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'''OpenGL extension ARB.uniform_buffer_object
This module customises the behaviour of the
OpenGL.raw.GL.ARB.uniform_buffer_object to provide a more
Python-friendly API
Overview (from the spec)
This extension introduces the concept of a group of GLSL uniforms
known as a "uniform block", and the API mechanisms to store "uniform
blocks" in GL buffer objects.
The extension also defines both a standard cross-platform layout in
memory for uniform block data, as well as mechanisms to allow the GL
to optimize the data layout in an implementation-defined manner.
Prior to this extension, the existing interface for modification of
uniform values allowed modification of large numbers of values using
glUniform* calls, but only for a single uniform name (or a uniform
array) at a time. However, updating uniforms in this manner may not
map well to heterogenous uniform data structures defined for a GL
application and in these cases, the application is forced to either:
A) restructure their uniform data definitions into arrays
or
B) make an excessive number of calls through the GL interface
to one of the Uniform* variants.
These solutions have their disadvantages. Solution A imposes
considerable development overhead on the application developer.
Solution B may impose considerable run-time overhead on the
application if the number of uniforms modified in a given frame of
rendering is sufficiently large.
This extension provides a better alternative to either (A) or (B) by
allowing buffer object backing for the storage associated with all
uniforms of a given GLSL program.
Storing uniform blocks in buffer objects enables several key use
cases:
- sharing of uniform data storage between program objects and
between program stages
- rapid swapping of sets of previously defined uniforms by storing
sets of uniform data on the GL server
- rapid updates of uniform data from both the client and the server
The data storage for a uniform block can be declared to use one of
three layouts in memory: packed, shared, or std140.
- "packed" uniform blocks have an implementation-dependent data
layout for efficiency, and unused uniforms may be eliminated by
the compiler to save space.
- "shared" uniform blocks, the default layout, have an implementation-
dependent data layout for efficiency, but the layout will be uniquely
determined by the structure of the block, allowing data storage to be
shared across programs.
- "std140" uniform blocks have a standard cross-platform cross-vendor
layout (see below). Unused uniforms will not be eliminated.
Any uniforms not declared in a named uniform block are said to
be part of the "default uniform block".
While uniforms in the default uniform block are updated with
glUniform* entry points and can have static initializers, uniforms
in named uniform blocks are not. Instead, uniform block data is updated
using the routines that update buffer objects and can not use static
initializers.
Rules and Concepts Guiding this Specification:
For reference, a uniform has a "uniform index" (subsequently
referred to as "u_index) and also a "uniform location" to
efficiently identify it in the uniform data store of the
implementation. We subsequently refer to this uniform data store of
the implementation as the "uniform database".
A "uniform block" only has a "uniform block index" used for queries
and connecting the "uniform block" to a buffer object. A "uniform
block" has no "location" because "uniform blocks" are not updated
directly. The buffer object APIs are used instead.
Properties of Uniforms and uniform blocks:
a) A uniform is "active" if it exists in the database and has a valid
u_index.
b) A "uniform block" is "active" if it exists in the database and
has a valid ub_index.
c) Uniforms and "uniform blocks" can be inactive because they don't
exist in the source, or because they have been removed by dead
code elimination.
d) An inactive uniform has u_index == INVALID_INDEX.
e) An inactive uniform block has ub_index == INVALID_INDEX.
f) A u_index or ub_index of INVALID_INDEX generates the
INVALID_VALUE error if given as a function argument.
g) The default uniform block, which is not assigned any ub_index, uses a
private, internal data storage, and does not have any buffer object
associated with it.
h) An active uniform that is a member of the default uniform block has
location >= 0 and it has offset == stride == -1.
i) An active uniform that is a member of a named uniform block has
location == -1.
j) A uniform location of -1 is silently ignored if given as a function
argument.
k) Uniform block declarations may not be nested
The official definition of this extension is available here:
http://www.opengl.org/registry/specs/ARB/uniform_buffer_object.txt
'''
from OpenGL import platform, constants, constant, arrays
from OpenGL import extensions, wrapper
from OpenGL.GL import glget
import ctypes
from OpenGL.raw.GL.ARB.uniform_buffer_object import *
### END AUTOGENERATED SECTION
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