DirectX Rendering Pipeline

Understanding the Graphics Pipeline for High-Performance Rendering

The DirectX Rendering Pipeline Overview

The DirectX rendering pipeline is a series of stages that a 3D model goes through from its definition in application memory to its final display on the screen. Understanding this pipeline is crucial for any developer aiming to achieve efficient and visually impressive graphics with DirectX.

Key Concepts

Pipeline Stages

The modern DirectX rendering pipeline is highly programmable, allowing developers to customize much of its behavior. However, it can be broadly divided into the following logical stages:

Input Assembler

Fetches vertex data from system memory and organizes it into primitives.

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Vertex Shader

Transforms each vertex from its model space to clip space.

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Tessellation (Optional)

Dynamically subdivides primitives to add detail.

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Geometry Shader (Optional)

Can create or delete primitives.

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Rasterizer

Determines which pixels on the screen are covered by each primitive.

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Pixel Shader

Computes the color for each covered pixel.

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Output Merger

Combines pixel colors with the render target, performing depth and stencil tests.

Programmable Stages: Shaders

Shaders are the heart of modern graphics programming. DirectX supports several types of shaders, with the Vertex Shader and Pixel Shader being the most fundamental.

Vertex Shader

The vertex shader receives individual vertices and is responsible for transforming them. This typically involves applying model, view, and projection matrices to convert vertex positions from the object's local space into screen space. It can also pass data (like texture coordinates or colors) to subsequent stages.

// Example HLSL Vertex Shader
struct VS_INPUT {
    float4 position : POSITION;
    float2 texCoord : TEXCOORD;
};

struct VS_OUTPUT {
    float4 position : SV_POSITION;
    float2 texCoord : TEXCOORD;
};

VS_OUTPUT VSMain(VS_INPUT input, uniform float4x4 worldViewProjection) {
    VS_OUTPUT output;
    output.position = mul(input.position, worldViewProjection);
    output.texCoord = input.texCoord;
    return output;
}

Pixel Shader

The pixel shader (also known as the fragment shader) operates on a per-pixel basis. After the rasterizer determines which pixels are covered by a primitive, the pixel shader calculates the final color for each of those pixels. This is where lighting, texturing, and other visual effects are typically applied.

// Example HLSL Pixel Shader
Texture2D shaderTexture;
SamplerState samplerLinear;

struct PS_INPUT {
    float4 position : SV_POSITION;
    float2 texCoord : TEXCOORD;
};

float4 PSMain(PS_INPUT input) : SV_TARGET {
    return shaderTexture.Sample(samplerLinear, input.texCoord);
}

Further Reading