extensions/ARB/ARB_half_float_vertex.txt - external/github.com/KhronosGroup/OpenGL-Registry - Git at Google

 Name

     ARB_half_float_vertex

 Name Strings

     GL_ARB_half_float_vertex

 Contact

     Daniel Koch, TransGaming, Inc (daniel 'at' transgaming.com)

 Notice

     Copyright (c) 2008-2013 The Khronos Group Inc. Copyright terms at
         http://www.khronos.org/registry/speccopyright.html

 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
         https://www.khronos.org/registry/OpenGL/docs/update_policy.php

 Status

     Approved by the ARB on July 11, 2008

 Version

     Last Modified Date:   August 7, 2008
     Version               5

 Number

     ARB Extension #48

 Dependencies

     This extension is written against the OpenGL 2.1 Specification

     Based on the NV_half_float and OES_vertex_half_float extensions.

 Overview

     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.


 Issues

     1. How is this extension different from NV_half_float or
        ARB_half_float_pixel?

     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
     types.

     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
     extensions.

     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
     extension.

 New Procedures and Functions

     None

 New Tokens

     Accepted by the <type> argument of VertexPointer, NormalPointer,
     ColorPointer, SecondaryColorPointer, FogCoordPointer, TexCoordPointer,
     and VertexAttribPointer:

     HALF_FLOAT                                       0x140B

 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,
                                              double
         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)

     None.


 Additions to Chapter 4 of the OpenGL 2.1 Specification (Per-Fragment
 Operations and the Framebuffer)

     None.


 Additions to Chapter 5 of the OpenGL 2.1 Specification (Special Functions)

     None.

 Additions to Chapter 6 of the OpenGL 2.1 Specification (State and
 State Requests)

     None.

 Additions to the AGL/GLX/WGL Specifications

     None.

 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.)

          ARRAY_INFO

             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
                 ...

 Errors

     None

 New State

     None

 New Implementation Dependent State

     None

 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
                               extensions.
       4   2/25/08  dgkoch     Add issue #4.
       5   8/07/08  jleech     Remove _ARB suffix.
	Name

	ARB_half_float_vertex

	Name Strings

	GL_ARB_half_float_vertex

	Contact

	Daniel Koch, TransGaming, Inc (daniel 'at' transgaming.com)

	Notice

	Copyright (c) 2008-2013 The Khronos Group Inc. Copyright terms at
	http://www.khronos.org/registry/speccopyright.html

	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
	https://www.khronos.org/registry/OpenGL/docs/update_policy.php

	Status

	Approved by the ARB on July 11, 2008

	Version

	Last Modified Date: August 7, 2008
	Version 5

	Number

	ARB Extension #48

	Dependencies

	This extension is written against the OpenGL 2.1 Specification

	Based on the NV_half_float and OES_vertex_half_float extensions.

	Overview

	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.


	Issues

	1. How is this extension different from NV_half_float or
	ARB_half_float_pixel?

	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
	types.

	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
	extensions.

	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
	extension.

	New Procedures and Functions

	None

	New Tokens

	Accepted by the <type> argument of VertexPointer, NormalPointer,
	ColorPointer, SecondaryColorPointer, FogCoordPointer, TexCoordPointer,
	and VertexAttribPointer:

	HALF_FLOAT 0x140B

	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,
	double
	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)

	None.


	Additions to Chapter 4 of the OpenGL 2.1 Specification (Per-Fragment
	Operations and the Framebuffer)

	None.


	Additions to Chapter 5 of the OpenGL 2.1 Specification (Special Functions)

	None.

	Additions to Chapter 6 of the OpenGL 2.1 Specification (State and
	State Requests)

	None.

	Additions to the AGL/GLX/WGL Specifications

	None.

	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.)

	ARRAY_INFO

	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
	...

	Errors

	None

	New State

	None

	New Implementation Dependent State

	None

	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
	extensions.
	4 2/25/08 dgkoch Add issue #4.
	5 8/07/08 jleech Remove _ARB suffix.