ID3D11DeviceContext1::CSSetConstantBuffers1 method (d3d11_1.h)

Article
10/13/2021

Sets the constant buffers that the compute-shader stage uses.

Syntax

void CSSetConstantBuffers1(
  [in]           UINT         StartSlot,
  [in]           UINT         NumBuffers,
  [in, optional] ID3D11Buffer * const *ppConstantBuffers,
  [in, optional] const UINT   *pFirstConstant,
  [in, optional] const UINT   *pNumConstants
);

Parameters

[in] StartSlot

Index into the zero-based array to begin setting constant buffers to (ranges from 0 to D3D11_COMMONSHADER_CONSTANT_BUFFER_API_SLOT_COUNT - 1).

[in] NumBuffers

Number of buffers to set (ranges from 0 to D3D11_COMMONSHADER_CONSTANT_BUFFER_API_SLOT_COUNT - StartSlot).

[in, optional] ppConstantBuffers

Array of constant buffers (see ID3D11Buffer) being given to the device.

[in, optional] pFirstConstant

An array that holds the offsets into the buffers that ppConstantBuffers specifies. Each offset specifies where, from the shader's point of view, each constant buffer starts. Each offset is measured in shader constants, which are 16 bytes (4*32-bit components). Therefore, an offset of 16 indicates that the start of the associated constant buffer is 256 bytes into the constant buffer. Each offset must be a multiple of 16 constants.

[in, optional] pNumConstants

An array that holds the numbers of constants in the buffers that ppConstantBuffers specifies. Each number specifies the number of constants that are contained in the constant buffer that the shader uses. Each number of constants starts from its respective offset that is specified in the pFirstConstant array. Each number of constants must be a multiple of 16 constants, in the range [0..4096].

Return value

None

Remarks

The runtime drops the call to CSSetConstantBuffers1 if the number of constants to which pNumConstants points is larger than the maximum constant buffer size that is supported by shaders (4096 constants). The values in the elements of the pFirstConstant and pFirstConstant + pNumConstants arrays can exceed the length of each buffer; from the shader's point of view, the constant buffer is the intersection of the actual memory allocation for the buffer and the window [value in an element of pFirstConstant, value in an element of pFirstConstant + value in an element of pNumConstants]. The runtime also drops the call to CSSetConstantBuffers1 on existing drivers that don't support this offsetting.

The runtime will emulate this feature for feature level 9.1, 9.2, and 9.3; therefore, this feature is supported for feature level 9.1, 9.2, and 9.3. This feature is always available on new drivers for feature level 10 and higher.

From the shader’s point of view, element [0] in the constant buffers array is the constant at pFirstConstant.

Out of bounds access to the constant buffers from the shader to the range that is defined by pFirstConstant and pNumConstants returns 0.

If pFirstConstant and pNumConstants arrays are NULL, you get the same result as if you were binding the entire buffer into view. You get this same result if you call the CSSetConstantBuffers method. If the buffer is larger than the maximum constant buffer size that is supported by shaders (4096 elements), the shader can access only the first 4096 constants.

If either pFirstConstant or pNumConstants is NULL, the other parameter must also be NULL.

Calling CSSetConstantBuffers1 with command list emulation

The runtime's command list emulation of CSSetConstantBuffers1 sometimes doesn't actually change the offsets or sizes for the arrays of constant buffers. This behavior occurs when

CSSetConstantBuffers1 doesn't effectively change the constant buffers at the beginning and end of the range of slots that you set to update. This section shows how to work around this

behavior.

Here is the code to check whether either the runtime emulates command lists or the driver supports command lists:


     HRESULT hr = S_OK;
     bool needWorkaround = false;
     D3D11_DEVICE_CONTEXT_TYPE contextType = pDeviceContext->GetType();

     if( D3D11_DEVICE_CONTEXT_DEFERRED == contextType)
     {
          D3D11_FEATURE_DATA_THREADING threadingCaps = { FALSE, FALSE };

          hr = pDevice->CheckFeatureSupport( D3D11_FEATURE_THREADING, &threadingCaps, sizeof(threadingCaps) );
          if( SUCCEEDED(hr) && !threadingCaps.DriverCommandLists )
          {
               needWorkaround = true; // the runtime emulates command lists.
          }
     }

If the runtime emulates command lists, you need to use one of these code snippets:

If you change the offset and size on only a single constant buffer, set the constant buffer to NULL first:


     pDeviceContext->CSSetConstantBuffers1(0, 1, &CBuf, &Offset, &Count);
     if( needWorkaround )
     {
          // Workaround for command list emulation
          pDeviceContext->CSSetConstantBuffers(0, 1, &NullCBuf);
     }
     pDeviceContext->CSSetConstantBuffers1(0, 1, &CBuf, &Offset, &Count);

If you change multiple constant buffers, set the first and last constant buffers of the range to NULL first:


     pDeviceContext->CSSetConstantBuffers1(0, 4, &CBufs, &Offsets, &Counts);
     if( needWorkaround )
     {
          // Workaround for command list emulation
          pDeviceContext->CSSetConstantBuffers(0, 1, &NullCBuf);
          pDeviceContext->CSSetConstantBuffers(3, 1, &NullCBuf);
     }
     pDeviceContext->CSSetConstantBuffers1(0, 4, &CBufs, &Offsets, &Counts);

Requirements

Requirement	Value
Minimum supported client	Windows 8 and Platform Update for Windows 7 [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2012 and Platform Update for Windows Server 2008 R2 [desktop apps \| UWP apps]
Target Platform	Windows
Header	d3d11_1.h
Library	D3D11.lib

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