首页 计算机图形学 C++ DirectX 渲染引擎开发

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# 利用 Direct3D 绘制几何体 (续)

# 构建 Shader

流程:
- 初始化 - 编译着色器并缓存到 ID3DBlob 中 - 设置着色器所需要从 CPU 端接受的点点着色器输入的布局描述 - 构建几何资源: BuildShapeGeometry (在这一步使用上传堆填充上面的布局描述) - 构建流水线时，将顶点着色器 Blob / 片元着色器 Blob/cb 布局以及数据等填充进 PSO (D3D12_GRAPHICS_PIPELINE_STATE_DESC) - 填充 constantBuffer,(包含 ObjectConstantsBuffer 和 PassConstantBuffer) - 构建流水线状态 (CreateGraphicsPipelineState) - Tips: 这里可以有多种流水线状态，如只显示网格流水线，显示三角填充流水线

  • 后初始化 (初始化后初次赋值) 和每次界面发生变更时
    • 逐 Object 判断是否是 Dirty, 同时填充有变动的 Object 的 Buffer

# 编译着色器

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void ShapesApp::BuildShadersAndInputLayout()
{
    mShaders["standardVS"] = d3dUtil::CompileShader(L"Shaders\\color.hlsl", nullptr, "VS", "vs_5_1");
    mShaders["opaquePS"] = d3dUtil::CompileShader(L"Shaders\\color.hlsl", nullptr, "PS", "ps_5_1");

    mInputLayout =
    {
        { "POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D12_INPUT_CLASSIFICATION_PER_VERTEX_DATA, 0 },
        { "COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 12, D3D12_INPUT_CLASSIFICATION_PER_VERTEX_DATA, 0 },
    };
}

在编译着色器阶段顺便设置了输入的布局信息 (还未绑定到 PSO 上), 这个是描述了下面这张图中的部分

# 绑定 ConstantBuffer

constantBuffer 是 Shader 中的 cb 部分，使用 register (寄存器) 表示，实际上是 GPU 上的一块内存空间，

  • 根签名中先配置两个 COnstantBufferView
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void ShapesApp::BuildRootSignature()
{
    //描述符表,ConstantBufferTable0,这里代表的是ObjectConstantBuffer
    CD3DX12_DESCRIPTOR_RANGE cbvTable0;
    cbvTable0.Init(D3D12_DESCRIPTOR_RANGE_TYPE_CBV, 1, 0);
    //PassConstantBuffer
    CD3DX12_DESCRIPTOR_RANGE cbvTable1;
    cbvTable1.Init(D3D12_DESCRIPTOR_RANGE_TYPE_CBV, 1, 1);

    //描述符插槽
    // Root parameter can be a table, root descriptor or root constants.
    CD3DX12_ROOT_PARAMETER slotRootParameter[2];

    // Create root CBVs.
    slotRootParameter[0].InitAsDescriptorTable(1, &cbvTable0);
    slotRootParameter[1].InitAsDescriptorTable(1, &cbvTable1);

    //RootSignature是root Parameters的数组
    // A root signature is an array of root parameters.
    CD3DX12_ROOT_SIGNATURE_DESC rootSigDesc(2, slotRootParameter, 0, nullptr,
        D3D12_ROOT_SIGNATURE_FLAG_ALLOW_INPUT_ASSEMBLER_INPUT_LAYOUT);

    //RootSignature也需要序列化,传递到GPU和CPU的映射中
    // create a root signature with a single slot which points to a descriptor range consisting of a single constant buffer
    ComPtr<ID3DBlob> serializedRootSig = nullptr;
    ComPtr<ID3DBlob> errorBlob = nullptr;
    HRESULT hr = D3D12SerializeRootSignature(&rootSigDesc, D3D_ROOT_SIGNATURE_VERSION_1,
        serializedRootSig.GetAddressOf(), errorBlob.GetAddressOf());

    if (errorBlob != nullptr)
    {
        ::OutputDebugStringA((char*)errorBlob->GetBufferPointer());
    }
    ThrowIfFailed(hr);
    //创建RootSignature,放到mRootSignature中
    ThrowIfFailed(md3dDevice->CreateRootSignature(
        0,
        serializedRootSig->GetBufferPointer(),
        serializedRootSig->GetBufferSize(),
        IID_PPV_ARGS(mRootSignature.GetAddressOf())));
}
  • 针对每个 Object 和 Pass 构建 ConstantBuffer

Tips:

所有 Object 的 ConstantBuffer 是在一个 ConstantBuffer 下的，使用 ConstantBufferView 来设置每个 Object 的 ObjectConstantBuffer 在那段内存空间内 (GPU)
所有 Pass 和 Object 同理，不过所有 Object 在每个 Pass 里共享一段 PassConstantBufferView

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void ShapesApp::BuildConstantBufferViews()
{
    //分配ObjectConstants的描述符
    //每个Object都有一个ObjectConstants cb
    UINT objCBByteSize = d3dUtil::CalcConstantBufferByteSize(sizeof(ObjectConstants));

    UINT objCount = (UINT)mOpaqueRitems.size();

    // Need a CBV descriptor for each object for each frame resource.
    for (int frameIndex = 0; frameIndex < gNumFrameResources; ++frameIndex)
    {
        auto objectCB = mFrameResources[frameIndex]->ObjectCB->Resource();
        for (UINT i = 0; i < objCount; ++i)
        {
            D3D12_GPU_VIRTUAL_ADDRESS cbAddress = objectCB->GetGPUVirtualAddress();

            // Offset to the ith object constant buffer in the buffer.
            cbAddress += i * objCBByteSize;

            // Offset to the object cbv in the descriptor heap.
            int heapIndex = frameIndex * objCount + i;
            auto handle = CD3DX12_CPU_DESCRIPTOR_HANDLE(mCbvHeap->GetCPUDescriptorHandleForHeapStart());
            handle.Offset(heapIndex, mCbvSrvUavDescriptorSize);

            D3D12_CONSTANT_BUFFER_VIEW_DESC cbvDesc;
            cbvDesc.BufferLocation = cbAddress;
            cbvDesc.SizeInBytes = objCBByteSize;
            //对每个Object实例化一个ObjectConstantBuffer(View),即一个ConstantBuffer下的一部分
            md3dDevice->CreateConstantBufferView(&cbvDesc, handle);
        }
    }

    //分配PassConstants的描述符
    //一个Pass一个
    UINT passCBByteSize = d3dUtil::CalcConstantBufferByteSize(sizeof(PassConstants));

    // Last three descriptors are the pass CBVs for each frame resource.
    for (int frameIndex = 0; frameIndex < gNumFrameResources; ++frameIndex)
    {
        auto passCB = mFrameResources[frameIndex]->PassCB->Resource();
        D3D12_GPU_VIRTUAL_ADDRESS cbAddress = passCB->GetGPUVirtualAddress();

        // Offset to the pass cbv in the descriptor heap.
        int heapIndex = mPassCbvOffset + frameIndex;
        auto handle = CD3DX12_CPU_DESCRIPTOR_HANDLE(mCbvHeap->GetCPUDescriptorHandleForHeapStart());
        handle.Offset(heapIndex, mCbvSrvUavDescriptorSize);

        D3D12_CONSTANT_BUFFER_VIEW_DESC cbvDesc;
        cbvDesc.BufferLocation = cbAddress;
        cbvDesc.SizeInBytes = passCBByteSize;

        md3dDevice->CreateConstantBufferView(&cbvDesc, handle);
    }
}
  • 更新 ConstantBuffer

现在实际上每个 Object 的 ConstantBuffer 里只有一个 world

更新ObjectConstntBuffer

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void ShapesApp::UpdateObjectCBs(const GameTimer& gt)
{
    auto currObjectCB = mCurrFrameResource->ObjectCB.get();
    for (auto& e : mAllRitems)
    {
        //每个Object都有一个ObjectConstant Buffer
        // Only update the cbuffer data if the constants have changed.  
        // This needs to be tracked per frame resource.
        //如果发生变化(标记为脏数据,则更新对应Obj的Cb)
        if (e->NumFramesDirty > 0)
        {
            XMMATRIX world = XMLoadFloat4x4(&e->World);

            ObjectConstants objConstants;
            XMStoreFloat4x4(&objConstants.World, XMMatrixTranspose(world));

            currObjectCB->CopyData(e->ObjCBIndex, objConstants);

            // 脏数据计数器
            e->NumFramesDirty--;
        }
    }
}

更新MainBuffer

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void ShapesApp::UpdateMainPassCB(const GameTimer& gt)
{
    XMMATRIX view = XMLoadFloat4x4(&mView);
    XMMATRIX proj = XMLoadFloat4x4(&mProj);

    XMMATRIX viewProj = XMMatrixMultiply(view, proj);
    XMMATRIX invView = XMMatrixInverse(&XMMatrixDeterminant(view), view);
    XMMATRIX invProj = XMMatrixInverse(&XMMatrixDeterminant(proj), proj);
    XMMATRIX invViewProj = XMMatrixInverse(&XMMatrixDeterminant(viewProj), viewProj);

    XMStoreFloat4x4(&mMainPassCB.View, XMMatrixTranspose(view));
    XMStoreFloat4x4(&mMainPassCB.InvView, XMMatrixTranspose(invView));
    XMStoreFloat4x4(&mMainPassCB.Proj, XMMatrixTranspose(proj));
    XMStoreFloat4x4(&mMainPassCB.InvProj, XMMatrixTranspose(invProj));
    XMStoreFloat4x4(&mMainPassCB.ViewProj, XMMatrixTranspose(viewProj));
    XMStoreFloat4x4(&mMainPassCB.InvViewProj, XMMatrixTranspose(invViewProj));
    mMainPassCB.EyePosW = mEyePos;
    mMainPassCB.RenderTargetSize = XMFLOAT2((float)mClientWidth, (float)mClientHeight);
    mMainPassCB.InvRenderTargetSize = XMFLOAT2(1.0f / mClientWidth, 1.0f / mClientHeight);
    mMainPassCB.NearZ = 1.0f;
    mMainPassCB.FarZ = 1000.0f;
    mMainPassCB.TotalTime = gt.TotalTime();
    mMainPassCB.DeltaTime = gt.DeltaTime();

    //PassCB和ObjectCB是在FrameResource.cpp中初始化的
    auto currPassCB = mCurrFrameResource->PassCB.get();
    currPassCB->CopyData(0, mMainPassCB);
}

# ConstantBuffer 如何绑定到每个 Object 的绘制中？

通过 CommandList 中设置 constantBufferViewHandle

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// For each render item...
for (size_t i = 0; i < ritems.size(); ++i)
{
    auto ri = ritems[i];

    cmdList->IASetVertexBuffers(0, 1, &ri->Geo->VertexBufferView());
    cmdList->IASetIndexBuffer(&ri->Geo->IndexBufferView());
    cmdList->IASetPrimitiveTopology(ri->PrimitiveType);

    //在ObjectConstantBuffer Heap中
    // 通过偏移找到当前Object的ConstantBuffer View的Index
    // Offset to the CBV in the descriptor heap for this object and for this frame resource.
    UINT cbvIndex = mCurrFrameResourceIndex * (UINT)mOpaqueRitems.size() + ri->ObjCBIndex;
    auto cbvHandle = CD3DX12_GPU_DESCRIPTOR_HANDLE(mCbvHeap->GetGPUDescriptorHandleForHeapStart());
    cbvHandle.Offset(cbvIndex, mCbvSrvUavDescriptorSize);

    //设置根签名中的ConstantBuffer渲染Hanlde(cbvTable0),PS: CommandList是有顺序的
    cmdList->SetGraphicsRootDescriptorTable(0, cbvHandle);

    cmdList->DrawIndexedInstanced(ri->IndexCount, 1, ri->StartIndexLocation, ri->BaseVertexLocation, 0);
}

注意：上面是逐 Object 进行的，即每个命令执行完之后，会在 GPU 中更改当前的 ObjectConstantBufferView 地址

# 添加绘制 CommandList