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, | |
void * 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_RGBA, and
GL_RGBA_INTEGER.
An implementation-chosen format will also be accepted.
This can be queried with glGet and
GL_IMPLEMENTATION_COLOR_READ_FORMAT.
type
Specifies the data type of the pixel data.
Must be one of
GL_UNSIGNED_BYTE,
GL_UNSIGNED_INT,
GL_UNSIGNED_INT_2_10_10_10_REV,
GL_INT, or
GL_FLOAT.
An implementation-chosen type will also be accepted.
This can be queried with glGet and
GL_IMPLEMENTATION_COLOR_READ_TYPE.
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 glPixelStorei.
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
for
and
.
This pixel is said to be the
th
pixel in the
th
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_RED,
GL_RED_INTEGER,
GL_RG,
GL_RG_INTEGER,
GL_RGB,
GL_RGB_INTEGER,
GL_RGBA,
GL_RGBA_INTEGER,
GL_LUMINANCE_ALPHA,
GL_LUMINANCE, and
GL_ALPHA
Finally, the indices or components
are converted to the proper format,
as specified by type.
If type is GL_FLOAT, then each integer index is converted to
single-precision floating-point format.
If format is
GL_RED,
GL_RG,
GL_RGB, or
GL_RGBA, 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_HALF_FLOAT
|
none | |||
GL_FLOAT
|
none | |||
GL_UNSIGNED_SHORT_5_6_5
|
||||
GL_UNSIGNED_SHORT_4_4_4_4
|
||||
GL_UNSIGNED_SHORT_5_5_5_1
|
||||
GL_UNSIGNED_INT_2_10_10_10_REV
|
||||
GL_UNSIGNED_INT_10F_11F_11F_REV
|
-- | Special | ||
GL_UNSIGNED_INT_5_9_9_9_REV
|
-- | Special |
Return values are placed in memory as follows.
If format is
GL_RED, or
GL_RED_INTEGER,
a single value is returned and the data for the
th
pixel in the
th
row
is placed in location
.
GL_RG and GL_RG_INTEGER return two values,
GL_RGB and GL_RGB_INTEGER return three values,
GL_RGBA and GL_RGBA_INTEGER return four values for each pixel,
with all values corresponding to a single pixel occupying contiguous space
in data.
See glPixelStorei for a description of parameters which affect
the packing of data into memory.
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.
Only three format/type parameter pairs are
accepted. For normalized fixed point rendering surfaces, GL_RGBA/GL_UNSIGNED_BYTE is
accepted. For signed integer rendering surfaces, GL_RGBA_INTEGER/GL_INT is accepted.
For unsigned integer rendering surfaces, GL_RGBA_INTEGER/GL_UNSIGNED_INT is accepted.
For GL_RGBA10_A2 rendering surfaces, GL_RGBA/GL_UNSIGNED_INT_2_10_10_10_REV is accepted.
The other acceptable pair can be discovered by querying
GL_IMPLEMENTATION_COLOR_READ_FORMAT and
GL_IMPLEMENTATION_COLOR_READ_TYPE. The implementation chosen format may also vary depending on the
format of the currently bound rendering surface.
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 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 GL_READ_BUFFER is GL_NONE or
if GL_READ_FRAMEBUFFER_BINDING is non-zero and the read buffer selects an attachment that has no image attached.
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 if the readbuffer of the currently bound framebuffer is
a fixed point normalized surface and format
and type are neither GL_RGBA and
GL_UNSIGNED_BYTE, respectively, nor the format/type pair
returned by querying GL_IMPLEMENTATION_COLOR_READ_FORMAT
and GL_IMPLEMENTATION_COLOR_READ_TYPE.
GL_INVALID_OPERATION is generated if the readbuffer of the currently bound framebuffer is
a floating point surface and format
and type are neither GL_RGBA and
GL_FLOAT, respectively, nor the format/type pair
returned by querying GL_IMPLEMENTATION_COLOR_READ_FORMAT
and GL_IMPLEMENTATION_COLOR_READ_TYPE.
GL_INVALID_OPERATION is generated if the readbuffer of the currently bound framebuffer is
a signed integer surface and format
and type are neither GL_RGBA_INTEGER and
GL_INT, respectively, nor the format/type pair
returned by querying GL_IMPLEMENTATION_COLOR_READ_FORMAT
and GL_IMPLEMENTATION_COLOR_READ_TYPE.
GL_INVALID_OPERATION is generated if the readbuffer of the currently bound framebuffer is
an unsigned integer surface and format
and type are neither GL_RGBA_INTEGER and
GL_UNSIGNED_INT, respectively, nor the format/type pair
returned by querying GL_IMPLEMENTATION_COLOR_READ_FORMAT
and GL_IMPLEMENTATION_COLOR_READ_TYPE.
GL_INVALID_FRAMEBUFFER_OPERATION is generated if
the currently bound framebuffer is not framebuffer complete (i.e. the
return value from glCheckFramebufferStatus
is not GL_FRAMEBUFFER_COMPLETE).
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 ES API Version | ||||
|---|---|---|---|---|
| Function Name | 2.0 | 3.0 | 3.1 | 3.2 |
| glReadPixels | ✔ | ✔ | ✔ | ✔ |
| glReadnPixels | - | - | - | ✔ |
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