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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 )

       delim $$

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 sub‐
       sequent glDrawPixels and glReadPixels as well as the unpacking of poly‐
       gon 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  $b	 sub  3$,  $b  sub  2$,	 $b  sub  1$,  $b  sub	0$  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 signifi‐
		 cant to most significant; otherwise, the first	 bit  in  each
		 byte is the most significant one.  This parameter is signifi‐
		 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

		 $k  ~=~~ left	{ ^ lpile { n l above {a over s left ceiling {
		 s n l } over a right ceiling}} ~~ lpile {s ~>=~ a above s ~<~
					     a }$

		 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

		 $k ~=~ 8 a left ceiling { n l } over { 8 a } ^ right ceiling$

		 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

		 $k ~=~~ left  { ~ lpile { n l h above {a over s left  ceiling
					  { s n l h }
		 over  a  ^ right ceiling}} ~~ lpile {s ~>=~  a above s ~<~  a
		 }$

		 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  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  sim‐
		 ply 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 num‐
		 ber 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 com‐
		 puted 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-align‐
		 ment),	 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 compo‐
	      nents within a pixel, only on the order of bytes	within	compo‐
	      nents 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 loca‐
	      tion $p$ in memory, then the location of the first pixel of  the
	      next row is obtained by skipping

	      $k ~=~~ left  { ~ lpile { n l above {a over s left ceiling { s n
					    l }
	      over a ^ right ceiling}} ~~ lpile {s  ~>=~ a above s ~<~	a }$

	      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 $width$	 argu‐
	      ment  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

		$k ~=~ 8 a left ceiling { n l } over { 8 a } right ceiling$

	      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	dimen‐
	      sion  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

	      $k  ~=~~ left  {~ lpile { n l h above {a over s left ceiling { s
					  n l h }
	      over a ^ right ceiling}} ~~ lpile {s ~ >=~  a above s  ~<~  a }$

	      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 $width$	 argu‐
	      ment 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 sin‐
	      gle 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 com‐
	      puted 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
	  ─────────────────────────────────────────────────────────────────

       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 stor‐
       age   modes   in	   effect    when    glColorTable,    glColorSubTable,
       glConvolutionFilter1D, glConvolutionFilter2D, of glSeparableFilter2D 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
       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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