OpenGL extension EXT.pixel_buffer_object
This module customises the behaviour of the
OpenGL.raw.GL.EXT.pixel_buffer_object to provide a more
Overview (from the spec)
This extension expands on the interface provided by buffer objects.
It is intended to permit buffer objects to be used not only with
vertex array data, but also with pixel data.
Buffer objects were promoted from the ARB_vertex_buffer_object
extension in OpenGL 1.5.
Recall that buffer objects conceptually are nothing more than arrays
of bytes, just like any chunk of memory. Buffer objects allow GL
commands to source data from a buffer object by binding the buffer
object to a given target and then overloading a certain set of GL
commands' pointer arguments to refer to offsets inside the buffer,
rather than pointers to user memory. An offset is encoded in a
pointer by adding the offset to a null pointer.
This extension does not add any new functionality to buffer
objects themselves. It simply adds two new targets to which buffer
objects can be bound: PIXEL_PACK_BUFFER and PIXEL_UNPACK_BUFFER.
When a buffer object is bound to the PIXEL_PACK_BUFFER target,
commands such as ReadPixels write their data into a buffer object.
When a buffer object is bound to the PIXEL_UNPACK_BUFFER target,
commands such as DrawPixels read their data from a buffer object.
There are a wide variety of applications for such functionality.
Some of the most interesting ones are:
- "Render to vertex array." The application can use a fragment
program to render some image into one of its buffers, then read
this image out into a buffer object via ReadPixels. Then, it can
use this buffer object as a source of vertex data.
- Streaming textures. If the application uses MapBuffer/UnmapBuffer
to write its data for TexSubImage into a buffer object, at least
one of the data copies usually required to download a texture can
be eliminated, significantly increasing texture download
- Asynchronous ReadPixels. If an application needs to read back a
number of images and process them with the CPU, the existing GL
interface makes it nearly impossible to pipeline this operation.
The driver will typically send the hardware a readback command
when ReadPixels is called, and then wait for all of the data to
be available before returning control to the application. Then,
the application can either process the data immediately or call
ReadPixels again; in neither case will the readback overlap with
the processing. If the application issues several readbacks into
several buffer objects, however, and then maps each one to process
its data, then the readbacks can proceed in parallel with the data
The official definition of this extension is available here:
|EXTENSION_NAME = 'GL_EXT_pixel_buffer_object'|
GL_PIXEL_PACK_BUFFER_BINDING_EXT = GL_PIXEL_PACK_BUFFER_BINDING_EXT
GL_PIXEL_PACK_BUFFER_EXT = GL_PIXEL_PACK_BUFFER_EXT
GL_PIXEL_UNPACK_BUFFER_BINDING_EXT = GL_PIXEL_UNPACK_BUFFER_BINDING_EXT
GL_PIXEL_UNPACK_BUFFER_EXT = GL_PIXEL_UNPACK_BUFFER_EXT
__file__ = '/home/mcfletch/pylive/OpenGL/GL/EXT/pixel_buffer_object.pyc'
__name__ = 'OpenGL.GL.EXT.pixel_buffer_object'
__package__ = 'OpenGL.GL.EXT'