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Daniel Koch, TransGaming, Inc (daniel 'at'
Copyright (c) 2008-2013 The Khronos Group Inc. Copyright terms at
Specification Update Policy
Khronos-approved extension specifications are updated in response to
issues and bugs prioritized by the Khronos OpenGL Working Group. For
extensions which have been promoted to a core Specification, fixes will
first appear in the latest version of that core Specification, and will
eventually be backported to the extension document. This policy is
described in more detail at
Approved by the ARB on July 11, 2008
Last Modified Date: August 7, 2008
Version 5
ARB Extension #48
This extension is written against the OpenGL 2.1 Specification
Based on the NV_half_float and OES_vertex_half_float extensions.
This extension extends the usage of the half-precision (16-bit) floating-
point quantities introduced in ARB_half_float_pixel for usage in specifying
vertex array data.
This extension allows applications to use half-precision floating point data
when specifying vertices. This can allow applications to reduce their
memory footprint, as well as the memory bandwidth required for vertex data.
This extension extends the existing vertex array commands to accept the new
data type.
1. How is this extension different from NV_half_float or
This extension adds the commands for specifying half-precision
vertex data that were initially introduced in the NV_half_float
extension but were specifically excluded from the
ARB_half_float_pixel extension. The functionality added in this
extension is a proper subset of the vertex functionality defined in
the NV_half_float extension.
2. Should we provide immediate-mode entry points for half-precision
vertex data?
No. We expect the immediate-mode API to be deprecated in the near
future and thus do not wish to encumber implementors with adding a
significant number of additional entry points that would have
limited usefulness. Additionaly, the half-precision floating point
vertex data is only interesting when it is specified in array format
(i.e., for saving storage space). If an application is using
immediate mode APIs to load the vertex data, it does not seem overly
onerous to require them to convert to one of the more standard data
3. What is the half-precision floating point format?
This is the same 16-bit floating point format that is defined in
Section 2.1.2 of the ARB_texture_float and ARB_half_float_pixel
4. How does this extension differ from OES_vertex_half_float?
It is intended to have the same functionality, however there are a
few minor changes spec-wise:
a) this extension defines the additional GLX protocol, as was done
in the NV_half_float extension.
b) this extension uses the value of the HALF_FLOAT_ARB (0x140B)
token that is already defined in the desktop version of the
ARB_half_float_pixel extension (which is the same as the value
of the HALF_FLOAT_NV token from the NV_half_float extension).
The OES_vertex_half_float and OES_texture_half_float extensions
use the HALF_FLOAT_OES (0x8D61) token.
The logical progression is to define this as an ARB extension which
is intended to supersede both the OES extension and the
functionality from NV_half_float.
5. Why don't the new tokens and entry points in this extension have
"ARB" suffixes like other ARB extensions?
RESOLVED: Unlike a normal ARB extension, this is a strict subset of
functionality already approved in OpenGL 3.0. This extension exists
only to support that functionality on older hardware that cannot
implement a full OpenGL 3.0 driver. Since there are no possible
behavior changes between the ARB extension and core features, source
code compatibility is improved by not using suffixes on the
New Procedures and Functions
New Tokens
Accepted by the <type> argument of VertexPointer, NormalPointer,
ColorPointer, SecondaryColorPointer, FogCoordPointer, TexCoordPointer,
and VertexAttribPointer:
Additions to Chapter 2 of the OpenGL 2.1 Specification (OpenGL Operation)
Modify Section 2.8, Vertex Arrays, p. 23
(Modify 1st paragraph on p. 24) ... For <type>, the values BYTE, SHORT,
INT, FLOAT, HALF_FLOAT, and DOUBLE indicate types byte, short, int,
float, half, and double, respectively. ...
(Modify Table 2.4, p. 25)
Command Sizes Types
------------------ ------- ---------------------------------
VertexPointer 2,3,4 short, int, float, half, double
NormalPointer 3 byte, short, int, float, half,
ColorPointer 3,4 byte, ubyte, short, ushort, int,
uint, float, half, double
SecondaryColorPointer 3 byte, ubyte, short, ushort, int,
uint, float, half, double
IndexPointer 1 ubyte, short, int, float, double
FogCoordPointer 1 float, half, double
TexCoordPointer 1,2,3,4 short, int, float, half, double
EdgeFlagPointer 1 boolean
VertexAttribPointer 1 byte, ubyte, short, ushort, int,
uint, float, half, double
Table 2.4: Vertex array sizes (values per vertex) and data types.
Modify Section 2.13, Colors and Coloring, p.44
(Modify Table 2.6, p. 59) Add new row to the table:
GL Type Conversion
------- ----------
half c
Additions to Chapter 3 of the OpenGL 2.1 Specification (Rasterization)
Additions to Chapter 4 of the OpenGL 2.1 Specification (Per-Fragment
Operations and the Framebuffer)
Additions to Chapter 5 of the OpenGL 2.1 Specification (Special Functions)
Additions to Chapter 6 of the OpenGL 2.1 Specification (State and
State Requests)
Additions to the AGL/GLX/WGL Specifications
GLX Protocol (Modification to the GLX 1.3 Protocol Encoding Specification)
Add to Section 1.4 (p.2), Common Types
FLOAT16 A 16-bit floating-point value in the format specified
in the ARB_half_float_pixel extension specification.
Modify Section 2.3.4, GL Rendering Commands That May Be Large (p. 127)
(Modify the ARRAY_INFO portion of the DrawArrays encoding (p.129) to
reflect the new data type supported by vertex arrays.)
4 enum data type
0x1400 i=1 BYTE
0x1401 i=1 UNSIGNED_BYTE
0x1402 i=2 SHORT
0x140B i=2 HALF_FLOAT
4 INT32 j
4 ENUM array type
New State
New Implementation Dependent State
Revision History
Rev. Date Author Changes
---- -------- --------- --------------------------------------------
1 1/22/08 dgkoch Initial version based on the NV_half_float
and ARB_half_float_pixel specification. Updated
to reference OpenGL 2.1 spec.
2 1/22/08 dgkoch Made some grammatical clarifications.
3 2/01/08 dgkoch Clarify dependencies and interactions with other
4 2/25/08 dgkoch Add issue #4.
5 8/07/08 jleech Remove _ARB suffix.