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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 Directx 11, 11.1, 11.2 Or Directx 12

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I recently put my directx contex creation to a dll und thereby i also wanted to upgrade my directx version. But i have some question regarding the version and how to use it properly.


1. Which version should i use to develop, version 11.3 (i need conservative rasteration) or 12 regarding driver robustness and cleanness of the api and does 11.3 hardware support 12 aswell?

2. If i want to use directx 11.3 and is not supported, though i use it partially using directx 11.2, how do i usefully call my directx functions.I mean i have an ID3D11Device2 or an ID3D11Device3.

3. If i use directx 11.3, can i combine/mixup calls like PSSetConstantBuffers and PSSetConstantBuffers1


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Hi. Can you explanation a bit more what you want to achieve?
Are you developing your own engine now on d3d9 or 10 and do you want to upgrade/ refactor?

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I would only go down that route if you think you'll really benefit from the reduced CPU overheard and multithreading capabilities, or if you're looking for an educational experience in keeping up with the latest API's


So is that how DirectX Development will work these days? DirectX 11 to get shit done relatively quickly and DirectX 12 to have multithreading capabilities? 

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but day to day DX12 coding isn't going to be any different than DX11 speedwise or anything else.

But if you already mastered DX11, DX12 shouldn't be that much different.


DX12 actually is quite different. Knowing DX11 is pretty much a requirement for starting off with 12 as certain concepts carry over, but all the handy higher level tools are stripped away so you have more fine-grained control.


One area I always like to bring up is resource binding; in 11 it's simply a matter of binding the shaders you need and calling ID3D11DeviceContext::XSSetShaderResources/SetUnorderedAccessViews/SetConstantBuffers/SetSamplers/etc, and you're good to go.


In DX12 it becomes a lot more complicated. First of all you start off with constructing a root signature, which raises the question of how you want to do root signature layouts. Want to do direct root parameters for constant buffers and structured buffers? Want to set up descriptor tables? Do you want constant directly embedded into the root signature? Static samplers? How many parameters can you fit into your root signature before it kicks into slow memory? What are the recommendations for the hardware architecture you're trying to target (hint: They can differ quite drastically)? How do you bundle your descriptor tables in such a way that it adheres to the resource binding tier you're targeting? How fine-grained is your root signature going to be? Are you creating a handful of large root signatures as a catch-all solution, or are you going with small specialized root signatures?


There's no general best practice here which applies to all cases, so you're going to want answers to those questions above. 


Once you have a root signature you get to choose how to deal with descriptor heaps. How are you dealing with descriptor allocation? How do you deal with descriptors which have different lifetimes (e.g. single frame vs multiple frames)? Are you going to use CPU-side staging before copying to a GPU descriptor heap?  What's your strategy for potentially carrying across bound resources when your root signature or PSO changes (if you even want this feature at all)?


Again, these questions will need answers before you can continue on. It's easy enough to find a tutorial somewhere and copy-paste code which does this for you, but then what's the point of using DX12 in the first place? If you need cookie-cutter solutions, then stick with DX11. No need to shoot yourself in the foot by using an API which is much more complex than what your application requires.


Have a look at this playlist to see how deep the root signature and resource binding rabbit hole can go.



This kind of stuff pretty much applies to every single aspect of DX12. Things which you could take for granted in 11 become very serious problems in 12. Things you didn't have to worry about like resource lifetime, explicit CPU-GPU synchronization, virtual memory management, resource state transitions, resource operation barriers, pipeline state pre-building, and a lot more become serious issues you really can't ignore.


If you're shipping an application, why go through the trouble of having to deal with all of this stuff when you know that an API like DX11 will suffice? As far as I'm aware, DX11.3 has feature parity with the highest available DX12 feature level, so it's not like you're missing out on any specific features, aside from potentially having more explicit control over multithreaded rendering (which is a massive can of worms in itself).


DirectX 12 is not something you need to use to write modern graphics applications. It's something you use when you know up front that you'll get some real gains out of it.

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