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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
      Hi,
      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.

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

      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 Draw rectangle Directx 12

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Hi I started to study directx12. I don't have any knowledge on prior versions.

I am following this example program HelloWorldTriangle which rendering a triangle. I want to draw a rectangle so,

I changed

Vertex triangleVertices[] =
        {
            { { 0.0f, 0.25f * m_aspectRatio, 0.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },
            { { 0.25f, -0.25f * m_aspectRatio, 0.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } },
            { { -0.25f, -0.25f * m_aspectRatio, 0.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } }

        };

m_commandList->DrawInstanced(3, 1, 0, 0);

to

Vertex triangleVertices[] =
            {
                { { 0.0f, 0.25f * m_aspectRatio, 0.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },
                { { 0.25f, -0.25f * m_aspectRatio, 0.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } },
                { { -0.25f, -0.3f * m_aspectRatio, 0.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } },
                { { -0.25f, -0.2f * m_aspectRatio, 0.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } },

            };

    m_commandList->DrawInstanced(4, 1, 0, 0);

But still draws a triangle with different angle .. Please explain what I have to change to get a rectangle.

It will be really helpful for me if you give some links or books to headstart directx12 ..

Thanks in advance ..

Hi I started to study directx12. I don't have any knowledge on prior versions.

I am following this example program HelloWorldTriangle which rendering a triangle. I want to draw a rectangle so,

I changed

Vertex triangleVertices[] =
        {
            { { 0.0f, 0.25f * m_aspectRatio, 0.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },
            { { 0.25f, -0.25f * m_aspectRatio, 0.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } },
            { { -0.25f, -0.25f * m_aspectRatio, 0.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } }

        };

m_commandList->DrawInstanced(3, 1, 0, 0);

to

Vertex triangleVertices[] =
            {
                { { 0.0f, 0.25f * m_aspectRatio, 0.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },
                { { 0.25f, -0.25f * m_aspectRatio, 0.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } },
                { { -0.25f, -0.3f * m_aspectRatio, 0.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } },
                { { -0.25f, -0.2f * m_aspectRatio, 0.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } },

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DX12 is intended for high-investment/high-performance programming. It's is alternative to DX11 rather than a replacement. Don't make the mistake of thinking that DX12 will give you better performance out of the box; you have to understand what's going on very well in order to make the kinds of changes required to see any improvement. If you're still at this stage of the game then just use DX11 until you have a strong understanding of the pipeline and process. Otherwise you'll spend a lot of extra time just to end up with a slower program.

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What @Khatharr said is very true not only about DX12, but Vulkan and Metal too. All these APIs exist for exactly same purpose. What's interesting is that indeed, "naive" code written using DX12 and Vulkan will probably be outperformed by equivalent code made with use of an older API. This is because the driver does LOTS of work trying to figure out what you want to do, how you want to do and takes care about parallelism etc. With DX12 you have to take care about it yourself. So it's not only graphics programming experience you need but you need to have knowledge about memory management ( I guess you didn't get yet to the resource transitions, descriptor heaps etc. ), synchronization ( using barriers is actually DIFFICULT even for experienced programmers! ), parallelism ( threading, proper way of distributing your workload, so you're not making a CPU be a bottleneck ).

 

There's one thing everyone who tries to touch those new APIs should know. Before the driver was doing all the work, but now it's YOU who write the driver. If you're ready for that ( and many programmers indeed are! ) then do it, but otherwise get more experienced. Understand what it takes to actually write such "driver-like" code.

 

Again, I don't want to discourage anybody. It's quite opposite. Get there, become DX12/Vulkan developer! Just do it following the right path. It's bit like learning for example physics. You're not going to start from learning about relativity etc. right? :) But once you have basics, understanding more complex topics comes more natural and easier :)

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I feel like there should be more of an emphasis in general on the fact that DirectX 12 and Vulkan are not APIs you want to dive into unless you actually have a need for them, or if you're planning on specifically refining your graphics engine development skills.

 

Starting with D3D12/Vulkan without any exposure to previous APIs just sets you up for a very very bad time with very bad results in the end (as mentioned above). Building a fully featured D3D12 engine which can outperform an established D3D11 engine is a complex task even for seasoned engineers.

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