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Found 15 results

  1. The latest release of Diligent Engine combines a number of recent updates (Vulkan on iOS, GLTF2.0 support, shadows), significantly improves performance of OpenGL backend, updates API, adds integration with Dear Imgui and implements new samples and tutorials. Some of the new features in this release: GLTF2.0 support (loader, PBR renderer and sample viewer) Shadowing Component and Shadows Sample Integration with Dear Imgui library and Dear Imgui demo Tutorial13 - Shadow Map Tutorial14 - Compute Shader Tutorial15 - Multiple Windows Check it out on GitHub.
  2. Hello! I need some guidance on CommandQueue/CommandAllocator/CommandList management. In my current project I have a few "systems" that need to execute graphical commands, such as rendering terrain, rendering water, rendering particles etc. Right now my project is very simple so I'm not even using command lists during initialization. However, that's starting to be required. Currently I'm just using a single command queue with a ring buffer of 2 command allocators that get recorded by a single command list. Each time I render the scene, a command allocator and a command list is being reset and then recorded. After all commands has been recorded, the list is executed and the swap chain is flipped. Here's some pseudo-code: void Initialize() { [...] device->CreateCommandQueue(...); device->CreateCommandAllocator(...); // commandAllocator[0] device->CreateCommandAllocator(...); // commandAllocator[1] device->CreateCommandList(...); commandList->Close(); [...] } void Render() { WaitForPreviousFrame(); commandAllocator[i]->Reset(); // i = swapChain->GetCurrentBackBufferIndex() commandList->Reset(...); RecordAllCommands(); commandList->Close(); commandQueue->ExecuteCommandLists(...); Signal(...); swapChain->Present(...); } The issue with this is that I cannot record commands during initialization, and with this design it's also quite cumbersome to execute command lists multiple times during one frame since the command allocator ring buffer is tied together with the swap chain buffer index. So I started to think about how I should redesign this, preferably also with future support for threading. And I've thought about it for quite some time now and can't come up with a good solution. One idea is that each system should have their own command list with a ring buffer of 2 command allocators, and then record it and just use a global command queue to execute the list. This works well from a parallel point of view, but the issue is that now each system need to check individually if the GPU is done with the commands before resetting the command allocator. This feels like a huge CPU waste. Another idea is that there is only one global command list, that is aviable already during initialization of other systems, and after the initialization this command list gets executed, before entering the game loop. During the game loop, the global command list gets executed once per frame as I do it now. However, there are 2 issues with this. First of all, some systems might want to execute their commands earlier than at the end of each frame. Secondly, if multiple threads record into the same command list, then we might get a situation like this: commandList->SetPipelineState(pipelineState1); // Thread 1 wants pipelineState1. commandList->SetPipelineState(pipelineState2); // Thread 2 wants pipelineState2. [...] commandList->DrawInstanced(...); // Thread 1 expects pipelineState1 to be set... I'm out of ideas of how to implement this in a simple and elegant way. Or maybe I'm doing this entirely wrong. Basically what I need is: Systems should be able to record commands already during initialization. Atleast during initialization, it should be possible to execute commands in multiple steps and even wait for the GPU to complete them. When rendering the scene, it would be nice if multiple threads could record commands in parallel. Does any of you have a good solution to this problem? What is the AAA game engine way of dealing with this?
  3. Here is my code snip: ID3D12DescriptorHeap* DescHeaps[] = { SRVHeapCache.GetDescriptorHeap() };// I want to bind Different RTV to this heap cache between Draw Calls CommandList->SetDescriptorHeaps(1, DescHeaps); CommandList->SetGraphicsRootSignature(RootSignature.Get()); CommandList->SetGraphicsRootConstantBufferView(2, PerPassConstants.GetResource()->GetGPUVirtualAddress()); CommandList->SetGraphicsRootConstantBufferView(1, PerObjectConstants.GetResource()->GetGPUVirtualAddress()); CommandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST); for (auto Actor : TheScene.Actors) { CommandList->SetGraphicsRootDescriptorTable(0, SRVHeapCache.GetGPUHandleStart()); Actor->Draw(D3dDevice.Get(), CommandList.Get(), SRVHeapCache.GetDescriptorHeap()); } And in Actor's Draw, I use CopyDescriptorsSimple: Device->CopyDescriptorsSimple(1, hDescriptor, Mgr->Textures[DiffTextureID].Texture.GetCPUHandle(), D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV); But this doesn't work. The content of HeapCache seems to never change in the runtime.
  4. Good day. I am find for information on how to create texture arrays in d3d12. In d3d11, I calmly figured out how to create a texture array from several textures: I upload several dds - textures of the same resolution in the engine I create ID3D11Texture2D* and map date into it all loaded textures in shader I use texture2darray in pixel shader: Texture2DArray textures : register(t0); Now I am looking for something like that for d3d12. For load the textures, I use DDSTextureLoader.h/.cpp from microsoft. So I'm loading a few textures. How can I create a texture array from them and pass it to a pixel shader? I will be glad to some example. Thank. PS: I searched the forum, but I didn’t find anything.
  5. Hello, I should say I'm new to DX12 and I have the following use case. I'm making a "simple" font rendering library that caches glyphs from DirectWrite into 2D textures/atlases as they're being requested by the user on the fly. I create multiple textures with fixed sizes so that I don't have to resize them if there's not enough space for a font's glyphs. A new texture is created if there's not enough space. Now, the problem is that there can be a command list being executed that is sampling these textures (because of a previous text render) while I need to insert some glyph to the atlas(es) (write to a texture region). Obviously, it is guaranteed that the texture data read by the previous render will not be modified since the glyph insert process only writes to free space. So my question is, is it possible to write to a texture while it's being read in this case, and how? If not, what's the best way to do what I want (or some good alternatives)? And another question: using this method I might end up having to use multiple textures for a draw call. How do I make the shader choose which texture to sample from depending on input data? There can be a dynamic number of textures in this case, but they're all the same size. Or is it better to split this into multiple draw calls and change resources between them?
  6. By looking at Microsoft's working code samples and people's posts on forums, it seems that people are doing double buffering in the following way: fence 0 frame 0: | submit command | execute command ..................................................... | frame 1: | submit command | execute command .....|......................................... It seems that, people tend to submit and execute their commands for the current frame first, _then_ fence and wait for previous frame to finish. This seems counter-intuitive to me, since this potential overlap means duplicating temporary per-frame data. My question is why not just do it this way instead: fence 0 frame 0: | submit command | execute command ..........................................| frame 1: | submit command | execute command .....|......................................... This way, CPU work still overlaps with GPU work, but no duplication needs to happen. Yes, de-overlapping frame 0 and frame 1 seems to be bad for performance, but can it be that bad? I feel like if frames are finished on time, this overlap should never occur in the first place? So I'm wondering why the majority prefers the first approach to the second approach, even though the second approach is simpler and seems more natural to me. Thanks.
  7. Hello! I am trying to implement the d3d12 window resizing function. First, I delete all the buffers referenced by SwapChain, and then run SwapChain :: ResizeBuffers. At this point I get the error: This is the code of the procedure for changing sizes of window: I put together a minimal self sufficient example for modeling the problem that described above: Tell me how to fix this problem. P.S.: I set my RTV names and text error replace: RTV number is always random.
  8. Hello, I am working on a DX12 renderer which is utilizing multiple threads to build command lists. I am currently trying to figure out a proper way to handle fencing and synchronization between the threads. My problem is that for some reason my waits seem to be passing through even if the fence hasn't yet been signaled. This is my structure: Render Thread: Supplies render data from scene and launches several render tasks on worker threads. Lastly uses GPU&CPU waits to check if all tasks are ready before executing Present. Worker threads: Builds command list for specified task. Uses cpu-waits if there are dependencies. Queues itself into Queue-thread for GPU-submission. Queue-thread: Runs continously, checking if any cmd list has been queued. Inserts gpu-waits if needed. Executes the cmd list and lastly signals fence. As noted, the fences seem to act as if they are signaled when Render thread reaches present. Am I missing something trivial? /Baemz
  9. I am running an Nvidia 1080 Ti with the latest drivers, and it seems as though even if I make a barebones application (creates a swapchain and just clears and fences between two frames), I have a perpetual, linear rise in memory usage when I use the DX Debug layer. Without the debug layer, I'm stable for hours at the same amount of memory used. Does anyone else see anything like this?
  10. Hey guys, My battle with DXR still goes one 🙂 This time I am trying to render three triangles and encounter flickering artifacts on two of them. For the sake of the test, each triangle represents a separate mesh. Their vertex and index data are stored in a global vertex and index buffers. For each of the meshes, I create a dedicated D3D12_RAYTRACING_GEOMETRY_DESC, specifying corresponding offsets in the vertex and index buffers. D3D12_BUILD_RAYTRACING_ACCELERATION_STRUCTURE_INPUTS BLASBuildInputs; BLASBuildInputs.Type = D3D12_RAYTRACING_ACCELERATION_STRUCTURE_TYPE_BOTTOM_LEVEL; BLASBuildInputs.Flags = D3D12_RAYTRACING_ACCELERATION_STRUCTURE_BUILD_FLAG_PREFER_FAST_TRACE; BLASBuildInputs.DescsLayout = D3D12_ELEMENTS_LAYOUT_ARRAY; BLASBuildInputs.NumDescs = (UINT)geometryDescs.size(); // 3 descs BLASBuildInputs.pGeometryDescs = geometryDescs.data(); If I specify only one geometry desc on D3D12_BUILD_RAYTRACING_ACCELERATION_STRUCTURE_INPUTS, it works fine for all of them. That is, BLASBuildInputs.NumDescs = 1; BLASBuildInputs.pGeometryDescs = &geometryDescs[0]; // works also with 1 and 2 But will not work, if I use three of them. My closest hit shader interpolates vertex colors and outputs the result in the payload. I also tried to output hardcoded "red" color to exclude interpolation issue, but did not help. Any ideas what could be upsetting it so much? 🙂 Thanks!
  11. Hey guys, I am working on my very first DXR "hello triangle" and hitting "DXGI_ERROR_DEVICE_HUNG: The Device took an unreasonable amount of time to execute its commands, or the hardware crashed/hung" in Present call. My program consists of ray generation, closest hit and miss shaders. I noticed that if I remove TraceRay call and write the result to output texture it works OK. I have checked twice all the setup and everything seems to be OK and debug layer does not complain. I have no more ideas what I could check. I am on GTX 1070 with the latest driver version. Any suggestions? Thanks!
  12. This article uses material originally posted on Diligent Graphics web site. Introduction Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed. There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy: Lightweight abstractions: the API should be as close to the underlying native APIs as possible to allow an application leverage all available low-level functionality. In many cases this requirement is difficult to achieve because specific features exposed by different APIs may vary considerably. Low performance overhead: the abstraction layer needs to be efficient from performance point of view. If it introduces considerable amount of overhead, there is no point in using it. Convenience: the API needs to be convenient to use. It needs to assist developers in achieving their goals not limiting their control of the graphics hardware. Multithreading: ability to efficiently parallelize work is in the core of Direct3D12 and Vulkan and one of the main selling points of the new APIs. Support for multithreading in a cross-platform layer is a must. Extensibility: no matter how well the API is designed, it still introduces some level of abstraction. In some cases the most efficient way to implement certain functionality is to directly use native API. The abstraction layer needs to provide seamless interoperability with the underlying native APIs to provide a way for the app to add features that may be missing. Diligent Engine is designed to solve these problems. 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 C++ front-end for all supported platforms and provides interoperability with underlying native APIs. It also supports integration with Unity and is designed to be used as graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. Full source code is available for download at GitHub and is free to use. Overview Diligent Engine API takes some features from Direct3D11 and Direct3D12 as well as introduces new concepts to hide certain platform-specific details and make the system easy to use. It contains the following main components: Render device (IRenderDevice interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.). Device context (IDeviceContext interface) is the main interface for recording rendering commands. Similar to Direct3D11, there are immediate context and deferred contexts (which in Direct3D11 implementation map directly to the corresponding context types). Immediate context combines command queue and command list recording functionality. It records commands and submits the command list for execution when it contains sufficient number of commands. Deferred contexts are designed to only record command lists that can be submitted for execution through the immediate context. An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread. The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs. In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary. Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen. Render device, device contexts and swap chain are created during the engine initialization. Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface. Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource. Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach. Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state. API Basics 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. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example: 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 ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure: 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 ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously. Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine. Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used. Initializing the Pipeline State As it was mentioned earlier, Diligent Engine follows next-gen APIs 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.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once. Creating Shaders 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 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.
  13. Introduction Explicit resource state management and synchronization is one of the main advantages and main challenges that modern graphics APIs such as Direct3D12 and Vulkan offer application developers. It makes rendering command recording very efficient, but getting state management right is a challenging problem. This article explains why explicit state management is important and introduces a solution implemented in Diligent Engine, a modern cross-platform low-level graphics library. Diligent Engine has Direct3D11, Direct3D12, OpenGL/GLES and Vulkan backends and supports Windows Desktop, Universal Windows, Linux, Android, Mac and iOS platforms. Its full source code is available on GitHub and is free to use. This article gives an introduction to Diligent Engine. Synchronization in Next-Gen APIs Modern graphics applications can best be described as client-server systems where CPU is a client that records rendering commands and puts them into queue(s), and GPU is a server that asynchronously pulls commands from the queue(s) and processes them. As a result, commands are not executed immediately when CPU issues them, but rather sometime later (typically one to two frames) when GPU gets to the corresponding point in the queue. Besides that, GPU architecture is very different from CPU because of the kind of problems that GPUs are designed to handle. While CPUs are great at running algorithms with lots of flow control constructs (branches, loops, etc.) such as handling events in an applicatio