Introduction

Multithreading is a powerful technique to improve the performance of your DirectX applications by leveraging multiple CPU cores. This section will cover the basics of multithreading in DirectX, including how to create and manage threads, synchronize resources, and optimize rendering performance.

Key Concepts

Multithreading Basics:
- Thread: A sequence of executable instructions that can run concurrently with other threads.
- Concurrency: The ability to run multiple threads simultaneously to perform different tasks.
- Parallelism: The actual simultaneous execution of multiple threads on different CPU cores.
DirectX and Multithreading:
- Command Lists: Used to record rendering commands that can be executed by the GPU.
- Command Queues: Used to submit command lists to the GPU for execution.
- Synchronization: Ensuring that resources are accessed safely by multiple threads.

Setting Up Multithreading in DirectX

Step 1: Creating Threads

To create threads in C++, you can use the <thread> library. Here’s a simple example:

#include <iostream>
#include <thread>

// Function to be executed by the thread
void renderTask() {
    std::cout << "Rendering on thread: " << std::this_thread::get_id() << std::endl;
}

int main() {
    // Create a thread
    std::thread renderThread(renderTask);

    // Wait for the thread to finish
    renderThread.join();

    return 0;
}

Step 2: Using Command Lists and Command Queues

In DirectX 12, you can use command lists and command queues to manage rendering tasks across multiple threads.

Creating Command Lists

ID3D12CommandAllocator* commandAllocator;
ID3D12GraphicsCommandList* commandList;

// Create command allocator
device->CreateCommandAllocator(D3D12_COMMAND_LIST_TYPE_DIRECT, IID_PPV_ARGS(&commandAllocator));

// Create command list
device->CreateCommandList(0, D3D12_COMMAND_LIST_TYPE_DIRECT, commandAllocator, nullptr, IID_PPV_ARGS(&commandList));

Recording Commands

commandList->Reset(commandAllocator, nullptr);

// Record rendering commands
commandList->ClearRenderTargetView(rtvHandle, clearColor, 0, nullptr);
commandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
commandList->DrawInstanced(3, 1, 0, 0);

commandList->Close();

Executing Command Lists

ID3D12CommandQueue* commandQueue;
device->CreateCommandQueue(&queueDesc, IID_PPV_ARGS(&commandQueue));

// Execute command list
ID3D12CommandList* commandLists[] = { commandList };
commandQueue->ExecuteCommandLists(_countof(commandLists), commandLists);

Step 3: Synchronizing Resources

To ensure that resources are accessed safely by multiple threads, you can use synchronization primitives such as mutexes and fences.

Using Mutexes

#include <mutex>

std::mutex mtx;

void renderTask() {
    std::lock_guard<std::mutex> lock(mtx);
    // Access shared resources safely
}

Using Fences

ID3D12Fence* fence;
UINT64 fenceValue = 0;

// Create fence
device->CreateFence(fenceValue, D3D12_FENCE_FLAG_NONE, IID_PPV_ARGS(&fence));

// Signal and wait for fence
commandQueue->Signal(fence, ++fenceValue);
if (fence->GetCompletedValue() < fenceValue) {
    HANDLE eventHandle = CreateEventEx(nullptr, FALSE, FALSE, EVENT_ALL_ACCESS);
    fence->SetEventOnCompletion(fenceValue, eventHandle);
    WaitForSingleObject(eventHandle, INFINITE);
    CloseHandle(eventHandle);
}

Practical Exercise

Exercise: Implement Multithreaded Rendering

Objective: Create a DirectX application that uses multiple threads to record and execute command lists.
Steps:
- Create multiple threads to record command lists.
- Use command queues to execute the recorded command lists.
- Synchronize access to shared resources using mutexes or fences.

Solution

#include <iostream>
#include <thread>
#include <mutex>
#include <d3d12.h>
#include <dxgi1_4.h>

std::mutex mtx;

void renderTask(ID3D12Device* device, ID3D12CommandQueue* commandQueue, ID3D12CommandAllocator* commandAllocator, ID3D12GraphicsCommandList* commandList) {
    std::lock_guard<std::mutex> lock(mtx);

    // Record commands
    commandList->Reset(commandAllocator, nullptr);
    commandList->ClearRenderTargetView(rtvHandle, clearColor, 0, nullptr);
    commandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
    commandList->DrawInstanced(3, 1, 0, 0);
    commandList->Close();

    // Execute command list
    ID3D12CommandList* commandLists[] = { commandList };
    commandQueue->ExecuteCommandLists(_countof(commandLists), commandLists);
}

int main() {
    // Initialize DirectX (device, commandQueue, commandAllocator, commandList, etc.)

    // Create threads
    std::thread thread1(renderTask, device, commandQueue, commandAllocator, commandList);
    std::thread thread2(renderTask, device, commandQueue, commandAllocator, commandList);

    // Wait for threads to finish
    thread1.join();
    thread2.join();

    return 0;
}

Conclusion

In this section, you learned how to implement multithreading in DirectX to improve rendering performance. You explored the basics of creating and managing threads, using command lists and command queues, and synchronizing resources. By leveraging multithreading, you can make your DirectX applications more efficient and responsive.

Next, you will delve into advanced topics such as deferred shading and post-processing effects to further enhance your DirectX skills.

Multithreading in DirectX

Introduction

Key Concepts

Setting Up Multithreading in DirectX

Step 1: Creating Threads

Step 2: Using Command Lists and Command Queues

Creating Command Lists

Recording Commands

Executing Command Lists

Step 3: Synchronizing Resources

Using Mutexes

Using Fences

Practical Exercise

Exercise: Implement Multithreaded Rendering

Solution

Conclusion

DirectX Programming Course

Module 1: Introduction to DirectX

Module 2: Direct3D Basics

Module 3: Working with Shaders

Module 4: Advanced Rendering Techniques

Module 5: 3D Models and Animation

Module 6: Performance Optimization

Module 7: Advanced Topics

Module 8: DirectX in Practice