# DX11 Update vertex buffer in non UI thread using DirectX11

## 5 posts in this topic

Hi,

 I want to render a object with a dynamic vertex buffer and I do rendering in UI thread. I am thinking is it possible to change this vertex buffer content in a non UI thread using Map and Unmap. Thanks. YL
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Yes, you can either call Map/Unmap on the main thread, but use another thread to fill the buffer.

Or, you can use a deferred context:

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Thanks Hodgman.

I am not clear about the first method you mentioned.

For example, I can run the following code in main thread,

m_d3dContext->Map(vertexBuffer2.Get(), 0, D3D11_MAP_WRITE_DISCARD, 0, &mappedResource);
//	Update the vertex buffer here.
memcpy(mappedResource.pData, vertices, sizeof(vertices));
m_d3dContext->Unmap(vertexBuffer2.Get(), 0);

To run the above code in two threads, I run map and unmap in main thread and memcpy in another thread.

However, is it safe to call unmap while another thread is updating the buffer?

Thanks.

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No that's unsafe.

You need to synchronise your threads so that the memcpy doesn't begin until after the call to Map, and the call to Unmap doesn't occur until some time after the memcpy is complete.

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Thanks, Hodgman!

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my idea:
BS1:
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-A : (0.4, 0.4, 0.0, 0.5)
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backbuffer.RGB: = (0.4, 0.0, 0.0) * 1 + (0.0, 0.0, 0.0) * (1-0.5)      = ( 0.4, 0.0, 0.0)
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==========================
BS3:

backbuffer.RGB = (0.4, 0.0, 0.0) + (0.0, 0.0, 0.0)  = (0.4, 0.0, 0.0)
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