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Being new to DirectX 12 I am looking for examples on how to use threading. I have done lots of OpenGL in the past and some DirectX, but with DX12 the threading magic is gone and I understand that threading is crucial to get good performance. In my project I currently have one thread doing it all. I have one command list, one command allocator, one bundle and one bundle allocator. I also have a million triangles, so it's about time that I start doing this.

How do I split things up? How many threads should I use? How many command lists and allocators?

I realize this is a beginner's question , but I have to begin somewhere. I would be grateful if someone could point me in a direction where I could find a simple code sample, tutorial or something similar. Thanks!

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5 hours ago, lubbe75 said:

I also have a million triangles, so it's about time that I start doing this.

Number of triangles is irrelevant to the CPU - how many draw calls do you have? If it's thousands, you may get some benefit from using multiple threads to record the draw commands. In my experience, with less than around a thousand draws, there's not much benefit in threaded draw submission. 

5 hours ago, lubbe75 said:

How many threads should I use?

Most engines these days make a pool of one thread per CPU core, and then split all of their workloads up amongst that pool. So on a quad core, I'd use a max of 4 threads, and as above, also no more than around (draws/1000)+1 threads. 

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We have a work-stealing task scheduler that spawns 1 thread for every core on the CPU (minus 1 for the main thread). Then we create a bunch of tasks for groups of draw calls, and throw them a the task scheduler. We've tried both 1 thread per logical core (Intel CPU's with hyperthreading have 2 logical cores for every physical core) as well as 1 thread per physical core, and we've generally found that trying to run our task scheduler thread on both logical cores to be somewhat counterproductive. But your mileage may vary. AMD has some code here that can show you how to query the relevant CPU information,

Writing your own task scheduler can be quite a bit of work (especially fixing all of the bugs!), but it can also be very educational. There's a pretty good series of articles here that can get you started. There's also third-party libraries like Intel's Thread Building Blocks (which is very comprehensive, but also a bit complex and very heavyweight), or Doug Bink's enkiTS (which is simple and lightweight, but doesn't have fancier high-level features). Windows also has a built-in thead pool API, but I've never used it myself so I can't really vouch for its effectiveness in a game engine scenario.

My general advice for starting on multithreading programming is to carefully plan out which data will be touched by each separate task. IMO the easiest (and fastest!) way to have multiple threads work effectively is to make sure that they never touch the same data, or at least do so as infrequently as possible. If you have lots of shared things it can messy, slow, and error-prone very quickly if you have to manually wrap things in critical sections. Also keep in mind that *reading* data from multiple threads is generally fine, and it's *writing* to the same data that usually gets you in trouble. So it can help to figure out exactly which data is immutable during a particular phase of execution, and perhaps also enforce that through judicious use of the "const" keyword.

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Thanks for the tips and the links! 

After reading a bit more I get the idea that threading is mainly for recording command lists. Is this correct? Would this also include executing command lists?

Before adding threads, will I benefit anything from using multiple command lists, command allocators or command queues?

I have read somewhere that using multiple command allocators can increase performance since I may not have to wait as often before recording the next frame. I guess it's a matter of experimenting with the number of allocators that would be needed in my case.

Would using multiple command lists or multiple command queues have the same effect as using multiple allocators, or will this only make sense with multi-threading? 

I'm currently in a stage where my Dx9 renderer is about 20 times faster than my Dx12 renderer, so I guessing it's mainly multi-threading that is missing. Do you know any other obvious and common beginner mistakes when starting with Dx12?

 

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Before messing around with threading, 1 thing you'll want to do is make sure that the CPU and GPU are working in parallel. When starting out with DX12, you'll probably have things set up like this:

Record command list for frame 0 -> submit command list for frame 0 - > wait for GPU to process frame 0 (by waiting on a fence -> Record comand list for frame 1

If you do it this way the GPU will be idle while the CPU is doing work, and the CPU will be idle while the GPU is doing work. To make sure that the CPU and GPU are pipelined (both working at the same time), you need to do it like this:

Record command list for frame 0 -> submit command list for frame 0 -> record command list for frame 1 -> submit command list for frame 1 -> wait for the GPU to finish frame 0 -> record command list for frame 2

With this setup the GPU will effectively be a frame behind the CPU, but your overall throughput (framerate) will be higher since the CPU and GPU will be working concurrently instead of in lockstep. The big catch is that since the CPU is preparing the next frame while the GPU is actively processing commands, you need to be careful not to modify things that the GPU is reading from. This is where the "multiple command allocators" thing comes in: if you switch back and forth between two allocators, you'll always be modifying one command allocator while the GPU is reading from the other one. The same concept applies to things like constant buffers that are written to by the CPU.

Once you've got that working, you can look into splitting things up into multiple command lists that are recorded by multiple threads. Without multiple threads there's no reason to have more than 1 command list unless you're also submitting to multiple queues. Multi-queue is quite complicated, and is definitely an advanced topic. COPY queues are generally useful for initializing resources like textures. COMPUTE queues can be useful for GPU's that support concurrently processing compute commands alongside graphics commands, which can result in higher overall throughput in certain scenarios. They can also be useful for cases where the compute work is completely independent of your graphics work, and therefore doesn't need to be synchronized with your graphics commands.

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On 12/8/2017 at 5:13 AM, lubbe75 said:

After reading a bit more I get the idea that threading is mainly for recording command lists. Is this correct? Would this also include executing command lists?

Before adding threads, will I benefit anything from using multiple command lists, command allocators or command queues?

Read through this document it should answer your questions.

https://developer.nvidia.com/sites/default/files/akamai/gameworks/blog/GDC16/GDC16_gthomas_adunn_Practical_DX12.pdf

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Thanks for that link, Infinisearch!

MJP, I have tried what you suggested, but I got poorer results compared to the straight forward 1-allocator method. Here is what I tried:

After initiating, setting frameIndex to 0 and resetting commandList with allocator 0 I run the following loop (pseudo-code):

populate commandList;
execute commandList;
reset commandList (using allocator[frameIndex]);
present the frame;
frameIndex = swapChain.CurrentBackBufferIndex; // 0 -> 1, 1 -> 0
 
if (frameIndex == 1) 
{
    // set the fence after frame 0, 2, 4, 6, 8, ...
    commandQueue.Signal(fence, fenceValue);
}
else
{
    // wait for the fence after frame 1, 3, 5, 7, 9, ...
    int currentFence = fenceValue;
    fenceValue++;
    if (fence.CompletedValue < currentFence)
    {
        fence.SetEventOnCompletion(currentFence, fenceEvent.SafeWaitHandle.DangerousGetHandle());
        fenceEvent.WaitOne();
    }
}

Have I understood the idea correctly (I think I do)? Perhaps something here gets done in the wrong order?

 

 

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That's not quite what I meant. You'll still want to signal your fence and wait on it every frame, you just need to wait on the value one frame later. The first frame you don't need to wait because there was no "previous" frame, but you do need to wait for every frame after that. Here's what my code looks like, minus a few things that aren't relevant:

void EndFrame(IDXGISwapChain4* swapChain, uint32 syncIntervals)
{
    DXCall(CmdList->Close());

    ID3D12CommandList* commandLists[] = { CmdList };
    GfxQueue->ExecuteCommandLists(ArraySize_(commandLists), commandLists);

    // Present the frame.
    DXCall(swapChain->Present(syncIntervals, syncIntervals == 0 ? DXGI_PRESENT_ALLOW_TEARING : 0));

    ++CurrentCPUFrame;

    // Signal the fence with the current frame number, so that we can check back on it
    FrameFence.Signal(GfxQueue, CurrentCPUFrame);

    // Wait for the GPU to catch up before we stomp an executing command buffer
    const uint64 gpuLag = DX12::CurrentCPUFrame - DX12::CurrentGPUFrame;
    Assert_(gpuLag <= DX12::RenderLatency);
    if(gpuLag >= DX12::RenderLatency)
    {
        // Make sure that the previous frame is finished
        FrameFence.Wait(DX12::CurrentGPUFrame + 1);
        ++DX12::CurrentGPUFrame;
    }

    CurrFrameIdx = DX12::CurrentCPUFrame % NumCmdAllocators;

    // Prepare the command buffers to be used for the next frame
    DXCall(CmdAllocators[CurrFrameIdx]->Reset());
    DXCall(CmdList->Reset(CmdAllocators[CurrFrameIdx], nullptr));
}

 

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13 hours ago, MJP said:

That's not quite what I meant. You'll still want to signal your fence and wait on it every frame, you just need to wait on the value one frame later. The first frame you don't need to wait because there was no "previous" frame, but you do need to wait for every frame after that. Here's what my code looks like, minus a few things that aren't relevant:

MJP I didn't look at the linked code but do you do anything for frame pacing in the full code?  I see that gamers on the internet complain about frame pacing quite a lot when they seem to percieve issues with it.  Your code snippet above would render a certain number of frames on the CPU as fast as possible and then wait for the GPU to catch up.  Wouldn't this lead to jerkiness in the input sampling and simulation?  Would you just add some timer code to the above to delay the next iteration of the game loop if necessary?  Or is it more complex?

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The code that I posted will let the CPU get no more than 1 frame ahead of the GPU. After the CPU submits command lists to the direct queue, it waits for the previous GPU frame to finish. So if the GPU is taking more time to complete a frame than the CPU is (or if VSYNC is enabled), the CPU will be effectively throttled by fence and will stay tied to the GPU's effective framerate. 

In my experience, frame pacing issues usually come from situations where the time delta being used for updating the game's simulation doesn't match the rate at which frames are actually presented on the screen. This can happen very easily if you use the length of the previous frame as your delta for the next frame. When you do this, you're basically saying "I expect the next frame to take just as long to update and render as the previous frame". This assumption will hold when you're locked at a steady framerate (usually due to VSYNC), but if your framerate is erratic then you will likely have mismatches between your simulation time delta and the actual frame time. It can be especially bad when missing VSYNC, since your frame times may go from 16.6ms up to 33.3ms, and perhaps oscillate back and forth.

I would probably suggest the following for mitigating this issue:

  1. Enable VSYNC, and never miss a frame! This will you 100% smooth results, but obviously it's much easier said than done.
  2. Detect when you're not making VSYNC, and increase the sync interval to 2. This will effectively halve your framerate (for instance, you'll go from 60Hz to 30Hz on a 60Hz display), but that may be preferable to "mostly" making full framerate with frequent dips.
  3. Alternatively, disable VSYNC when you're not quite making it. This is common on consoles, where you have the ability to do this much better than you do on PC. It's good for when you're just barely missing your VSYNC rate, since in that case most of the screen will still get updated at full rate (however there will be a horizontal tear line). It will also keep you from dropping to half the VSYNC rate, which will reduce the error in your time delta assumption.
  4. Triple buffering can also give you similar results to disabling VSYNC, but also prevent tearing (note that non-fullscreen D3D apps on Windows are effectively triple-buffered by default since they go through the desktop compositor)
  5. You could also try filtering your time deltas a bit to keep them from getting too erratic when you don't make VSYNC. I've never tried this myself, but it's possible that having a more consistent but smaller errors in your time delta is better than less frequent but larger errors. 

Hopefully someone else can chime in with more thoughts if they have experience with this. I haven't really done any specific research or experimentation with this issue outside of making games feel good when they ship, so don't consider me an authority on this issue. :)

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@MJP I will just add a short note about VSYNC and triple-buffering. Players in competitive action games will generally disable both of them.

"Missing" VSYNC (and therefore delaying frame present for another X ms) will put you at severe disadvantage, and triple buffering means you're basically presenting frame that is some short time old (and yes - even though hard to distinguish for "us" - casuls - professional players will notice the difference and different feel).

 

So in the end, it really matters what is your target product.

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After testing I always seem to get into the wait section on every frame (gpuLag == 2 on every frame) except for the first frame.

In your code, where does CurrentGPUFrame advance one number, except for in the wait section?

Maybe I am really confused by the SharpDX equivalent of the code. I can't really find any SharpDX documentation on fencing, or even some of the involved functions. Maybe someone with SharpDX experience can bring clarification here?

Here is my rendering code:

Note:

  • frameIndex is 0 or 1
  • fence does not have a Wait function in SharpDX
  • fenceEvent is an AutoResetEvent
// populating & executing commandList, presenting ...

CurrentCPUFrame++;
commandQueue.Signal(fence, CurrentCPUFrame);
int gpuLag = CurrentCPUFrame - CurrentGPUFrame;

if (gpuLag >= 2)
{
  fence.SetEventOnCompletion(CurrentGPUFrame + 1, fenceEvent.SafeWaitHandle.DangerousGetHandle());
  fenceEvent.WaitOne();

  CurrentGPUFrame++;
}

frameIndex = swapChain.CurrentBackBufferIndex;

// reseting commandList with allocator[frameIndex]

 

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14 hours ago, lubbe75 said:

After testing I always seem to get into the wait section on every frame (gpuLag == 2 on every frame) except for the first frame.

That's exactly what should be happening: it's where the CPU waits for the GPU to wait for the previous frame. You always need to wait in order to make sure that you don't overwrite a command buffer that the GPU is reading from. For instance, say the CPU is submitting frame 60 and the GPU is working on frame 59. The CPU will have generated command buffers using command allocator index 0, and the GPU is consuming command buffers from allocator index 1. If the CPU doesn't wait for the GPU to finish the previous frame and starts writing to a command buffer using allocator index 0, it will write to data that the GPU is reading from.

If you're GPU-bound (the GPU is taking longer than the CPU to complete a frame), then you should expect to spend some time waiting on the fence. The be more precise, if the GPU is taking N milliseconds to present a frame and it's taking the CPU M milliseconds to process a frame and submit it to the GPU, then you'll end up waiting ~N-M milliseconds for the fence to be signaled. So if the GPU is VSYNC'ed at 16.6ms and it only takes you 1ms to submit a frame on the CPU, you'll spend ~15.6ms waiting for the fence.

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Hi,

I am following this series:

https://www.braynzarsoft.net/viewtutorial/q16390-03-initializing-directx-12

It gives a very short intro to multi threading. If it works or not in practice I do not know.

I personally have not yet reached the next step -doing multi-threading of my own project.

Good luck,

Kim

 

 

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OK. So if I always get into the wait section it means that the GPU is doing the lengthy work compared to the CPU. Would I gain anything here by adding more allocators? I'm already at good speed, but I'm aiming for all the low-hanging fruit here :)

So, without doing multithreading, does it mean that I'm only using one GPU, even if the hardware has more than one? Does the Dx12 driver ever utilise multiple GPUs without me telling it to do so?

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      While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
      SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
      When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
      The following is an example of shader initialization:
      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      Creating the Pipeline State Object
      After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
      PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
    • By turanszkij
      I am doing a DX12 graphics wrapper, and I would like to update constant buffers. I found the ID3D12GraphicsCommandList2::WriteBufferImmediate method, which is apparently available from a Windows 10 Creators update only. I couldn't really find any info about this (and couldn't try it yet), am I correct to assume this would be useful for writing to constant buffers without much need to do synchronization? It seems to me like this method copies data to the command list itself and then that data will be copied into the DEFAULT resource address which I provided? The only synchronization needed here would be transition barriers to COPY_DEST before WriteBufferImmediate() and back to GENERIC_READ afterwards? I could be totally off though, I'm still wrapping my head around a lot of things.
      What other use cases would this method allow for?
    • By hiya83
      Hi,
      I apologize for creating multiple questions here for dx12 since information is sparse so far. Anyway in some Dx12 api's, there's a node mask for multiple node support, for e.g. D3D12_COMMAND_QUEUE_DESC for CreateCommandQueue & CreateCommandList itself has a node mask. However, these API's are all called on the D3D12Device itself, and when creating the D12Device (D3D12CreateDevice), there isn't an option for it to be a multi-adapter device; you just pass in a single adapter. So what is the point of the node masks in the other API calls? Is there some other use case I am not aware of yet?
      Thanks!
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