| Name |
| |
| AMD_shader_explicit_vertex_parameter |
| |
| Name Strings |
| |
| GL_AMD_shader_explicit_vertex_parameter |
| |
| Contact |
| |
| Qun Lin, AMD (Quentin.Lin 'at' amd.com) |
| |
| Contributors |
| |
| Qun Lin, AMD |
| Graham Sellers, AMD |
| Daniel Rakos, AMD |
| Dominik Witczak, AMD |
| |
| Status |
| |
| Pending |
| |
| Version |
| |
| Last Modified Date: 04/21/2016 |
| Author Revision: 2 |
| |
| Number |
| |
| OpenGL Extension #485 |
| |
| Dependencies |
| |
| OpenGL 2.0 or ARB_shader_objects is required. |
| |
| This extension is written against the OpenGL Shading Language |
| Specification, Version 4.50. |
| |
| Overview |
| |
| Unextended GLSL provides a set of fixed function interpolation modes and |
| even those are limited to certain types of interpolants (for example, |
| interpolation of integer and double isn't supported). |
| |
| This extension introduces new built-in functions allowing access to vertex |
| parameters explicitly in the fragment shader. It also exposes barycentric |
| coordinates as new built-in variables, which can be used to implement |
| custom interpolation algorithms using shader code. |
| |
| IP Status |
| |
| None. |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| None. |
| |
| Modifications to the OpenGL Shading Language Specification, Version 4.50 |
| |
| Including the following line in a shader can be used to control the |
| language features described in this extension: |
| |
| #extension GL_AMD_shader_explicit_vertex_parameter : <behavior> |
| |
| where <behavior> is as specified in section 3.3. |
| |
| New preprocessor #defines are added to the OpenGL Shading Language: |
| |
| #define GL_AMD_shader_explicit_vertex_parameter 1 |
| |
| Additions to Chapter 3 of the OpenGL Shading Language (GLSL) Specification, |
| version 4.50, (Basics) |
| |
| Modify section 3.6, Keywords p. 17 |
| |
| (Add __explicitInterpAMD to the list of keywords) |
| ...smooth noperspective __explicitInterpAMD |
| |
| Additions to Chapter 4 of the OpenGL Shading Language (GLSL) Specification, |
| version 4.50, (Variables and Types) |
| |
| Modify section 4.5, Interpolation Qualifiers p.81 |
| |
| (Add explicitInterpAMD to interpolation qualifier list) |
| |
| +-------------------+------------------------------------------------+ |
| | Qualifier | Meaning | |
| +-------------------+------------------------------------------------+ |
| | explicitInterpAMD | Explicit interpolation | |
| +-------------------+------------------------------------------------+ |
| |
| (Add a new paragraph after the description of noperspective) |
| |
| A variable qualified as __explicitInterpAMD can only be used as the |
| parameter of the built-in function interpolateAtVertex in fragment shader, |
| and it cannot be qualified with any other auxiliary storage qualifiers. |
| |
| Additions to Chapter 7 of the OpenGL Shading Language (GLSL) Specification, |
| version 4.50 (Built-in variables) |
| |
| |
| Modify Section 7.1, Built-in Languages Variable, p. 110 |
| |
| (Add to the list of built-in variables for the fragment languages) |
| |
| In the fragment language, built-in variables are intrinsically declared as: |
| |
| in vec2 gl_BaryCoordNoPerspAMD; |
| in vec2 gl_BaryCoordNoPerspCentroidAMD; |
| in vec2 gl_BaryCoordNoPerspSampleAMD; |
| in vec2 gl_BaryCoordSmoothAMD; |
| in vec2 gl_BaryCoordSmoothCentroidAMD; |
| in vec2 gl_BaryCoordSmoothSampleAMD; |
| in vec3 gl_BaryCoordPullModelAMD |
| |
| The built-in variables <gl_BaryCoord??AMD> are fragment shader input |
| variables. Except the <gl_BaryCoordPullModelAMD>, the variables provide |
| the (I,J) pair of the barycentric coordinates interpolated at a fixed |
| location within the pixel. The K coordinate can be derived given the |
| identity I+J+K=1.0. |
| |
| <gl_BaryCoordPullModelAMD> returns (1/W, 1/I, 1/J) at the pixel center and |
| the shader can use it to calculate gradients and to interpolate I, J, and |
| W to any desired sample location. |
| |
| The interpolation mode of gl_BaryCoord??AMD variables are as follows |
| +---------------------------------+-----------------------------------------------------------+ |
| | Variable name | Description | |
| +---------------------------------+-----------------------------------------------------------+ |
| | gl_BaryCoordNoPerspAMD | Linear interpolation evaluated at the pixel's center | |
| | gl_BaryCoordNoPerspCentroidAMD | Linear interpolation evaluated at the centroid | |
| | gl_BaryCoordNoPerspSampleAMD | Linear interpolation evaluated at each covered sample | |
| | gl_BaryCoordSmoothAMD | Perspective interpolation evaluated at the pixel's center | |
| | gl_BaryCoordSmoothCentroidAMD | Perspective interpolation evaluated at the centroid | |
| | gl_BaryCoordSmoothSampleAMD | Perspective interpolation evaluated at each covered sample| |
| +---------------------------------+-----------------------------------------------------------+ |
| |
| Additions to Chapter 8 of the OpenGL Shading Language (GLSL) Specification, |
| version 4.30 (Built-in functions) |
| |
| Modify Section 8.13.2, "Interpolation Functions", p. 180 |
| |
| (Add to the end of last paragraph in this page) |
| The return value of the functions interpolateAtCentroid, |
| interpolateAtSample, and interpolateAtOffset is undefined if <interpolant> |
| is declared with __explicitInterpAMD. |
| |
| add to the table of functions, p.181: |
| |
| +----------------------------------------------------+--------------------------------------------------------+ |
| | Syntax | Description | |
| +----------------------------------------------------+--------------------------------------------------------+ |
| | genType interpolateAtVertexAMD(genType | Returns the value of the input <interpolant> without | |
| | interpolant, uint vertexIdx) | any interpolation. i.e. the raw output value of | |
| | genIType interpolateAtVertexAMD(genIType | previous shader stage. <vertexIdx> selects for which | |
| | interpolant, uint vertexIdx) | vertex of the primitive the value of <interpolant> is | |
| | genUType interpolateAtVertexAMD(genUType | returned. | |
| | interpolant, uint vertexIdx) | This return value is equivalent with interpolating | |
| | | the input <interpolant> using the following | |
| | | set of barycentric coordinates, depending on | |
| | | the value of <vertexIdx>: | |
| | | | |
| | | vertexIdx Barycentric coordinates | |
| | | 0 I=0, J=0, K=1 | |
| | | 1 I=1, J=0, K=0 | |
| | | 2 I=0, J=1, K=0 | |
| | | | |
| | | However this order has no association with the vertex | |
| | | order specified by the application in the originating | |
| | | draw. | |
| | | The value of <vertexIdx> must be constant integer | |
| | | expression with a value in the range [0, 2]. | |
| +----------------------------------------------------+--------------------------------------------------------+ |
| |
| Additions to Chapter 9 of the OpenGL Shading Language (GLSL) Specification, |
| version 4.30, (Shading Language Grammar) |
| |
| Modify Chapter 9, Shading Language Grammar for Core Profile, p. 187 |
| |
| (Add new token __EXPLICITINTERPAMD to list) |
| ... NOPERSPECTIVE FLAT SMOOTH __EXPLICITINTERPAMD |
| |
| Modify Chapter 9, Shading Language Grammar for Core Profile, p. 194 |
| |
| (Add __EXPLICITINTERPAMD to grammar interpolation_qualifier) |
| |
| interpolation_qualifier: |
| SMOOTH |
| FLAT |
| NOPERSPECTIVE |
| __EXPLICITINTERPAMD |
| |
| Additions to the AGL/GLX/WGL Specifications |
| |
| None. |
| |
| GLX Protocol |
| |
| None. |
| |
| Errors |
| |
| None. |
| |
| Issues |
| |
| |
| Revision History |
| |
| Rev. Date Author Changes |
| ---- -------- -------- ----------------------------------------- |
| 2 05/19/2016 dwitczak Minor update. |
| 1 04/21/2016 qlin Internal revisions. |
