NAME
fglPixelStoref, fglPixelStorei - set pixel storage modes
FORTRAN SPECIFICATION
SUBROUTINE fglPixelStoref( INTEGER*4 pname,
REAL*4 param )
SUBROUTINE fglPixelStorei( INTEGER*4 pname,
INTEGER*4 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_SKIP_PIXELS,
GL_PACK_SKIP_ROWS, 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_SKIP_PIXELS,
GL_UNPACK_SKIP_ROWS, and GL_UNPACK_ALIGNMENT.
param Specifies the value that pname is set to.
DESCRIPTION
fglPixelStore sets pixel storage modes that affect the
operation of subsequent fglDrawPixels and fglReadPixels as
well as the unpacking of polygon stipple patterns (see
fglPolygonStipple), bitmaps (see fglBitmap), and texture
patterns (see fglTexImage1D, fglTexImage2D,
fglTexSubImage1D, and fglTexSubImage2D).
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, and are therefore significant only for fglReadPixels
commands. 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 , b , b , b ,
it is stored in memory as b , b , b , b if 3
GL_PACK_SWAP_BYTES is true.3 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. 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 = |_|___| 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|__|
|8a|
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_SKIP_PIXELS and GL_PACK_SKIP_ROWS
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 fglReadPixels. Setting
GL_PACK_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_PACK_SKIP_ROWS
to j is equivalent to incrementing the pointer by
jk components or indices, where k is the number of
components or indices per row, as just computed in
the GL_PACK_ROW_LENGTH 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 fglDrawPixels, fglTexImage1D, fglTexImage2D,
fglTexSubImage1D, fglTexSubImage2D, fglBitmap, and
fglPolygonStipple. 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 , b , b , b , it is taken from memory as b ,
b , b , b 0if GL_UNPACK_SWAP_BYTES is true. 3
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. 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 = |_|___| 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 = 8a|__|
|8a|
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_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
fglDrawPixels, fglTexImage1D, fglTexImage2D,
fglTexSubImage1D, fglTexSubImage2D, fglBitmap, or
fglPolygonStipple. 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 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 fglPixelStore.
_________________________________________________________________
| 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,oo) |
| GL_PACK_SKIP_ROWS | integer | 0 | [0,oo) |
| GL_PACK_SKIP_PIXELS | integer | 0 | [0,oo) |
| 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,oo) |
| GL_UNPACK_SKIP_ROWS | integer | 0 | [0,oo) |
|______________________|_________|_______________|_______________|
|GL_UNPACK_SKIP_PIXELS | integer | 0 | [0,oo) |
| GL_UNPACK_ALIGNMENT | integer | 4 | 1, 2, 4, or 8 |
|______________________|_________|_______________|_______________|
fglPixelStoref 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, fglPixelStorei 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 fglDrawPixels,
fglReadPixels, fglTexImage1D, fglTexImage2D,
fglTexSubImage1D, fglTexSubImage2D, fglBitmap, or
fglPolygonStipple is placed in a display list control the
interpretation 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
fglPushClientAttrib and fglPopClientAttrib.
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 fglPixelStore is
executed between the execution of fglBegin and the
corresponding execution of fglEnd.
ASSOCIATED GETS
fglGet with argument GL_PACK_SWAP_BYTES
fglGet with argument GL_PACK_LSB_FIRST
fglGet with argument GL_PACK_ROW_LENGTH
fglGet with argument GL_PACK_SKIP_ROWS
fglGet with argument GL_PACK_SKIP_PIXELS
fglGet with argument GL_PACK_ALIGNMENT
fglGet with argument GL_UNPACK_SWAP_BYTES
fglGet with argument GL_UNPACK_LSB_FIRST
fglGet with argument GL_UNPACK_ROW_LENGTH
fglGet with argument GL_UNPACK_SKIP_ROWS
fglGet with argument GL_UNPACK_SKIP_PIXELS
fglGet with argument GL_UNPACK_ALIGNMENT
SEE ALSO
fglBitmap, fglDrawPixels, fglPixelMap, fglPixelTransfer,
fglPixelZoom,
fglPolygonStipple, fglPushClientAttrib, fglReadPixels,
fglTexImage1D, fglTexImage2D, fglTexSubImage1D,
fglTexSubImage2D