]
GL_UNPACK_IMAGE_HEIGHT integer 0 [0,inf]
GL_UNPACK_SKIP_ROWS integer 0 [0,inf]
GL_UNPACK_SKIP_PIXELS integer 0 [0,inf]
GL_UNPACK_SKIP_IMAGES integer 0 [0,inf]
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 parame-ters parameters
ters 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 con-trol control
trol 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(3G), glColorTable(3G), glColorSubTable(3G), glConvolutionFilter1D(3G), glConvolutionFilter2D(3G),
glSeparableFilter2D(3G), glDrawPixels(3G), glHistogram(3G), glMinmax(3G), glPixelMap(3G), glPixelTransfer(3G), glPixelZoom(3G),
glPolygonStipple(3G), glPushClientAttrib(3G), glReadPixels(3G), glTexImage1D(3G), glTexImage2D(3G), glTexImage3D(3G),
glTexSubImage1D(3G), glTexSubImage2D(3G), glTexSubImage3D(3G)
GLPIXELSTORE(3G)
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