MSDN Documentation

HLSL Fundamentals

High-Level Shading Language (HLSL) is a proprietary shading language developed by Microsoft for its DirectX graphics API. It provides a powerful and flexible way to program the graphics processing unit (GPU) for a wide range of computational tasks, from rendering complex visual effects to general-purpose GPU (GPGPU) computations.

Why HLSL?

HLSL offers several advantages:

• Abstraction: Hides the complexities of underlying hardware.
• Portability: Code can be compiled for different GPU architectures.
• Performance: Designed for efficient execution on the GPU.
• Integration: Seamlessly integrates with DirectX APIs.

Basic Syntax

HLSL syntax is C-like, making it familiar to many developers. Key elements include:

• Statements end with a semicolon (;).
• Code blocks are enclosed in curly braces ({ }).
• Comments can be single-line (//) or multi-line (/* */).

Data Types

HLSL supports a variety of data types:

• Scalar types: bool, int, half, float, double.
• Vector types: float2, float3, float4, int2, int4, etc. These are used extensively for colors, positions, and normals.
• Matrix types: float2x2, float3x3, float4x4, etc.
• Texture types: Texture1D, Texture2D, TextureCube, etc.
• Sampler types: SamplerState, SamplerComparisonState.

Example using vector types:

float4 position = float4(1.0f, 2.0f, 3.0f, 1.0f);
float3 color = float3(0.5f, 0.1f, 0.9f);
                

Variables and Operators

Variables are declared with their type, name, and optionally initialized. HLSL supports standard arithmetic, comparison, and logical operators.

float scale = 2.0f;
float4 transformedPosition = position * scale;

bool isVisible = true;
int count = 10;

if (count > 5) {
    // Do something
}
                

Functions

Functions in HLSL can take parameters and return values. They are used to encapsulate reusable logic.

float4 MyShaderFunction(float4 inputColor, float alpha) {
    float4 outputColor = inputColor;
    outputColor.a = alpha;
    return outputColor;
}
                

Control Flow

HLSL supports standard control flow statements like if, else, for, while, and switch.

for (int i = 0; i < 10; ++i) {
    // Loop body
}

while (someCondition) {
    // While loop body
}
                

Structures

Custom data structures can be defined to group related variables.

struct VertexInput {
    float4 position : POSITION;
    float2 texCoord : TEXCOORD0;
};

struct PixelOutput {
    float4 color : SV_TARGET;
};
                

Semantics

Semantics are crucial in HLSL, defining the meaning and usage of variables. They link shader input/output to the graphics pipeline. Common semantics include POSITION, COLOR, TEXCOORD, and SV_POSITION (for clip-space position in the pixel shader).

Built-in Functions

HLSL provides a rich set of built-in functions for mathematical operations, texture sampling, and more.

• Math: sin, cos, pow, dot, cross, normalize.
• Texture Sampling: tex2D, texCUBE.
• Common: lerp, saturate.

float4 sampledColor = tex2D(mySampler, texCoord);
float3 normal = normalize(inputNormal);
                

Resources

Shaders interact with GPU resources like textures and buffers. These are typically declared using resource types.

Texture2D myTexture;
SamplerState mySampler;

float4 SampleTexture(float2 uv) {
    return myTexture.Sample(mySampler, uv);
}
                

Constant Buffers

Constant buffers are memory regions used to pass constant data (e.g., transformation matrices, lighting parameters) from the CPU to the GPU. They are declared using the cbuffer keyword.

cbuffer PerFrameConstants {
    float4x4 g_worldViewProjection;
    float3 g_lightDirection;
};

// Use in shader:
float4 vertexPosition = mul(input.position, g_worldViewProjection);
                

Understanding these fundamental concepts is the first step towards mastering HLSL and creating breathtaking graphics and efficient GPU computations.