1. Introducing Qt 3D Sean Harmer sean.harmer@kdab.com Paul Lemire

2. Entity Component System Drawing with Qt 3D Handling Input
Topics
What is Qt 3D?
Entity Component System
Drawing with Qt 3D
Handling Input
Controlling the Renderer
The Future of Qt 3D

3. The Leading C++ Cross-Platform Framework
Cross-Platform Class Library
One Technology for All Platforms
Integrated Development Tools
Shorter Time-to-Market
Cross-Platform IDE, Qt Creator
Productive development environment
Used by over 800,000 developers in 70+ industries
Proven & tested technology – since 1994

4. Ecosystems and whole SDKs
Qt is used for…
Application
Development
on Desktop,
Mobile and Embedded
Creating
Powerful Devices
Device GUIs,
Ecosystems and whole SDKs

5. Qt Applications Are Native Applications
Qt / Windows
Windows GDI
Windows Kernel
PC HW
Qt / OSX
Cocoa
Mac Kernel
MacHW
Qt / Embedded
X11, Wayland, EGLFS
Linux Kernel
Embedded HW
Qt / Android
Android NDK
Android Kernel
Android HW

6. What is Qt 3D? Not only about 3D graphics!
Multi-purpose – not “just” a game engine
Soft real-time simulation engine
Designed to be scalable
Extensible and flexible
An open collaboration between KDAB and The Qt Company

7. Simulation Engine The Qt 3D Core is not inherently about 3D graphics
Supports multiple domains at once:
AI, Logic, Audio, etc.
Of course it contains a 3D renderer too!
Allows you to write complex simulation systems:
Mechanical
Robotics
Physics
… and yes games too 

8. Scalability Qt 3D has a strong Frontend / Backend split
Frontend is lightweight and on the main thread
Bags of properties
Backend executed on secondary thread
Where the real simulation runs
Non-blocking frontend / backend communication
Backend maximises throughput via a thread pool

9. Extensibility & Flexibility
Domains added via independent aspects
If something not already fitting your needs
An Entity Component System is used to combine behaviour in your own objects
No deep inheritance hierarchy
More on this soon…
Qt 3D provides both C++ and QML APIs
Integrates with rest of Qt
Pull simulation data from a database or over the network?

10. Entity Component System (ECS)
ECS is an architectural pattern
Popular in game engines (they are simulation engines too)
Favours composition over inheritance
An Entity is a general purpose object
An Entity gets behaviour by combining data
Data comes from typed Components

11. Entity Component System (ECS)

12. Entity Component System (ECS)

13. Why an ECS? Traditional Object Oriented Design Big class hierarchies
Inflexible – assumptions baked at design time
Features tend to migrate to base class (bloated)
Let’s analyse a simple example:
Space Invaders!

14. Why an ECS?

15. Why an ECS?

16. Why an ECS?

17. Why an ECS?

18. Why an ECS?

19. Why an ECS?

20. Why an ECS?

21. Why an ECS?

22. Why an ECS?
ECS Pros:
Avoids deep, wide, complex inheritance hierarchies
Flexible – can change object behaviour at runtime (add/remove components)
Extensible – add more component types later
Qt 3D ECS is high performance by Aspects (Systems) offloading work to backend
ECS Cons:
Often new to OOP programmers – takes a while to adjust thinking
More objects – Entity plus Components

23. What does Qt 3D Provide in Qt 5.7?
Qt3DCore
ECS framework; dependency-aware, tasking thread pool; frontend / backend communications
Qt3DRender
3D Rendering framework; Material/Effect/Technique subsystem; Frame Graph (renderer configuration)
Qt3DInput
Basic Mouse and Keyboard input; Advanced input device mapping
Qt3DLogic
Execute code per-frame

24. What does Qt 3D Provide in Qt 5.7?
Qt3DExtras
Higher level helpers: Materials, Standard geometric shapes, Window integrations
Scene3D
Custom Qt Quick 2 Item to composite Qt 3D content with Qt Quick 2D UI

25. Hello Donut Example (C++)
Good practice having Qt3DCore::QEntity to represent the scene
One Qt3DCore::QEntity per “object” in the scene
Objects given behaviour by attaching Qt3DCore::QComponent subclasses
For an Qt3DCore::QEntity to be drawn it needs:
A mesh geometry describing its shape
A material describing its surface appearance

26. Hello Donut Example (QML)
Good practice having Entity to represent the scene
One Entity per “object” in the scene
Objects given behaviour by attaching component subclasses
For an Entity to be drawn it needs:
A mesh geometry describing its shape
A material describing its surface appearance

27. C++ vs QML API
QML API is a mirror of the C++ API
C++ class names like rest of Qt
Qt 3D uses namespaces to avoid collisions
QML element names don’t have Q prefix
Qt3DCore::QNode vs Node
Qt3DCore::QEntity vs Entity

28. Qt 3D Simulation
Simulation executed by Qt3DCore::QAspectEngine
Qt3DCore::QAbstractAspect subclass instances registered with the engine
Behaviour comes from aspects processing component data
Aspects represent a domain of the simulation
Qt 3D provides (so far):
Qt3DRender::QRenderAspect
Qt3DInput::QInputAspect
Qt3DLogic::QLogicAspect
Aspects have no API of their own – all on components

29. Drawing with Qt 3D: Transforms
Scene graph provides spatial representation of the simulation
Qt3DCore::QEntity: simulated object
Qt3DCore::QTransform: where it is, the scale it has, the orientation it has
Hierarchical transforms are controlled by the parent/child relationship
Analogous to QWidget, QQuickItem, QGraphicsItem etc.
To render a 3D scene we need a point of view on it:
Provided by Qt3DRender::QCamera

30. Drawing with Qt 3D: Geometries
Render aspect draws entities with a shape
Qt3DRender::QGeometryRenderer’s geometry property specifies the shape
Qt 3D provides convenience subclasses of Qt3DRender::QGeometryRenderer:
Qt3DExtras::QSphereMesh
Qt3DExtras::QCuboidMesh
Qt3DExtras::QPlaneMesh
Qt3DExtras::QTorusMesh
Qt3DExtras::QConeMesh
Qt3DExtras::QCylinderMesh
Qt3DRender::QMesh loads from file
Easy to provide your own geometries

31. Drawing with Qt 3D: Materials
With only a geometry, an entity will appear black
The Qt3DRender::Qmaterial component provides a surface appearance
Qt 3D provides convenience subclasses:
Qt3DExtras::QPhongMaterial
Qt3DExtras::QPhongAlphaMaterial
Qt3DExtras::QDiffuseMapMaterial
Qt3DExtras::QGoochMaterial …
Easy to provide your own materials

32. Drawing with Qt 3D: Textures
Many materials vary across the surface
Handled using textures
A collection of one or more images
Subclasses of Qt3DRender::QAbstractTexture provide various types of texture:
1D – useful for lookup functions
2D – most common type
3D – typically volumetric data
Arrays of 2D…
Qt3DRender::QTextureLoader supports all texture types loaded from DDS files.

33. Drawing with Qt 3D: Lights
The built-in materials work with lights
Provided by subclasses of Qt3DRender::QAbstractLight component
Point light
Directional light
Spotlight
Lights do not get rendered, we only see their effect on other entities

34. Handling Input
Input Events
Subclasses of Qt3DInput::QAbstractPhysicalDevice represent devices
Qt3DInput::QKeyboardDevice, Qt3DInput::QMouseDevice
Basic Input
Qt3DInput::QKeyboardHandler component – supports focus
Qt3DInput::QMouseHandler component
Advanced Input
Qt3DInput::QLogicalDevice
Maps physical devices
Supports collections of actions and analog axis values
Qt3DRender::ObjectPicker component provides high level picking

35. Controlling the Renderer
Why do we need to control the renderer?
There is no one ideal algorithm for all types of application
Such control usually means writing low level C++ code
Qt 3D provides a concept called the frame graph:
Tree structure describing rendering algorithm
Several node types for selecting the camera, render target, layers of entities, viewport dimensions, render state, material etc.
Data-driven – can be changed dynamically at run time
No low level C++ required
Flexible enough to describe almost any rendering algorithm
Still high performance
Big topic warranting its own presentation!

36. Integrating Qt 3D with Qt Quick
How to composite Qt 3D and Qt Quick 2:
Provide your Qt Quick 2 scene
Provide your Qt 3D scene
Wrap your Qt 3D scene in a Scene3D custom Qt Quick 2 item
That’s it... Almost
Control focus
Which aspects are registered
Antialiasing …

37. The Future of Qt 3D
Qt 3D Core
Efficiency improvements
Backend thread pool and job improvement – recursive jobs
Qt 3D Render
Use Qt Quick or QPainter to render into a texture
Level of detail (LOD) support for meshes
Billboards – camera facing entities
Text support – 2D and 3D
Additional materials – Physics Based Rendering (PBR Materials)
Particle systems
Asset conditioning

38. The Future of Qt 3D
Qt 3D Input
Additional device types
Enumerated inputs – 8 way hat switches or dials
Higher level axis types – calculate position, velocity, acceleration
New aspects:
Collision detection aspect
Animation aspect
Physics aspect
Geometry processor aspect
AI, 3D positional audio, …

39. The Future of Qt 3D: Tooling
Scene Editor

40. The Future of Qt 3D: Tooling
Qt 3D Profiler / debugger

41. The Future of Qt 3D: Tooling
Introspection in GammaRay –

42. More information
Qt documentation
Mailing lists:
IRC: #qt-3d on freenode
Conferences:
Qt World Summit
QtCon
Professional support / consulting
KDAB Qt 3D training course coming soon…

43. Thank you for listening!
Any Questions?
Thank you for listening!