GLAPI/glPixelStore

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glPixelStore
Core in version 4.4
Core since version 1.0

glPixelStore: set pixel storage modes

Function Definition

 void glPixelStoref(GLenum pname​, GLfloat param​);
 void glPixelStorei(GLenum pname​, GLint param​);
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 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 b0, b1, b2, b3, it is stored in memory as b3, b2, b1, b0 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
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
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
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 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 jm 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 kp, 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 b0, b1, b2, b3, it is taken from memory as b3, b2, b1, b0 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
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
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

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 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 jm components or indices, where m 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

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.

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.

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

glReadPixels, glTexImage1D, glTexImage2D, glTexImage3D, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D, glCompressedTexImage1D, glCompressedTexImage2D, glCompressedTexImage3D, glCompressedTexSubImage1D, glCompressedTexSubImage2D, glCompressedTexSubImage3D

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/.