extensions/ANGLE_blob_cache.txt

Name

    ANGLE_blob_cache

Name Strings

    GL_ANGLE_blob_cache

Contributors

    Geoff Lang

Contact

    Geoff Lang (geofflang 'at' google.com)

Notice

    Copyright (c) 2024 The Khronos Group Inc. Copyright terms at
        http://www.khronos.org/registry/speccopyright.html

Status

    Draft

Version

    Version 1, October 4, 2024

Number

    OpenGL ES Extension #??

Dependencies

    Requires OpenGL ES 2.0

    Written against the OpenGL ES 3.2 specification.

Overview

    This extension provides a mechanism for an OpenGL context to cache binary
    blobs. The application must implement the cache and is in control of caching
    behavior.

    This extension adds caching callbacks per-context which is useful for
    isolating cached data and providing extra security.


New Procedures and Functions

    void SetBlobCacheFuncsANGLE(SETBLOBPROCANGLE set,
                                GETBLOBPROCANGLE get,
                                const void* userParam);

    void GetPointervANGLE(enum pname, void **params);

New Types

    The callback functions that applications can define, and
    are accepted by SetBlobCacheFuncsANGLE, are defined as:

        typedef GLsizeiptr (GL_APIENTRY *GLGETBLOBPROCANGLE)(const void *key,
                                                             GLsizeiptr keySize,
                                                             void *value,
                                                             GLsizeiptr valueSize,
                                                             const void *userParam);

        typedef void (GL_APIENTRY *GLSETBLOBPROCANGLE)(const void *key,
                                                       GLsizeiptr keySize,
                                                       const void *value,
                                                       GLsizeiptr valueSize,
                                                       const void *userParam);

    Note that these function pointers are defined as having the same calling
    convention as the GL functions.

New Tokens

    Tokens accepted by the <pname> parameter of GetPointerv:

        BLOB_CACHE_GET_FUNCTION_ANGLE                0x96BF
        BLOB_CACHE_SET_FUNCTION_ANGLE                0x96EF
        BLOB_CACHE_USER_PARAM_ANGLE                  0x972D

Additions to the OpenGL ES Specification

    Add a new section after 18 Debug Output:

    "Chapter 19
    Persistent Caching

    Application developers can set callback functions which GL may use for
    getting and setting persistently cached data blobs. The command

        void SetBlobCacheFuncsANGLE(SETBLOBPROCANGLE set,
                                    GETBLOBPROCANGLE get,
                                    const void* userParam);

    stores the get and set callbacks and user parameter. Only one blob cache
    get and set function can be installed on the current context. Specifying NULL
    for the callbacks will clear the current callbacks and disable blob caching.
    Applications can provide user-specified data through the pointer <userParam>.
    The context  will store this pointer and will include it as one of the parameters
    in each call to the callback function.

    Applications can query the current callback functions and the current
    user-specified parameter by obtaining the values of
    BLOB_CACHE_GET_FUNCTION_ANGLE, BLOB_CACHE_SET_FUNCTION_ANGLE and
    BLOB_CACHE_USER_PARAM_ANGLE.

    To insert a new binary value into the cache and associate it with a given
    key, a GL context can call the application-provided callback function

        sizeiptr get(const void *key, sizeiptr keySize, void *value, sizeiptr valueSize,
                     const void *userParam);

    <key> and <value> are pointers to the beginning of the key and value,
    respectively, that are to be inserted. <keySize> and <valueSize> specify
    the size in bytes of the data pointed to by <key> and <value> respectively.

    To retrieve the binary value associated with a given key from the cache, a
    GL context can call the application-provided callback function

        set(const void *key, sizeiptr keySize, const void *value, sizeiptr valueSize,
            const void *userParam);


    <key> is a pointer to the beginning of the key. <keySize> specifies the
    size in bytes of the binary key pointed to by <key>. If the cache contains
    a value associated with the given key then the size of that binary value in
    bytes is returned. Otherwise 0 is returned.

    If the cache contains a value for the given key and its size in bytes is
    less than or equal to <valueSize> then the value is written to the memory
    pointed to by <value>. Otherwise nothing is written to the memory pointed
    to by <value>.

    Additionally, these callbacks must be declared with the same platform-dependent
    calling convention used in the definition of the type GLGETBLOBPROCANGLE and
    GLSETBLOBPROCANGLE. Anything else will result in undefined behavior.

Errors

    An INVALID_OPERATION error is generated by SetBlobCacheFuncsANGLE if one of
    <get> or <set> are NULL and the other is non-NULL.

New State

    Modify Table 21.57: Miscellaneous

    Add:

                                                       Initial
    Get Value                         Type Get Command Value   Description
    --------------------------------- ---- ----------- ------- ---------------------
    GL_BLOB_CACHE_GET_FUNCTION_ANGLE  Y    GetPointerv NULL    Blob cache getter function
    GL_BLOB_CACHE_SET_FUNCTION_ANGLE  Y    GetPointerv NULL    Blob cache setter function
    GL_BLOB_CACHE_USER_PARAM_ANGLE    Y    GetPointerv NULL    Blob cache callback user
                                                               data parameter

Conformance Tests

    TBD

Issues

    None

Revision History

    Rev.    Date         Author                 Changes
    ----  -------------  ---------              ----------------------------------------
      1   Oct 4, 2024    geofflang              Initial version