OpenGL.GL.EXT.pixel_buffer_object

OpenGL extension EXT.pixel_buffer_object
This module customises the behaviour of the OpenGL.raw.GL.EXT.pixel_buffer_object to provide a more Python-friendly API
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 performance.
  • 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 processing.
The official definition of this extension is available here: http://www.opengl.org/registry/specs/EXT/pixel_buffer_object.txt

Functions

glInitPixelBufferObjectEXT( )
Return boolean indicating whether this extension is available

Constants

GL_PIXEL_PACK_BUFFER_BINDING_EXT (35053)
GL_PIXEL_PACK_BUFFER_EXT (35051)
GL_PIXEL_UNPACK_BUFFER_BINDING_EXT (35055)
GL_PIXEL_UNPACK_BUFFER_EXT (35052)