table of contents
GLPIXELSTORE(3G) | [FIXME: manual] | GLPIXELSTORE(3G) |
NAME¶
glPixelStore - set pixel storage modesC SPECIFICATION¶
void
glPixelStoref(GLenum pname,
GLfloat param);
void
glPixelStorei(GLenum pname,
GLint param);
PARAMETERS¶
pnameSpecifies 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¶
If true, byte ordering for multibyte color
components, depth components, or stencil indices is reversed. That is, if a
four-byte component consists of bytes b 0, b 1, b 2, b 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 format 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.
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 = n l a s s n l a 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 = 8 a n l 8 a
components or indices.
The word component in this description refers to the nonindex values red,
green, blue, alpha, and depth. Storage format 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
k = n l h a s s n l h a
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 format 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 glTexImage1D(),
glTexImage2D(), glTexImage3D(), glTexSubImage1D(),
glTexSubImage2D(), and glTexSubImage3D()
They are as follows:
GL_UNPACK_SWAP_BYTES
If true, byte ordering for multibyte color
components, depth components, or stencil indices is reversed. That is, if a
four-byte component consists of bytes b 0, b 1, b 2, b 3, it is taken from
memory as b 3, b 2, b 1, b 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 format 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.
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 = n l a s s n l a 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_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 = 8 a n l 8 a
components or indices.
The word component in this description refers to the nonindex values red,
green, blue, alpha, and depth. Storage format 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
k = n l h a s s n l h a
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_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 format 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 glTexImage1D(),
glTexImage2D(), glTexSubImage1D() or glTexSubImage2D().
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 | Initial Value | Valid 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 |
GL_PACK_IMAGE_HEIGHT | integer | 0 | 0 |
GL_PACK_SKIP_ROWS | integer | 0 | 0 |
GL_PACK_SKIP_PIXELS | integer | 0 | 0 |
GL_PACK_SKIP_IMAGES | integer | 0 | 0 |
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 |
GL_UNPACK_IMAGE_HEIGHT | integer | 0 | 0 |
GL_UNPACK_SKIP_ROWS | integer | 0 | 0 |
GL_UNPACK_SKIP_PIXELS | integer | 0 | 0 |
GL_UNPACK_SKIP_IMAGES | integer | 0 | 0 |
GL_UNPACK_ALIGNMENT | integer | 4 | 1, 2, 4, or 8 |
ERRORS¶
ASSOCIATED GETS¶
SEE ALSO¶
COPYRIGHT¶
Copyright © 1991-2006 Silicon Graphics, Inc. © 2011 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.05/30/2012 | [FIXME: source] |