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• ### Similar Content

• 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?

• 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.
<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?!?!

# DX12 Root parameter decriptor table with a mix of range types

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Hello!

Is it possible to mix ranges of samplers and ranges of SRVs and ranges of UAVs in one root parameter descriptor table? Like so:

D3D12_DESCRIPTOR_RANGE ranges[3];
D3D12_ROOT_PARAMETER param;
param.ParameterType = D3D12_ROOT_PARAMETER_TYPE_DESCRIPTOR_TABLE;
param.DescriptorTable.NumDescriptorRanges = 3;
param.DescriptorTable.pDescriptorRanges = ranges;

range[0].RangeType = D3D12_DESCRIPTOR_RANGE_TYPE_SRV;
..
range[1].RangeType = D3D12_DESCRIPTOR_RANGE_TYPE_UAV;
..
range[2].RangeType = D3D12_DESCRIPTOR_RANGE_TYPE_SAMPLER;
..

I wonder especially about CopyDescriptors, that will need to copy a range of D3D12_DESCRIPTOR_HEAP_TYPE_SAMPLER and a range of D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV.

Thanks if anyone knows (while I try it :))

.P

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Aaaaaand I think I have my answer:

Quote

The D3D12_ROOT_DESCRIPTOR_TABLE structure declares the layout of a descriptor table as a collection of descriptor ranges that appear one after the other in a descriptor heap. Samplers are not allowed in the same descriptor table as CBV/UAV/SRVs.

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IIRC samplers are on there own heap thats why you can't do it.

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While I'm here, I'm wondering about what exactly is CopyDesciptors doing (CopyDescriptorsSimple is... simple).

Can the number of destination and source ranges be different? E.g. is it good for gathering scattered descriptors before the draw? Like copy 10 scattered SRVs into 1 contiguous range and 5 scattered UAVs into another contiguous range? The documentation doesn't say anything.

Also, are we allowed to copy/write descriptors into a GPU visible descriptor heap from CPU (or GPU) directly, i.e. without CopyDescriptors? The descriptor heap has a CPU virtual address (pointer), the size of the descriptor is known...

Edited by pcmaster

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Yes, CopyDescriptors can do arbitrary scatter/gather. The only requirement is that the total number of descriptors specified in the source ranges and dest ranges must be equal. How they're divided among the ranges is unimportant.

You can write into GPU-visible descriptor heaps at will, either via creates or copies, but cannot copy out of them.

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Awesome, that's what I hoped

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Do not perform the copy in the back of D3D tho, some hardware may need extra processing. An example is the sampler state, the border colors are not inline but indexed in a shared table on AMD.