OpenGL.GLX.ARB.vertex_buffer_object

OpenGL extension ARB.vertex_buffer_object

This module customises the behaviour of the OpenGL.raw.GLX.ARB.vertex_buffer_object to provide a more Python-friendly API

Overview (from the spec)

This extension defines an interface that allows various types of data (especially vertex array data) to be cached in high-performance graphics memory on the server, thereby increasing the rate of data transfers.

Chunks of data are encapsulated within "buffer objects", which conceptually are nothing more than arrays of bytes, just like any chunk of memory. An API is provided whereby applications can read from or write to buffers, either via the GL itself (glBufferData, glBufferSubData, glGetBufferSubData) or via a pointer to the memory.

The latter technique is known as "mapping" a buffer. When an application maps a buffer, it is given a pointer to the memory. When the application finishes reading from or writing to the memory, it is required to "unmap" the buffer before it is once again permitted to use that buffer as a GL data source or sink. Mapping often allows applications to eliminate an extra data copy otherwise required to access the buffer, thereby enhancing performance. In addition, requiring that applications unmap the buffer to use it as a data source or sink ensures that certain classes of latent synchronization bugs cannot occur.

Although this extension only defines hooks for buffer objects to be used with OpenGL's vertex array APIs, the API defined in this extension permits buffer objects to be used as either data sources or sinks for any GL command that takes a pointer as an argument. Normally, in the absence of this extension, a pointer passed into the GL is simply a pointer to the user's data. This extension defines a mechanism whereby this pointer is used not as a pointer to the data itself, but as an offset into a currently bound buffer object. The buffer object ID zero is reserved, and when buffer object zero is bound to a given target, the commands affected by that buffer binding behave normally. When a nonzero buffer ID is bound, then the pointer represents an offset.

In the case of vertex arrays, this extension defines not merely one binding for all attributes, but a separate binding for each individual attribute. As a result, applications can source their attributes from multiple buffers. An application might, for example, have a model with constant texture coordinates and variable geometry. The texture coordinates might be retrieved from a buffer object with the usage mode "STATIC_DRAW", indicating to the GL that the application does not expect to update the contents of the buffer frequently or even at all, while the vertices might be retrieved from a buffer object with the usage mode "STREAM_DRAW", indicating that the vertices will be updated on a regular basis.

In addition, a binding is defined by which applications can source index data (as used by DrawElements, DrawRangeElements, and MultiDrawElements) from a buffer object. On some platforms, this enables very large models to be rendered with no more than a few small commands to the graphics device.

It is expected that a future extension will allow sourcing pixel data from and writing pixel data to a buffer object.

The official definition of this extension is available here: http://www.opengl.org/registry/specs/ARB/vertex_buffer_object.txt