Qt and 3D QtCS2015

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Subject

Qt 5.5 brings:

  • Canvas3D -- WebGL-like API for QML JavaScript with three.js port available.
  • Qt 3D 2.0 TechPreview -- Fully data driven C++ 3D scene graph.

Let's Discuss:

  • How easy are these to approch at the moment?
  • Performance expectations?
  • 3D tooling requirements in Qt Scope?
  • What kind of use cases should we be looking at and optimising for?

Canvas3D runthrough

  • "Planets" example, planetary demo, three.js based
  • "OneQt" example, cube as a UI thing, three.js based
  • CarVisualizer demo, port of app done by +360 Degrees, but we tweaked it a bit:
    • Animating the color changes, material properties change...
    • Shows how QML animations can gracefully work with your 3D stuff
    • 2 days of work (1 day was just descrambling the original code)

Qt 3D runthrough

  • Sphere rotating around a torus
  • Embedded into QML
  • Plane flying through rings, anaglyphic stereoscopic rendering (green/red)
  • It is all a scene graph in QML, including the Render Graph
  • SceneGraph and camera, materials and all can be built in QML and C++
  • Pretty likely that we can use Vulkan underneath it in the future

Discussion

  • Writing WebGL is of course quite elaborate and tedious, but because we have three.js it can be quite nice to work with
    • Builds the scene using Javascript, rather than QML, but similar level (scene, camera, objects...)
  • What about performance and memory?
    • Porting the Planets example to Qt 3D found some issues
    • TypedArrays in V4 VM now
    • The JS code is only used to build the tree. We don't run JS once the tree is running
  • What about porting three.js to Canvas3D?
    • Need to pick out the HTML bits and replace them by Canvas3D
    • The three.js port has some convenient portability layer stuff
    • Maybe we could provide some of the HTML DOM things so it "just works" with Qt
  • Canvvas3D has a benefit over HTML/WebGL because once it works on top of Qt, there is nothing more needed
  • For Qt 3D, the ease of use is often
    • still learning what people expect from it
    • need a lot more examples to show how things work
    • to do Oculus 3D, take the current stereo and adapt it
    • default framegraphs
  • Importing models -> done using assimp
    • Results in a Qt 3D subtree
    • Basic description of the materials which is mapped to Qt 3D materials,
      • several built in ones
      • PhongMaterial, etc..
    • You can't get the fancy materials.

Tooling

  • Visualizer, tree visualizer
    • This is something we're very likely to build
    • Pick and drag and look at properties and stuff
  • How much tooling do you really need.
    • Qt Quick Designer
      • Canvas3D component is available, but it shows up as box in the designer.
      • Qt 3D scene could be a subtree in the designer?
  • Qt 3D can do deep bindings because it is QML all the way
  • Canvas3D + three.js requires you to have JS code to pass the property values from QML to JS.
  • Render same scene from multiple angles
  • The FrameGraph is fully flexible and any type rendering technique can be put together
    • Again, more examples are needed..
  • What is the minimal. The old Qt 3D could do a model in 5 lines?
    • How minimal does it make sense to have it?
    • Convenience needs to be added based on what people need
    • Mustardy "shit" yellow phong material
    • Forwards renderer
    • Can probably do better, but we're maybe around 10 lines now.
  • Could we build a QML API on top of three.js?
    • Could make sense as that could help in building single tooling for both Canvas 3D and Qt 3D.
  • Physics?
    • Qt 3D is a 3D scene system, so different aspects can do different things
      • 3D sound
      • physics
      • picking aspect
    • a physics system is just another aspect which can do work on the scene.
    • We probably don't want to maintain a physics engine under the Qt project
      • unless there is plenty of money in it
    • Probably better to just include an open source one if it exists...
    • There is a bullet aspect..
    • three.js has a physics library called Physijs, not tried yet with ported three.js.
  • What about input?
    • Qt3D default picking methods?
    • three.js has raycasting as primary method.