Safe Haskell | None |
---|---|
Language | Haskell2010 |
Name
VK_NV_geometry_shader_passthrough - device extension
VK_NV_geometry_shader_passthrough
- Name String
VK_NV_geometry_shader_passthrough
- Extension Type
- Device extension
- Registered Extension Number
- 96
- Revision
- 1
- Extension and Version Dependencies
- Requires Vulkan 1.0
- Contact
Other Extension Metadata
- Last Modified Date
- 2017-02-15
- Interactions and External Dependencies
- This extension requires SPV_NV_geometry_shader_passthrough
- This extension provides API support for GL_NV_geometry_shader_passthrough
- This extension requires the
geometryShader
feature.
- Contributors
- Piers Daniell, NVIDIA
- Jeff Bolz, NVIDIA
Description
This extension adds support for the following SPIR-V extension in Vulkan:
SPV_NV_geometry_shader_passthrough
Geometry shaders provide the ability for applications to process each
primitive sent through the graphics pipeline using a programmable
shader. However, one common use case treats them largely as a
“passthrough”. In this use case, the bulk of the geometry shader code
simply copies inputs from each vertex of the input primitive to
corresponding outputs in the vertices of the output primitive. Such
shaders might also compute values for additional built-in or
user-defined per-primitive attributes (e.g., Layer
) to be assigned to
all the vertices of the output primitive.
This extension provides access to the PassthroughNV
decoration under
the GeometryShaderPassthroughNV
capability. Adding this to a geometry
shader input variable specifies that the values of this input are copied
to the corresponding vertex of the output primitive.
When using GLSL source-based shading languages, the passthrough
layout
qualifier from GL_NV_geometry_shader_passthrough
maps to the
PassthroughNV
decoration. To use the passthrough
layout, in GLSL the
GL_NV_geometry_shader_passthrough
extension must be enabled. Behaviour
is described in the GL_NV_geometry_shader_passthrough
extension
specification.
New Enum Constants
New Variable Decoration
New SPIR-V Capabilities
Issues
1) Should we require or allow a passthrough geometry shader to specify the output layout qualifiers for the output primitive type and maximum vertex count in the SPIR-V?
RESOLVED: Yes they should be required in the SPIR-V. Per GL_NV_geometry_shader_passthrough they are not permitted in the GLSL source shader, but SPIR-V is lower-level. It is straightforward for the GLSL compiler to infer them from the input primitive type and to explicitly emit them in the SPIR-V according to the following table.
Input Layout | Implied Output Layout |
---|---|
points | layout(points, max_vertices=1) |
lines | layout(line_strip, max_vertices=2) |
triangles | layout(triangle_strip, max_vertices=3) |
2) How does interface matching work with passthrough geometry shaders?
RESOLVED: This is described in
Passthrough Interface Matching.
In GL when using passthough geometry shaders in separable mode, all
inputs must also be explicitly assigned location layout qualifiers. In
Vulkan all SPIR-V shader inputs (except built-ins) must also have
location decorations specified. Redeclarations of built-in varables that
add the passthrough layout qualifier are exempted from the rule
requiring location assignment because built-in variables do not have
locations and are matched by BuiltIn
decoration.
Sample Code
Consider the following simple geometry shader in unextended GLSL:
layout(triangles) in; layout(triangle_strip) out; layout(max_vertices=3) out; in Inputs { vec2 texcoord; vec4 baseColor; } v_in[]; out Outputs { vec2 texcoord; vec4 baseColor; }; void main() { int layer = compute_layer(); for (int i = 0; i < 3; i++) { gl_Position = gl_in[i].gl_Position; texcoord = v_in[i].texcoord; baseColor = v_in[i].baseColor; gl_Layer = layer; EmitVertex(); } }
In this shader, the inputs gl_Position
, Inputs.texcoord
, and
Inputs.baseColor
are simply copied from the input vertex to the
corresponding output vertex. The only “interesting” work done by the
geometry shader is computing and emitting a gl_Layer
value for the
primitive.
The following geometry shader, using this extension, is equivalent:
#extension GL_NV_geometry_shader_passthrough : require layout(triangles) in; // No output primitive layout qualifiers required. // Redeclare gl_PerVertex to pass through "gl_Position". layout(passthrough) in gl_PerVertex { vec4 gl_Position; } gl_in[]; // Declare "Inputs" with "passthrough" to automatically copy members. layout(passthrough) in Inputs { vec2 texcoord; vec4 baseColor; } v_in[]; // No output block declaration required. void main() { // The shader simply computes and writes gl_Layer. We don't // loop over three vertices or call EmitVertex(). gl_Layer = compute_layer(); }
Version History
Revision 1, 2017-02-15 (Daniel Koch)
- Internal revisions
See Also
No cross-references are available
Document Notes
For more information, see the Vulkan Specification
This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.
Documentation
pattern NV_GEOMETRY_SHADER_PASSTHROUGH_SPEC_VERSION :: forall a. Integral a => a Source #
type NV_GEOMETRY_SHADER_PASSTHROUGH_EXTENSION_NAME = "VK_NV_geometry_shader_passthrough" Source #
pattern NV_GEOMETRY_SHADER_PASSTHROUGH_EXTENSION_NAME :: forall a. (Eq a, IsString a) => a Source #