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Vertex-shader stage

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The vertex-shader (VS) stage processes vertices from the input assembler, performing per-vertex operations such as transformations, skinning, morphing, and per-vertex lighting. Vertex shaders always operate on a single input vertex and produce a single output vertex. The vertex-shader stage must always be active for the pipeline to execute. If no vertex modification or transformation is required, a pass-through vertex shader must be created and set to the pipeline.

The Vertex-shader

Each vertex shader input vertex can be comprised of up to 16 32-bit vectors (up to 4 components each) and each output vertex can be comprised of as many as 16 32-bit 4-component vectors. All vertex-shaders must have a minimum of one input and one output, which can be as little as one scalar value.

The vertex-shader stage can consume two system generated values from the input assembler: VertexID and InstanceID (see System-value semantics). Since VertexID and InstanceID are both meaningful at a vertex level, and IDs generated by hardware can only be fed into the first stage that understands them, these ID values can only be fed into the vertex-shader stage.

Vertex shaders are always run on all vertices, including adjacent vertices in input primitive topologies with adjacency. The number of times that the vertex-shader has been executed can be queried from the CPU using the VSInvocations pipeline statistic.

A vertex-shader can perform load and texture sampling operations where screen-space derivatives are not required (using HLSL intrinsic functions: Sample (DirectX HLSL Texture Object), SampleCmpLevelZero (DirectX HLSL Texture Object), and SampleGrad (DirectX HLSL Texture Object)).