org.lwjgl.vulkan

Class NVGeometryShaderPassthrough

java.lang.Object

org.lwjgl.vulkan.NVGeometryShaderPassthrough

public final class NVGeometryShaderPassthrough
extends java.lang.Object

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.

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();
 }

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

• Daniel Koch dgkoch

Last Modified Date

2017-02-15

Interactions and External Dependencies

• This extension requires the SPV_NV_geometry_shader_passthrough SPIR-V extension.
• This extension requires the GL_NV_geometry_shader_passthrough extension for GLSL source languages.
• This extension requires the geometryShader feature.

Contributors

• Piers Daniell, NVIDIA
• Jeff Bolz, NVIDIA

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	VK_NV_GEOMETRY_SHADER_PASSTHROUGH_EXTENSION_NAME The extension name.
static int	VK_NV_GEOMETRY_SHADER_PASSTHROUGH_SPEC_VERSION The extension specification version.

Method Summary

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

VK_NV_GEOMETRY_SHADER_PASSTHROUGH_SPEC_VERSION

public static final int VK_NV_GEOMETRY_SHADER_PASSTHROUGH_SPEC_VERSION

The extension specification version.

See Also:

Constant Field Values

VK_NV_GEOMETRY_SHADER_PASSTHROUGH_EXTENSION_NAME

public static final java.lang.String VK_NV_GEOMETRY_SHADER_PASSTHROUGH_EXTENSION_NAME

The extension name.

See Also:

Constant Field Values