Shader Programming - DirectX Computational Graphics Tutorials

Introduction to Shader Programming with DirectX

Welcome to this in-depth tutorial on shader programming within the DirectX ecosystem. Shaders are small programs that run on the GPU, controlling how vertices are transformed and how pixels are colored. Mastering shaders is crucial for creating modern, visually rich applications and games.

What are Shaders?

Shaders are the heart of modern graphics rendering. They break down the complex process of rendering into manageable stages, each handled by a specific type of shader:

Vertex Shaders: Process individual vertices, transforming them from model space to clip space. This includes operations like translation, rotation, scaling, and projection.
Pixel Shaders (Fragment Shaders): Determine the final color of each pixel on the screen. This involves texture sampling, lighting calculations, and applying various visual effects.
Geometry Shaders: (Optional) Generate or modify primitives (points, lines, triangles) on the fly.
Hull Shaders & Domain Shaders: (Tessellation) Used for dynamically subdividing geometry to add fine detail.
Compute Shaders: For general-purpose computation on the GPU, not directly tied to rendering a scene.

High-Level Shading Language (HLSL)

DirectX utilizes High-Level Shading Language (HLSL) to write shaders. HLSL is a C-style language that is compiled into bytecode executable by the GPU. It provides constructs for vector and matrix operations, texture sampling, and control flow.

Getting Started with a Simple Vertex Shader

Let's begin with a basic vertex shader. Its primary role is to pass vertex data and a world-view-projection matrix to the rasterizer.

Consider this simple vertex shader written in HLSL:


struct VS_INPUT
{
    float4 Pos : POSITION;
    float2 Tex : TEXCOORD0;
};

struct VS_OUTPUT
{
    float4 Pos : SV_POSITION;
    float2 Tex : TEXCOORD0;
};

cbuffer ConstantBuffer : register(b0)
{
    matrix WorldViewProjection;
};

VS_OUTPUT main(VS_INPUT input)
{
    VS_OUTPUT output = (VS_OUTPUT)0;

    // Transform the vertex position
    output.Pos = mul(input.Pos, WorldViewProjection);

    // Pass through the texture coordinate
    output.Tex = input.Tex;

    return output;
}

In this shader:

VS_INPUT defines the structure of data coming into the vertex shader (position and texture coordinates).
VS_OUTPUT defines the structure of data going out of the vertex shader. SV_POSITION is a semantic that indicates the clip-space position.
A constant buffer ConstantBuffer is used to pass the WorldViewProjection matrix.
The main function performs the core transformation.

A Basic Pixel Shader

The pixel shader's job is to output the final color for each pixel. Here's a simple example that samples a texture:


Texture2D Texture : register(t0);
SamplerState Sampler : register(s0);

struct PS_INPUT
{
    float4 Pos : SV_POSITION;
    float2 Tex : TEXCOORD0;
};

float4 main(PS_INPUT input) : SV_TARGET
{
    // Sample the texture at the given UV coordinate
    float4 color = Texture.Sample(Sampler, input.Tex);
    return color;
}

This pixel shader:

Takes interpolated texture coordinates from the vertex shader.
Uses a Texture2D object and a SamplerState to sample the texture.
SV_TARGET semantic indicates the render target (the output color).

Further Exploration

This is just the tip of the iceberg. Advanced shader programming involves complex lighting models (Phong, Blinn-Phong, physically-based rendering), normal mapping, specular maps, environment mapping, post-processing effects like bloom and depth of field, and much more.

Dive deeper into the official DirectX documentation and explore resources dedicated to HLSL optimization and common shader techniques.

Explore Advanced Shader Techniques