[DirectX12] 22) Instancing

같은 물체를 다수를 그려야할 때

DrawCall은 성능을 많이 잡아먹는데, Setting 하는 부분이 많은 부분을 굉장한 부하를 주기 때문

=> Instancing으로 묶어 진행한다면?

 

완전히 똑같은 물체를 만들 때 Instancing으로 묶어 만들 수 있음

SV_InstanceID를 통해 추적, 그거에 따른 배치 정보를 활용

 

Particle은 배치정보를 어떻게 기입?

=> Particle 같은 경우는 Compute Shader을 사용해서 t_register에 넣기위해 SturcturedBuffer을 사용

 

Instancing  같은 경우는?

=> Rendering을 할 때 IASetVertexBuffer을 이용하는데, 여러개의 슬롯을 사용함

---

InstancingBuffer.h

#pragma once

struct InstancingParams
{
	Matrix matWorld;
	Matrix matWV;
	Matrix matWVP;
};

class InstancingBuffer
{
public:
	InstancingBuffer();
	~InstancingBuffer();

	void Init(uint32 maxCount = 10);

	void Clear();
	void AddData(InstancingParams& params);
	void PushData();

public:
	uint32				GetCount() { return static_cast<uint32>(_data.size()); }
	ComPtr<ID3D12Resource>		GetBuffer() { return _buffer; }
	D3D12_VERTEX_BUFFER_VIEW	GetBufferView() { return _bufferView; }

	void	SetID(uint64 instanceId) { _instanceId = instanceId; }
	uint64	GetID() { return _instanceId; }

private:
	uint64						_instanceId = 0;
	ComPtr<ID3D12Resource>		_buffer;
	D3D12_VERTEX_BUFFER_VIEW	_bufferView;

	uint32						_maxCount = 0;
	vector<InstancingParams>	_data;
};

InstancingBuffer.cpp

#include "pch.h"
#include "InstancingBuffer.h"
#include "Engine.h"

InstancingBuffer::InstancingBuffer()
{
}

InstancingBuffer::~InstancingBuffer()
{
}

void InstancingBuffer::Init(uint32 maxCount)
{
	_maxCount = maxCount;

	const int32 bufferSize = sizeof(InstancingParams) * maxCount;
	D3D12_HEAP_PROPERTIES heapProperty = CD3DX12_HEAP_PROPERTIES(D3D12_HEAP_TYPE_UPLOAD);
	D3D12_RESOURCE_DESC desc = CD3DX12_RESOURCE_DESC::Buffer(bufferSize);

	DEVICE->CreateCommittedResource(
		&heapProperty,
		D3D12_HEAP_FLAG_NONE,
		&desc,
		D3D12_RESOURCE_STATE_GENERIC_READ,
		nullptr,
		IID_PPV_ARGS(&_buffer));
}

void InstancingBuffer::Clear()
{
	_data.clear();
}

void InstancingBuffer::AddData(InstancingParams& params)
{
	_data.push_back(params);
}

void InstancingBuffer::PushData()
{
	const uint32 dataCount = GetCount();
	if (dataCount > _maxCount)
		Init(dataCount);

	const uint32 bufferSize = dataCount * sizeof(InstancingParams);

	void* dataBuffer = nullptr;
	D3D12_RANGE readRange{ 0, 0 };
	_buffer->Map(0, &readRange, &dataBuffer);
	memcpy(dataBuffer, &_data[0], bufferSize);
	_buffer->Unmap(0, nullptr);

	_bufferView.BufferLocation = _buffer->GetGPUVirtualAddress();
	_bufferView.StrideInBytes = sizeof(InstancingParams);
	_bufferView.SizeInBytes = bufferSize;
}

---

InstancingManager.h

#pragma once
#include "InstancingBuffer.h"

class GameObject;

class InstancingManager
{
	DECLARE_SINGLE(InstancingManager);

public:
	void Render(vector<shared_ptr<GameObject>>& gameObjects);

	void ClearBuffer();
	void Clear() { _buffers.clear(); }

private:
	void AddParam(uint64 instanceId, InstancingParams& data);

private:
	map<uint64/*instanceId*/, shared_ptr<InstancingBuffer>> _buffers;
};

InstancingManager.cpp

#include "pch.h"
#include "InstancingManager.h"
#include "InstancingBuffer.h"
#include "GameObject.h"
#include "MeshRenderer.h"
#include "Transform.h"
#include "Camera.h"

void InstancingManager::Render(vector<shared_ptr<GameObject>>& gameObjects)
{
	map<uint64, vector<shared_ptr<GameObject>>> cache;

	//물체 배치
	for (shared_ptr<GameObject>& gameObject : gameObjects)
	{
		const uint64 instanceId = gameObject->GetMeshRenderer()->GetInstanceID();
		cache[instanceId].push_back(gameObject);
	}

	for (auto& pair : cache)
	{
		const vector<shared_ptr<GameObject>>& vec = pair.second;

		//물체 분류
		if (vec.size() == 1)
		{
			// 1개일 경우 원래방식과 같음
			vec[0]->GetMeshRenderer()->Render();
		}
		else
		{
			// 한번에 그리기 위해 모으는중
			const uint64 instanceId = pair.first;

			for (const shared_ptr<GameObject>& gameObject : vec)
			{
				InstancingParams params;
				params.matWorld = gameObject->GetTransform()->GetLocalToWorldMatrix();
				params.matWV = params.matWorld * Camera::S_MatView;
				params.matWVP = params.matWorld * Camera::S_MatView * Camera::S_MatProjection;

				AddParam(instanceId, params);
			}

			shared_ptr<InstancingBuffer>& buffer = _buffers[instanceId];
			vec[0]->GetMeshRenderer()->Render(buffer);
		}
	}
}

void InstancingManager::ClearBuffer()
{
	for (auto& pair : _buffers)
	{
		shared_ptr<InstancingBuffer>& buffer = pair.second;
		buffer->Clear();
	}
}

void InstancingManager::AddParam(uint64 instanceId, InstancingParams& data)
{
	if (_buffers.find(instanceId) == _buffers.end())
		_buffers[instanceId] = make_shared<InstancingBuffer>();

	_buffers[instanceId]->AddData(data);
}

---

Unity에서 Compute Buffer 를 사용하여 GPU 인스턴싱을 이용하는 기법 (참고자료)

▶ https://rito15.github.io/posts/unity-compute-buffer-gpu-instancing/