Diligent integration with Qt

[AnloWho]

I'm looking into using DiligentEngine as backend for graphics in Qt. Does anyone around here have experience in that? would it work?

[TheMostDiligent]

I don't have experience with Qt, but I think there should be no problems making it work with Diligent.
As long as you can get the window handle from the library, you can attach Diligent swap chain to it and render.

[promerosenabre]

It works fine while not opengl is not activated on your Qt App. I want to combine two qwidgets in same layout, one is QOpenGLWidget and other use diligent engine, and diligent engine doesn't work, I get error Diligent::GLContextState::BindSampler().
when I demote QOpenGLWidget to QWidget, diligent engine qwidget works fine. Any idea ? I guess problem is because context is managed by qt...
THANKS

[TheMostDiligent]

I guess problem is because context is managed by qt

This is very likely. Try attaching to existing context created by QT with the AttachToActiveGLContext

DiligentCore/Graphics/GraphicsEngineOpenGL/interface/EngineFactoryOpenGL.h

Lines 82 to 85 in 3e17a10

	VIRTUAL void METHOD(AttachToActiveGLContext)(THIS_
	const EngineGLCreateInfo REF EngineCI,
	IRenderDevice** ppDevice,
	IDeviceContext** ppImmediateContext) PURE;

[promerosenabre]

Thanks, I have changed my code without sucessfull, sorry, but I think I am close to find the solution.
Anycase, I still have some questions about ( I am analizing plugun Unity on samples )

now I use
pFactoryOpenGL->AttachToActiveGLContext(EngineCI, &m_pDevice, &m_pImmediateContext);
it means I don't have to use
pFactoryOpenGL->CreateDeviceAndSwapChainGL(EngineCI, &m_pDevice, &m_pImmediateContext, SCDesc,&m_pSwapChain);

if yes, what happens with m_pSwapChain how to generate it ?

I see on Unity sample :

auto &DefaultAllocator = DefaultRawMemoryAllocator::GetAllocator();
auto pProxySwapChainGL = NEW_RC_OBJ(DefaultAllocator, "ProxySwapChainGL instance", ProxySwapChainGL)(m_UnityGraphicsGL, m_pDevice, m_pDeviceCtx, SCDesc);
pProxySwapChainGL->QueryInterface(IID_SwapChain, reinterpret_cast<IObject>(static_cast<ISwapChain**>(&m_pProxySwapChain)));
RefCntAutoPtr(m_pDeviceCtx, IID_DeviceContextGL)->SetSwapChain(pProxySwapChainGL);**

and I undestand this sample use rendertotexture and share the image between diligine and unity

Do I have to do the same because I am working with external opengl ?

or I only have to generate a correct m_pSwapChain ?

unity sample uses m_pSwapChainGL.
and
RefCntAutoPtr(m_pDeviceCtx, IID_DeviceContextGL)->SetSwapChain(pProxySwapChainGL);*

Sorry, I am confused about this step.

Thanks

[TheMostDiligent]

it means I don't have to use pFactoryOpenGL->CreateDeviceAndSwapChainGL(EngineCI, &m_pDevice, &m_pImmediateContext, SCDesc,&m_pSwapChain);

Yes, you only call AttachToActiveGLContext

if yes, what happens with m_pSwapChain how to generate it ?

In OpenGL, context and swap chain are both attached to the window. If your application creates the context, it is also responsible for presenting (e.g. calling glSwapBuffers). Diligent can't create the swap chain and present.

Unity sample may not be the best example. You application outline should look something like this:

Initialization:

• Qt initializes OpenGL context
• Call AttachToActiveGLContext to get Diligent device and immediate context
• Get OpenGL handle from the texture you want to share with Diligent, call CreateTextureFromGLHandle to create Diligent texture

Rendering:

• Qt starts rendering
• Switch to Diligent, call InvalidateState
• Render with Diligent
• Present with Qt

[promerosenabre]

Thank you for your quick replay, I apreciate it.
I have simplified the initialization of diligent without mistakes. Thanks

I try to replicate on Qt the sample "Tutorial03_Texturing" that works fine without opengl Qt activated.

Now I get a mistake on
MapHelper CBConstants(m_pImmediateContext, this->modelCube.materials[this->modelCube.items[cont].indexMaterial].m_VSConstants, MAP_WRITE, MAP_FLAG_DISCARD);

inside render. it is sense because I use AttachToActiveGLContext ?

it works fine without opengl

any idea ? sorry for all this questions, I hope will be usefull for others than try to use diligent on Qt.

[promerosenabre]

Error solved after define correctly SetRenderTargets with apropiate ITextureView.

[AnloWho]

Thank you for your quick replay, I apreciate it. I have simplified the initialization of diligent without mistakes. Thanks

I try to replicate on Qt the sample "Tutorial03_Texturing" that works fine without opengl Qt activated.

Now I get a mistake on MapHelper CBConstants(m_pImmediateContext, this->modelCube.materials[this->modelCube.items[cont].indexMaterial].m_VSConstants, MAP_WRITE, MAP_FLAG_DISCARD);

inside render. it is sense because I use AttachToActiveGLContext ?

it works fine without opengl

any idea ? sorry for all this questions, I hope will be usefull for others than try to use diligent on Qt.

@promerosenabre what do you mean by "without opengl" it works fine in Qt? I'm struggling with sorting out the connection between Qt and Diligent.

[AnloWho]

Very interesting. I'll also explore the land to hook up diligent to qt. It's enough with Diligent Core if I want to do basic polygon rendering with textures and so. Right?

…

On Thu, Mar 6, 2025, 20:32 promero ***@***.***> wrote: Error solved after define correctly SetRenderTargets with apropiate ITextureView. — Reply to this email directly, view it on GitHub <#625 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AF2XO3ENT6SWO63SDHFKWMT2TCPDPAVCNFSM6AAAAABPAZZKDKVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTENBRHAYTCMY> . You are receiving this because you authored the thread.Message ID: <DiligentGraphics/DiligentCore/repo-discussions/625/comments/12418113@ github.com>

[TheMostDiligent]

Yes, there is no official way to select an adapter on GL, but there are Nvidia and amd-specific workarounds, which seem to work

[AnloWho]

I also managed to get it to work in Qt. Currently the widget inherits from QOpenGLWidget and I use the CreateDeviceAndSwapChainGL() method provided by Diligent.

Hi AnlOwho, I tried to run dirigent engine on Qt with QOpenGLWidget , but my knowledge is not enough. Could you send me a basic example of how you achieved this? I'd really appreciate it. Thanks !!
I basically do this for my so called DiligentViewport class:
class DiligentViewport : public QOpenGLWidget, protected QOpenGLFunctions
{
public:
DiligentViewport(QWidget* parent = nullptr);
~DiligentViewport();

virtual void paintGL() override;
virtual void resizeGL(int width, int height) override;
virtual void initializeGL() override;

private:
bool initializeDiligentEngine();
void createPipelineState();
void createVertexBuffer();
void createIndexBuffer();

in the initializeGL() method I would run all the private methods in order of appearance.
I'm still discovering, so I don't say this is the correct way, but I got it to work with the first triangle tutorial. It shows inside the MainWindowView (that inherits from QMainWindow). A crucial point was this cast to get the handle from the application windows down to the engine (in initializeDiligentEngine())

I don't do swapChain_->present() anywhere. I don't know if any of this I just mentioned is useful. Maybe it doesn't work for more complex scenarios. But if I can get it to work with the cube , why not the rest?

[promerosenabre]

Hi, if triangle tutorial is working, I guess won't be a problem to run all samples, Let me try it and I will inform you asap. Thank you very
much !!

[AnloWho]

OK. I'm struggling with the Cube. I realized it is very important (on my system) to set the path to the folder where you have the shaders. And that path has to be absolute it seems. Use the method CreateDefaultShaderSourceStreemFactory() for your engine factory.

[TheMostDiligent]

Diligent does not do anything special with files. Shaders are just files, they need to be somewhere the system can find them. The paths may be relative or absolute.

[AnloWho]

Any idea why I get this error in the render() method when trying to setup the MapHelper?
Diligent Engine: ERROR in Diligent::BufferGLImpl::MapRange() (BufferGLImpl.cpp, 374): glMapBufferRange() failed GL Error Code: 1281
Diligent Engine: ERROR: Debug assertion failed in Diligent::BufferGLImpl::MapRange(), file BufferGLImpl.cpp, line 374:
I'm on my littel Qt test app where I before managed to draw the triangle from tutorial 01.
It's the line 253 in the Tutorial02_Cube.cpp.

    {
        // Map the buffer and write current world-view-projection matrix
        MapHelper<float4x4> CBConstants(m_pImmediateContext, m_VSConstants, MAP_WRITE, MAP_FLAG_DISCARD);
        *CBConstants = m_WorldViewProjMatrix;
    }

[TheMostDiligent]

Are there any other messages in the output?
Since annoyingly the error in OpenGL remains until the time when glGetError is called, this error may not be caused by the glMapBufferRange. It may be an error from some previous operation.

[AnloWho]

Sorry for bugging you, but abandoned the Opengl integration into Qt for now and have looked at using Vulkan instead. I got the clear color to show up in my Qt window, but I have these warning (in debug build) which suggest something is wrong:
Diligent Engine: Warning: Render target view '0x13C197717A0' is not bound to the device context. ClearRenderTarget command is more efficient if render target view is bound to the device context. In OpenGL backend this is a requirement.
and
Diligent Engine: Warning: Depth-stencil view 'Default DSV of texture 'Main depth buffer'' is not bound to the device context. ClearDepthStencil command is more efficient when depth-stencil view is bound to the context. In OpenGL backend this is a requirement.

I know it can be difficult to answer since you don't have all the code, but I have used the handle from the QWindow to create a Win32NativeWindow before calling CreateSwapChainVk.

Also, the immediateContext->Draw(drawAttrs) fails in the PrepareForDraw() with No render pass is active while executing draw command.
Any pointer what I should do?

[AnloWho]

ok, I just put in:
immediateContext_->SetRenderTargets(1, &pRTV, pDSV, RESOURCE_STATE_TRANSITION_MODE_TRANSITION);
after clearing the RenderTarget and DepthStencil and now I got this :)

I still have those Warnings in the Debug console as described above though...

[TheMostDiligent]

You need to set the render targets before clearing them. This is what the error message is trying to say, may it needs to be more clear.

[AnloWho]

I don't know. I just missed that part looking at the Tutorials. My bad. I still get weird memory leak warning on closing the app. I need to understand in what order to tear down things here. Is there a common practice in Diligent on what to do on object destruction? I see Flush and Release being used.

[TheMostDiligent]

Calling Flush is reasonable.
On release, you should destroy all objects you created. If you use the smart pointer, they will destroy the objects automatically.