[Interest] [QT3D] How Do I render multiple QEntities in different QViewports in C++?

[Pierre Chicoine]

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.

Thank you again.

On Apr 30, 2016 10:55 AM, "Sean Harmer" <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 | 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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