Computational Graphics with DirectX

Computational graphics involves using the GPU not just for traditional rendering tasks, but also for general-purpose computation. DirectX provides powerful compute shaders and associated APIs that allow developers to leverage the massive parallelism of modern GPUs for a wide range of applications beyond visual rendering.

Overview

DirectX's compute capabilities are primarily accessed through Compute Shaders. Unlike vertex or pixel shaders that are part of the graphics pipeline, compute shaders can be dispatched independently. This flexibility makes them ideal for tasks such as:

  • Physics Simulations: Simulating fluid dynamics, cloth, particles, and rigid bodies.
  • Image Processing: Applying filters, performing color transformations, and image upscaling.
  • Machine Learning: Accelerating neural network inference and training.
  • Data Analysis: Performing parallel computations on large datasets.
  • Ray Tracing and Path Tracing: Advanced rendering techniques.

Key Components

Compute Shaders

Compute shaders are programs written in High-Level Shading Language (HLSL) that run on the GPU. They are executed in thread groups, and each thread within a group can cooperate using shared memory and synchronization primitives.


// Example of a simple compute shader
#define THREAD_GROUP_SIZE 64

RWTexture2D<float4> outputTexture : register(u0);
RWBuffer<float>  outputBuffer  : register(u1);
ConstantBuffer<float> constants : register(b0);

[numthreads(THREAD_GROUP_SIZE, 1, 1)]
void CSMain(uint3 dispatchThreadID : SV_DispatchThreadID)
{
    // Example: Write a value to an output buffer
    outputBuffer[dispatchThreadID.x] = dispatchThreadID.x * constants.someValue;

    // Example: Calculate a pixel color for an output texture
    float4 color = float4(dispatchThreadID.xy / float2(outputTexture.GetWidth(), outputTexture.GetHeight()), 0.0f, 1.0f);
    outputTexture[dispatchThreadID.xy] = color;
}

Dispatching Compute Shaders

In your application code (typically C++), you'll set up the necessary DirectX objects and then dispatch the compute shader. This involves:

  1. Creating a compute shader object from your HLSL code.
  2. Binding the necessary input and output resources (e.g., textures, buffers).
  3. Setting any constant buffer values.
  4. Calling the Dispatch or DispatchIndirect method on your command list.

Resource Binding

Compute shaders interact with data through various resources:

  • Unordered Access Views (UAVs): Essential for compute shaders as they allow read and write access to textures and buffers.
  • Shader Resource Views (SRVs): For reading data, such as input textures or vertex data.
  • Constant Buffers: To pass parameters to the shader.

Common Use Cases

Parallel Sorting

GPUs are excellent at parallel sorting algorithms, which can be a bottleneck in complex simulations or data processing.

Particle Systems

Simulating the behavior of thousands or millions of particles, including their physics, collisions, and interactions, is a prime application for compute shaders.

Mesh Generation and Deformation

Dynamically generating or modifying meshes on the GPU can significantly improve performance for procedural content or complex character animations.

Learning Resources