[T18] Constant buffer

핵심 개념

Constant buffer: 상수버퍼에는 [파이프라인(셰이더)로부터 적은 레이턴시로 액세스], [CPU로 인한 빈번한 갱신]같은 성능이 요구된다. 이로 인해 상수버퍼의 메모리 구조에는 [4바이트 얼리어너먼트]로 [각 요소는 16바이트를 경계를 사이에 걸친 형태로는 할 수 없으며 전체 사이즈는 16의 배수(최대 4096 x 16 바이트)] 라는 조건이 붙어있다. 즉 버퍼사이즈는 16의 배수이어야 한다.

상수버퍼에 값을 쓰는 것은 버퍼의 Usage가 D3D11_USAGE_DEFAULT일 때의 서브리소스에 쓰는 방식과 D3D11_USAGE_DYNAMIC일 때에 ID3D11Device::Map~ UnMap을 사용하는 방식이 있다.

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Graphics.cpp

void Graphics::DrawTestTriangle( float angle )
{
	HRESULT hr;

	struct Vertex
	{
		struct {
			float x;
			float y;
		} pos;
		struct {
			unsigned char r;
			unsigned char g;
			unsigned char b;
			unsigned char a;
		} color;
	};

	// create vertex buffer (1 2d triangle at center of screen)
	Vertex vertices[] =
	{
		{ 0.0f,0.5f,255,0,0,0 },
		{ 0.5f,-0.5f,0,255,0,0 },
		{ -0.5f,-0.5f,0,0,255,0 },
		{ -0.3f,0.3f,0,255,0,0 },
		{ 0.3f,0.3f,0,0,255,0 },
		{ 0.0f,-1.0f,255,0,0,0 },
	};
	vertices[0].color.g = 255;
	wrl::ComPtr<ID3D11Buffer> pVertexBuffer;
	D3D11_BUFFER_DESC bd = {};
	bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
	bd.Usage = D3D11_USAGE_DEFAULT;
	bd.CPUAccessFlags = 0u;
	bd.MiscFlags = 0u;
	bd.ByteWidth = sizeof( vertices );
	bd.StructureByteStride = sizeof( Vertex );
	D3D11_SUBRESOURCE_DATA sd = {};
	sd.pSysMem = vertices;
	GFX_THROW_INFO( pDevice->CreateBuffer( &bd,&sd,&pVertexBuffer ) );
	
	// Bind vertex buffer to pipeline
	const UINT stride = sizeof( Vertex );
	const UINT offset = 0u;
	pContext->IASetVertexBuffers( 0u,1u,pVertexBuffer.GetAddressOf(),&stride,&offset );

	// create index buffer
	const unsigned short indices[] =
	{
		0,1,2,
		0,2,3,
		0,4,1,
		2,1,5,
	};
	wrl::ComPtr<ID3D11Buffer> pIndexBuffer;
	D3D11_BUFFER_DESC ibd = {};
	ibd.BindFlags = D3D11_BIND_INDEX_BUFFER;
	ibd.Usage = D3D11_USAGE_DEFAULT;
	ibd.CPUAccessFlags = 0u;
	ibd.MiscFlags = 0u;
	ibd.ByteWidth = sizeof( indices );
	ibd.StructureByteStride = sizeof( unsigned short );
	D3D11_SUBRESOURCE_DATA isd = {};
	isd.pSysMem = indices;
	GFX_THROW_INFO( pDevice->CreateBuffer( &ibd,&isd,&pIndexBuffer ) );

	// bind index buffer
	pContext->IASetIndexBuffer( pIndexBuffer.Get(),DXGI_FORMAT_R16_UINT,0u );

	// create constant buffer for transformation matrix
	struct ConstantBuffer
	{
		struct
		{
			float element[4][4];
		} transformation;
	};
	const ConstantBuffer cb =
	{
		{
			(3.0f / 4.0f) * std::cos( angle ),	std::sin( angle ),	0.0f,	0.0f,
			(3.0f / 4.0f) * -std::sin( angle ),	std::cos( angle ),	0.0f,	0.0f,
			0.0f,								0.0f,				1.0f,	0.0f,
			0.0f,								0.0f,				0.0f,	1.0f,
		}
	};
	wrl::ComPtr<ID3D11Buffer> pConstantBuffer;
	D3D11_BUFFER_DESC cbd;
	cbd.BindFlags = D3D11_BIND_CONSTANT_BUFFER;
	cbd.Usage = D3D11_USAGE_DYNAMIC;
	cbd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
	cbd.MiscFlags = 0u;
	cbd.ByteWidth = sizeof( cb );
	cbd.StructureByteStride = 0u;
	D3D11_SUBRESOURCE_DATA csd = {};
	csd.pSysMem = &cb;
	GFX_THROW_INFO( pDevice->CreateBuffer( &cbd,&csd,&pConstantBuffer ) );

	// bind constant buffer to vertex shader
	pContext->VSSetConstantBuffers( 0u,1u,pConstantBuffer.GetAddressOf() );

	// create pixel shader
	wrl::ComPtr<ID3D11PixelShader> pPixelShader;
	wrl::ComPtr<ID3DBlob> pBlob;
	GFX_THROW_INFO( D3DReadFileToBlob( L"PixelShader.cso",&pBlob ) );
	GFX_THROW_INFO( pDevice->CreatePixelShader( pBlob->GetBufferPointer(),pBlob->GetBufferSize(),nullptr,&pPixelShader ) );

	// bind pixel shader
	pContext->PSSetShader( pPixelShader.Get(),nullptr,0u );

	// create vertex shader
	wrl::ComPtr<ID3D11VertexShader> pVertexShader;
	GFX_THROW_INFO( D3DReadFileToBlob( L"VertexShader.cso",&pBlob ) );
	GFX_THROW_INFO( pDevice->CreateVertexShader( pBlob->GetBufferPointer(),pBlob->GetBufferSize(),nullptr,&pVertexShader ) );

	// bind vertex shader
	pContext->VSSetShader( pVertexShader.Get(),nullptr,0u );

	// input (vertex) layout (2d position only)
	wrl::ComPtr<ID3D11InputLayout> pInputLayout;
	const D3D11_INPUT_ELEMENT_DESC ied[] =
	{
		{ "Position",0,DXGI_FORMAT_R32G32_FLOAT,0,0,D3D11_INPUT_PER_VERTEX_DATA,0 },
		{ "Color",0,DXGI_FORMAT_R8G8B8A8_UNORM,0,8u,D3D11_INPUT_PER_VERTEX_DATA,0 },
	};
	GFX_THROW_INFO( pDevice->CreateInputLayout(
		ied,(UINT)std::size( ied ),
		pBlob->GetBufferPointer(),
		pBlob->GetBufferSize(),
		&pInputLayout
	) );

	// bind vertex layout
	pContext->IASetInputLayout( pInputLayout.Get() );

	// bind render target
	pContext->OMSetRenderTargets( 1u,pTarget.GetAddressOf(),nullptr );

	// Set primitive topology to triangle list (groups of 3 vertices)
	pContext->IASetPrimitiveTopology( D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST );

	// configure viewport
	D3D11_VIEWPORT vp;
	vp.Width = 800;
	vp.Height = 600;
	vp.MinDepth = 0;
	vp.MaxDepth = 1;
	vp.TopLeftX = 0;
	vp.TopLeftY = 0;
	pContext->RSSetViewports( 1u,&vp );

	GFX_THROW_INFO_ONLY( pContext->DrawIndexed( (UINT)std::size( indices ),0u,0u ) );
}

VertexShader.hlsl

struct VSOut
{
	float3 color : Color;
	float4 pos : SV_Position;
};

cbuffer CBuf
{
	row_major matrix transform;
};

VSOut main( float2 pos : Position,float3 color : Color )
{
	VSOut vso;
	vso.pos = mul( float4(pos.x,pos.y,0.0f,1.0f),transform );
	vso.color = color;
	return vso;
}