ID3D12GraphicsCommandList::ExecuteIndirect method

Apps perform indirect draws/dispatches using the ExecuteIndirect method.

Syntax

void ExecuteIndirect(
  ID3D12CommandSignature *pCommandSignature,
  UINT                   MaxCommandCount,
  ID3D12Resource         *pArgumentBuffer,
  UINT64                 ArgumentBufferOffset,
  ID3D12Resource         *pCountBuffer,
  UINT64                 CountBufferOffset
);

Parameters

pCommandSignature

Type: ID3D12CommandSignature*

Specifies a ID3D12CommandSignature. The data referenced by pArgumentBuffer will be interpreted depending on the contents of the command signature. Refer to Indirect Drawing for the APIs that are used to create a command signature.

MaxCommandCount

Type: UINT

There are two ways that command counts can be specified:

  • If pCountBuffer is not NULL, then MaxCommandCount specifies the maximum number of operations which will be performed. The actual number of operations to be performed are defined by the minimum of this value, and a 32-bit unsigned integer contained in pCountBuffer (at the byte offset specified by CountBufferOffset).
  • If pCountBuffer is NULL, the MaxCommandCount specifies the exact number of operations which will be performed.

pArgumentBuffer

Type: ID3D12Resource*

Specifies one or more ID3D12Resource objects, containing the command arguments.

ArgumentBufferOffset

Type: UINT64

Specifies an offset into pArgumentBuffer to identify the first command argument.

pCountBuffer

Type: ID3D12Resource*

Specifies a pointer to a ID3D12Resource.

CountBufferOffset

Type: UINT64

Specifies a UINT64 that is the offset into pCountBuffer, identifying the argument count.

Return Value

This method does not return a value.

Remarks

The semantics of this API are defined with the following pseudo-code:

Non-NULL pCountBuffer:

// Read draw count out of count buffer
UINT CommandCount = pCountBuffer->ReadUINT32(CountBufferOffset);

CommandCount = min(CommandCount, MaxCommandCount)

// Get pointer to first Commanding argument
BYTE* Arguments = pArgumentBuffer->GetBase() + ArgumentBufferOffset;

for(UINT CommandIndex = 0; CommandIndex < CommandCount; CommandIndex++)
{
  // Interpret the data contained in *Arguments
  // according to the command signature
  pCommandSignature->Interpret(Arguments);

  Arguments += pCommandSignature ->GetByteStride();
}

NULL pCountBuffer:

// Get pointer to first Commanding argument
BYTE* Arguments = pArgumentBuffer->GetBase() + ArgumentBufferOffset;

for(UINT CommandIndex = 0; CommandIndex < MaxCommandCount; CommandIndex++)
{
  // Interpret the data contained in *Arguments
  // according to the command signature
  pCommandSignature->Interpret(Arguments);

  Arguments += pCommandSignature ->GetByteStride();
}

The debug layer will issue an error if either the count buffer or the argument buffer are not in the D3D12_RESOURCE_STATE_INDIRECT_ARGUMENT state. The core runtime will validate:

  • CountBufferOffset and ArgumentBufferOffset are 4-byte aligned
  • pCountBuffer and pArgumentBuffer are buffer resources (any heap type)
  • The offset implied by MaxCommandCount, ArgumentBufferOffset, and the drawing program stride do not exceed the bounds of pArgumentBuffer (similarly for count buffer)
  • The command list is a direct command list or a compute command list (not a copy or JPEG decode command list)
  • The root signature of the command list matches the root signature of the command signature
The functionality of two APIs from earlier versions of Direct3D, DrawInstancedIndirect and DrawIndexedInstancedIndirect, are encompassed by ExecuteIndirect.

Bundles

ID3D12GraphicsCommandList::ExecuteIndirect is allowed inside of bundle command lists only if all of the following are true:
  • CountBuffer is NULL (CPU-specified count only).
  • The command signature contains exactly one operation. This implies that the command signature does not contain root arguments changes, nor contain VB/IB binding changes.

Obtaining buffer virtual addresses

The ID3D12Resource::GetGPUVirtualAddress method enables an app to retrieve the GPU virtual address of a buffer.

Apps are free to apply byte offsets to virtual addresses before placing them in an indirect argument buffer. Note that all of the D3D12 alignment requirements for VB/IB/CB still apply to the resulting GPU virtual address.

Examples

The D3D12ExecuteIndirect sample uses ID3D12GraphicsCommandList::ExecuteIndirect as follows:

// Data structure to match the command signature used for ExecuteIndirect.
struct IndirectCommand
{
    D3D12_GPU_VIRTUAL_ADDRESS cbv;
    D3D12_DRAW_ARGUMENTS drawArguments;
};

The call to ExecuteIndirect is near the end of this listing, below the comment "Draw the triangles that have not been culled."

// Fill the command list with all the render commands and dependent state.
void D3D12ExecuteIndirect::PopulateCommandLists()
{
    // Command list allocators can only be reset when the associated 
    // command lists have finished execution on the GPU; apps should use 
    // fences to determine GPU execution progress.
    ThrowIfFailed(m_computeCommandAllocators[m_frameIndex]->Reset());
    ThrowIfFailed(m_commandAllocators[m_frameIndex]->Reset());

    // However, when ExecuteCommandList() is called on a particular command 
    // list, that command list can then be reset at any time and must be before 
    // re-recording.
    ThrowIfFailed(m_computeCommandList->Reset(m_computeCommandAllocators[m_frameIndex].Get(), m_computeState.Get()));
    ThrowIfFailed(m_commandList->Reset(m_commandAllocators[m_frameIndex].Get(), m_pipelineState.Get()));

    // Record the compute commands that will cull triangles and prevent them from being processed by the vertex shader.
    if (m_enableCulling)
    {
        UINT frameDescriptorOffset = m_frameIndex * CbvSrvUavDescriptorCountPerFrame;
        D3D12_GPU_DESCRIPTOR_HANDLE cbvSrvUavHandle = m_cbvSrvUavHeap->GetGPUDescriptorHandleForHeapStart();

        m_computeCommandList->SetComputeRootSignature(m_computeRootSignature.Get());

        ID3D12DescriptorHeap* ppHeaps[] = { m_cbvSrvUavHeap.Get() };
        m_computeCommandList->SetDescriptorHeaps(_countof(ppHeaps), ppHeaps);

        m_computeCommandList->SetComputeRootDescriptorTable(
            SrvUavTable,
            CD3DX12_GPU_DESCRIPTOR_HANDLE(cbvSrvUavHandle, CbvSrvOffset + frameDescriptorOffset, m_cbvSrvUavDescriptorSize));

        m_computeCommandList->SetComputeRoot32BitConstants(RootConstants, 4, reinterpret_cast<void*>(&m_csRootConstants), 0);

        // Reset the UAV counter for this frame.
        m_computeCommandList->CopyBufferRegion(m_processedCommandBuffers[m_frameIndex].Get(), CommandBufferSizePerFrame, m_processedCommandBufferCounterReset.Get(), 0, sizeof(UINT));

        D3D12_RESOURCE_BARRIER barrier = CD3DX12_RESOURCE_BARRIER::Transition(m_processedCommandBuffers[m_frameIndex].Get(), D3D12_RESOURCE_STATE_COPY_DEST, D3D12_RESOURCE_STATE_UNORDERED_ACCESS);
        m_computeCommandList->ResourceBarrier(1, &barrier);

        m_computeCommandList->Dispatch(static_cast<UINT>(ceil(TriangleCount / float(ComputeThreadBlockSize))), 1, 1);
    }

    ThrowIfFailed(m_computeCommandList->Close());

    // Record the rendering commands.
    {
        // Set necessary state.
        m_commandList->SetGraphicsRootSignature(m_rootSignature.Get());

        ID3D12DescriptorHeap* ppHeaps[] = { m_cbvSrvUavHeap.Get() };
        m_commandList->SetDescriptorHeaps(_countof(ppHeaps), ppHeaps);

        m_commandList->RSSetViewports(1, &m_viewport);
        m_commandList->RSSetScissorRects(1, m_enableCulling ? &m_cullingScissorRect : &m_scissorRect);

        // Indicate that the command buffer will be used for indirect drawing
        // and that the back buffer will be used as a render target.
        D3D12_RESOURCE_BARRIER barriers[2] = {
            CD3DX12_RESOURCE_BARRIER::Transition(
                m_enableCulling ? m_processedCommandBuffers[m_frameIndex].Get() : m_commandBuffer.Get(),
                m_enableCulling ? D3D12_RESOURCE_STATE_UNORDERED_ACCESS : D3D12_RESOURCE_STATE_NON_PIXEL_SHADER_RESOURCE,
                D3D12_RESOURCE_STATE_INDIRECT_ARGUMENT),
            CD3DX12_RESOURCE_BARRIER::Transition(
                m_renderTargets[m_frameIndex].Get(),
                D3D12_RESOURCE_STATE_PRESENT,
                D3D12_RESOURCE_STATE_RENDER_TARGET)
        };

        m_commandList->ResourceBarrier(_countof(barriers), barriers);

        CD3DX12_CPU_DESCRIPTOR_HANDLE rtvHandle(m_rtvHeap->GetCPUDescriptorHandleForHeapStart(), m_frameIndex, m_rtvDescriptorSize);
        CD3DX12_CPU_DESCRIPTOR_HANDLE dsvHandle(m_dsvHeap->GetCPUDescriptorHandleForHeapStart());
        m_commandList->OMSetRenderTargets(1, &rtvHandle, FALSE, &dsvHandle);

        // Record commands.
        const float clearColor[] = { 0.0f, 0.2f, 0.4f, 1.0f };
        m_commandList->ClearRenderTargetView(rtvHandle, clearColor, 0, nullptr);
        m_commandList->ClearDepthStencilView(dsvHandle, D3D12_CLEAR_FLAG_DEPTH, 1.0f, 0, 0, nullptr);

        m_commandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP);
        m_commandList->IASetVertexBuffers(0, 1, &m_vertexBufferView);

        if (m_enableCulling)
        {
            // Draw the triangles that have not been culled.
            m_commandList->ExecuteIndirect(
                m_commandSignature.Get(),
                TriangleCount,
                m_processedCommandBuffers[m_frameIndex].Get(),
                0,
                m_processedCommandBuffers[m_frameIndex].Get(),
                CommandBufferSizePerFrame);
        }
        else
        {
            // Draw all of the triangles.
            m_commandList->ExecuteIndirect(
                m_commandSignature.Get(),
                TriangleCount,
                m_commandBuffer.Get(),
                CommandBufferSizePerFrame * m_frameIndex,
                nullptr,
                0);
        }

        // Indicate that the command buffer may be used by the compute shader
        // and that the back buffer will now be used to present.
        barriers[0].Transition.StateBefore = D3D12_RESOURCE_STATE_INDIRECT_ARGUMENT;
        barriers[0].Transition.StateAfter = m_enableCulling ? D3D12_RESOURCE_STATE_COPY_DEST : D3D12_RESOURCE_STATE_NON_PIXEL_SHADER_RESOURCE;
        barriers[1].Transition.StateBefore = D3D12_RESOURCE_STATE_RENDER_TARGET;
        barriers[1].Transition.StateAfter = D3D12_RESOURCE_STATE_PRESENT;

        m_commandList->ResourceBarrier(_countof(barriers), barriers);

        ThrowIfFailed(m_commandList->Close());
    }
}

See Example Code in the D3D12 Reference.

Requirements

   
Target Platform Windows
Header d3d12.h
Library D3d12.lib
DLL D3d12.dll

See Also

ID3D12GraphicsCommandList

Indirect Drawing