domainshader

Domain shader is a shader stage in modern GPU pipelines that handles the evaluation of tessellated patches. It runs after the hull shader and the tessellator, and its primary job is to produce the final vertex attributes for each generated point on a tessellated surface. In this stage, the domain shader maps parametric domain coordinates to positions in 3D space and computes per-vertex data such as normals, texture coordinates, and other attributes needed by later stages of the pipeline.

The domain shader receives input from the tessellator in the form of domain coordinates that describe where on the tessellated patch a vertex lies. The exact coordinates depend on the tessellation domain being used: quad domains provide two coordinates (u and v), triangle domains use a barycentric-like two- or three-component coordinate system, and isoline domains use a single coordinate along each line. The shader also has access to per-patch constants produced by the hull shader, as well as the patch’s control points, enabling it to evaluate the surface defined by the patch. The output of the domain shader is the vertex position in clip space (or transformed space) and any additional per-vertex attributes, which are then interpolated and passed on to subsequent pipeline stages.

In practice, the domain shader evaluates a surface defined by the tessellated patch, often using Bézier or spline representations, to produce smooth geometry at higher detail than the original control mesh. It can also generate or refine attributes such as normals and texture coordinates, enabling effects like displacement mapping or procedurally generated detail. The domain shader concept exists in Direct3D as the tessellation evaluation shader and in OpenGL as the tessellation evaluation stage. Its performance characteristics are tied to tessellation factor and the complexity of the surface evaluation it performs.