Migrating from Photon to Qt
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The document discusses the migration from the QNX Photon microgui to the Qt framework, providing an overview of both systems and their architectures. It compares the functionality of widgets, signals, and event-driven applications in both environments, highlighting the advantages of Qt's modern capabilities. Additionally, it covers considerations for porting and the need for modern development practices, including object-oriented design.
Migrating from Photon to Qt
- 1. © Integrated Computer Solutions, Inc. All Rights Reserved Migrating from QNX Photon to Qt Bobby Chawla <bchawla@ics.com> 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?