How to perform raytracing on a non-RTX graphics card? - c++

Question

I want to simulate a raytracing on non-RTX graphics card but I can't. I got this error "Raytracing not supported on device" that I indicate in a code at bottom. I set m_useWarpDevice to true but why I still got the error? According to my understand WARP makes an application run any feature (including raytracing) even the hardware is not supported, but why it doesn't work?
Question: How to perform raytracing on a non-RTX graphics card? The reason I insist is I tried to ask the question in Microsoft Forum but no answer.
What is Windows Advanced Rasterization Platform (WARP) Guide?
From https://learn.microsoft.com/en-us/windows/win32/direct3darticles/directx-warp
WARP does not require graphics hardware to execute. It can execute even in situations where hardware is not available or cannot be initialized.
From https://alternativesp.com/software/alternative/windows-advanced-rasterization-platform-warp/
In Windows 10, WARP has been updated to support Direct3D 12 at level 12_1; under Direct3D 12, WARP also replaces the reference rasterizer.
Compiler: Visual Studio 2019
Graphic card: NVIDIA GeForce 920M (non-RTX)
DXSample.cpp
From https://github.com/ScrappyCocco/DirectX-DXR-Tutorials/blob/master/01-Dx12DXRTriangle/Project/DXSample.cpp
At line 19
DXSample::DXSample(const UINT width, const UINT height, const std::wstring name) :
m_width(width),
m_height(height),
m_useWarpDevice(true), // <-- It was false but I set it to true.
m_title(name)
{
m_aspectRatio = static_cast<float>(width) / static_cast<float>(height);
}
D3D12HelloTriangle.cpp
From https://github.com/ScrappyCocco/DirectX-DXR-Tutorials/blob/master/01-Dx12DXRTriangle/Project/D3D12HelloTriangle.cpp
At line 91
if (m_useWarpDevice) { // m_useWarpDevice = true
ComPtr<IDXGIAdapter> warpAdapter;
ThrowIfFailed(factory->EnumWarpAdapter(IID_PPV_ARGS(&warpAdapter))); // <-- Success
ThrowIfFailed(D3D12CreateDevice(warpAdapter.Get(), D3D_FEATURE_LEVEL_12_1, IID_PPV_ARGS(&m_device))); // <-- Success
}
else {
ComPtr<IDXGIAdapter1> hardwareAdapter;
GetHardwareAdapter(factory.Get(), &hardwareAdapter);
ThrowIfFailed(D3D12CreateDevice(hardwareAdapter.Get(), D3D_FEATURE_LEVEL_12_1, IID_PPV_ARGS(&m_device)));
}
At line 494
void D3D12HelloTriangle::CheckRaytracingSupport() const {
D3D12_FEATURE_DATA_D3D12_OPTIONS5 options5 = {};
ThrowIfFailed(m_device->CheckFeatureSupport(D3D12_FEATURE_D3D12_OPTIONS5, &options5, sizeof(options5)));
if (options5.RaytracingTier < D3D12_RAYTRACING_TIER_1_0) // <-- options5.RaytracingTier = 0 on my computer which means that raytracing is not suppored.
throw std::runtime_error("Raytracing not supported on device"); // <-- I got this error.
}
Off-topic (just help in the future in case I forget):
https://alternativesp.com/software/alternative/windows-advanced-rasterization-platform-warp/
To force an application to use WARP without disabling the display driver, install the Direct X SDK. http://www.microsoft.com/en-us/download/details.aspx?id=6812 , go to C: / windows / system32, run dxcpl.exe, under “Scope” click “Edit list”, add the path to the application.
I tried to use dxcpl.exe to force WARP but options5.RaytracingTier is always 0.

Answer 1

Instead of using warp device you can use the dx12 RTX fallback layer.
https://github.com/microsoft/DirectX-Graphics-Samples/tree/e5ea2ac7430ce39e6f6d619fd85ae32581931589/Libraries/D3D12RaytracingFallback
Please note that is has a few limitations (resource binding is slightly different, also it's unlikely that they will continue to support it).
Also of course since it emulates the on chip RTX with compute shaders, performances are not as good as native.