[Interest] [QT3D] How Do I render multiple QEntities in different QViewports in C++?
Sean Harmer
sean.harmer at kdab.com
Sun May 1 10:15:52 CEST 2016
On 30/04/2016 21:02, Pierre Chicoine wrote:
>
> Thank you Sean. Very descriptive. Since I have such a large system,
> I will create an example and pass it to you.
>
> By the way a large percentage of your examples on 5.7 beta don't work.
> But I'm sure you're aware of that.
>
Yup, we're replacing something at the moment. Lots of commits lined up
but the CI is broken.
Sean
> Thank you again.
>
> On Apr 30, 2016 10:55 AM, "Sean Harmer" <sean.harmer at kdab.com
> <mailto:sean.harmer at kdab.com>> wrote:
> >
> > Hi,
> >
> > There's two things you need to consider:
> >
> > 1) The scene graph - the Entities that you wish to draw.
> > 2) The framegraph - specifies the algorithm used to draw the scene graph
> >
> > I assume from your screenshot that you are more or less happy with
> defining
> > QEntity's to construct your scene graph. If you wish some entities
> to be drawn
> > in one part of the window (viewport) and the others in another
> viewport then
> > we need some way of saying "select this set of entities but not that
> set".
> >
> > One way of doing this is by using a QLayer component attached to
> your entities
> > that says which layer that entity is part of. This is just like layers
> > photoshop, gimp, blender etc. Create a QLayer, give it a name, and
> aggregate
> > it onto your QEntity as you do the other components (mesh, transform and
> > material).
> >
> > Doing this doesn't change anything in the rendering on it's own. To
> affect the
> > change we also need to modify the framegraph. To do this, make sure the
> > concept of the framegraph is clear in your mind. Have a read of:
> >
> > https://www.kdab.com/qt3d-2-0-framegraph/
> >
> > Each leaf node, corresponds to a portion of your overall scene. To
> keep things
> > simple, lets only consider the viewports and layer filters you will
> need. You
> > will need other things in the framegraph too (rendersurfaceselector
> (if using
> > 5.7), camera selector, technique selector etc). The parts of the
> framegraph
> > concerned with viewports and layers will look something like this:
> >
> > Root (e.g. TechniqueSelector)
> > |- Viewport [left half of window]
> > |- LayerFilter [names="layer1"] (*)
> > |- Viewport [right half of window]
> > |- LayerFilter [names="layer2"] (**)
> >
> > Where:
> >
> > (*) <-- draws entities on "layer1" in left viewport
> > (**) <-- draws entities on "layer2" in right viewport
> >
> > If you then want to use different cameras in the different viewports
> then you
> > can include a QCameraSelector node in each sub-tree.
> >
> > Root (e.g. TechniqueSelector)
> > |- Viewport [left half of window]
> > |- CameraSelector [camera1]
> > |- LayerFilter [names="layer1"] (*)
> > |- Viewport [right half of window]
> > |- CameraSelector [camera2]
> > |- LayerFilter [names="layer2"] (**)
> >
> > Where:
> >
> > (*) <-- draws entities on "layer1" in left viewport using "camera1"
> > (**) <-- draws entities on "layer2" in right viewport using "camera2"
> >
> > Hopefully that makes sense. In the future, I hope we can provide
> tooling and
> > perhaps higher level ways of building custom framegraphs. The
> framegraph is
> > hugely powerful as it totally allows changing the rendering algorithm at
> > runtime without having to touch low level C++ graphics code.
> However, it is a
> > bit tricky to get to grips with at first.
> >
> > Cheers,
> >
> > Sean
> >
> > On Thursday 28 April 2016 13:34:58 Pierre Chicoine wrote:
> > > Dear Sirs
> > >
> > > First: Thank you for Qt3d. The KDAB people are heroes in my book.
> > >
> > > I have two problems in C++ Qt3D.
> > >
> > > 1. I am having a difficult time figuring out how to render
> QEntities into
> > > separate QViewports. All my 3d objects draw to the first
> QViewport, the
> > > rest are black. I have read all your articles and comments
> everywhere on
> > > the Internet that I can find and I am basically confused.
> > >
> > > Is there a c++ example that would show multiple viewports with
> distinct
> > > separate QEntities? I can't seem to duplicate The QML example
> multiviewport
> > > in my code. What classes would get me there?
> > >
> > > 2. Also I'm also confused about QNodes and QEntitys and their
> > > relationships. Maybe it's the use of Qt3d version 1 that is
> messing me up .
> > > I use to have a scene node and all the entities would hang off of
> one scene
> > > node for each scene. But that doesn't seem to work in version 2.
> Or do I
> > > use the addComponent on a QFrameGraph instead of a node? Or do I hang
> > > Entities off of a viewport?
> > >
> > > Attached is a pic of my progress which draws all the objects into
> the same
> > > viewport. The window tiles 2 windows properly but I only draw to one
> > > viewport, the second or third stay black. The code here is what I
> repeat in
> > > each scene class. It's a bit of a mess thrown together to test
> Qt3D classes
> > > because I don't understand the relationships between all the Qt3D
> classes
> > > used to place objects in a viewport.
> > >
> > >
> > > Qt3DCore::QCamera *cameraEntity = new Qt3DCore::QCamera(
> pParentNode);
> > >
> > > cameraEntity->setObjectName(QStringLiteral("cameraEntity"));
> > >
> > >
> cameraEntity->setProjectionType(Qt3DCore::QCameraLens::PerspectiveProjectio
> > > n);
> > >
> > > cameraEntity->setAspectRatio(1024 / 768);
> > >
> > > cameraEntity->setUpVector(QVector3D(0.0f, 1.0f, 0.0f));
> > >
> > > cameraEntity->setViewCenter(QVector3D(0.0f, 3.5f, 0.0f));
> > >
> > > //cameraEntity->lens()->setPerspectiveProjection(60.0f, 16.0f/9.0f,
> > > 0.1f, 1000.0f);
> > >
> > >
> > > if(pScenesSet) // if it's a scene then we want to set it where
> they want it
> > >
> > > cameraEntity->setPosition(QVector3D(pScenesSet->CamXPos - 20,
> > > pScenesSet->CamYPos + 80, pScenesSet->CamZPos));
> > >
> > > else // so it's a schematic
> > >
> > > cameraEntity->setPosition(QVector3D(-20, 65, 180));
> > >
> > >
> > > theApp->input->setCamera(cameraEntity); // not sure about this
> > > relationship??
> > >
> > >
> > > // FrameGraph
> > >
> > > pQFrameGraph = new Qt3DRender::QFrameGraph();
> > >
> > > pQTechniqueFilter = new Qt3DRender::QTechniqueFilter();
> > >
> > > pQViewport = new Qt3DRender::QViewport(pQTechniqueFilter);
> > >
> > > Qt3DRender::QClearBuffer *clearBuffer = new
> > > Qt3DRender::QClearBuffer(pQViewport);
> > >
> > > Qt3DRender::QCameraSelector *cameraSelector = new
> > > Qt3DRender::QCameraSelector(clearBuffer);
> > >
> > > Qt3DRender::QRenderPassFilter * pQRenderPassFilter = new
> > > Qt3DRender::QRenderPassFilter(cameraSelector);
> > >
> > > Qt3DRender::QRenderTargetSelector * m_gBufferTargetSelector = new
> > > Qt3DRender::QRenderTargetSelector(pQTechniqueFilter);
> > >
> > > // Qt3DRender::QLayerFilter * m_sceneFilter = new
> > > Qt3DRender::QLayerFilter(theApp->pCThreeDWindow);
> > >
> > > // TechiqueFilter and renderPassFilter are not implement yet
> > >
> > > pQViewport->setRect(QRectF(0, 0, 1, 1));
> > >
> > > clearBuffer->setBuffers(Qt3DRender::QClearBuffer::ColorDepthBuffer);
> > >
> > > pQFrameGraph->setActiveFrameGraph(pQTechniqueFilter);
> > >
> > > // Setting the pQFrameGraph
> > >
> > >
> > > // I add a framegraph component to: class CThreeDWindow : public
> > > Qt3DCore::QEntity
> > >
> > > // public:
> > >
> > > // CThreeDWindow(Qt3DCore::QNode *parent = 0);
> > >
> > >
> > > theApp->pCThreeDWindow->addComponent(pQFrameGraph);
> > >
> > >
> > > if(pScenesSet) // if it's a scene then we want to set it where
> they want it
> > >
> > > pQViewport->setClearColor(QColor(pScenesSet->BackRed,
> > > pScenesSet->BackGreen, pScenesSet->BackBlue));
> > >
> > > else
> > >
> > > pQViewport->setClearColor(QColor(0, 0, 0));
> > >
> > >
> > > cameraSelector->setCamera(cameraEntity);
> > >
> > > //m_gBufferTargetSelector->setTarget(m_sceneFilter);
> > >
> > >
> > >
> > > Any help would be appreciated.
> > >
> > > Thank you
> >
> > --
> > Dr Sean Harmer | sean.harmer at kdab.com <mailto:sean.harmer at kdab.com>
> | Managing Director UK
> > Klarälvdalens Datakonsult AB, a KDAB Group company
> > Tel. UK +44 (0)1625 809908, Sweden (HQ) +46-563-540090
> > KDAB - Qt Experts - Platform-independent software solutions
>
>
>
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--
Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
KDAB (UK) Ltd, a KDAB Group company
Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
Mobile: +44 (0)7545 140604
KDAB - Qt Experts
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