Shaders

Shaders are small programs that run on the graphics processing unit (GPU) to perform specific tasks in the graphics pipeline. They are essential for rendering complex and visually rich graphics. DirectX supports several types of shaders, each with a distinct role in processing graphical data.

Types of Shaders

The primary shader stages in DirectX include:

Vertex Shaders

Vertex shaders operate on individual vertices of 3D models. Their primary responsibilities include:

Transforming vertex positions from model space to world space, view space, and projection space.
Passing per-vertex data (like normals, texture coordinates, colors) to subsequent shader stages.
Performing lighting calculations on vertices.

A typical vertex shader might look like this:


// HLSL example for a simple vertex shader
struct VertexShaderInput
{
    float4 position : POSITION;
    float2 texCoord : TEXCOORD;
};

struct VertexShaderOutput
{
    float4 clipPos : SV_POSITION;
    float2 texCoord : TEXCOORD;
};

VertexShaderOutput main(VertexShaderInput input)
{
    VertexShaderOutput output;
    output.clipPos = mul(input.position, worldViewProjectionMatrix);
    output.texCoord = input.texCoord;
    return output;
}

Hull Shaders & Domain Shaders (Tessellation)

These shaders work together to implement tessellation, a technique that dynamically subdivides geometric primitives (like triangles) to add finer detail. Hull shaders control the tessellation factors, and domain shaders generate the new vertices within the subdivided patches.

Geometry Shaders

Geometry shaders are executed after the vertex or hull/domain shaders. They have the ability to:

Create new primitives (points, lines, triangles) from existing ones.
Discard existing primitives.
Modify primitive topology.

This stage is useful for effects like procedural generation of geometry or particle systems.

Pixel Shaders (Fragment Shaders)

Pixel shaders, also known as fragment shaders, operate on individual pixels or fragments generated during rasterization. They determine the final color of each pixel by:

Sampling textures.
Applying lighting and material properties.
Performing post-processing effects.

Their output is the color that will be written to the render target.


// HLSL example for a simple pixel shader
Texture2D myTexture;
SamplerState mySamplerState;

struct PixelShaderInput
{
    float4 clipPos : SV_POSITION;
    float2 texCoord : TEXCOORD;
};

float4 main(PixelShaderInput input) : SV_TARGET
{
    return myTexture.Sample(mySamplerState, input.texCoord);
}

Compute Shaders

Compute shaders are more general-purpose and are not part of the fixed-function graphics pipeline. They can be used for a wide range of parallel computations on the GPU, such as:

Physics simulations.
Image processing.
AI calculations.
Data manipulation.

Shader Languages

Shaders for DirectX are typically written in:

High-Level Shading Language (HLSL): A C-like language that is compiled into intermediate shader code. It's the primary language for modern DirectX development.
Assembly Shaders: Lower-level, hardware-specific instructions that offer maximum control but are more complex to write and maintain.

Shader Compilation and Loading

Shaders are compiled offline into bytecode using tools like the DirectX Shader Compiler (DXC) or fxc. This bytecode is then loaded and managed by the DirectX API at runtime, where it's bound to the appropriate shader stages of the graphics pipeline.

Documentation