Provided by: opengl-4-man-doc_1.0~svn33624-1_all bug

NAME

       glReadPixels, glReadnPixels - read a block of pixels from the frame buffer

C SPECIFICATION

       void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format,
                         GLenum type, GLvoid * data);

       void glReadnPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format,
                          GLenum type, GLsizei bufSize, void *data);

PARAMETERS

       x, y
           Specify the window coordinates of the first pixel that is read from the frame buffer.
           This location is the lower left corner of a rectangular block of pixels.

       width, height
           Specify the dimensions of the pixel rectangle.  width and height of one correspond to
           a single pixel.

       format
           Specifies the format of the pixel data. The following symbolic values are accepted:
           GL_STENCIL_INDEX, GL_DEPTH_COMPONENT, GL_DEPTH_STENCIL, GL_RED, GL_GREEN, GL_BLUE,
           GL_RGB, GL_BGR, GL_RGBA, and GL_BGRA.

       type
           Specifies the data type of the pixel data. Must be one of GL_UNSIGNED_BYTE, GL_BYTE,
           GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, GL_HALF_FLOAT, GL_FLOAT,
           GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5,
           GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
           GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8,
           GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2,
           GL_UNSIGNED_INT_2_10_10_10_REV, GL_UNSIGNED_INT_24_8, GL_UNSIGNED_INT_10F_11F_11F_REV,
           GL_UNSIGNED_INT_5_9_9_9_REV, or GL_FLOAT_32_UNSIGNED_INT_24_8_REV.

       bufSize
           Specifies the size of the buffer data for glReadnPixels function.

       data
           Returns the pixel data.

DESCRIPTION

       glReadPixels and glReadnPixels return pixel data from the frame buffer, starting with the
       pixel whose lower left corner is at location (x, y), into client memory starting at
       location data. Several parameters control the processing of the pixel data before it is
       placed into client memory. These parameters are set with glPixelStore(). This reference
       page describes the effects on glReadPixels and glReadnPixels of most, but not all of the
       parameters specified by these three commands.

       If a non-zero named buffer object is bound to the GL_PIXEL_PACK_BUFFER target (see
       glBindBuffer()) while a block of pixels is requested, data is treated as a byte offset
       into the buffer object's data store rather than a pointer to client memory.

       glReadPixels and glReadnPixels return values from each pixel with lower left corner at x +
       i y + j for 0 <= i < width and 0 <= j < height. This pixel is said to be the ith pixel in
       the jth row. Pixels are returned in row order from the lowest to the highest row, left to
       right in each row.

       format specifies the format for the returned pixel values; accepted values are:

       GL_STENCIL_INDEX
           Stencil values are read from the stencil buffer.

       GL_DEPTH_COMPONENT
           Depth values are read from the depth buffer. Each component is converted to floating
           point such that the minimum depth value maps to 0 and the maximum value maps to 1.
           Each component is clamped to the range 0 1.

       GL_DEPTH_STENCIL
           Values are taken from both the depth and stencil buffers. The type parameter must be
           GL_UNSIGNED_INT_24_8 or GL_FLOAT_32_UNSIGNED_INT_24_8_REV.

       GL_RED, GL_GREEN, GL_BLUE, GL_RGB, GL_BGR, GL_RGBA, GL_BGRA
           Color values are taken from the color buffer.

       Finally, the indices or components are converted to the proper format, as specified by
       type. If format is GL_STENCIL_INDEX and type is not GL_FLOAT, each index is masked with
       the mask value given in the following table. If type is GL_FLOAT, then each integer index
       is converted to single-precision floating-point format.

       If format is GL_RED, GL_GREEN, GL_BLUE, GL_RGB, GL_BGR, GL_RGBA, or GL_BGRA and type is
       not GL_FLOAT, each component is multiplied by the multiplier shown in the following table.
       If type is GL_FLOAT, then each component is passed as is (or converted to the client's
       single-precision floating-point format if it is different from the one used by the GL).

       ┌──────────────────────────────────┬────────────────────────────────────┬────────────────────────────────────────────────────┐
       │typeIndex MaskComponent Conversion                │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_BYTE                  │ 2                                  │     2                                              │
       │                                  │                                 8  │                                             8      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_BYTE                           │ 2                                  │ 2                                                  │
       │                                  │                                 7  │                                                 8  │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                                 -  │
       │                                  │                                 1  │                                                 1  │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                         ⁢          │
       │                                  │                                    │                                         c          │
       │                                  │                                    │                                         -          │
       │                                  │                                    │                                         1          │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                 2                  │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT                 │ 2                                  │     2                                              │
       │                                  │                                 16 │                                             16     │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_SHORT                          │ 2                                  │ 2                                                  │
       │                                  │                                 15 │                                                 16 │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                                 -  │
       │                                  │                                 1  │                                                 1  │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                         ⁢          │
       │                                  │                                    │                                         c          │
       │                                  │                                    │                                         -          │
       │                                  │                                    │                                         1          │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                 2                  │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT                   │ 2                                  │     2                                              │
       │                                  │                                 32 │                                             32     │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_INT                            │ 2                                  │ 2                                                  │
       │                                  │                                 31 │                                                 32 │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                                 -  │
       │                                  │                                 1  │                                                 1  │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                         ⁢          │
       │                                  │                                    │                                         c          │
       │                                  │                                    │                                         -          │
       │                                  │                                    │                                         1          │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                 2                  │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_HALF_FLOAT                     │                none                │                         c                          │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_FLOAT                          │                none                │                         c                          │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_BYTE_3_3_2            │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_BYTE_2_3_3_REV        │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT_5_6_5           │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT_5_6_5_REV       │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT_4_4_4_4         │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT_4_4_4_4_REV     │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT_5_5_5_1         │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_SHORT_1_5_5_5_REV     │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_8_8_8_8           │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_8_8_8_8_REV       │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_10_10_10_2        │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_2_10_10_10_REV    │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_24_8              │ 2                                  │     2                                              │
       │                                  │                                 N  │                                             N      │
       │                                  │                                    │                                                    │
       │                                  │                                 -  │                                             -      │
       │                                  │                                 1  │                                             1      │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                                    │
       │                                  │                                    │                                     ⁢              │
       │                                  │                                    │                                     c              │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_10F_11F_11F_REV   │                 --                 │                      Special                       │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_UNSIGNED_INT_5_9_9_9_REV       │                 --                 │                      Special                       │
       ├──────────────────────────────────┼────────────────────────────────────┼────────────────────────────────────────────────────┤
       │GL_FLOAT_32_UNSIGNED_INT_24_8_REV │                none                │                   c (Depth Only)                   │
       └──────────────────────────────────┴────────────────────────────────────┴────────────────────────────────────────────────────┘

       Return values are placed in memory as follows. If format is GL_STENCIL_INDEX,
       GL_DEPTH_COMPONENT, GL_RED, GL_GREEN, or GL_BLUE, a single value is returned and the data
       for the ith pixel in the jth row is placed in location j ⁢ width + i.  GL_RGB and GL_BGR
       return three values, GL_RGBA and GL_BGRA return four values for each pixel, with all
       values corresponding to a single pixel occupying contiguous space in data. Storage
       parameters set by glPixelStore(), such as GL_PACK_LSB_FIRST and GL_PACK_SWAP_BYTES, affect
       the way that data is written into memory. See glPixelStore() for a description.

       glReadnPixels function will only handle the call if bufSize is at least of the size
       required to store the requested data. Otherwise, it will generate a GL_INVALID_OPERATION
       error.

NOTES

       Values for pixels that lie outside the window connected to the current GL context are
       undefined.

       If an error is generated, no change is made to the contents of data.

ERRORS

       GL_INVALID_ENUM is generated if format or type is not an accepted value.

       GL_INVALID_VALUE is generated if either width or height is negative.

       GL_INVALID_OPERATION is generated if format is GL_STENCIL_INDEX and there is no stencil
       buffer.

       GL_INVALID_OPERATION is generated if format is GL_DEPTH_COMPONENT and there is no depth
       buffer.

       GL_INVALID_OPERATION is generated if format is GL_DEPTH_STENCIL and there is no depth
       buffer or if there is no stencil buffer.

       GL_INVALID_ENUM is generated if format is GL_DEPTH_STENCIL and type is not
       GL_UNSIGNED_INT_24_8 or GL_FLOAT_32_UNSIGNED_INT_24_8_REV.

       GL_INVALID_OPERATION is generated if type is one of GL_UNSIGNED_BYTE_3_3_2,
       GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5, or GL_UNSIGNED_SHORT_5_6_5_REV and
       format is not GL_RGB.

       GL_INVALID_OPERATION is generated if type is one of GL_UNSIGNED_SHORT_4_4_4_4,
       GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
       GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, or
       GL_UNSIGNED_INT_2_10_10_10_REV and format is neither GL_RGBA nor GL_BGRA.

       GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the
       GL_PIXEL_PACK_BUFFER target and the buffer object's data store is currently mapped.

       GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the
       GL_PIXEL_PACK_BUFFER target and the data would be packed to the buffer object such that
       the memory writes required would exceed the data store size.

       GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the
       GL_PIXEL_PACK_BUFFER target and data is not evenly divisible into the number of bytes
       needed to store in memory a datum indicated by type.

       GL_INVALID_OPERATION is generated if GL_READ_FRAMEBUFFER_BINDING is non-zero, the read
       framebuffer is complete, and the value of GL_SAMPLE_BUFFERS for the read framebuffer is
       greater than zero.

       GL_INVALID_OPERATION is generated by glReadnPixels if the buffer size required to store
       the requested data is greater than bufSize.

ASSOCIATED GETS

       glGet() with argument GL_PIXEL_PACK_BUFFER_BINDING

VERSION SUPPORT

       ┌──────────────┬───────────────────────────────────────────────────────────────────────┐
       │              │                OpenGL Version                                         │
       ├──────────────┼─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┤
       │Function2.02.13.03.13.23.34.04.14.24.34.44.5 │
       │/             │     │     │     │     │     │     │     │     │     │     │     │     │
       │Feature       │     │     │     │     │     │     │     │     │     │     │     │     │
       │Name          │     │     │     │     │     │     │     │     │     │     │     │     │
       ├──────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
       │glReadPixels  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │  ✔  │
       ├──────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
       │glReadnPixels │  -  │  -  │  -  │  -  │  -  │  -  │  -  │  -  │  -  │  -  │  -  │  ✔  │
       └──────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘

SEE ALSO

       glPixelStore(), glReadBuffer()

COPYRIGHT

       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/.

COPYRIGHT

       Copyright © 1991-2006 Silicon Graphics, Inc.
       Copyright © 2010-2014 Khronos Group

[FIXME: source]                             01/03/2018                           GLREADPIXELS(3G)