Native bindings to the OES_required_internalformat extension.

The ES 1.1 API allows an implementation to store texture data internally with arbitrary precision, regardless of the format and type of the data supplied by the application. Similarly, ES allows an implementation to choose an arbitrary precision for the internal storage of image data allocated by glRenderbufferStorageOES.

While this allows flexibility for implementations, it does mean that an application does not have a reliable means to request the implementation maintain a specific precision or to find out what precision the implementation will maintain for a given texture or renderbuffer image.

For reference, "Desktop" OpenGL uses the internalformat argument to glTexImage*, glCopyTexImage* and glRenderbufferStorageEXT as a hint, defining the particular base format and precision that the application wants the implementation to maintain when storing the image data. Further, the application can choose an internalformat with a different base internal format than the source format specified by format. The implementation is not required to exactly match the precision specified by internalformat when choosing an internal storage precision, but it is required to match the base internal format of internalformat.

In addition, ES 1.1 does not allow an implementation to fail a request to glTexImage2D for any of the legal format and type, even if the implementation does not natively support data stored in that external format and type. However, there are no additional requirements placed on the implementation. The ES implementation is free to store the texture data with lower precision than originally specified, for instance. Further, since ES removes the ability to query the texture object to find out what internal format it chose, there is no way for the application to find out that this has happened.

This extension addresses the situation in two ways:

1. This extension introduces the ability for an application to specify the desired "sized" internal formats for texture image allocation.
2. This extension guarantees to maintain at least the specified precision of all available sized internal formats.

An implementation that exports this extension is committing to support all of the legal values for internalformat, subject to the extension dependencies described herein. That is to say, the implementation is guaranteeing that choosing an internalformat argument with a value from these tables will not cause an image allocation request to fail. Furthermore, it is guaranteeing that for any sized internal format, the renderbuffer or texture data will be stored with at least the precision prescribed by the sized internal format.