I saw this part from the battlefield3 presentation (http://dice.se/wp-content/uploads/GDC11_DX11inBF3_Public.pdf) on page 30 where they show how they transfer transformations of each instance to the shader using a single big buffer and a const buffer with indices to index this buffer at the right position using the SV_InstanceID semantic. Can someone tell me what exactly this buffer is ?

This part here:

Buffer<float4> instanceVectorBuffer : register(t0);

I'm not too familiar with buffers in directx11 beyond constant buffers...

Isn't register(t0) for texture slots ? Also they seem to use 3x4 floats for their transformations, so does that mean they construct their transformation matrix inside the shader using translation, rotation and scale vectors ?

And last how would I set such a buffer in the DX11 API ?

The MSDN documentation is very lacking in explaining these concepts...

IIRC:

The t registers are similar to the c registers, but they're designed for random memory access patterns (like texture lookups) rather than constant memory access patterns (e.g. it's assumed that every pixel will read the same constants, but may read different texels). You can bind both textures and DX11 buffer objects to the t registers and then load values from them in the shader.

You bind values to the t registers using *SSetShaderResources, which takes "shader resource views". You can create a view of a texture, which is the common case, but you can also create a view of a buffer.

As mentioned above, you should prefer this method of binding buffers to t registers when you're going to be performing random lookups into the buffer. If every pixel/vertex/etc is going to read the same values from the buffer, then you should bind it to a c register using the usual method.

Also they seem to use 3x4 floats for their transformations, so does that mean they construct their transformation matrix inside the shader using translation, rotation and scale vectors ?

No, in a regular transformation matrix that's been constructed from a traslation + rotation + scale, the 4th row/column (depending on your conventions) will always be [0,0,0,1] so you can hard-code that value in the shader to save some space in the buffer.

I'm still not as experienced with DX11 as I am with DX9, so I hope that's correct

Yes I meant 3 x float4 (sorry for the confusing syntax )

Alright thanks for the info.

EDIT: By the way this buffer then should be dynamic, correct? Since I need to put in or remove elements during rendering.

Yeah by the looks of it, they'd potentially be updating the entire buffer every frame.

EDIT: Nevermind got it fixed...my shader wasn't up to date when I ran it

The advantage of a buffer over cbuffer is the size (128mb vs 64kb, although in typical scenario 2-4mb should be enough)

Ok this may sound stupid, but what about just using regular instancing?Has this method been benchmarked against regular instancing with a second vertex buffer?

So..I've created the buffer like this:

	D3D11_BUFFER_DESC instanceBufferDesc = {};
	
	instanceBufferDesc.Usage = D3D11_USAGE_DYNAMIC;
	instanceBufferDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE;
	instanceBufferDesc.ByteWidth = sizeof(XMFLOAT4);
	instanceBufferDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
	instanceBufferDesc.MiscFlags = 0;
	instanceBufferDesc.StructureByteStride = 0;

	hr = this->device->CreateBuffer(&instanceBufferDesc, NULL, &this->instanceTransformBuffer);

is that correct so far ?

	D3D11_SHADER_RESOURCE_VIEW_DESC shaderResourceDesc;
	shaderResourceDesc.Format = DXGI_FORMAT_R32_FLOAT;
	shaderResourceDesc.ViewDimension = D3D11_SRV_DIMENSION_BUFFER;
	shaderResourceDesc.Buffer.FirstElement = 0;
	shaderResourceDesc.Buffer.ElementWidth = 4;
	shaderResourceDesc.Buffer.ElementOffset = 0;

	hr = this->device->CreateShaderResourceView(this->instanceTransformBuffer, &shaderResourceDesc, &this->instanceTransformBuffer_SRV);