glReadPixels, glReadnPixels — read a block of pixels from the frame buffer
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); |
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.
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
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 .
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).
type
|
Index Mask | Component Conversion |
|---|---|---|
GL_UNSIGNED_BYTE
|
||
GL_BYTE
|
||
GL_UNSIGNED_SHORT
|
||
GL_SHORT
|
||
GL_UNSIGNED_INT
|
||
GL_INT
|
||
GL_HALF_FLOAT
|
none | |
GL_FLOAT
|
none | |
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
|
-- | Special |
GL_UNSIGNED_INT_5_9_9_9_REV
|
-- | Special |
GL_FLOAT_32_UNSIGNED_INT_24_8_REV
|
none | (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
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.
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.
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.
glGet
with argument GL_PIXEL_PACK_BUFFER_BINDING
| OpenGL Version | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Function / Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5 |
glReadPixels
|
✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
glReadnPixels
|
- | - | - | - | - | - | - | - | - | - | - | ✔ |
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/.