WebGL OES_vertex_array_object Khronos Ratified Extension Specification

Name

OES_vertex_array_object

Contact

WebGL working group (public_webgl 'at' khronos.org)

Contributors

Members of the WebGL working group

Version

Last modified date: July 15, 2014
Revision: 11

Number

WebGL extension #5

Dependencies

Written against the WebGL API 1.0 specification.

Promoted to core and no longer available as an extension in WebGL API 2.0 specification.

Overview

This extension exposes the OES_vertex_array_object functionality to WebGL.

There are no WebGL-specific behavioral changes.

Consult the above extension for documentation, issues and new functions and enumerants.

IDL

[NoInterfaceObject]
interface WebGLVertexArrayObjectOES : WebGLObject {
};

[NoInterfaceObject]
interface OES_vertex_array_object {
    const GLenum VERTEX_ARRAY_BINDING_OES = 0x85B5;

    WebGLVertexArrayObjectOES? createVertexArrayOES();
    void deleteVertexArrayOES(WebGLVertexArrayObjectOES? arrayObject);
    [WebGLHandlesContextLoss] GLboolean isVertexArrayOES(WebGLVertexArrayObjectOES? arrayObject);
    void bindVertexArrayOES(WebGLVertexArrayObjectOES? arrayObject);
};
  

New Functions

WebGLVertexArrayObjectOES? createVertexArrayOES()

void deleteVertexArrayOES(WebGLVertexArrayObjectOES? arrayObject)

GLboolean isVertexArrayOES(WebGLVertexArrayObjectOES? arrayObject)

Returns false if the vertex array object's invalidated flag is set.

void bindVertexArrayOES(WebGLVertexArrayObjectOES? arrayObject)

Issues

The OES_vertex_array_object spec does not make it clear what happens to buffers that are deleted when they are referenced by vertex array objects. It is inferred that all buffers are reference counted.

Before OES_vertex_array_object there was no way to use a deleted buffer in a single context as the spec states it would be unbound from all bind points. After OES_vertex_array_object it is now possible to use deleted buffers.

Furthermore, the OpenGL ES 2.0 spec specifies that using a deleted buffer has undefined results including possibly corrupt rendering and generating GL errors. Undefined behavior is unacceptable for WebGL.

• RESOLVED: Buffers should be reference counted when attached to a vertex array object. This is consistent with the OpenGL ES 3.0 spec's implementation of Vertex Array Objects and matches the behavior of other WebGL objects, such as textures that are attached to framebuffers.

  This will require that most implementations do not call glDeleteBuffer when the user calls deleteBuffer on the WebGL context. Instead the implementation must wait for all references to be released before calling glDeleteBuffer to prevent undefined behavior.

  If a buffer object is deleted while it is attached to the currently bound vertex array object, then it is as if BindBuffer had been called, with a buffer of 0, for each target to which this buffer was attached in the currently bound vertex array object. In other words, this buffer is first detached from all attachment points in the currently bound vertex array object. Note that the buffer is specifically not detached from any other vertex array object. Detaching the buffer from any other vertex array objects is the responsibility of the application.

Revision History

Revision 1, 2011/01/27

• Initial revision.

Revision 2, 2011/11/12

• Demotion to draft.

Revision 3, 2011/12/06

• Added vendor-specific name strings for draft extension per discussion on WebGL mailing list.

Revision 4, 2011/12/07

• Renamed "Name Strings" section to "Alias Name Strings".
• Sorted Revision History in ascending order.

Revision 5, 2012/01/03

• Removed webgl module per changes to Web IDL spec.

Revision 6, 2012/09/24

• Added resolution to deleted buffer issue

Revision 7, 2012/10/16

• Based on feedback on public_webgl, moved from draft to community approved, and removed aliases.

Revision 8, 2013/05/08

• Made WebGLVertexArrayObjectOES return values and arguments nullable on feedback from Benoit Jacob.

Revision 9, 2013/05/14

• Based on pull request from J Kenneth King, added WebGLHandlesContextLoss extended attribute to isVertexArrayOES and added markup for new functions.

Revision 10, 2013/05/15

• Ratified by Khronos Board of Promoters.

Revision 11, 2014/07/15

• Added NoInterfaceObject extended attribute to extension and WebGLVertexArrayObjectOES interface.