| Name |
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| NV_primitive_shading_rate |
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| Name Strings |
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| GL_NV_primitive_shading_rate |
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| Contact |
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| Pat Brown, NVIDIA Corporation (pbrown 'at' nvidia.com) |
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| Contributors |
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| Jeff Bolz, NVIDIA |
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| Status |
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| Shipping |
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| Version |
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| Last Modified: October 30, 2020 |
| Revision: 1 |
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| Number |
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| OpenGL Extension #554 |
| OpenGL ES Extension #332 |
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| Dependencies |
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| This extension is written against the OpenGL 4.6 Specification |
| (Compatibility Profile), dated February 2, 2019. |
| |
| OpenGL 4.5 or OpenGL ES 3.2 is required. |
| |
| NV_shading_rate_image is required. |
| |
| This extension requires support from the OpenGL Shading Language (GLSL) |
| extension "NV_primitive_shading_rate", which can be found at the Khronos |
| Group Github site here: |
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| https://github.com/KhronosGroup/GLSL |
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| This extension interacts with NV_mesh_shader. |
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| Overview |
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| This extension builds on top of the NV_shading_rate_image extension to |
| provide OpenGL API support for using a per-primitive shading rate value to |
| control the computation of the rate used to process each fragment. |
| |
| In the NV_shading_rate_image extension, the shading rate for each fragment |
| produced by a primitive is determined by looking up a texel in the bound |
| shading rate image and using that value as an index into a shading rate |
| palette. That extension provides a separate shading rate image lookup |
| enable and palette for each viewport. When a primitive is rasterized, the |
| implementation uses the enable and palette associated with the primitive's |
| viewport to determine the shading rate. |
| |
| This extension decouples the shading rate image enables and palettes from |
| viewports. The number of enables/palettes now comes from the |
| implementation-dependent constant SHADING_RATE_IMAGE_PALETTE_COUNT_NV. When |
| SHADING_RATE_IMAGE_PER_PRIMITIVE_NV (added here) is enabled, the value of |
| the new gl_ShadingRateNV built-in output is used to select an enable and |
| palette to determine the shading rate. Otherwise, the viewport number for |
| the primitive is used, as in NV_shading_rate_image. |
| |
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| New Procedures and Functions |
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| None. |
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| New Tokens |
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| Accepted by the <cap> parameter of Enable, Disable, and IsEnabled and by the |
| <pname> parameter of GetBooleanv, GetIntegerv, GetInteger64v, GetFloatv, |
| GetDoublev: |
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| SHADING_RATE_IMAGE_PER_PRIMITIVE_NV 0x95B1 |
| |
| Accepted by the <pname> parameter of GetBooleanv, GetDoublev, |
| GetIntegerv, and GetFloatv: |
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| SHADING_RATE_IMAGE_PALETTE_COUNT_NV 0x95B2 |
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| Modifications to the OpenGL 4.6 Specification (Compatibility Profile) |
| |
| Modify Section 14.3.1, Multisampling, as modified by the |
| NV_shading_rate_image extension. |
| |
| (modify the introduction of the shading rate image functionality to decouple |
| shading rate image enables and viewports) |
| |
| When using a shading rate image (Section 14.4.1), rasterization may produce |
| fragments covering multiple pixels, where each pixel is treated as a sample. |
| If any of the SHADING_RATE_IMAGE_NV enables is enabled, primitives will be |
| processed with multisample rasterization rules, regardless of the |
| MULTISAMPLE enable or the value of SAMPLE_BUFFERS. ... |
| |
| |
| Modify Section 14.4.1, Shading Rate Image, as added by the |
| NV_shading_rate_image extension. |
| |
| (rework the introduction of the shading rate image functionality to decouple |
| shading rate image enables and viewports) |
| |
| Applications can specify the use of a shading rate that varies by (x,y) |
| location using a _shading rate image_. For each primitive, the shading rate |
| image is enabled or disabled by selecting a single enable in an array of |
| enables whose size is given by the implementation-dependent constant |
| SHADING_RATE_IMAGE_PALETTE_COUNT_NV. Use of a shading rate image is enabled |
| or disabled globally by using Enable or Disable with target |
| SHADING_RATE_IMAGE_NV. A single shading rate image enable can be modified |
| by calling Enablei or Disablei with the constant SHADING_RATE_IMAGE_NV and |
| the index of the selected enable. The shading rate image may only be used |
| with a framebuffer object. When rendering to the default framebuffer, the |
| shading rate image enables are ignored and operations in this section are |
| disabled. In the initial state, all shading rate image enables are |
| disabled. |
| |
| The method used to select a single shading rate image enable used to process |
| each primitive is controlled by calling Enable or Disable with the target |
| SHADING_RATE_IMAGE_PER_PRIMITIVE_NV. When enabled, a shading rate enable |
| used for a primitive is selected using an index taken from the value of the |
| built-in output gl_ShadingRateNV for the primitive's provoking vertex. If |
| the value of gl_ShadingRateNV is negative or greater than or equal to the |
| number of shading rate enables, the shading rate used for a primitive is |
| undefined. When SHADING_RATE_IMAGE_PER_PRIMITIVE_NV is disabled, a shading |
| rate enable is selected using the index of the viewport used for processing |
| the primitive. In the initial state, SHADING_RATE_IMAGE_PER_PRIMITIVE_NV is |
| disabled. |
| |
| |
| (rework the introduction of the shading rate image functionality to decouple |
| shading rate image palettes and viewports) |
| |
| A shading rate index is mapped to a _base shading rate_ using a lookup table |
| called the shading rate image palette. There is a separate palette |
| associated with each shading rate image enable. As with the shading rate |
| image enables, a single palette is selected for a primitive according to the |
| enable SHADING_RATE_IMAGE_PER_PRIMITIVE_NV. The number of palettes and the |
| number of entries in each palette are given by the implementation-dependent |
| constants SHADING_RATE_IMAGE_PALETTE_COUNT_NV and |
| SHADING_RATE_IMAGE_PALETTE_SIZE_NV, respectively. The base shading rate for |
| an (x,y) coordinate with a shading rate index of <i> will be given by entry |
| <i> of the selected palette. If the shading rate index is greater than or |
| equal to the palette size, the results of the palette lookup are undefined. |
| |
| |
| (rework the introduction of ShadingRateImagePaletteNV to decouple shading |
| rate image palettes and viewports) |
| |
| Shading rate image palettes are updated using the command |
| |
| void ShadingRateImagePaletteNV(uint viewport, uint first, sizei count, |
| const enum *rates); |
| |
| <viewport> specifies the number of the palette that should be updated. |
| [[ Note: The formal parameter name <viewport> is a remnant of the |
| original NV_shading_rate_image extension, where palettes were tightly |
| coupled with viewports. ]] <rates> is an array ... |
| |
| |
| (modify the discussion of ShadingRateImagePaletteNV errors to decouple |
| shading rate image palettes and viewports) |
| |
| INVALID_VALUE is generated if <viewport> is greater than or equal to |
| SHADING_RATE_IMAGE_PALETTE_COUNT_NV. |
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| INVALID_VALUE is generated if <first> plus <count> is greater than |
| SHADING_RATE_IMAGE_PALETTE_SIZE_NV. |
| |
| |
| (modify the discussion of GetShadingRateImagePaletteNV to decouple shading |
| rate image palettes and viewports) |
| |
| Individual entries in the shading rate palette can be queried using the |
| command: |
| |
| void GetShadingRateImagePaletteNV(uint viewport, uint entry, |
| enum *rate); |
| |
| where <viewport> specifies the number of the palette to query and... |
| <entry> specifies the palette entry number. [[ Note: The formal |
| parameter name <viewport> is a remnant of the original |
| NV_shading_rate_image extension, where palettes were tightly coupled |
| with viewports. ]] A single enum from Table X.1 is returned in <rate>. |
| |
| Errors |
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| INVALID_VALUE is generated if <viewport> is greater than or equal to |
| SHADING_RATE_IMAGE_PALETTE_COUNT_NV. |
| |
| INVALID_VALUE is generated if <first> plus <count> is greater than |
| SHADING_RATE_IMAGE_PALETTE_SIZE_NV. |
| |
| |
| Modify Section 14.9.3, Multisample Fragment Operations, as edited by |
| NV_shading_rate_image. |
| |
| (modify the discussion of the shading rate image multisample functionality |
| to decouple shading rate image enables and viewports) |
| |
| ... This step is skipped if MULTISAMPLE is disabled or if the value of |
| SAMPLE_BUFFERS is not one, unless one or more of the SHADING_RATE_IMAGE_NV |
| enables are enabled. |
| |
| |
| Dependencies on NV_mesh_shader |
| |
| When NV_mesh_shader is supported, the "NV_primitive_shading_rate" GLSL |
| extension allows multi-view mesh shaders to write separate per-primitive |
| shading rates for each view using the built-in gl_ShadingRatePerViewNV[]. |
| When gl_ShadingRatePerViewNV[] is used with |
| SHADING_RATE_IMAGE_PER_PRIMITIVE_NV enabled, a separate shading rate image |
| enable and palette will be used for each view. |
| |
| |
| Additions to the AGL/GLX/WGL Specifications |
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| None |
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| Errors |
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| See the "Errors" sections for individual commands above. |
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| New State |
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| Get Value Get Command Type Initial Value Description Sec. Attribute |
| --------- --------------- ---- ------------- ----------- ---- --------- |
| SHADING_RATE_IMAGE_ IsEnabled B FALSE Use per-primitive shading 14.4.1 enable |
| PER_PRIMITIVE_NV rate to select shading |
| rate images/palettes |
| |
| New Implementation Dependent State |
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| Minimum |
| Get Value Type Get Command Value Description Sec. |
| --------- ----- --------------- ------- ------------------------ ------ |
| SHADING_RATE_IMAGE_ Z+ GetIntegerv 16 Number of shading rate image 14.4.1 |
| PALETTE_COUNT_NV enables/palettes supported |
| |
| Issues |
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| (1) How should we name this extension? |
| |
| RESOLVED: We are calling this extension "NV_primitive_shading_rate" |
| because it adds a new per-primitive shading rate to the variable-rate |
| shading functionality added by NV_shading_rate_image. |
| |
| (2) Do we need to add queries like LAYER_PROVOKING_VERTEX and |
| VIEWPORT_INDEX_PROVOKING_VERTEX to determine the vertex used to obtain |
| the per-primitive shading rate for each primitive? |
| |
| RESOLVED: No -- we will always use the provoking vertex. In the event |
| that this extension is standardized in the future with behavior that |
| diverges between implementations, such a query could be added as part of |
| that effort. |
| |
| Revision History |
| |
| Revision 1 (pbrown) |
| - Internal revisions. |
