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    • By Jason Smith
      While working on a project using D3D12 I was getting an exception being thrown while trying to get a D3D12_CPU_DESCRIPTOR_HANDLE. The project is using plain C so it uses the COBJMACROS. The following application replicates the problem happening in the project.
      #define COBJMACROS #pragma warning(push, 3) #include <Windows.h> #include <d3d12.h> #include <dxgi1_4.h> #pragma warning(pop) IDXGIFactory4 *factory; ID3D12Device *device; ID3D12DescriptorHeap *rtv_heap; int WINAPI wWinMain(HINSTANCE hinst, HINSTANCE pinst, PWSTR cline, int cshow) { (hinst), (pinst), (cline), (cshow); HRESULT hr = CreateDXGIFactory1(&IID_IDXGIFactory4, (void **)&factory); hr = D3D12CreateDevice(0, D3D_FEATURE_LEVEL_11_0, &IID_ID3D12Device, &device); D3D12_DESCRIPTOR_HEAP_DESC desc; desc.NumDescriptors = 1; desc.Type = D3D12_DESCRIPTOR_HEAP_TYPE_RTV; desc.Flags = D3D12_DESCRIPTOR_HEAP_FLAG_NONE; desc.NodeMask = 0; hr = ID3D12Device_CreateDescriptorHeap(device, &desc, &IID_ID3D12DescriptorHeap, (void **)&rtv_heap); D3D12_CPU_DESCRIPTOR_HANDLE rtv = ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart(rtv_heap); (rtv); } The call to ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart throws an exception. Stepping into the disassembly for ID3D12DescriptorHeap_GetCPUDescriptorHandleForHeapStart show that the error occurs on the instruction
      mov  qword ptr [rdx],rax
      which seems odd since rdx doesn't appear to be used. Any help would be greatly appreciated. Thank you.
    • By lubbe75
      As far as I understand there is no real random or noise function in HLSL. 
      I have a big water polygon, and I'd like to fake water wave normals in my pixel shader. I know it's not efficient and the standard way is really to use a pre-calculated noise texture, but anyway...
      Does anyone have any quick and dirty HLSL shader code that fakes water normals, and that doesn't look too repetitious? 
    • By turanszkij
      I finally managed to get the DX11 emulating Vulkan device working but everything is flipped vertically now because Vulkan has a different clipping space. What are the best practices out there to keep these implementation consistent? I tried using a vertically flipped viewport, and while it works on Nvidia 1050, the Vulkan debug layer is throwing error messages that this is not supported in the spec so it might not work on others. There is also the possibility to flip the clip scpace position Y coordinate before writing out with vertex shader, but that requires changing and recompiling every shader. I could also bake it into the camera projection matrices, though I want to avoid that because then I need to track down for the whole engine where I upload matrices... Any chance of an easy extension or something? If not, I will probably go with changing the vertex shaders.
    • By NikiTo
      Some people say "discard" has not a positive effect on optimization. Other people say it will at least spare the fetches of textures.
      if (color.A < 0.1f) { //discard; clip(-1); } // tons of reads of textures following here // and loops too
      Some people say that "discard" will only mask out the output of the pixel shader, while still evaluates all the statements after the "discard" instruction.

      discard: Do not output the result of the current pixel.
      clip: Discards the current pixel..

      As usual it is unclear, but it suggests that "clip" could discard the whole pixel(maybe stopping execution too)

      I think, that at least, because of termal and energy consuming reasons, GPU should not evaluate the statements after "discard", but some people on internet say that GPU computes the statements anyways. What I am more worried about, are the texture fetches after discard/clip.

      (what if after discard, I have an expensive branch decision that makes the approved cheap branch neighbor pixels stall for nothing? this is crazy)
    • By NikiTo
      I have a problem. My shaders are huge, in the meaning that they have lot of code inside. Many of my pixels should be completely discarded. I could use in the very beginning of the shader a comparison and discard, But as far as I understand, discard statement does not save workload at all, as it has to stale until the long huge neighbor shaders complete.
      Initially I wanted to use stencil to discard pixels before the execution flow enters the shader. Even before the GPU distributes/allocates resources for this shader, avoiding stale of pixel shaders execution flow, because initially I assumed that Depth/Stencil discards pixels before the pixel shader, but I see now that it happens inside the very last Output Merger state. It seems extremely inefficient to render that way a little mirror in a scene with big viewport. Why they've put the stencil test in the output merger anyway? Handling of Stencil is so limited compared to other resources. Does people use Stencil functionality at all for games, or they prefer discard/clip?

      Will GPU stale the pixel if I issue a discard in the very beginning of the pixel shader, or GPU will already start using the freed up resources to render another pixel?!?!

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DX12 uber shader/ uber PSO management in DX12

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Hey Guys,


I am currently working on a hobby project where I try to compare different dynamic volume rendering techniques and settings under DX12 framework. So in this project I have GUI to be able to switch different volume buffer types, different spacial data structures and different voxel data type (16bit, 32bit per channel) and enable/disable different features (compute iso surface normals for example), you can get the idea from the attached image.



However with that in mind I end up with lots of shaders and therefore lots of PSOs (basically the combination of almost all the features). Thus I have these ugly code:

    ComputePSO _cptUpdatePSO[ManagedBuf::kNumType][SparseVolume::kNumStruct];
    GraphicsPSO _gfxUpdatePSO[ManagedBuf::kNumType][SparseVolume::kNumStruct];
    GraphicsPSO _gfxVolumeRenderPSO[ManagedBuf::kNumType]
    GraphicsPSO _gfxISOSurfRenderPSO
    GraphicsPSO _gfxStepInfoPSO;...

so I managed with multi-dimension array of PSOs and the dimension will increase if more feature added. But I don't think this is the proper way of doing this kind of thing. 


I've heard in a typical game, you guys will have more than 30000+ shaders on the fly, so probably in development, you guys also need to face this same kind of situation where you have this PSO explosion, and I really appreciate it if someone could talk about how they deal with those shader/PSO management.



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Here's a list of the options that game engines generally use. Not every option is suited to every situation.


1. Compile every possible shader up front. This can generate lots of shaders. Ideally you'd only compile the variations that you know you actually need in the game.


2. Use conditionals within the shader code, based on values in constant buffers, to control some or more features. This will usually make the shaders slower to execute.


3. Combine multiple passes of a simple shader to get the complete end result. For example you could render an object once per light, with additive blending, to handle an arbitrary number of lights. This again will reduce performance compared to doing it in a single pass.


4. Compile the actual shader you need on the fly. This is a reasonable option for an editor where it doesn't matter too much if switching shader takes a few seconds. This can be combined with a cache of recently used shaders.

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