glReadPixels man page on Darwin
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GLREADPIXELS(3G) OpenGL 3.3 GLREADPIXELS(3G)
NAME
glReadPixels - 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);
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.
data
Returns the pixel data.
DESCRIPTION
glReadPixels returns 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 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 returns 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. Each index is
converted to fixed point, shifted left or right depending on the
value and sign of GL_INDEX_SHIFT, and added to GL_INDEX_OFFSET. If
GL_MAP_STENCIL is GL_TRUE, indices are replaced by their mappings
in the table GL_PIXEL_MAP_S_TO_S.
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 then
multiplied by GL_DEPTH_SCALE, added to GL_DEPTH_BIAS, and finally
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
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).
┌──────────────────────────────────┬────────────────────────────────────┬────────────────────────────────────────────────────┐
│type │ │ │
│ │ Index │ Component │
│ │ Mask │ 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.
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.
ASSOCIATED GETS
glGet() with argument GL_INDEX_MODE
glGet() with argument GL_PIXEL_PACK_BUFFER_BINDING
SEE ALSO
glPixelStore(), glReadBuffer()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
OpenGL 3.3 03/08/2011 GLREADPIXELS(3G)
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