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DX12 short cmdlist vs. long cmdlist

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Hey Guys,

 

For recommendations of building commandlist in dx12, I remembered one which said that a good strategy is to have 12~20 draw calls per commandlist. Without wondering the reason behind it, I blindly target to fill around 12 draw/dispatch calls before submit my cmdlist to GPU in my 'single-thread' renderer.... Today after I fixed a GPU time stamp bug, I realized that my GPU always idled half of frame time.... GPU is waiting CPU 'accumulating enough draw calls' to hand the cmdlist to GPU...

 

Now I totally changed my strategy: as long as I know some draw/dispatch will take reasonable time for GPU, I submit it immediately to GPU even there may only be 1 draw/dispatch in that cmdlist, so while GPU is working on the job, CPU is building new jobs for GPU... (please let me know if that strategy is also not recommended...)

 

But why it is recommend to have 12~20 draw/dispatch per commandlist?   what's the difference between short and long cmdlist in terms of CPU/GPU overhead?

 

Thanks in advance 

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If you've noticed a difference in GPU idling between those two cases, I would guess that it's because you're syncing every frame instead of the recommended practice of having 1 frame of latency between CPU and GPU. This is mosly down to your presentation code.

You should have quite a few draws per submission because there's a large CPU cost involved in submission. One of D3D12's advantages is that draws are cheap, but doing one submit per draw-call will negate this benefit.

In my tests I found that ~500 draws per command list performed best in my game.

Thanks Hodgman,  could you elaborate on how to do the 1 frame of latency? or point me some resource about that? I have 5 frame buffers but I guess I get confused and lost somewhere. My engine is based on Microsoft's MiniEngine link though I modified lots of things, but the main framework is almost the same: So basically I record commandlist and submit it before present within the same frame.... 

My current project is more like academic research project so don't have ton of stuffs to draw, so typically I only have around 50 draw/dispatch calls per frame, I mean currently I can have CPU wait for GPU but definitely not the other way around. So what's your suggestion? 

 

also since my project have the following logic per frame, I feel it's very tricky to adapt '1frame of latency' strategy though.

do{
    m = CPU_ICPSolver( result ); // Nothing to do with GPU inside

    GPU_PrepareWorkingBuffer(
        depth_and_normalmap1, // input as SRV
        depth_and_normalmap2, // input as SRV
        matrix,               // input as CBV
        workingBuf);          // output as UAV (all 7 buffer)
    
    for (int i = 0; i < 7; ++i) {
        GPU_Reduction::Process(workingBuf[i]); // reduction to 1 float4 value inside GPU, but not copied to ReadBack buffer
    }
    GPU_Reduction::Readback( result ); // Read the reduction result, copy from default heap to readback heap, need to wait GPU inside

    reprojection_error = GetReprojectionError( result );
}while(iterations < 20 && reprojection_error > threshold) 

so my project has a long GPU, CPU work dependency chain here, any suggestions? thanks 

Edited by Mr_Fox

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I remembered one which said that a good strategy is to have 12~20 draw calls per commandlist.

Actually IIRC the suggestion is 12-20 draw calls per command list minimum.  The document Practical_DX12_Programming_Model_and_Hardware_Capabilities.pdf (on page 7) actually suggests to aim for  15 to 30 command lists per frame split across 5 to 10 execute command lists invocations.  I think you can do more command lists then the recommendation but I think I remember reading or someone saying don't exceed 10 execute command lists calls per frame.

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I assume you have compute tasks with GPU<->CPU dependencies, but maybe while waiting you can do some draw calls based on the compute results from the previous frame.

This way you might be able to fill the bubbles and utilize Hodgmans suggestion, but probably at the cost of double buffering some memory.

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The problem you have is that readback - you are going to stall the GPU while you wait for the tasks pre-readback to complete, then do the readback, and then loop again.
Every time you wait on the result you will cause the CPU and GPU to sync - this is bad voodoo.

If you are only doing that loop in your application, well, you'll have to suck it up.

Games, however, will typically run something like that over a few frames or find some other method of keeping it all on the GPU for the whole loop in order to remove that readback stall, or at least minimise the impact; say do all the work, issue a readback via the copy queue and at the last moment stall for the result if it isn't ready while doing as much work as possible on the CPU/GPU to cover the copy time and avoid stalling. As you've a CPU-GPU data dependency this could be tricky without reworking the algorithm somewhat.

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I remembered one which said that a good strategy is to have 12~20 draw calls per commandlist.

Actually IIRC the suggestion is 12-20 draw calls per command list minimum.  The document Practical_DX12_Programming_Model_and_Hardware_Capabilities.pdf (on page 7) actually suggests to aim for  15 to 30 command lists per frame split across 5 to 10 execute command lists invocations.  I think you can do more command lists then the recommendation but I think I remember reading or someone saying don't exceed 10 execute command lists calls per frame.

 

Thanks infinisearch, what I curious is how this overhead affect execution time line:  Is this overhead totally on CPU side and doesn't stall GPU? so GPU can still work on previous tasks while CPU is finishing up sending cmdlist? I think if that is the case, I do have tons of spare CPU cycles to saturate GPU by paying such overhead. But if there are any GPU-CPU sync points in this overhead, I guess I probably have to rethink my algorithm.... :(

Thanks

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I assume you have compute tasks with GPU<->CPU dependencies, but maybe while waiting you can do some draw calls based on the compute results from the previous frame. This way you might be able to fill the bubbles and utilize Hodgmans suggestion, but probably at the cost of double buffering some memory.

If you are only doing that loop in your application, well, you'll have to suck it up. Games, however, will typically run something like that over a few frames or find some other method of keeping it all on the GPU for the whole loop in order to remove that readback stall, or at least minimise the impact; say do all the work, issue a readback via the copy queue and at the last moment stall for the result if it isn't ready while doing as much work as possible on the CPU/GPU to cover the copy time and avoid stalling. As you've a CPU-GPU data dependency this could be tricky without reworking the algorithm somewhat.
 

 

Thanks JoeJ and phantom. Sadly that GPU<->CPU dependency chain is very sensitive to latency, so can't spread it into multiple frame to hide the GPU stall. The best bit is replacing CPU_ICPSolver with GPU_ICPSolver....  the main task of that function is solving a 6x6 linear system, so if you guys know any GPU solver exist already, that will be my silver bullet! And given the matrix size is fixed 6x6 I think it should totally be doable.... but please do let me know if you think a GPU linear solver is super slow, unstable and not worth it, thanks

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Thanks infinisearch, what I curious is how this overhead affect execution time line:  Is this overhead totally on CPU side and doesn't stall GPU? so GPU can still work on previous tasks while CPU is finishing up sending cmdlist? I think if that is the case, I do have tons of spare CPU cycles to saturate GPU by paying such overhead. But if there are any GPU-CPU sync points in this overhead, I guess I probably have to rethink my algorithm.... Thanks

I think the number of command lists is a CPU optimization and the number of execute command lists is a GPU optimization.  For the latter read towards the end of this thread: https://www.gamedev.net/topic/677701-d3d12-resource-barriers-in-multiple-command-lists/

 

However I doubt this is causing you significant performance problems.

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However I doubt this is causing you significant performance problems.

Thanks Infinisearch, could you give me some suggestions where else should I look at?  I found the GPU idle time by placing timestamps before and after dispatch/draw and related PSO setting, descriptor moving and transition command with in each commandlist. But since I only have one thread generate commandlist, I also use cross commandlist timestamp pairs (one at the end of previous cmdlist, and one at the begin of current cmdlist) thus this cross cmdlist timestamps pair could effectively tell me the GPU idle time between this two cmdlist (one thing I think worth noting is that present call may between such timestamp pair, so I have no idea how that affect the timing.....)  Also I understand it is possible that other GPU task (from other application) may get inserted between my two consecutive cmdlist, so GPU may not be idle during such 'idle time' (please correct me if such thing is trickier than I thought). But what I noticed is around 5ms 'GPU idle' time with only Kinect service (which I believe use GPU to perform some work, but definitly not 5ms) runing in background, so I guess at least there must be something wrong with the way I generate cmdlist....

 

Please let me know is it safe to use cross cmdlist timestamp to measure GPU idle time (especially no present call get inbetween), and it will be great if you could list some other thing which may possibly cause such GPU idle time.

 

Thanks

Edited by Mr_Fox

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Cross command list time stamps are fine under SetStablePowerState or the gpu clock can vary between the command list ( in practice, as you start pushing load on the gpu or forcing clock in a control panel, should not be a problem ), and if stable power is on, the gpu may run at a slower speed than optimal. It is worth to mention that command list order is not guarantee in a single Execute call, the driver can reorder if he think it is better for him.

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It is worth to mention that command list order is not guarantee in a single Execute call, the driver can reorder if he think it is better for him.

 

What makes you think this? I don't believe that to be true. If they executed out of order then any resource transitions within the 2 (or more) command lists could be executed in any order, potentially conflicting with the current state of the resource.

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However I doubt this is causing you significant performance problems.

Thanks Infinisearch, could you give me some suggestions where else should I look at?  I found the GPU idle time by placing timestamps before and after dispatch/draw and related PSO setting, descriptor moving and transition command with in each commandlist. But since I only have one thread generate commandlist, I also use cross commandlist timestamp pairs (one at the end of previous cmdlist, and one at the begin of current cmdlist) thus this cross cmdlist timestamps pair could effectively tell me the GPU idle time between this two cmdlist (one thing I think worth noting is that present call may between such timestamp pair, so I have no idea how that affect the timing.....)  Also I understand it is possible that other GPU task (from other application) may get inserted between my two consecutive cmdlist, so GPU may not be idle during such 'idle time' (please correct me if such thing is trickier than I thought). But what I noticed is around 5ms 'GPU idle' time with only Kinect service (which I believe use GPU to perform some work, but definitly not 5ms) runing in background, so I guess at least there must be something wrong with the way I generate cmdlist....

 

Please let me know is it safe to use cross cmdlist timestamp to measure GPU idle time (especially no present call get inbetween), and it will be great if you could list some other thing which may possibly cause such GPU idle time.

 

Thanks

 

First off let me clarify why I said I doubt its causing you significant performance problems.  Didn't you say in one of your threads that you have like 50 draw/dispatch calls total?  Also in this thread you said you submit 10-12 calls per executecommandlists call.  This means you'd have 5 calls to executecommandlists which is well within the guidelines.  But the real question is what does your profiler tell you?  I am not sure if your timestamp method of measurement is valid or not so I can't really help you there.  I myself am only beginning to learn to use a GPU profiler.  Can you try this on a machine with a working GPU profiler to confirm your results?  As far as suggestion as to what is wrong I'd suggest making sure your performance results are correct first.

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      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 tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample 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, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
    • By turanszkij
      Hi, right now building my engine in visual studio involves a shader compiling step to build hlsl 5.0 shaders. I have a separate project which only includes shader sources and the compiler is the visual studio integrated fxc compiler. I like this method because on any PC that has visual studio installed, I can just download the solution from GitHub and everything just builds without additional dependencies and using the latest version of the compiler. I also like it because the shaders are included in the solution explorer and easy to browse, and double-click to open (opening files can be really a pain in the ass in visual studio run in admin mode). Also it's nice that VS displays the build output/errors in the output window.
      But now I have the HLSL 6 compiler and want to build hlsl 6 shaders as well (and as I understand I can also compile vulkan compatible shaders with it later). Any idea how to do this nicely? I want only a single project containing shader sources, like it is now, but build them for different targets. I guess adding different building projects would be the way to go that reference the shader source project? But how would they differentiate from shader type of the sources (eg. pixel shader, compute shader,etc.)? Now the shader building project contains for each shader the shader type, how can other building projects reference that?
      Anyone with some experience in this?
    • By DiligentDev
      Hello!
      I would like to introduce Diligent Engine, a project that I've been recently working on. Diligent Engine is a light-weight cross-platform abstraction layer between the application and the platform-specific graphics API. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common front-end for all supported platforms and provides interoperability with underlying native API. Shader source code converter allows shaders authored in HLSL to be translated to GLSL and used on all platforms. Diligent Engine supports integration with Unity and is designed to be used as a graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. It is distributed under Apache 2.0 license and is free to use. Full source code is available for download on GitHub.
      Features:
      True cross-platform Exact same client code for all supported platforms and rendering backends No #if defined(_WIN32) ... #elif defined(LINUX) ... #elif defined(ANDROID) ... No #if defined(D3D11) ... #elif defined(D3D12) ... #elif defined(OPENGL) ... Exact same HLSL shaders run on all platforms and all backends Modular design Components are clearly separated logically and physically and can be used as needed Only take what you need for your project (do not want to keep samples and tutorials in your codebase? Simply remove Samples submodule. Only need core functionality? Use only Core submodule) No 15000 lines-of-code files Clear object-based interface No global states Key graphics features: Automatic shader resource binding designed to leverage the next-generation rendering APIs Multithreaded command buffer generation 50,000 draw calls at 300 fps with D3D12 backend Descriptor, memory and resource state management Modern c++ features to make code fast and reliable The following platforms and low-level APIs are currently supported:
      Windows Desktop: Direct3D11, Direct3D12, OpenGL Universal Windows: Direct3D11, Direct3D12 Linux: OpenGL Android: OpenGLES MacOS: OpenGL iOS: OpenGLES API Basics
      Initialization
      The engine can perform initialization of the API or attach to already existing D3D11/D3D12 device or OpenGL/GLES context. For instance, the following code shows how the engine can be initialized in D3D12 mode:
      #include "RenderDeviceFactoryD3D12.h" using namespace Diligent; // ...  GetEngineFactoryD3D12Type GetEngineFactoryD3D12 = nullptr; // Load the dll and import GetEngineFactoryD3D12() function LoadGraphicsEngineD3D12(GetEngineFactoryD3D12); auto *pFactoryD3D11 = GetEngineFactoryD3D12(); EngineD3D12Attribs EngD3D12Attribs; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[0] = 1024; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[1] = 32; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[2] = 16; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[3] = 16; EngD3D12Attribs.NumCommandsToFlushCmdList = 64; RefCntAutoPtr<IRenderDevice> pRenderDevice; RefCntAutoPtr<IDeviceContext> pImmediateContext; SwapChainDesc SwapChainDesc; RefCntAutoPtr<ISwapChain> pSwapChain; pFactoryD3D11->CreateDeviceAndContextsD3D12( EngD3D12Attribs, &pRenderDevice, &pImmediateContext, 0 ); pFactoryD3D11->CreateSwapChainD3D12( pRenderDevice, pImmediateContext, SwapChainDesc, hWnd, &pSwapChain ); Creating Resources
      Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. To create a buffer, you need to populate BufferDesc structure and call IRenderDevice::CreateBuffer(). The following code creates a uniform (constant) buffer:
      BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); Similar, to create a texture, populate TextureDesc structure and call IRenderDevice::CreateTexture() as in the following example:
      TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); Initializing Pipeline State
      Diligent Engine follows Direct3D12 style to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.)
      Creating Shaders
      To create a shader, populate ShaderCreationAttribs structure. An important member is ShaderCreationAttribs::SourceLanguage. The following are valid values for this member:
      SHADER_SOURCE_LANGUAGE_DEFAULT  - The shader source format matches the underlying graphics API: HLSL for D3D11 or D3D12 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. See shader converter for details. SHADER_SOURCE_LANGUAGE_GLSL  - The shader source is in GLSL. There is currently no GLSL to HLSL converter. To allow grouping of resources based on the frequency of expected change, Diligent Engine introduces classification of shader variables:
      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. This post describes the resource binding model in Diligent Engine.
      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
      To create a pipeline state object, define instance of PipelineStateDesc structure. The structure defines the pipeline specifics such as if the pipeline is a compute pipeline, number and format of render targets as well as depth-stencil format:
      // This is a graphics pipeline PSODesc.IsComputePipeline = false; PSODesc.GraphicsPipeline.NumRenderTargets = 1; PSODesc.GraphicsPipeline.RTVFormats[0] = TEX_FORMAT_RGBA8_UNORM_SRGB; PSODesc.GraphicsPipeline.DSVFormat = TEX_FORMAT_D32_FLOAT; The structure also defines depth-stencil, rasterizer, blend state, input layout and other parameters. For instance, rasterizer state can be defined as in the code snippet below:
      // Init rasterizer state RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; //RSDesc.MultisampleEnable = false; // do not allow msaa (fonts would be degraded) RasterizerDesc.AntialiasedLineEnable = False; When all fields are populated, call IRenderDevice::CreatePipelineState() to create the PSO:
      m_pDev->CreatePipelineState(PSODesc, &m_pPSO); Binding Shader Resources
      Shader resource binding in Diligent Engine is based on grouping variables in 3 different groups (static, mutable and dynamic). Static variables 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. They are bound directly to the shader object:
       
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new object called Shader Resource Binding (SRB), which is created by the pipeline state:
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Dynamic and mutable resources are then bound through SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "tex2DDiffuse")->Set(pDiffuseTexSRV); m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); The difference between mutable and dynamic resources is that mutable ones can only be set once for every instance of a shader resource binding. Dynamic resources can be set multiple times. It is important to properly set the variable type as this may affect performance. Static variables are generally most efficient, followed by mutable. Dynamic variables are most expensive from performance point of view. This post explains shader resource binding in more details.
      Setting the Pipeline State and Invoking Draw Command
      Before any draw command can be invoked, all required vertex and index buffers as well as the pipeline state should be bound to the device context:
      // Clear render target const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); // 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); m_pContext->SetPipelineState(m_pPSO); Also, all shader resources must be committed to the device context:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); When all required states and resources are bound, IDeviceContext::Draw() can be used to execute draw command or IDeviceContext::DispatchCompute() can be used to execute compute command. Note that for a draw command, graphics pipeline must be bound, and for dispatch command, compute pipeline must be bound. Draw() 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); Tutorials and Samples
      The GitHub repository contains a number of tutorials and sample applications that demonstrate the API usage.
      Tutorial 01 - Hello Triangle This tutorial shows how to render a simple triangle using Diligent Engine API.   Tutorial 02 - Cube This tutorial demonstrates how to render an actual 3D object, a cube. It shows how to load shaders from files, create and use vertex, index and uniform buffers.   Tutorial 03 - Texturing This tutorial demonstrates how to apply a texture to a 3D object. It shows how to load a texture from file, create shader resource binding object and how to sample a texture in the shader.   Tutorial 04 - Instancing This tutorial demonstrates how to use instancing to render multiple copies of one object using unique transformation matrix for every copy.   Tutorial 05 - Texture Array This tutorial demonstrates how to combine instancing with texture arrays to use unique texture for every instance.   Tutorial 06 - Multithreading This tutorial shows how to generate command lists in parallel from multiple threads.   Tutorial 07 - Geometry Shader This tutorial shows how to use geometry shader to render smooth wireframe.   Tutorial 08 - Tessellation This tutorial shows how to use hardware tessellation to implement simple adaptive terrain rendering algorithm.  
      AntTweakBar sample demonstrates how to use AntTweakBar library to create simple user interface.

       
      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 textures, using compute shaders and unordered access views, etc. 

       
      The repository includes Asteroids performance benchmark based on this demo developed by Intel. It renders 50,000 unique textured asteroids and lets compare performance of D3D11 and D3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures. 

      Integration with Unity
      Diligent Engine supports integration with Unity through Unity low-level native plugin interface. The engine relies on Native API Interoperability to attach to the graphics API initialized by Unity. After Diligent Engine device and context are created, they can be used us usual to create resources and issue rendering commands. GhostCubePlugin shows an example how Diligent Engine can be used to render a ghost cube only visible as a reflection in a mirror.

       
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