Migrating from Photon to Qt
- 1. © Integrated Computer Solutions, Inc. All Rights Reserved Migrating from QNX Photon to Qt Bobby Chawla <[email protected]> Integrated Computer Solutions, Inc.
- 2. © Integrated Computer Solutions, Inc. All Rights Reserved Introduction ● Working with ICS for about four years now ● Taste for real-time software development ● Used to work with Process Control Systems for industry: ○ Pulp & Paper machines ○ Lots of QNX development ● Offered to work on QNX itself ● About five years developing various parts of Photon
- 3. © Integrated Computer Solutions, Inc. All Rights Reserved Agenda ● Introduction ● What is (was) Photon? ● What is Qt? ● Anatomy of an application ● Architecture differences ● Qt Signals and slots ● Widget comparisons ● When to port ● Porting from QNX ● Conclusion
- 4. © Integrated Computer Solutions, Inc. All Rights Reserved What is (was) Photon? ● Photon : A name with multiple meanings: ○ Light particle ○ QNX/Photon MicroGUI ■ typically used with Neutrino ○ Photon UI project (Javascript framework to create UIs) ○ Photon OS distribution … Probably More … .
- 5. © Integrated Computer Solutions, Inc. All Rights Reserved What is (was) Photon? ● Photon : A name with multiple meanings: ○ Light particle ○ QNX/Photon MicroGUI ■ typically used with Neutrino ○ Photon UI project (Javascript framework to create UIs) ○ Photon OS distribution We are talking about the QNX/Photon MicroGUI .
- 6. © Integrated Computer Solutions, Inc. All Rights Reserved What is (was) Photon… cont. ● Started in the Mid-90s ● Had a Windows 95 look and feel: ○ “modern” at the time ● Evolved with more GUI options
- 7. © Integrated Computer Solutions, Inc. All Rights Reserved What is(was) Photon… cont. ● Deprecated Could say Depreciated - Appropriate verb ● QNX v6.32 - Full implementation ● QNX v6.4 - Reduced widget set: ○ Removed browser & email applications ○ Removed PtTerminal ■ though PtTty was still there ● QNX v6.5 - Essentially the windowing system was still there: ○ But not designed to be a desktop OS ● QNX v6.6 - Unsupported: ○ But die-hards could import the 6.5 executables ● QNX v7 - Unavailable - Now it’s deprecated
- 8. © Integrated Computer Solutions, Inc. All Rights Reserved What is Qt? ● Cross-platform application framework ● Supports all major desktop, mobile, embedded platforms ○ Windows, Mac OS, Linux, iOS, Android, QNX, etc. ● Written in C++ ● Not just for GUI, but includes portable abstraction for most OS features ○ File i/o, strings, containers, networking, etc. ● Around since 1991 ● Used by approximately 1 million developers in over 70 industries ● Owned by The Qt Company ● Available under GPL/LGPL and commercial licenses
- 9. © Integrated Computer Solutions, Inc. All Rights Reserved What is Qt? - Qt Widgets ● Traditional building blocks for GUI applications in Qt: ○ e.g. QButton, QLabel, QTextEdit ● Can use Qt Designer - a GUI builder for designing dialogs and screens ● Have native look on each platform ● Originally designed for desktop applications, but also usable on mobile and embedded.
- 10. © Integrated Computer Solutions, Inc. All Rights Reserved What is Qt? - QML (aka Qt Quick) ● Simple JSON-like declarative language ● Provides basic elements to build up user interfaces ● Elements support properties, signals, methods ● Makes it easy to define animated, fluid, touchscreen interfaces ● Qt Quick Controls provide widget-like UI elements ● Backed by full JavaScript engine ● Qt Creator IDE has a QML Designer ○ developers typically write code by hand (QML Designer getting better) ● Mostly targeted at mobile and embedded ○ but also supported on desktop platforms
- 11. © Integrated Computer Solutions, Inc. All Rights Reserved What is Qt? - Qt on QNX ● Qt has been available as an option for QNX development since 2010 ● Qt widgets provide similar classes and mechanisms to Photon’s ● Typically find source code to Qt, configure for QNX, and compile ● Given the current customer base of QNX-7 - QNX is encouraging QML: ○ Partially configured for QML already in Momentics ○ Since this presentation is about porting from Photon, ■ we will focus on Qt widgets
- 12. © Integrated Computer Solutions, Inc. All Rights Reserved Anatomy of an Application ● At a high level, both Photon & Qt GUI applications are: ○ Event driven ○ Similar parent/child relationships ■ parent window ■ every widget has a parent which helps keep things organized ● e.g. when the parent gets deleted, the child cleans up as well ■ dialogs - children of parent’s windows ○ Interactions ■ Photon uses callbacks vs. Qt using “signals and slots” ○ Qt separates widgets from layout managers
- 13. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences ● Photon (conceptually) is an entire graphical system: ○ Though not as well documented, just as easy to create an app that captures Photon events, thus being able to create your own: ■ graphics driver ■ mouse controller ■ screen capture app ■ virtual keyboard ■ other IO device
- 14. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences… cont. ● Those of you familiar with Photon will know about: ○ Pg….() functions - Raw graphics functions ○ Ph….() functions - Open Photon channels, create regions, collect/emit events ○ Pt….() functions - Create, Manipulate & Destroy widgets ● Qt: ○ Qt widget classes map mostly to Pt….() functions ○ Mature ecosystem of other classes for portability & convenience ■ e.g. stacks, accessing filesystem, strings
- 15. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences… cont. ● Typically Qt is run in a third-party’s windowing environment: ○ Qt has backends for different graphics rendering environments ■ X11/xcb, OpenGL/ES, Linux frame buffer, etc. ■ look & feel designed to look native on the device ● same application looks/behaves slightly differently on a Mac than on Linux or Windows ○ If working with a specialized board ■ need to speak with the hardware (BSP) vendor to interface with new devices
- 16. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences… cont. Application development: PhAB , Qt Designer (GUI builder) & Qt Creator (IDE).
- 17. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences… cont. ● Photon uses “PhAB”, ● Can compile/link in PhAB ● PhAB - not your average application builder: ○ No source code created for PhAB windows/dialog ○ GUI component info written as binary data as part of the executable
- 18. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences… cont. ● Qt Creator (and Designer) is not your average application builder either: ○ Full development suite ○ Architecture-safe classes ○ PhAB/Photon users will appreciate how easily tasks get done (e.g. menus)
- 19. © Integrated Computer Solutions, Inc. All Rights Reserved Architecture Differences… menus
- 20. © Integrated Computer Solutions, Inc. All Rights Reserved Qt Signals & Slots ● Another term that can have different meanings: “Signals”: ○ QNX developers associate “Signals” as an operating system message ■ Signal can be passed from one process to another ■ Interrupts the receiving process, and process the signal ■ The call does not block the calling process ● Qt “Signals” are not the same as Linux/POSIX signals above: ○ Qt Signals & Slots are a one-to-many messaging system that lets Qt “Objects” communicate within a process ○ Could be blocking function call, or could be queued ○ No “return” values from a signal ● Which differ from Boost Signals/Slots - allow return values from the “slots”
- 21. © Integrated Computer Solutions, Inc. All Rights Reserved Qt Signals & Slots… cont. ● Qt signals are an expanded form of callbacks that allow separation of UI elements from business logic ● Signals are emitted by Qt objects when event occurs (e.g. button pressed) ● Slots are methods that can be called in response to a signal ● Typically connect signals and slots at run-time ● Qt uses “moc” tool to generate meta object information about signals/slots ● Type safe alternative to callbacks, checked at compile time or run time
- 22. © Integrated Computer Solutions, Inc. All Rights Reserved Widget Comparison - Menus and Options Functionality Photon Qt Major Differences Horizontal Menubar PtMenuBar QMenuBar QMenuBar has several insert Item methods. Pulldown Popup Menu PtMenu QMenu Qt provides a cleaner abstraction using QMenu. The common object for pulldowns popups, and menubars Menu button PtMenuButton QMenu Combo Box PtComboBox QComboBox Toggle or Multiple-selection options PtToggleButton (Pt_TOGGLE_RADIO) QRadioButton or QCheckBox
- 23. © Integrated Computer Solutions, Inc. All Rights Reserved Widget Comparison - Dialogs Functionality Photon Qt Error PtAlert() QErrorMessage Information PtNotice() QMessageBox Question PtAlert() QMessageBox Warning PtAlert() QMessageBox Progress PtProgress widget QProgressDialog Simple Input PtPrompt() QInputDialog File Chooser PtFileSelection() QFileDialog HTML/Web display PtWebClient widget QWebView Generic/Custom PtWindow container QDialog ● Italicized Photon items (such as PtAlert()) are convenience functions which use widgets to build a dialog
- 24. © Integrated Computer Solutions, Inc. All Rights Reserved Widget Comparison… cont. ● Examples of widgets that are not 1 to 1 relationships: ○ PtTimer ○ RtTrend ● Qt has a large user base with many contributors: ○ Many sophisticated Qt widgets that don't exist in Photon are available from 3rd party vendors
- 25. © Integrated Computer Solutions, Inc. All Rights Reserved Widget Comparison - Containers vs. Layouts ● PtContainer (or it’s subclasses) allow the automatic placement of widgets in a: ○ FILL_LAYOUT (Horizontal / Vertical) ○ ROW_LAYOUT (Horizontal/Vertical with options for Justify, Wrap and Pack) ○ GRID_LAYOUT ○ ANCHOR_LAYOUT ● In Qt, layouts are more sophisticated: ○ Layouts are separated from any widget subclassed off of QWidget ○ Container widgets can manage their children using QWidget::setLayout()
- 26. © Integrated Computer Solutions, Inc. All Rights Reserved When to Port / When to Consider Rewrite ● Photon is deprecated / newer hardware not supported ○ Eventually will run out of hardware options ○ Or user expectations for a device increase ● What code can you typically keep and what do you need to rewrite? ● Design aspects that makes it easier to port, e. g. ○ Good separation of UI and business logic. ○ Much of your application can be dissected into Model-View-Controller (MVC) portions
- 27. © Integrated Computer Solutions, Inc. All Rights Reserved Object Oriented Design 101 ● Qt is based off C++: ○ Photon apps are usually ‘C’ based ○ Need to port some or all of your code to C++. ○ Your team may need to learn object-oriented design. ○ May require re-architecting (e.g. to separate GUI from business logic). ● C++ applications typically better at compartmentalizing, ○ Scale better for larger projects
- 28. © Integrated Computer Solutions, Inc. All Rights Reserved Object Oriented Design “101”
- 29. © Integrated Computer Solutions, Inc. All Rights Reserved Object Oriented Design 101… cont. ● Created the same application in Photon & Qt ● In Photon had a functional relation PtText → callback → PtSetArg( PtLabel ) ● Can do a similar connection with Qt: ○ QLineEdit → signal to QObject::AddHello → signal to QLabel ● However, a cleaner implementation is to create a ‘Hello’ widget: ○ Create a QHelloLabel as a subclass of QLabel, ○ QHelloLabel displays the string with ‘Hello’ prepended ○ QLineEdit → signal to QHelloLabel Less code, less portions that can break, easier to test, ….
- 30. © Integrated Computer Solutions, Inc. All Rights Reserved Porting from QNX Note for native QNX-ers ● QNX has been, and continues to be a “Message passing” architecture: ○ Lightweight transition from one process to another ○ Designed for many thousands (millions) of messages ○ Many aspects of QNX based on message passing ○ Photon is no exception ● If porting to other operating systems: ○ Can’t rely as heavily on OS-level message passing ○ Buffered streams more common ○ QNX is a POSIX OS, therefore a port to Linux should be easier
- 31. © Integrated Computer Solutions, Inc. All Rights Reserved Conclusion ● Most applications would have one to one mapping to Qt widgets ● Need help getting started? ICS developers: ○ Have many years of experience with Qt and QNX/Photon ○ Can assist you with the port (while your developers continue advancing with current development) ○ Can help you get started by analyzing your application and coming up with a plan of action
- 32. © Integrated Computer Solutions, Inc. All Rights Reserved Questions?