glPixelStore man page on DigitalUNIX

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glPixelStore(3G)					      glPixelStore(3G)

NAME
       glPixelStore, glPixelStoref, glPixelStorei - set pixel storage modes

SYNOPSIS
       void glPixelStoref(
	       GLenum pname,
	       GLfloat param ); void glPixelStorei(
	       GLenum pname,
	       GLint param );

PARAMETERS
       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.

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(),   glTexSubIm‐
       age3D()). Additionally, if the GL_ARB_imaging extension	is  supported,
       pixle  storage  modes  affect convlution filters (see glConvolutionFil‐
       ter1D(), glConvolutionFilter2D(), and glSeparableFilter2D(), color  ta‐
       ble (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 compo‐
       nents 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 com‐
	      ponent (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  tex‐
	      ture  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 glRead‐
	      Pixels(). 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	compo‐
	      nents   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 require‐
	      ments 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  glDrawPix‐
       els(),	glTexImage1D(),	 glTexImage2D(),  glTexImage3D(),  glTexSubIm‐
       age1D(), glTexSubImage2D(), glTexSubImage3D(), glBitmap(), and  glPoly‐
       gonStipple().

       Additionally,  if  the  GL_ARB_imaging  extension  is supported, glCol‐
       orTable(), glColorSubTable(),  glConvolutionFilter1D(),	glConvolution‐
       Filter2D(),  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 compo‐
       nent 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 signifi‐
       cant; 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 loca‐
       tion 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	 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	 skip‐
	      ping 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 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 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(),  glTexSubIm‐
	      age2D(),	   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 (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	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,Infin‐
							ity)
       GL_PACK_IMAGE_HEIGHT	integer	  0		[0,  Infin‐
							ity)
       GL_PACK_SKIP_ROWS	integer	  0		[0,Infin‐
							ity)
       GL_PACK_SKIP_PIXELS	integer	  0		[0,Infin‐
							ity)
       GL_PACK_SKIP_IMAGES	integer	  0		[0,Infin‐
							ity)
       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,Infin‐
							ity)
       GL_UNPACK_IMAGE_HEIGHT	integer	  0		[0,Infin‐
							ity)
       GL_UNPACK_SKIP_ROWS	integer	  0		[0,Infin‐
							ity)
       GL_UNPACK_SKIP_PIXELS	integer	  0		[0,Infin‐
							ity)
       GL_UNPACK_SKIP_IMAGES	integer	  0		[0,Infin‐
							ity)
       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(), glConvolu‐
       tionFilter1D(), 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().

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(3),   glColorTable(3),	glColorSubTable(3),  glConvolutionFil‐
       ter1D(3), glConvolutionFilter2D(3), glSeparableFilter2D(3),  glDrawPix‐
       els(3), glHistogram(3), glMinmax(3), glPixelMap(3), glPixelTransfer(3),
       glPixelZoom(3), glPolygonStipple(3), glPushClientAttrib(3),  glReadPix‐
       els(3),	glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glTexSubIm‐
       age1D(3), glTexSubImage2D(3), glTexSubImage3D(3)

							      glPixelStore(3G)
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