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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.
       
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      Hi,
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    • 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.
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      <MSN

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    • 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.
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      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 [Dx12] Need help with DescriptorHeap

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Hi, I was playing around with dx12 using sharpdx beta.

I'm able to render simple models now. However I went into troubles when trying to render models with several sub parts. The texture I uploaded is not displaying for second part.

 

This is how I do it:

 

1. Create a root signature

var rootSignatureDesc = new RootSignatureDescription(

                RootSignatureFlags.AllowInputAssemblerInputLayout,
                // Root Parameters
                new[]
                {
                    new RootParameter(ShaderVisibility.All,
                        new []
                        {
                            new DescriptorRange()
                            {
                                RangeType = DescriptorRangeType.ShaderResourceView,
                                DescriptorCount = 2,
                                OffsetInDescriptorsFromTableStart = -1,
                                BaseShaderRegister = 0
                            },
                            new DescriptorRange()
                            {
                                RangeType = DescriptorRangeType.ConstantBufferView,
                                DescriptorCount = 1,
                                OffsetInDescriptorsFromTableStart = -1,
                                BaseShaderRegister = 0
                            }
                        }),
                    new RootParameter(ShaderVisibility.Pixel,
                        new DescriptorRange()
                        {
                            RangeType = DescriptorRangeType.Sampler,
                            DescriptorCount = 1,
                            OffsetInDescriptorsFromTableStart = -1,
                            BaseShaderRegister = 0
                        }),
                });

2. Create Descriptor Heap for srv and cbf


var srvCbvHeapDesc = new DescriptorHeapDescription()
            {
                DescriptorCount = 3,
                Flags = DescriptorHeapFlags.ShaderVisible,
                Type = DescriptorHeapType.ConstantBufferViewShaderResourceViewUnorderedAccessView
            };

            srvCbvHeap = device.CreateDescriptorHeap(srvCbvHeapDesc);

3.Upload textures

var tex = Texture.LoadFromFile("../../models/test.tga");
            byte[] textureData = tex.Data;
            TextureWidth = tex.Width; TextureHeight = tex.Height;

            var textureDesc = ResourceDescription.Texture2D(Format.B8G8R8A8_UNorm, TextureWidth, TextureHeight, 1, 1, 1, 0, ResourceFlags.None, TextureLayout.Unknown, 0);
            texture = device.CreateCommittedResource(new HeapProperties(HeapType.Upload), HeapFlags.None, textureDesc, ResourceStates.GenericRead, null);
          
            texture.Name = "Texture";

            var handle = GCHandle.Alloc(textureData, GCHandleType.Pinned);
            var ptr = Marshal.UnsafeAddrOfPinnedArrayElement(textureData, 0);
            texture.WriteToSubresource(0, null, ptr, TextureWidth * 4, textureData.Length);
            handle.Free();

4. Create Shader Resource View Description for each texture by offsetting the heap address


var Step = device.GetDescriptorHandleIncrementSize(DescriptorHeapType.ConstantBufferViewShaderResourceViewUnorderedAccessView);
......
device.CreateShaderResourceView(texture[i], srvDesc, srvCbvHeap.CPUDescriptorHandleForHeapStart + I * Step);

5.When building command list I set the descriptor table for each texture resource by offsetting


commandList.SetGraphicsRootSignature(rootSignature);
            DescriptorHeap[] descHeaps = new[] { srvCbvHeap, samplerViewHeap };
            commandList.SetDescriptorHeaps(descHeaps.GetLength(0), descHeaps);
            commandList.SetGraphicsRootDescriptorTable(0, srvCbvHeap.GPUDescriptorHandleForHeapStart);
            commandList.SetGraphicsRootDescriptorTable(1, samplerViewHeap.GPUDescriptorHandleForHeapStart);

......
draw first
......

commandList.SetGraphicsRootDescriptorTable(0, srvCbvHeap.GPUDescriptorHandleForHeapStart + Step * i);

......
draw second
......

But the thing is only the first part will have texture. I'm still trying to understand how the whole resource management works but it looks so complex. Please help, I checked the cpp sample code on GitHub but can't find what I did wrong.

 

Thanks in advance.

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Hi, I'm using SharpDx too.

Well, how I can see you are using 3 items (2 for textures and 1 constant buffer) in the same RootParameters

 

so, from any position in your heap, D3D expects this 3 items

For example

tex1,tex2,constant buffer.

If you set offset to 0 D3D will start loading resource from tex1 position.

 

But if you increase just by one you'll have it starting from tex2 and read like this

tex2,constant buffer,??? 

so you must pay attention. It doesn't seem right.

 

 

When you combine many resources in one RootParameter you must pay attention that items are in the right number and order.

 

I've published some demo in SharpDx on Github

 

https://github.com/RobyDX/SharpDX_D3D12HelloWorld

and I've a website too (http://www.notjustcode.net) where I've started Direct3D12 tutorial using SharpDx. It's in italian but you can try to translate with bar I've added?

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