Class NVGeometryShaderPassthrough
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 do not
// loop over three vertices or call EmitVertex().
gl_Layer = compute_layer();
}
VK_NV_geometry_shader_passthrough
- Name String
VK_NV_geometry_shader_passthrough
- Extension Type
- Device extension
- Registered Extension Number
- 96
- Revision
- 1
- Contact
- Daniel Koch dgkoch
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.
- This extension requires
- Contributors
- Piers Daniell, NVIDIA
- Jeff Bolz, NVIDIA
-
Field Summary
Modifier and TypeFieldDescriptionstatic final String
The extension name.static final int
The extension specification version. -
Method Summary
-
Field Details
-
VK_NV_GEOMETRY_SHADER_PASSTHROUGH_SPEC_VERSION
public static final int VK_NV_GEOMETRY_SHADER_PASSTHROUGH_SPEC_VERSIONThe extension specification version.- See Also:
-
VK_NV_GEOMETRY_SHADER_PASSTHROUGH_EXTENSION_NAME
The extension name.- See Also:
-