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Drawing

Each core is now a pencil

Drawing is done by recording commands to a ID3D12GraphicsCommandList. No real work is done until the command list is set to a queue to be executed.


Record commands
Reset and Close - DB
To re-use a command list start with running ID3D12GraphicsCommandList::Reset() on it. This can be done after the ExecuteCommandList() has been called. To submit command lists for execution they need to be closed. To close a command list use ID3D12GraphicsCommandList::Close().

Clear the screen
To clear a rendertarget use ID3D12GraphicsCommandList::ClearRenderTargetView(). The rendertarget should be in state D3D12_RESOURCE_STATE_RENDER_TARGET for this command. To clear depth or stencil target use ID3D12GraphicsCommandList::ClearDepthStencilView(). The depth target should be in state D3D12_RESOURCE_STATE_DEPTH_WRITE.

Select RenderTarget
Select the target to render to with ID3D12GraphicsCommandList::OMSetRenderTargets(). It is possible to give an array of descriptors to render targets and a descriptor to any depth/stencil target. Set the viewports with ID3D12GraphicsCommandList::RSSetViewports() and the scissor rectangles with ID3D12GraphicsCommandList::RSSetScissorRects()

Select state
Set the rootsignature with ID3D12GraphicsCommandList::SetGraphicsRootSignature(). Set the PSO to use with the ID3D12GraphicsCommandList::SetPipelineState() function.

Bind shader data
The data in the root signature that are used by the shaders are set by root signature slot with these functions. One need to use the correct function depending on what data is in that rootparameter one is setting.

Root Constants: Use SetGraphicsRoot32BitConstant() to set a single value and SetGraphicsRoot32BitConstants() to set a group of them.
Root Descriptors: Depending on the type of descriptor SetGraphicsRootConstantBufferView(), SetGraphicsRootShaderResourceView() or SetGraphicsRootUnorderedAccessView() is used. Each one takes the GPU virtual address of the resource.
Descriptors tables: To set a table use SetGraphicsRootDescriptorTable() and send in the GPU descriptor handle of the first descriptor in the table.

SetBuffers
To set the vertex buffers and index buffer to use call ID3D12GraphicsCommandList::IASetVertexBuffers() and ID3D12GraphicsCommandList::IASetIndexBuffer().

Primitive
Select the typ of primitive to render with ID3D12GraphicsCommandList::IASetPrimitiveTopology().

Draw
There are two functions used to draw things, ID3D12GraphicsCommandList::DrawInstanced() and ID3D12GraphicsCommandList::DrawIndexedInstanced().

ExecuteBundle
The ID3D12GraphicsCommandList::ExecuteBundle can only be used on a direct command list and the argument must be a bundle list. The bundle will inherit all the state from the bundle and the things that change in the bundle will affect the rest of the command list.

Query

BeginQuery, EndQuery and ResolveQueryData

SOSetTargets

ResolveSubresource

OMSetStencilRef

OMSetBlendFactor

Guidelines
Frequency of use
 High Set Constant/Root Descriptor/Descriptor table IASetVertexBuffers/IASetIndexBuffer
 Medium SetPipelineState 
 Low SetGraphicsRootSignature SetDescriptorHeaps

Render Loop
    SetGraphicsRootSignature
    foreach batch:
        SetPipelineState
        foreach draw:
            set root parameters
            set vertex/index buffer
            draw


Executing
Command Lists are send to the command queue by using ID3D12CommandQueue::ExecuteCommandLists(). Try to batch up as many commandlists as possible in the same call. The caller need to ensure that the GPU is not using any of submitted command lists from a previous execution.


Swap and show
To show the frame call IDXGISwapChain::Present().

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