table of contents
GLREADPIXELS(3G) | [FIXME: manual] | GLREADPIXELS(3G) |
NAME¶
glReadPixels, glReadnPixels - read a block of pixels from the frame bufferC 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, ySpecify 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_INDEXStencil 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).
type | Index Mask | Component Conversion |
GL_UNSIGNED_BYTE | 2 8 - 1 | 2 8 - 1 c |
GL_BYTE | 2 7 - 1 | 2 8 - 1 c - 1 2 |
GL_UNSIGNED_SHORT | 2 16 - 1 | 2 16 - 1 c |
GL_SHORT | 2 15 - 1 | 2 16 - 1 c - 1 2 |
GL_UNSIGNED_INT | 2 32 - 1 | 2 32 - 1 c |
GL_INT | 2 31 - 1 | 2 32 - 1 c - 1 2 |
GL_HALF_FLOAT | none | c |
GL_FLOAT | none | c |
GL_UNSIGNED_BYTE_3_3_2 | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_BYTE_2_3_3_REV | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_SHORT_5_6_5 | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_SHORT_5_6_5_REV | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_SHORT_4_4_4_4 | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_SHORT_4_4_4_4_REV | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_SHORT_5_5_5_1 | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_SHORT_1_5_5_5_REV | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_INT_8_8_8_8 | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_INT_8_8_8_8_REV | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_INT_10_10_10_2 | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_INT_2_10_10_10_REV | 2 N - 1 | 2 N - 1 c |
GL_UNSIGNED_INT_24_8 | 2 N - 1 | 2 N - 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) |
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_BINDINGVERSION SUPPORT¶
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 | - | - | - | - | - | - | - | - | - | - | - | ✔ |
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.08/26/2014 | [FIXME: source] |