extensions/NV/NV_shader_noperspective_interpolation.txt - external/github.com/KhronosGroup/OpenGL-Registry - Git at Google

 Name

     NV_shader_noperspective_interpolation

 Name Strings

     GL_NV_shader_noperspective_interpolation

 Contact

     Daniel Koch, NVIDIA (dkoch 'at' nvidia.com)

 Contributors

     Pat Brown, NVIDIA
     Michael Chock, NVIDIA

 Status

     Complete

 Version

     Last Modified Date: October 24, 2014
     Revision: 2

 Number

     OpenGL ES Extension #201

 Dependencies

     OpenGL ES 3.0 and GLSL ES 3.00 are required.

     This specification is written against the OpenGL ES 3.1 (March 17,
     2014) and OpenGL ES 3.10 Shading Language (May 14, 2014) specifications.

     This extension interacts with OES_shader_multisample_interpolation.

     This extension trivially interacts with EXT_geometry_shader.

     This extension trivially interacts with EXT_tessellation_shader.

 Overview

     In OpenGL 3.0 and later, and in other APIs, there are three types of
     interpolation qualifiers that are available for fragment shader inputs:
     flat, smooth, and noperspective.  The 'flat' qualifier indicates that no
     interpolation should be used. This is mandatory for integer-type
     variables. The 'smooth' qualifier indicates that interpolation should be
     performed in a perspective0correct manner. This is the default for
     floating-point type variables.  The 'noperspective' qualifier indicates
     that interpolation should be performed linearly in screen space.

     While perspective-correct (smooth) and non-interpolated (flat) are the
     two types of interpolation that most commonly used, there are important
     use cases for linear (noperspective) interpolation.  In particular, in
     some work loads where screen-space aligned geometry is common, the use of
     linear interpolation can result in performance and/or power improvements.

     The smooth and flat interpolation qualifiers are already supported in
     OpenGL ES 3.0 and later. This extension adds support for noperspective
     interpolation to OpenGL ES.

 New Procedures and Functions

     None.

 New Tokens

     None.

 Additions to the OpenGL ES 3.1 Specification

     Modifications to Section 12.4.1 (Clipping Shader Outputs)

     (Insert a new paragraph as the second-to-last paragraph of the section)

     For vertex shader outputs specified to be interpolated without
     perspective correction (using the "noperspective" qualifier), the value
     of <t> used to obtain the output value associated with P will be adjusted
     to produce results that vary linearly in screen space.


     Modifications to Section 13.4.1 (Basic Line Segment Rasterization)

     (Replace the last paragraph of the section with the following language
     which adds in the description of noperspective interpolation)

     The "noperspective" and "flat" keywords used to declare shader outputs
     affect how they are interpolated.  When neither keyword is specified,
     interpolation is performed as described in equation 13.4.  When the
     "noperspective" keyword is specified, interpolation is performed in the
     same fashion as for depth values, as described in equation 13.5.  When
     the "flat" keyword is specified, no interpolation is performed, and
     outputs are taken from the corresponding input value of the provoking
     vertex corresponding to that primitive (see section 12.3).


     Modifications to Section 13.5.1 (Basic Polygon Rasterization)

     (Replace the paragraph which describes the interpolation keywords in
     the middle of p. 298)

     The "noperspective" and "flat" keywords used to declare shader outputs
     affect how they are interpolated.  When neither keyword is specified,
     interpolation is performed as described in equation 13.7.  When the
     "noperspective" keyword is specified, interpolation is performed in the
     same fashion as for depth values, as described in equation 13.8. When
     the "flat" keyword is specified, no interpolation is performed, and
     outputs are taken from the corresponding input value of the provoking
     vertex corresponding to that primitive (see section 12.3).


     Modifications to Section 13.5.3 (Polygon Multisample Rasterization)

     (replace the last paragraph of the section)

     The "noperspective" and "flat" qualifiers affect how shader outputs are
     interpolated in the same fashion as described for basic polygon
     rasterization in section 13.5.1.

 Dependencies on OES_shader_multisample_interpolation

     If OES_shader_multisample_interpolation is not supported, ignore
     references to the interpolation functions in section 8.13.

 Dependencies on EXT_geometry_shader

     If EXT_geometry_shader is supported the, noperspective keyword
     can be used on the outputs from geometry shaders.

     If EXT_geometry_shader is not support, ignore references to
     geometry shaders.

 Dependencies on EXT_tessellation_shader

     If EXT_tessellation_shader is supported, the noperspective keyword
     can be used on the outputs from tessellation shaders.

     If EXT_tessellation_shader is not support, ignore references to
     tessellation shaders.

 New State

     None.

 Additions to the OpenGL ES Shading Language 3.10 Specification

     Including the following line in a shader can be used to control the
     language features described in this extension:

       #extension GL_NV_shader_noperspective_interpolation : <behavior>

     where <behavior> is as specified in section 3.4.

     A new preprocessor #define is added to the OpenGL ES Shading Language:

       #define GL_NV_shader_noperspective_interpolation 1


     Modifications to Section 3.6 (Keywords):

     Remove "noperspective" from the list of reserved keywords and add it to
     the list of keywords.


     Modifications to Section 4.3 (Storage Qualifiers):

     (Add to the table of interpolation qualifiers)

     Qualifier          Meaning
     ---------          -------
     noperspective      linear interpolation


     Modifications to Section 4.3.4 (Input Variables):

     (Add to the list of fragment input examples:)

         noperspective in float temperature;
         noperspective centroid in vec2 myTexCoord;


     Modifications to Section 4.3.6 (Output Variables):

     (Add to the list of vertex (or tessellation or geometry) output examples:)

         noperspective out float temperature;
         noperspective centroid out vec2 myTexCoord;


     Modifications to Section 4.5 (Interpolation Qualifiers):

     (Add to the table of interpolation qualifiers:)

     Qualifier          Meaning
     ---------          -------
     noperspective      linear interpolation

     (Following the description of "smooth" add the following description:)

     "A variable qualified as "noperspective" must be interpolated linearly
     in screen space as described in equation 13.5 of the OpenGL ES Graphics
     System Specification, section 13.4 "Line Segments".


     Modifications to Section 8.13 (Fragment Processing Functions), as modified
     by OES_shader_multisample_interpolation:

     (Add to the end of the paragraph describing the interpolation functions)

     "For all the interpolation functions ...
     If <interpolant> is declared with the "noperspective" qualifier, the
     interpolated value will be computed without perspective correction."


     Modifications to Section 9 (Shading Language Grammar)

     (Add to the list of tokens returned from lexical analysis)

     NOPERSPECTIVE

     (update the interpolation_qualifier rule to be)

     interpolation_qualifier:
         SMOOTH
         FLAT
         NOPERSPECTIVE


 Issues

     (1) Is this any different from the 'noperspective' functionality
     that was added in OpenGL 3.0?

     RESOLVED. No. This is intended to be identical and the language used
     for this specification was based on the deltas between GL 4.4 and
     ES 3.1.

     (2) What should we call this extension?

     RESOLVED: Options considered included:
      - shader_interpolation_noperspective
      - shader_noperspective_interpolation
     Using the second option as this is consistent with the naming of
     OES_shader_multisample_interpolation which added support for
     per-sample interpolation.

     (3) This is a small extension. Is there anything else we should add at
     the same time?

     RESOLVED. No. All the other related functionality is supported in ES
     or already has an extension.

 Revision History

     Rev.    Date    Author    Changes
     ----  --------  --------- -------------------------------------------------
       1   06/05/14  dkoch     Initial draft based on GL 4.4 and GLSL 4.40
       2   10/24/14  dkoch     Mark complete, resolve issue.
	Name

	NV_shader_noperspective_interpolation

	Name Strings

	GL_NV_shader_noperspective_interpolation

	Contact

	Daniel Koch, NVIDIA (dkoch 'at' nvidia.com)

	Contributors

	Pat Brown, NVIDIA
	Michael Chock, NVIDIA

	Status

	Complete

	Version

	Last Modified Date: October 24, 2014
	Revision: 2

	Number

	OpenGL ES Extension #201

	Dependencies

	OpenGL ES 3.0 and GLSL ES 3.00 are required.

	This specification is written against the OpenGL ES 3.1 (March 17,
	2014) and OpenGL ES 3.10 Shading Language (May 14, 2014) specifications.

	This extension interacts with OES_shader_multisample_interpolation.

	This extension trivially interacts with EXT_geometry_shader.

	This extension trivially interacts with EXT_tessellation_shader.

	Overview

	In OpenGL 3.0 and later, and in other APIs, there are three types of
	interpolation qualifiers that are available for fragment shader inputs:
	flat, smooth, and noperspective. The 'flat' qualifier indicates that no
	interpolation should be used. This is mandatory for integer-type
	variables. The 'smooth' qualifier indicates that interpolation should be
	performed in a perspective0correct manner. This is the default for
	floating-point type variables. The 'noperspective' qualifier indicates
	that interpolation should be performed linearly in screen space.

	While perspective-correct (smooth) and non-interpolated (flat) are the
	two types of interpolation that most commonly used, there are important
	use cases for linear (noperspective) interpolation. In particular, in
	some work loads where screen-space aligned geometry is common, the use of
	linear interpolation can result in performance and/or power improvements.

	The smooth and flat interpolation qualifiers are already supported in
	OpenGL ES 3.0 and later. This extension adds support for noperspective
	interpolation to OpenGL ES.

	New Procedures and Functions

	None.

	New Tokens

	None.

	Additions to the OpenGL ES 3.1 Specification

	Modifications to Section 12.4.1 (Clipping Shader Outputs)

	(Insert a new paragraph as the second-to-last paragraph of the section)

	For vertex shader outputs specified to be interpolated without
	perspective correction (using the "noperspective" qualifier), the value
	of <t> used to obtain the output value associated with P will be adjusted
	to produce results that vary linearly in screen space.


	Modifications to Section 13.4.1 (Basic Line Segment Rasterization)

	(Replace the last paragraph of the section with the following language
	which adds in the description of noperspective interpolation)

	The "noperspective" and "flat" keywords used to declare shader outputs
	affect how they are interpolated. When neither keyword is specified,
	interpolation is performed as described in equation 13.4. When the
	"noperspective" keyword is specified, interpolation is performed in the
	same fashion as for depth values, as described in equation 13.5. When
	the "flat" keyword is specified, no interpolation is performed, and
	outputs are taken from the corresponding input value of the provoking
	vertex corresponding to that primitive (see section 12.3).


	Modifications to Section 13.5.1 (Basic Polygon Rasterization)

	(Replace the paragraph which describes the interpolation keywords in
	the middle of p. 298)

	The "noperspective" and "flat" keywords used to declare shader outputs
	affect how they are interpolated. When neither keyword is specified,
	interpolation is performed as described in equation 13.7. When the
	"noperspective" keyword is specified, interpolation is performed in the
	same fashion as for depth values, as described in equation 13.8. When
	the "flat" keyword is specified, no interpolation is performed, and
	outputs are taken from the corresponding input value of the provoking
	vertex corresponding to that primitive (see section 12.3).


	Modifications to Section 13.5.3 (Polygon Multisample Rasterization)

	(replace the last paragraph of the section)

	The "noperspective" and "flat" qualifiers affect how shader outputs are
	interpolated in the same fashion as described for basic polygon
	rasterization in section 13.5.1.

	Dependencies on OES_shader_multisample_interpolation

	If OES_shader_multisample_interpolation is not supported, ignore
	references to the interpolation functions in section 8.13.

	Dependencies on EXT_geometry_shader

	If EXT_geometry_shader is supported the, noperspective keyword
	can be used on the outputs from geometry shaders.

	If EXT_geometry_shader is not support, ignore references to
	geometry shaders.

	Dependencies on EXT_tessellation_shader

	If EXT_tessellation_shader is supported, the noperspective keyword
	can be used on the outputs from tessellation shaders.

	If EXT_tessellation_shader is not support, ignore references to
	tessellation shaders.

	New State

	None.

	Additions to the OpenGL ES Shading Language 3.10 Specification

	Including the following line in a shader can be used to control the
	language features described in this extension:

	#extension GL_NV_shader_noperspective_interpolation : <behavior>

	where <behavior> is as specified in section 3.4.

	A new preprocessor #define is added to the OpenGL ES Shading Language:

	#define GL_NV_shader_noperspective_interpolation 1


	Modifications to Section 3.6 (Keywords):

	Remove "noperspective" from the list of reserved keywords and add it to
	the list of keywords.


	Modifications to Section 4.3 (Storage Qualifiers):

	(Add to the table of interpolation qualifiers)

	Qualifier Meaning
	--------- -------
	noperspective linear interpolation


	Modifications to Section 4.3.4 (Input Variables):

	(Add to the list of fragment input examples:)

	noperspective in float temperature;
	noperspective centroid in vec2 myTexCoord;


	Modifications to Section 4.3.6 (Output Variables):

	(Add to the list of vertex (or tessellation or geometry) output examples:)

	noperspective out float temperature;
	noperspective centroid out vec2 myTexCoord;


	Modifications to Section 4.5 (Interpolation Qualifiers):

	(Add to the table of interpolation qualifiers:)

	Qualifier Meaning
	--------- -------
	noperspective linear interpolation

	(Following the description of "smooth" add the following description:)

	"A variable qualified as "noperspective" must be interpolated linearly
	in screen space as described in equation 13.5 of the OpenGL ES Graphics
	System Specification, section 13.4 "Line Segments".


	Modifications to Section 8.13 (Fragment Processing Functions), as modified
	by OES_shader_multisample_interpolation:

	(Add to the end of the paragraph describing the interpolation functions)

	"For all the interpolation functions ...
	If <interpolant> is declared with the "noperspective" qualifier, the
	interpolated value will be computed without perspective correction."


	Modifications to Section 9 (Shading Language Grammar)

	(Add to the list of tokens returned from lexical analysis)

	NOPERSPECTIVE

	(update the interpolation_qualifier rule to be)

	interpolation_qualifier:
	SMOOTH
	FLAT
	NOPERSPECTIVE


	Issues

	(1) Is this any different from the 'noperspective' functionality
	that was added in OpenGL 3.0?

	RESOLVED. No. This is intended to be identical and the language used
	for this specification was based on the deltas between GL 4.4 and
	ES 3.1.

	(2) What should we call this extension?

	RESOLVED: Options considered included:
	- shader_interpolation_noperspective
	- shader_noperspective_interpolation
	Using the second option as this is consistent with the naming of
	OES_shader_multisample_interpolation which added support for
	per-sample interpolation.

	(3) This is a small extension. Is there anything else we should add at
	the same time?

	RESOLVED. No. All the other related functionality is supported in ES
	or already has an extension.

	Revision History

	Rev. Date Author Changes
	---- -------- --------- -------------------------------------------------
	1 06/05/14 dkoch Initial draft based on GL 4.4 and GLSL 4.40
	2 10/24/14 dkoch Mark complete, resolve issue.