glPixelStore

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Set pixel storage modes.

C Specification[edit]

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


Parameters[edit]

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 datafrommemory: 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[edit]

 glPixelStore sets pixel storage modes that affect the operation of subsequent glReadPixels as well as the unpacking of texture patterns (see glTexImage1D , glTexImage2D , glTexImage3D , glTexSubImage1D , glTexSubImage2D , glTexSubImage3D ), glCompressedTexImage1D , glCompressedTexImage2D , glCompressedTexImage3D , glCompressedTexSubImage1D , glCompressedTexSubImage2D or glCompressedTexSubImage1D .

 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, or stencil indices is reversed. That is, if a four-byte component consists of bytes [math][/math] , [math][/math] , [math][/math] , [math][/math] , it is stored in memory as [math][/math] , [math][/math] , [math][/math] , [math][/math] 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 [math][/math] in memory, then the location of the first pixel of the next row is obtained by skipping [math]k={[/math] components or indices, where [math][/math] is the number of components or indices in a pixel, [math][/math] is the number of pixels in a row ( GL_PACK_ROW_LENGTH if it is greater than 0, the [math][/math] argument to the pixel routine otherwise), [math][/math] is the value of GL_PACK_ALIGNMENT , and [math][/math] is the size, in bytes, of a single component (if [math]a\lt s[/math] , then it is as if [math]a=s[/math] ). In the case of 1-bit values, the location of the next row is obtained by skipping [math]k=8⁢a⁢⌈⌉[/math] components or indices.The wordcomponentin 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 [math][/math] in memory, then the location of the first pixel of the next row is obtained by skipping [math]k={[/math] components or indices, where [math][/math] is the number of components or indices in a pixel, [math][/math] is the number of pixels in a row ( GL_PACK_ROW_LENGTH if it is greater than 0, the [math][/math] argument to glTexImage3D otherwise), [math][/math] is the number of rows in a pixel image ( GL_PACK_IMAGE_HEIGHT if it is greater than 0, the [math][/math] argument to the glTexImage3D routine otherwise), [math][/math] is the value of GL_PACK_ALIGNMENT , and [math][/math] is the size, in bytes, of a single component (if [math]a\lt s[/math] , then it is as if [math]a=s[/math] ).The wordcomponentin 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 , andGL_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 [math][/math] is equivalent to incrementing the pointer by [math]i⁢n[/math] components or indices, where [math][/math] is the number of components or indices in each pixel. Setting GL_PACK_SKIP_ROWS to [math][/math] is equivalent to incrementing the pointer by [math]j⁢m[/math] components or indices, where [math][/math] 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 [math][/math] is equivalent to incrementing the pointer by [math]k⁢p[/math] , where [math][/math] 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 [math][/math] , [math][/math] , [math][/math] , [math][/math] , it is taken from memory as [math][/math] , [math][/math] , [math][/math] , [math][/math] 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 [math][/math] in memory, then the location of the first pixel of the next row is obtained by skipping [math]k={[/math] components or indices, where [math][/math] is the number of components or indices in a pixel, [math][/math] is the number of pixels in a row ( GL_UNPACK_ROW_LENGTH if it is greater than 0, the [math][/math] argument to the pixel routine otherwise), [math][/math] is the value of GL_UNPACK_ALIGNMENT , and [math][/math] is the size, in bytes, of a single component (if [math]a\lt s[/math] , then it is as if [math]a=s[/math] ). In the case of 1-bit values, the location of the next row is obtained by skipping [math]k=8⁢a⁢⌈⌉[/math] components or indices.The wordcomponentin 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 [math][/math] in memory, then the location of the first pixel of the next row is obtained by skipping [math]k={[/math] components or indices, where [math][/math] is the number of components or indices in a pixel, [math][/math] is the number of pixels in a row ( GL_UNPACK_ROW_LENGTH if it is greater than 0, the [math][/math] argument to glTexImage3D otherwise), [math][/math] is the number of rows in an image ( GL_UNPACK_IMAGE_HEIGHT if it is greater than 0, the [math][/math] argument to glTexImage3D otherwise), [math][/math] is the value of GL_UNPACK_ALIGNMENT , and [math][/math] is the size, in bytes, of a single component (if [math]a\lt s[/math] , then it is as if [math]a=s[/math] ).The wordcomponentin 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 andGL_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 [math][/math] is equivalent to incrementing the pointer by [math]i⁢n[/math] components or indices, where [math][/math] is the number of components or indices in each pixel. Setting GL_UNPACK_SKIP_ROWS to [math][/math] is equivalent to incrementing the pointer by [math]j⁢k[/math] components or indices, where [math][/math] 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  [math][0,∞)[/math] 
GL_PACK_IMAGE_HEIGHT  integer 0  [math][0,∞)[/math] 
GL_PACK_SKIP_ROWS  integer 0  [math][0,∞)[/math] 
GL_PACK_SKIP_PIXELS  integer 0  [math][0,∞)[/math] 
GL_PACK_SKIP_IMAGES  integer 0  [math][0,∞)[/math] 
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  [math][0,∞)[/math] 
GL_UNPACK_IMAGE_HEIGHT  integer 0  [math][0,∞)[/math] 
GL_UNPACK_SKIP_ROWS  integer 0  [math][0,∞)[/math] 
GL_UNPACK_SKIP_PIXELS  integer 0  [math][0,∞)[/math] 
GL_UNPACK_SKIP_IMAGES  integer 0  [math][0,∞)[/math] 
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 an 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.


Errors[edit]

 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.


Associated Gets[edit]

 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 


Version Support[edit]

 glPixelStoref  2.0+
 glPixelStorei  2.0+

See Also[edit]

 glReadPixels , glTexImage1D , glTexImage2D , glTexImage3D , glTexSubImage1D , glTexSubImage2D , glTexSubImage3D , glCompressedTexImage1D , glCompressedTexImage2D , glCompressedTexImage3D , glCompressedTexSubImage1D , glCompressedTexSubImage2D , glCompressedTexSubImage1D .


Copyright[edit]

Copyright© 1991-2006 Silicon Graphics, Inc. Copyright© 2010-2014 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.