| Name |
| |
| NV_stereo_view_rendering |
| |
| Name Strings |
| |
| GL_NV_stereo_view_rendering |
| |
| Contact |
| |
| Kedarnath Thangudu, NVIDIA Corporation (kthangudu 'at' nvidia.com) |
| |
| Contributors |
| |
| Mark Kilgard, NVIDIA Corporation |
| Pat Brown, NVIDIA Corporation |
| Jason Schmidt, NVIDIA Corporation |
| |
| Status |
| |
| Shipping in NVIDIA release 367.XX drivers and up. |
| |
| Version |
| |
| Last Modified Date: November 25, 2017 |
| NVIDIA Revision: 3 |
| |
| Number |
| |
| OpenGL Extension #489 |
| OpenGL ES Extension #296 |
| |
| Dependencies |
| |
| This extension is written against OpenGL 4.5 Specification |
| (Compatibility Profile). |
| |
| This extension interacts with the OpenGL ES 3.1 Specification. |
| |
| The extension requires NV_viewport_array2. |
| |
| This extension interacts with NV_gpu_program4 and NV_gpu_program5. |
| |
| This extension interacts with EXT_tessellation_shader. |
| |
| Overview |
| |
| Virtual reality (VR) applications often render a single logical scene |
| from multiple views corresponding to a pair of eyes. The views (eyes) are |
| separated by a fixed offset in the X direction. |
| |
| Traditionally, multiple views are rendered via multiple rendering passes. |
| This is expensive for the GPU because the objects in the scene must be |
| transformed, rasterized, shaded, and fragment processed redundantly. This |
| is expensive for the CPU because the scene graph needs to be visited |
| multiple times and driver validation happens for each view. Rendering N |
| passes tends to take N times longer than a single pass. |
| |
| This extension provides a mechanism to render binocular (stereo) views |
| from a single stream of OpenGL rendering commands. Vertex, tessellation, |
| and geometry (VTG) shaders can output two positions for each vertex |
| corresponding to the two eye views. A built-in "gl_SecondaryPositionNV" |
| is added to specify the second position. The positions from each view may |
| be sent to different viewports and/or layers. A built-in |
| "gl_SecondaryViewportMaskNV[]" is also added to specify the viewport mask |
| for the second view. A new layout-qualifier "secondary_view_offset" is |
| added for built-in output "gl_Layer" which allows for the geometry from |
| each view to be sent to different layers for rendering. |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| None. |
| |
| Additions to Chapter 11 of the OpenGL 4.5 (Compatibility Profile) Specification |
| (Programmable Vertex Processing) |
| |
| Add to Section 11.1.3.10 (Shader Outputs) |
| |
| The built-in output variables gl_SecondaryPositionNV and |
| gl_SecondaryViewportMaskNV[] hold the homogeneous vertex position and the |
| viewport mask for the secondary view, as described in Section 11.5 |
| (Stereo Offsetted Rendering). |
| |
| [Section 11.2 of the OpenGL 4.5 specification corresponds to |
| Section 11.1ts of the OpenGL ES 3.1 specification, and |
| Section 11.3 of the OpenGL 4.5 specification corresponds to |
| Section 11.1gs of the OpenGL ES 3.1 specification] |
| |
| In Section 11.2.1.2.2 (Tessellation Control Shader Inputs), modify the |
| line describing members of gl_in[] to include gl_SecondaryPositionNV |
| |
| The members of each element of the gl_in[] array are gl_Position, |
| gl_SecondaryPositionNV, gl_PointSize, ... |
| |
| Add to Section 11.2.1.2.3 (Tessellation Control Shader Outputs) |
| |
| The built-in output variables gl_SecondaryPositionNV and |
| gl_SecondaryViewportMaskNV[] hold the homogeneous vertex position and the |
| viewport mask for the secondary view, as described in Section 11.5 |
| (Stereo Offsetted Rendering). |
| |
| In Section 11.2.3.3 (Tessellation Evaluation Shader Outputs), modify the |
| line describing members of gl_in[] to include gl_SecondaryPositionNV |
| |
| The members of each element of the gl_in[] array are gl_Position, |
| gl_SecondaryPositionNV, gl_PointSize, ... |
| |
| Add to Section 11.2.3.4 (Tessellation Evaluation Shader Outputs) |
| |
| The built-in output variables gl_SecondaryPositionNV and |
| gl_SecondaryViewportMaskNV[] hold the homogeneous vertex position and the |
| viewport mask for the secondary view, as described in Section 11.5 |
| (Stereo Offsetted Rendering). |
| |
| In Section 11.3.4.4 (Geometry Shader Inputs), add to the list of members |
| of gl_in[] |
| |
| The members of each element of the gl_in[] array are: |
| ... |
| * Structure member gl_SecondaryPositionNV holds the per-vertex position |
| of the secondary view, written by the upstream shader to the built-in |
| output variable gl_SecondaryPositionNV. Note that writing to |
| gl_SecondaryPositionNV from either the upstream or geometry shader is |
| optional (also see section 7.1("Built-In Variables") of the OpenGL |
| Shading Language Specification). |
| |
| Add to Section 11.2.3.5 (Geometry Shader Outputs) |
| |
| The built-in output variables gl_SecondaryPositionNV and |
| gl_SecondaryViewportMaskNV[] hold the homogeneous vertex position and the |
| viewport mask for the secondary view, as described in Section 11.5 |
| (Stereo Offsetted Rendering). |
| |
| |
| Modify Section 11.4 (Layer and Viewport Selection) to include |
| gl_SecondaryViewportMaskNV[] wherever gl_ViewportMask[] is mentioned. |
| |
| Add a new Section 11.5 (Stereo Offsetted Rendering) |
| |
| Application may render a single logical scene from two views, |
| corresponding to a pair of eyes, that are separated only in the X |
| direction by fixed offset. Vertex, tessellation, and geometry (VTG) |
| shaders may compute and write the vertex coordinates for each of the pair |
| of stereo views. The input/output built-ins "gl_Position" and |
| "gl_SecondaryPositionNV" may be used to read/write the positions |
| corresponding to the primary and secondary views respectively. Only the |
| "x" coordinate is expected to differ between these views, so the "yzw" |
| coordinates for secondary position are also obtained from the "gl_Position" |
| and writes to "gl_SecondaryPositionNV.yzw" are ignored. |
| |
| VTG shaders may also write to "gl_SecondaryViewportMaskNV[]" to specify a |
| viewport mask for primitives in the secondary view. If |
| "gl_SecondaryViewportMaskNV[]" is not specified, "gl_ViewportMask[]" will |
| be used as the viewport mask for primitives from both views. |
| |
| Primitives from each view may be sent to different layers as described |
| in Section 7.1 of the GLSL specification. |
| |
| Additions to Chapter 13 of the OpenGL 4.5 (Compatibility Profile) |
| Specification (Fixed-Function Vertex Post-Processing) |
| |
| Modify Section 13.2 (Transform Feedback), p. 453 [section 12.1 in OpenGL ES] |
| |
| Modify the first paragraph: |
| |
| ...The vertices are fed back after vertex color clamping, but before |
| viewport mask expansion, stereo view expansion, flat-shading, and |
| clipping. ... |
| |
| Modify Section 13.6.1 (Controlling the Viewport) |
| [section 12.5.1 in OpenGL ES] to include |
| gl_SecondaryViewportMaskNV[] wherever gl_ViewportMask[] is mentioned. |
| |
| |
| New Implementation Dependent State |
| |
| None. |
| |
| New State |
| |
| None. |
| |
| Additions to the AGL/GLX/WGL/EGL Specifications |
| |
| None. |
| |
| GLX Protocol |
| |
| 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_NV_stereo_view_rendering : <behavior> |
| |
| where <behavior> is as specified in section 3.3 |
| |
| New preprocessor #defines are added to the OpenGL Shading Language: |
| |
| #define GL_NV_stereo_view_rendering 1 |
| |
| Modify Section 7.1 (Built-In Language Variables), p. 118 |
| |
| Add to the list of vertex shader built-ins: |
| |
| out gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| highp int gl_SecondaryViewportMaskNV[]; |
| }; |
| |
| Add to the list of geometry shader built-ins: |
| |
| in gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| } gl_in[]; |
| |
| out gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| highp int gl_SecondaryViewportMaskNV[]; |
| }; |
| |
| Add to the list of tessellation control shader built-ins: |
| |
| in gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| } gl_in[gl_MaxPatchVertices]; |
| |
| out gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| highp int gl_SecondaryViewportMaskNV[]; |
| } gl_out[]; |
| |
| Add to the list of tessellation evaluation shader built-ins: |
| |
| in gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| } gl_in[gl_MaxPatchVertices]; |
| |
| out gl_PerVertex { |
| highp vec4 gl_SecondaryPositionNV; |
| highp int gl_SecondaryViewportMaskNV[]; |
| }; |
| |
| Add the following descriptions for gl_SecondaryPositionNV and |
| gl_SecondaryViewportMaskNV[]: |
| |
| The output variables gl_SecondaryPositionNV and gl_SecondaryViewportMaskNV[] |
| are available in vertex, tessellation, and geometry languages to specify |
| the position and the viewport mask for the secondary view respectively. |
| The input variable gl_SecondaryPositionNV is available in the tessellation |
| and geometry languages to read the secondary position written by a |
| previous shader stage. See section 11.5 ("Stereo Offsetted Rendering") of |
| the OpenGL 4.5 specification for more information. |
| |
| |
| Add the following to the description of gl_Layer |
| |
| The shader output gl_Layer may be redeclared with the following layout |
| qualifier which is available in vertex, tessellation, and geometry |
| shaders: |
| |
| layout-qualifier-id |
| secondary_view_offset = integer-constant-expression |
| |
| along with the <viewport-relative> layout qualifier introduced in |
| NV_viewport_array2. When using layered rendering, the layout qualifier |
| <secondary_view_offset> may be used to indicate the layer offset for the |
| primitives in the second view. If gl_Layer is redeclared with both |
| <viewport_relative> and <secondary_view_offset>, the layer used for |
| rendering the primitives of the second view is computed by first adding |
| the viewport index and then the offset value specified by |
| <secondary_view_offset>. |
| |
| |
| Errors |
| |
| None. |
| |
| Interactions with EXT_tessellation_shader |
| |
| If implemented on OpenGL ES and EXT_tessellation_shader is not supported, |
| remove all language referring to the tessellation control and tessellation |
| evaluation pipeline stages. |
| |
| Interactions with NV_gpu_program4 and NV_gpu_program5 |
| |
| If NV_gpu_program4 is supported and the "NV_stereo_view_rendering" program |
| option is specified, vertex, tessellation control/evaluation, and geometry |
| program result variable "result.secondaryposition" can be used to specify |
| the vertex's position coordinates from the second view and |
| "result.secondaryviewportmask[]" can be used to specify the mask of |
| viewports that the primitives from the second view will be emitted to. When |
| this program option is specified in tessellation control/evaluation, and/or |
| geometry programs, a vertex attribute "vertex[m].secondaryposition" is also |
| available to read the secondary position computed in a previous shader |
| stage. |
| |
| Modify Section 2.X.2 of NV_gpu_program4, Program Grammar |
| |
| (add the following rule to the NV_gpu_program4 grammar for Geometry and |
| Tessellation Control/Eval programs) |
| |
| <attribBasic> ::= ... |
| | <vtxPrefix> "secondaryposition" |
| |
| (add the following rule to the NV_gpu_program4 grammar for Vertex, |
| Geometry, and Tessellation Control/Eval programs) |
| |
| <declaration> ::= ... |
| | "SECONDARY_VIEW_LAYER_OFFSET" <optSign> <int> |
| |
| <resultBasic> ::= ... |
| | <resPrefix> "secondaryposition" |
| | <resPrefix> "secondaryviewportmask" arrayMemAbs |
| |
| (add the following to the tables of Geometry and Tessellation |
| Control/Eval Program Attribute Bindings) |
| |
| Binding Components Description |
| --------------------------- ---------- --------------------------- |
| vertex[m].secondaryposition (x,y,z,w) object coordinates for the |
| second view |
| |
| (add the following subsection to section 2.X.3.2 of NV_gpu_program4, |
| Program Attribute Variables) |
| |
| If an attribute binding in a geometry/tessellation program matches |
| "vertex[m].secondaryposition", the "x" component of the attribute provides |
| the "x" coordinate for the secondary view position. The "y", "z", and "w" |
| components will be the same as the "y", "z", and "w" components of |
| "vertex[m].position". |
| |
| |
| (add the following to the tables of Vertex, Geometry, and Tessellation |
| Control/Eval Program Result Variable Bindings) |
| |
| Binding Components Description |
| ----------------------------- ---------- ---------------------------- |
| result.secondaryposition (x,y,z,w) object coordinates for the |
| second view |
| result.secondaryviewportmask[] (v,-,-,-) viewport array mask for the |
| second view |
| |
| (add the following subsection to section 2.X.3.5 of NV_gpu_program4, |
| Program Results.) |
| |
| If a result variable binding matches "result.secondaryposition", updates |
| to the "x" component of the result variable provide the "x" coordinate for |
| the position from the secondary view. The y, z, and w coordinates for the |
| secondary view position are expected to be the same as the primary |
| position and are taken from the "result.position". Updates to y, z, and w |
| components of "result.secondaryposition" are ignored. |
| |
| If a result variable binding matches "result.secondaryviewportmask[]", |
| updates to the "x" component of the result variable provide a single |
| integer that serves as a mask of viewport indices for the secondary |
| view. The mask must be written as an integer value; writing a floating- |
| point value will produce undefined results. If the value has bits greater |
| than or equal to MAX_VIEWPORTS set, the number of viewports the primitive |
| is emitted to and which viewports are used undefined. If a program |
| specifies "NV_stereo_view_rendering" program option and does not write the |
| "result.secondaryviewportmask[]", then "result.viewportmask[]" will be |
| used as the viewport mask for both the views. |
| |
| If the "NV_stereo_view_rendering" program option is not specified, the |
| "result.secondaryposition" and "result.secondaryviewportmask[]" bindings |
| are unavailable. |
| |
| (add the following to Section 2.X.6.Y, Program Options) |
| |
| + Stereo Offsetted Rendering (NV_stereo_view_rendering) |
| |
| If a vertex, geometry, tessellation control, or tessellation evaluation |
| program specifies the "NV_stereo_view_rendering" option, the result |
| bindings "result.secondaryposition" and "result.secondaryviewportmask[]" |
| will be available to specify the secondary position and viewportmask |
| respectively. |
| |
| (add the following to Section 2.X.7.Y, Program Declarations) |
| |
| + Layer Offset for the Secondary View (NV_SECONDARY_VIEW_LAYER_OFFSET) |
| |
| The NV_SECONDARY_VIEW_LAYER_OFFSET statement declares the layer offset |
| value to be added to the "result.layer" for the secondary view. If the |
| program also specifies the "NV_layer_viewport_relative" option, both the |
| viewport index and the above offset are added to the "result.layer" for |
| the second view. |
| |
| Issues |
| |
| (1) Where does the stereo view expansion occur? |
| |
| RESOLVED: This operation occurs right before viewport mask expansion |
| (NV_viewport_array2). The primary primitive is broadcast to different |
| viewports based on the viewport id/viewport mask followed by the secondary |
| primitive. This specification applies the stereo view expansion after |
| transform feedback, and makes all primitive queries except for clipping |
| primitives only count each primitive once. Clipping primitives' queries |
| count the primitives once for each view. |
| |
| (2) Do we need "gl_SecondaryViewportIdNV" for the second view? |
| |
| RESOLVED: No. "gl_SecondaryViewportMaskNV[]" should cover that functionality. |
| |
| (3) Should the secondary position be readable from the tessellation |
| control/evaluation and geometry shaders? |
| |
| RESOLVED: Yes. If the secondary position is written by the vertex shader, |
| tessellation shader should be able to read position to evaluate the |
| interpolated positions for the second view. |
| |
| Revision History |
| |
| Revision 3 2017/11/25 (pbrown) |
| - Add to the OpenGL ES Extension Registry |
| Revision 2 2017/02/21 (jaschmidt) |
| - Formally add OpenGL ES interactions |
| Revision 1 |
| - Internal revisions. |
