HLSL

High-Level Shading Language (HLSL) is a shading language developed by Microsoft for use with the DirectX API. It is used to write programs that run on graphics processing units (GPUs) to perform tasks such as vertex transformation, pixel shading, geometry processing, and general-purpose compute operations. HLSL code is compiled into shader bytecode and executed by the Direct3D pipeline, with shaders bound to specific stages and resources.

HLSL has evolved alongside DirectX, with support spanning DirectX 9 through DirectX 12. Shaders target different pipeline stages with shader models that specify available features. Common stages include vertex shaders, pixel (fragment) shaders, geometry shaders, hull and domain shaders for tessellation, and compute shaders for general-purpose GPU compute. Modern usage often employs the DirectX Raytracing (DXR) extension for ray tracing tasks, implemented through specialized shader entry points.

The language itself is C-like and includes a range of data types, such as scalar, vector (for example float3, float4), and matrix types. It supports user-defined structures, functions, and control flow constructs. HLSL provides a binding model for resources, including constant buffers, structured buffers, textures, and samplers, with semantics and registers to connect shader inputs and outputs to the rest of the pipeline. Entry points are functions named main by default, with inputs and outputs annotated by semantic attributes (for example SV_POSITION, SV_TARGET, TEXCOORD). The way resources are bound and indexed has evolved across DirectX versions, influencing how shaders interface with application code.

Compilation is performed by tools such as the fxc compiler or the newer DirectX Shader Compiler (DXC). The compiled shaders are loaded into the Direct3D device and used to configure the graphics or compute pipelines at runtime. HLSL remains the primary shading language for Windows-based DirectX development, with cross-compilation workflows enabling some integration with other graphics APIs.