Name

    CHROMIUM_texture_mailbox

Name Strings

    GL_CHROMIUM_texture_mailbox

Version

    Last Modifed Date: August 3, 2016

Dependencies

    OpenGL ES 2.0 is required.

Overview

    This extension defines a way of sharing texture image data between texture
    objects in different contexts where the contexts would not normally share
    texture resources. Five new functions are exported. glGenMailboxCHROMIUM
    generates a name that can be used to identify texture image data outside
    the scope of a context group. glProduceMailboxCHROMIUM and 
    glProduceTextureDirectCHROMIUM associate a texture object with a global
    mailbox name. glConsumeMailboxCHROMIUM and glCreateAndConsumeTextureCHROMIUM
    associate the texture object referenced by a mailbox name to a texture name.

New Procedures and Functions

    void glGenMailboxCHROMIUM (GLbyte *mailbox)

    Generates a unique name identifying a mailbox. The name is generated using
    a cryptographic random number generator and is intended to be difficult to
    guess. The scope of the name is implementation specific, for example it
    might not span multiple displays.

    <mailbox> returns a GL_MAILBOX_SIZE_CHROMIUM byte sized name


    void glProduceTextureCHROMIUM (GLenum target, const GLbyte *mailbox)

    Associates the currently bound texture object with the mailbox name. A
    given texture object can be associated with several mailbox names. If a
    mailbox name was previously associated with a texture object, that
    previous association is broken. The currently bound texture object is not
    modified by the operation.

    If glProduceTextureCHROMIUM generates an error, the mailbox name keeps its
    current association, if any.

    The mailbox does not keep a reference to the texture object. When the
    texture object is destroyed (deleted from all context groups, and unbound
    from all texture units and framebuffer attachments), the mailbox is
    disassociated from the texture object.

    <target> uses the same parameters as TexImage2D.

    <mailbox> identifies a GL_MAILBOX_SIZE_CHROMIUM byte sized name returned by
    glGenMailboxCHROMIUM.

    INVALID_OPERATION is generated if <target> is not a valid target.

    INVALID_OPERATION is generated if <mailbox> is invalid.


    void glProduceTextureDirectCHROMIUM (GLuint texture, GLenum target,
        const GLbyte *mailbox)

    Associates the specified texture object with the mailbox name. Performs
    identically to glProduceTextureCHROMIUM except that the texture specified by
    <texture> is used instead of the currently bound texture. This operation
    does not change the texture bindings or alter the bound texture in any
    way. If <texture> is 0 then any previous association of the mailbox with a
    texture object is broken and no new association is created.

    <texture> Specifies the name of a texture.


    void glConsumeTextureCHROMIUM (GLenum target, const GLbyte *mailbox)

    <target> uses the same parameters as TexImage2D.

    <mailbox> identifies a GL_MAILBOX_SIZE_CHROMIUM byte sized name returned by
    glGenMailboxCHROMIUM.
    
    Deletes the currently bound texture object, and redefines its texture name
    to point to the texture object associated with the mailbox name. All the
    contexts that have consumed the texture object, as well as produced it share
    the texture object, as if the contexts were part of the share group. The
    texture object is deleted once all contexts have deleted the texture name
    associated with the texture object, and detached it from all framebuffer
    objects as well as texture unit bindings. See Appendix C of the OpenGL ES
    2.0 specification for details relative to visibility in one context of
    changes to the shared texture object in another context.

    If glConsumeTextureCHROMIUM generates an error, the currently bound texture
    object is preserved.

    INVALID_OPERATION is generated if <target> is not a valid target.

    INVALID_OPERATION is generated if <mailbox> is invalid.

    INVALID_OPERATION is generated if <mailbox> is not associated with a texture
    object.

    INVALID_OPERATION is generated if the texture object associated with
    <mailbox> has a different target than <target>.

    INVALID_OPERATION is generated if the currently bound texture was previously
    deleted (for example in another context), hence doesn't have a name.


    GLuint glCreateAndConsumeTextureCHROMIUM (GLenum target,
        const GLbyte *mailbox)
    
    Returns a new texture name associated with the given target pointing to the
    texture object associated with the mailbox name. Does not alter the texture
    bindings or alter the currently bound texture in any way. Otherwise performs
    identically to glConsumeTextureCHROMIUM.

New Tokens

    The size of a mailbox name in bytes.

        GL_MAILBOX_SIZE_CHROMIUM                             64

Errors

    None.

New Tokens

    None.

New State

    None.

Revision History

    4/25/2011    Documented the extension
    5/23/2013    Major revision in Produce/Consume semantics, introducing
                 sharing.
    6/02/2014    Added glProduceTextureDirectCHROMIUM and
                 glCreateAndConsumeTextureCHROMIUM definitions.
    8/03/2016    Allow unbinding mailbox using glProduceTextureDirectCHROMIUM.