Sunday, 15 June 2025
This is the release schedule the release team agreed on
https://community.kde.org/Schedules/KDE_Gear_25.08_Schedule
Dependency freeze is in around 2 weeks (July 3) and feature freeze one
after that. Get your stuff ready!
This is the release schedule the release team agreed on
https://community.kde.org/Schedules/KDE_Gear_25.08_Schedule
Dependency freeze is in around 2 weeks (July 3) and feature freeze one
after that. Get your stuff ready!
🎉 New Clazy Release: Stability Boost & New Checks!
We’re excited to roll out a new Clazy release packed with bug fixes, a new check, and improvements to existing checks. This release included 34 commits from 5 contributors.
New Check: readlock-detaching
Detects unsafe and likely unwanted detachment of member-containers while holding a read lock.
For example, when calling .first()
on the mutable member instead of .constFirst()
Expanded Support for Detaching Checks
Additional methods now covered when checking for detaching temporary or member lists/maps.
This includes reverse iterators on many Qt containers and keyValueBegin
/keyValueEnd
on QMap.
All those methods have const
counterparts that allow you to avoid detaching.
Internal Changes With this release, Clang 19 or later is a required dependency. All older versions needed compatibility logic and were not thouroughly tested on CI. In case you are on an older Version of a Debian based distro, consider using https://apt.llvm.org/ and compile Clazy from source ;)
install-event-filter
: Fixed crash when no child exists at the given depth.
BUG: 464372
fully-qualified-moc-types
: Now properly evaluates enum
and enum class
types.
BUG: 423780
qstring-comparison-to-implicit-char
: Fixed and edgecase where assumptions about function definition were fragile.
BUG: 502458
fully-qualified-moc-types
: Now evaluates complex signal expressions like std::bitset<int(8)>
without crashing.
#28
qvariant-template-instantiation
: Crash fixed for certain template patterns when using pointer types.
Also, thanks to Christoph Grüninger, Johnny Jazeix, Marcel Schneider and Andrey Rodionov for contributing to this release!
I had mentioned a number of new Transitous features in a previous post. As those largely depend on the corresponding data being available, here’s an overview of how you can help to find, add and improve that data.
Transitous is a community-run public transport routing service build on top of the MOTIS routing engine and thousands of datasets from all over the world. Transitous backs public transport related features in applications like GNOME Maps, KDE Itinerary or Träwelling.
Just like OpenStreetMap this needs people on the ground identifying issues or gaps in the data, figuring out where things go wrong and who to talk to at the local operators to get things fixed.
The first step to help is just comparing data you get from Transitous with the reality around you, ie. does the public transport schedule match what’s actually happening, and are all relevant services included?
If there’s things missing or outdated, a list of the types of datasets consumed by Transitous, and how to inspect and add those, follows below.
The central part in this are a bunch of JSON files in the Transitous Git repository, which define all the datasets to be used as well as a few parameters and metadata for those. Once a day those are then retrieved, validated, filtered and post-processed for importing into MOTIS by Transitous’ import pipeline.
The backbone of public transport routing is static GTFS schedule data, that’s the bare minimum for Transitous to work in a region. GTFS feeds are essentially zip files containing a set of CSV tables, making them relatively easy to inspect, although especially nationwide aggregated feeds can get rather large.
GTFS feeds ideally contain data for several months into the future, but can nevertheless receive regular updates. Transitous checks for updates daily, so for this to work practically we also need a stable URL for them (that might seem obvious to you, but apparently not to all feed providers…).
We currently have more than 1800 of those, from 55 countries. The Transitous map view gives you an impression how well an area is covered, each of the colored markers there is an (estimated) current position of a public transport vehicle.
If your area is incomplete or not covered at all, the hardest part to change that is probably finding the corresponding GTFS feeds. There’s a few places worth looking at:
Adding a GTFS feed to Transitous is then usually just a matter of a few lines of JSON pointing to the feed. In rare cases it might require a bit more automation work, such as in France where there’s hundreds of small feeds to manage.
And every feed is welcome, no matter whether it’s a nation-wide railway operator or a single community-run bus to help people in a rural area, as long as it’s for a service open to the general public.
So far this is all static though. For properly dealing with delay, disruptions and all kinds of other unplanned and short-notice service changes we also need GTFS Realtime (RT) feeds. Those are polled once a minute for updates.
GTFS-RT feeds come in three different flavors:
MOTIS can handle the first two so far. Support for vehicle positions is also on the wishlist, and not just for showing current positions on a map, vehicle positions could also be used to interpolate trip updates when those are not available.
Adding GTFS-RT feeds to Transitous is very similar to adding static GTFS feeds, however GTFS-RT feeds usually only work in combination with their respective static equivalent. Combining a smaller realtime feed of a single operator with a nationwide aggregated static feed will thus usually not work out of the box. There’s ways to exclude certain operators from a larger static feed though, so with a bit of puzzle work this can usually be made to work as well.
GTFS-RT feeds use Protocol Buffers, but there’s nevertheless simple way to look at their content:
curl https://the.feed.url | protoc gtfs-realtime.proto --decode=transit_realtime.FeedMessage | less
The Protocol Buffers schema file needed for this can be downloaded here.
To see the realtime coverage available in Transitous, you can toggle the color coding of vehicles on its map view in the upper right corner. A green/yellow/red gradient shows the amount of delay for the corresponding trip, while gray vehicles have no realtime information.
Transitous doesn’t just handle scheduled public transport though, but also vehicle sharing, which can be particularly interesting for the first and last mile of a trip.
The data for this is provided by GBFS feeds. This includes information about the type of vehicles (bikes, cargo bikes, kickscooters, mopeds, cars, etc) and their method of propulsion (human powered, electric, etc), where to pick them up and where to return them (same location as pickup, designated docks of the provider, free floating within a specific area, etc) and most importantly where vehicles are currently available.
Adding GBFS feeds to Transitous is also just a matter of a few lines of JSON. We currently don’t have a built-in UI to see the results, showing all available vehicles on the map is certainly on the wishlist though. GBFS is relatively easy to inspect manually, the entry point is a small JSON manifest that contains links to JSON files with the actual information, generally split up by how often certain aspects are expected to change.
Same as for GTFS feeds, any service accessible to the general public is welcome here, whether it’s a small community run OpenBike instance or a provider with hundreds of vehicles.
Somewhere between scheduled transport and shared mobility are on-demand services. That is, services that require some form or booking beforehand and might be anything from an on-demand bus that still follows a somewhat fixed route with pre-defined stops to something closer to a taxi with a more flexible route that picks up or drops off passengers anywhere in a given area.
These services are often used in times and/or areas with fewer demand, thus making them often the only mobility option then/there. That makes it all the more important to have those covered as well.
Modeling on-demand services is challenging, given the variety on how those services work and their inherently very dynamic nature. There’s the relatively new GTFS-Flex standard covering this, which MOTIS supports since v2.0.66.
GTFS-Flex feeds might be included in static GTFS data or provided separately, and adding them to Transitous works again by just a few lines of JSON.
There’s one caveat though, the validator we use in pre-processing, gtfsclean, doesn’t support GTFS-Flex yet, so those feeds are currently imported without any sanity checking or validation. Therefore we need to be extra careful with adding such feeds until that is fixed. If you know a bit of Go and want to help with that, get in touch!
For GTFS-Flex data there’s some diagnostic visualization in the map view in debug mode, when zooming in far enough.
A crucial dataset for all road-based and in-building routing is OpenStreetMap. While that is generally very comprehensive and up-to-date, there’s one aspect that more often needs fixes, the floor level separation. That’s not visible in most OSM-based maps and thus is easy to miss while mapping. For Transitous this is particularly important for in-building routing in train stations.
When zoomed in enough the map view of Transitous will offer you a floor level selector at the lower right. That can give you a first indication if elements are misplaced (showing up on the wrong level) or not assigned to a floor level at all (showing up on all levels). For reviewing smaller elements indoor= can also be useful, and for fixing things JOSM has a built-in level selector on the top left.
In most cases adding or fixing the level tag is all that’s needed. Elements allowing to move between levels (stairs, ramps, elevators, escalators, etc) are especially important for routing.
All of the above is just the current state, there’s much more to look at though, such as:
In other words, plenty of rabbit holes to explore, no matter whether you are into code, data, math, trains, busses, IT operations or lobby work :)
Check around you whether information from Transitous matches the reality on the ground, join the Transitous Matrix channel, join the Transitous Hack Weekend in a few weeks and join the Open Transport Community Conference in October!
Welcome to a new issue of This Week in Plasma! Every week we cover the highlights of what’s happening in the world of KDE Plasma and its associated apps like Discover, System Monitor, and more.
This week we finished polishing up Plasma 6.4 for release, and started to turn our heads to bigger topics — notably including Wayland protocols and accessibility!
Implemented support for an experimental version of the Wayland picture-in-picture protocol that allows apps also implementing it (such as Firefox) to finally display proper PiP windows in advance of the upstream version of the protocol eventually being merged. (Vlad Zahorodnii, link)
Reduced the rate at which the “visual bell” accessibility feature can flash the screen so there’s no way it can cause seizures. (Nicolas Fella, link)
Made the Kicker Application Menu widget able to horizontally scroll for searches that return results from many KRunner plugins, so you have the opportunity to see them all. (Christoph Wolk, link)
Improved text contrast for labels used in subtitles or other secondary roles throughout Plasma. (Nate Graham, link 1, link 2, link 3, link 4, link 5, link 6, and link 7)
Discover’s search field now trims all whitespace, to prevent errors when copy-pasting text that ends in a space or something. (Nate Graham, link)
In System Settings, moved the Invert and Zoom settings into the Accessibility page, which is a more sensible place for them than the Desktop Effects page was. (Oliver Beard, link 1, link 2, and link 3)
Merged KWin’s Background Contrast effect into the Blur effect, since neither makes to turn on or off without the other. (Marco Martin, link 1 and link 2)
On Wayland, virtual desktops can now be re-ordered from the Pager widget, and re-ordering them in the Overview effect’s grid view now re-orders them in the Pager widget too. (Marco Martin and Vlad Zahorodnii, link 1, link 2, and link 3)
Spectacle now makes it clearer that you can end a screen recording by pressing the same keyboard shortcut you used to start it, by telling you this in the notification and also by using clearer names for the global shortcuts. (Noah Davis, link)
The Breeze application style’s animated effects for clicking checkboxes and radio buttons now work in QtQuick-based apps and System Settings pages as well. (Kai Uwe Broulik, link)
The Disks & Devices, Networks, and Bluetooth widgets now use standard-style section headers. (Nate Graham, link 1, link 2, and link 3)
Improved the searching UX in the Emoji Selector app: now the search field is always visible, and doing a search will always search through the full set of all emojis if there aren’t any matches on the current page. (Nate Graham, link 1, link 2)
The Display Configuration widget and OSD no longer thinks your primary screen is always connected to a laptop; now it uses more generic terminology. (Nate Graham, link)
Using a non-default font or font size no longer causes the selection rectangles for files or folders on the desktop to be displayed at the wrong size and cause subtle layout and positioning glitches. (Nate Graham, link)
Fixed several more cases where putting a widget on a huge panel could cause Plasma to freeze. (Christoph Wolk, link 1, link 2, link 3, link 4, link 5, link 6, and link 7)
Fixed a case where Discover could crash while offering you the replacement for an end-of-support Flatpak app. (Akseli Lahtinen, link)
Fixed a bug that caused the Open/Save dialogs invoked from Flatpak-based browsers (or when forcing the use of portal-based dialogs) to sometimes not allow the preview pane to be opened. (David Redondo, link)
Fixed a weird bug that could cause a standalone Folder View widget on the desktop to become visually glitchy when you drag files or folders to it from Dolphin. (Akseli Lahtinen, link)
Fixed a bug that broke printing at the correct sizes in Flatpak-packaged GTK apps. (David Redondo, link)
Installing or uninstalling an app no longer unexpectedly clears the search field and results view in Kicker or Kickoff if they happened to be visible at the moment the transaction completed. (Christoph Wolk, link)
Fixed a cause of crashes in apps and Plasma system services using System Monitor charts. (Arjen Hiemstra, link)
Fixed an intermittent source of crashes in System Monitor when switching process views. (Arjen Hiemstra, link)
Fixed a weird issue that could cause Open/ Save dialogs to close when hovering over certain files. (David Redondo, link)
Fixed an issue that could cause the thumbnailer to crash on X11 when using certain widget styles. (Nicolas Fella, link)
Improved startup speed for System Monitor by loading the column configuration dialog’s content on-demand, rather than at launch. (David Edmundson, link)
Made sure that the Environment Canada data source for weather reports keeps working, since the provider is changing their data format soon and we needed to adapt. (Ismael Asensio, link)
Improved startup speed for System Monitor by loading the tree view indicator arrows on demand, rather than at launch. (David Edmundson, link)
KDE has become important in the world, and your time and contributions have helped us get there. As we grow, we need your support to keep KDE sustainable.
You can help KDE by becoming an active community member and getting involved somehow. Each contributor makes a huge difference in KDE — you are not a number or a cog in a machine!
You don’t have to be a programmer, either. Many other opportunities exist:
You can also help us by making a donation! Any monetary contribution — however small — will help us cover operational costs, salaries, travel expenses for contributors, and in general just keep KDE bringing Free Software to the world.
To get a new Plasma feature or a bugfix mentioned here, feel free to push a commit to the relevant merge request on invent.kde.org.
Let’s go for my web review for the week 2025-24.
Tags: tech, web, google, search, monopoly, economics
There’s clearly something tempting about a web index somehow separated from Google. It always felt like a natural monopoly and so a type of public service. Now that push arrives a tad late so the impacts are unclear. Overall I still think this would be a net positive if there are more web search companies built onto such an index.
https://arstechnica.com/google/2025/06/googles-nightmare-how-a-search-spin-off-could-remake-the-web/
Tags: tech, dns, privacy
Early days for that service. Let’s hope it improves infrastructure wise.
https://techlog.jenslink.net/posts/dns4eu/
Tags: tech, ai, machine-learning, gpt, copilot, programming, cognition, scam, criticism
An excellent piece which explains well why the current “debate” is rotten to the core. There’s no good way to engage with those tools without reinforcing some biases. Once the hype cycle is over we have a chance at proper research on the impacts… unfortunately it’s not happening now when it’s badly needed.
https://www.baldurbjarnason.com/2025/trusting-your-own-judgement-on-ai/
Tags: tech, ai, machine-learning, gpt, copilot, programming, cognition, scam, criticism
A nice followup which acts as a TL;DR for the previous piece which was fairly long indeed.
https://www.baldurbjarnason.com/2025/followup-on-trusting-your-own-judgement/
Tags: tech, ai, machine-learning, gpt, copilot, security
OK, this is definitely concerning for the use of tools with so called coding agents. The trust model is really not appropriate at this stage and that opens the door to a wide range of attacks.
Tags: tech, gitlab, git, complexity, profiling, optimization
Nice simple fix in Git but with a large impact on backups. A good proof that profiling and keeping an eye on algorithmic complexity can go a long way in improving software.
Tags: tech, unix, system, sandbox
Interesting paper about the use of sandboxing in several ecosystems. It’s not used much directly but there are clear differences in term of complexity to set them up.
https://arxiv.org/abs/2405.06447
Tags: tech, tools, shell
Interesting thinking and trick. We clearly pile up too much noise in our shell history.
https://esham.io/2025/05/shell-history
Tags: tech, shell, scripting
Didn’t know bash got this feature now. I’m torn between “it looks so cool” and “we’ll never see the end of debugging issues which use this”.
https://gist.github.com/izabera/e4717562e20eb6cfb6e05f8019883efb
Tags: tech, unix, system, filesystem
Need to play with file descriptors on Unix systems? This is a fun and gentle introduction.
https://mattrighetti.com/2025/06/04/too-many-files-open
Tags: tech, rust, c, performance
Or why this kind of question never have an absolute answer.
https://steveklabnik.com/writing/is-rust-faster-than-c/
Tags: tech, programming, rust, type-systems, data
Interesting selection of options to model data structure with some variability in Rust.
https://mcmah309.github.io/posts/patterns-for-modeling-overlapping-variant-data-in-rust/
Tags: tech, gpu, memory, performance
The memory models for GPU programming are complex. This isn’t easy to squeeze more performance without introducing subtle bugs.
Tags: tech, multithreading, caching, cpu, rust
A good example of how you can get bitten by cache coherency algorithms in the CPU.
https://www.conviva.com/platform/the-concurrency-trap-how-an-atomic-counter-stalled-a-pipeline/
Tags: tech, programming, ux, design
A long essay but contains a lot of interesting insights. There’s definitely more to do design wise to produce software people can really bend to their needs.
https://www.inkandswitch.com/essay/malleable-software/
Tags: tech, tests, business
This is one way to frame it I guess. Code is indeed an investment, tests are here to protect it.
https://www.yegor256.com/2025/06/08/pull-request-without-test.html
Tags: tech, tdd, tests, design
A good reminder of the reasons why the organization of your tests shouldn’t necessarily match the organization of the application code. You don’t want fragile tests, do you?
https://blog.cleancoder.com/uncle-bob/2017/10/03/TestContravariance.html
Tags: tech, legacy, tests
I’m using the term regularly when dealing with legacy code. Finally remembered when I saw it first.
https://wiki.c2.com/?PinningTests
Tags: tech, failure, safety, distributed
Interesting paper about metastable failures and novel approaches to try to analyse them. It’s early days but we would need to get toward better prevention.
https://muratbuffalo.blogspot.com/2025/06/analyzing-metastable-failures-in.html?m=1
Tags: tech, architecture, design, rust
Of course, don’t take everything at face value here. Still this gives good ideas on how to combine some design and architectural ideas together. The whole thing is not really Rust specific.
https://dpc.pw/posts/how-i-structure-my-apps-in-rust-and-other-languages
Tags: tech, architecture
Nice little post helping advocate for the use of Architectural Decision Records.
https://www.beflagrant.com/blog/adrs
Tags: tech, xp, design
Nice and short explanation on the design rules Kent Beck had in mind when devising XP. It still generally applies in my opinion.
https://martinfowler.com/bliki/BeckDesignRules.html
Tags: tech, quality, technical-debt, project-management
Definitely this, too often I see projects treating the technical debt as one-off large tasks. Really it’s something you should deal with bite sized and over time.
https://software.rajivprab.com/2025/05/10/tech-debt-cant-be-solved-as-a-roadmap-item/
Tags: tech, agile, technical-debt, planning, risk
It will fluctuate with time so it needs to be kept in check. Indeed, some things are commodities so can be decided upfront, but the rest of the functional envelope will change over time. Also make sure you drive the project by risks to have early feedback where it matters most.
https://lizkeogh.com/2012/01/30/the-real-cost-of-change/
Tags: tech, failure, culture, management
Mistakes happen, but shrugging them off with blaming people or pushing them to be more careful is counter-productive. Instead, you want to find the organizational issues which made them possible in the first place.
https://www.etsy.com/codeascraft/blameless-postmortems/
Tags: tech, research, leadership, tech-lead, organization
Not fond of the metaphor used here which leads to quite some noise. Still, this article contains interesting ideas to try to push R&D initiatives forward. Definitely needed to improve any kind of organisation.
Tags: tech, agile, tests, tdd, teaching
This is one of those workshops I like to do with teams from time to time. Didn’t do it for a while. I wish this resource was on a safer space than google docs.
https://docs.google.com/document/d/1TCuuu-8Mm14oxsOnlk8DqfZAA1cvtYu9WGv67Yj_sSk/pub
Tags: management
This kind of articles are always a bit caricatural. Still there is some good advice in there. Keep an eye open for the harmful behaviors.
https://blog.eladgil.com/p/5-people-who-destroy-your-culture
Bye for now!
Learn how to use Cucumber-CPP and Gherkin to implement better black box tests for a C++ library. We developed a case-study based on Qt OPC UA.
Continue reading Improved Black Box Testing with Cucumber-CPP at basysKom GmbH.
Friday, 13 June 2025
KDE today announces the release of KDE Frameworks 6.15.0.
This release is part of a series of planned monthly releases making improvements available to developers in a quick and predictable manner.
fchown()
fails. Commit.One of the largest hurdles in any job or activity is getting your resources set up. Luckily for you, Krita has one of the most detailed and straightforward documentation for setup. In this blog I will go over my experience setting up Krita and provide quick links to answer all the questions you may have during set up.
One Stop Shop for Links
Download and Install Ubuntu
Create KDE account
Fork Krita Repository
Follow build instructions
If you use QTCreator to Build and Run Krita follow this video
Krita Chat - Create account, join chat room, introduce yourself and ask questions
The goal is to get Krita running on your machine. For my setup and for simplicity of instructions, I use Oracle's Virtualbox to run a virtual machine(VM) with Ubuntu on my windows machine. You can use any VM host for set up. The Follow build instructions should be straightforward to follow. The great thing about these instructions is that you don't need to know a lot of detail about docker or C++ yet, but you will need to understand some basic linux and git commands.
In the above links, follow the instruction in the hyperlink title.
When I set up Krita for the first time, I felt a sense of accomplishment. Not only was I able to set up Krita, but I was able to deepen my understanding of git, learn about docker, VMs and QT.
I think the biggest take away from setting up Krita is to never give up, ask questions in chat, ask yourself "What do I not understand?" before moving to the next instruction.
Setting up Krita is as simple as you make it out to be. The hardest part is finding the resources to be successful. I hope this blog post can simplify set up for newcomers and experienced users.
To anyone reading this, please feel free to reach out to me. I’m always open to suggestions and thoughts on how to improve as a developer and as a person.
Email: ross.erosales@gmail.com
Matrix: @rossr:matrix.org
To briefly recap, Natalie Clarius and I applied for an NLnet grant to improve gesture support in Plasma, and they accepted our project proposal. We thought it would be a good idea to meet in person and workshop this topic from morning to evening for three days in a row. Props to Natalie taking the trip from far away in Germany to my parents' place, where we were kindly hosted and deliciously fed.
Our project plan starts with me adding stroke gesture support to KWin in the first place, while Natalie works on making multi-touch gestures customizable. Divvying up the work along these lines allows us to make progress independently without being blocked on each other's work too often. But of course there is quite a bit of overlap, which is why we applied to NLnet together as a single project.
The common thread is that both kinds of gestures can result in similar actions being triggered, for example:
So if we want to avoid duplicating lots of code, we'll want a common way to assign actions to a gesture. We need to know what to store in a config file, how Plasma code will make use of it, and how System Settings can provide a user interface that makes sense to most people. These are the topics we focused on. Time always runs out faster than you'd like, ya gotta make it count.
Getting to results is an iterative process. You start with some ideas for a good user experience (UX) and make your way to the required config data, or you start with config data and make your way to actual code, or you hit a wall and start from the other end going from code to UX until you hit another wall again. Rinse and repeat until you like it well enough to ship it.
On day 1, we:
kcm_keys
.On day 2, we:
On day 3, we:
kglobalshortcutsrc
file instead.What I just wrote is a lie, of course. I needed to break up the long bullet point list into smaller sections. In reality we jumped back and forth across all of these topics in order to reach some sort of conclusion at the end. Fortunately, we make for a pretty good team and managed to answer a good amount of questions together. We even managed to make time for ice cream and owl spottings along the way.
Since you asked for it, here's a picture of Natalie and I drawing multi-touch gestures in the air.
So there are some good ideas, we need to make them real. Since the sprint, I've been trying my hand on more detailed mockups for our rough design sketches. This always raises a few more issues, which we want to tackle before asking for opinions from KWin maintainers and Plasma's design community. There isn't much to share with the community yet, but we'll involve other contributors before too long.
Likewise, my first KWin MR for stroke gesture infrastructure is not quite there yet, but it's getting closer. The first milestone will be to make it possible for someone to provide stroke gesture actions. The second milestone will be for Plasma/KWin to provide stroke gesture actions by itself and offer a nice user interface for it.
Baby steps. Keep chiseling away at it and trust that you'll create something decent eventually. This is not even among the largest efforts in KDE, and yet there are numerous pieces to fit and tasks to tackle. Sometimes I'm frankly in awe of communities like KDE that manage to maintain a massive codebase together, with very little overhead, through sheer dedication and skill. Those donations don't go to waste.
At this point I would also like to apologize to anyone who was looking for reviews or other support from me elsewhere in Plasma (notably, PowerDevil) which I haven't helped with. I get stressed when having to divide my time and focus between different tasks, so I tend to avoid it, in the knowledge that someone or something will be left wanting. I greatly admire people who wear lots of different hats simultaneously, and it would surely be so nice to have the aptitude for that, but it kills me so I have to pick one battle at a time.
Right now, that's gestures. Soon, a little bit of travel. Then gestures again. Once that's done, we'll see what needs work most urgently or importantly.
Take care & till next time!
Developing an application for desktop or embedded platforms often means choosing between Qt Widgets and Qt Quick to develop the UI. There are pros and cons to each. Qt, being the flexible framework that it is, lets you combine these in various ways. How you should integrate these APIs will depend on what you're trying to achieve. In this entry I will show you how to display Qt Widget windows on an application written primarily using Qt Quick.
Qt Quick is great for software that puts emphasis on visual language. A graphics pipeline, based around the Qt Quick Scene Graph, will efficiently render your UI using the GPU. This means UI elements can be drawn, decorated, and animated efficiently as long as you pick the right tools (e.g. Shaders, Animators, and Qt's Shapes API instead of its implementation of HTML's Canvas).
From the Scene Graph also stem some of Quick's weaknesses. UI elements that in other applications would extend outside of the application's window, such as tool tips and the ComboBox control, can only be rendered inside of Qt Quick windows. When you see other app's tooltips and dropdowns extend beyond the window, those items are being rendered onto a separate windows; one without window decorations (a.k.a. borderless windows). Rendering everything on the same window helps ensure your app will be compatible with systems that can only display a single window at a time, such as Android and iOS, but it could result in wasted space if your app targets PC desktop environments.
An animation shows a small window with QML's and Widget's ComboBoxes opening for comparison purposes
QML ComboBox is confined to the Qt Quick window while the Widgets ComboBox extends beyond the window
Qt lets us combine Widgets and Quick in a few ways. The most common approach is to embed a Qt Quick view into your Widgets app, using QQuickWidget. That approach is fitting for applications that primarily use Widgets. Another option is to render Widgets inside a Qt Quick component, by rendering it through a QQuickPaintedItem. However, this component will be limited to the same window confines as the rest of the items in your Quick window and it won't benefit from Scene Graph rendering optimizations, meaning you get the worst of both worlds.
A third solution is to open widget windows from your Qt Quick apps. This has none of the aforementioned drawbacks, however, the approach has a couple of drawback of its own. First, the app would need to be run from a multi-window per screen capable environment. Second, widget windows are not parentable to Qt Quick windows; meaning certain window z-stack related features, such as setting window modality to Qt::WindowModal, won't have effect on the triggering window when a Widget is opened from Qt Quick. You can work around that by setting modality to Qt::ApplicationModal instead, if you're okay with blocking all other windows for modality.
Displaying Widget windows in Qt Quick applications has been useful to me in the past, and is something I haven't seen documented anywhere, hence this tutorial.
Displaying a Qt Widget window from Qt Quick is simpler than it seems. You'll need two classes:
You might be tempted to forgo the interface class and instantiate the widget directly. However, this would result in a crash. We'll display the widget window by running Widget::show
from the interface class.
CMakeLists.txt
In addition to those classes, you'll also need to make sure that your app links to both Qt::Quick
and Qt::Widgets
libraries. Here's what that looks like for a CMake project
// Locate libraries
find_package(Qt6 6.5 REQUIRED COMPONENTS
Quick
Widgets)
// Link build target to libraries
target_link_libraries(${TARGET_NAME} PRIVATE
Qt6::Quick
Qt6::Widgets)
// Replace ${TARGET_NAME} with the name of your target executable
main.cpp
In addition to that, in main.cpp
you'll need to use QApplication in place of QGuiApplication.
QApplication app(argc, argv);
Prepare the interface layer as you would any C++ based Quick component. By this I mean: derive from QObject
, and use the Q_OBJECT
and QML_ELEMENT
macros to make your class available from QML.
// widgetFormHandler.h
#pragma once
class WidgetFormHandler : public QObject
{
Q_OBJECT
QML_ELEMENT
public:
explicit WidgetFormHandler(QObject *parent = nullptr);
};
// widgetFormHandler.cpp
WidgetFormHandler::WidgetFormHandler(QObject *parent)
: QObject(parent)
{
}
// widgetFormHandler.h
#pragma once
class WidgetsForm;
class WidgetFormHandler : public QObject
{
Q_OBJECT
QML_ELEMENT
public:
explicit WidgetFormHandler(QObject *parent = nullptr);
~WidgetFormHandler();
private:
std::unique_ptr<WidgetsForm> m_window;
}
Use std::make_unique
in the constructor to initialize the unique pointer to m_window.
Define the instantiating class' destructor to ensure the pointers are de-alocated, thus preventing memory leaks. If you stick to using smart pointers, C++ will do all the work for you; simply use the default destructor, like I do here. Make sure to define it outside of the class' header; some compilers have trouble dealing with the destructor when it's defined inside the header.
// widgetFormHandler.cpp
#include "widgetFormHandler.h"
WidgetFormHandler::WidgetFormHandler(QObject *parent)
: QObject(parent)
, m_window(std::make_unique<WidgetsForm>())
{
// ...
}
WidgetFormHandler::~WidgetFormHandler() = default;
Now we want to make properties from the widget available in QML. How we do this will depend on the property and on whether we will manipulate the property's value from both directions or only from one side only and update on the other.
Let's look at a bi-directional example in which we add the ability to control the visible state of the widget window from QML. We'll add a property called "visible" to the C++ interface so that it matches the visible that we get from Qt Quick windows in QML. Declare the property using Q_PROPERTY
. Use READ and WRITE functions to control the window's state.
Here's what that would look like:
// widgetFormHandler.h
#pragma once
class WidgetsForm;
class WidgetFormHandler : public QObject
{
Q_OBJECT
QML_ELEMENT
Q_PROPERTY(bool visible READ isVisible WRITE setVisible NOTIFY visibleChanged)
public:
explicit WidgetFormHandler(QObject *parent = nullptr);
~WidgetFormHandler();
const bool isVisible();
void setVisible(bool);
signals:
void visibleChanged();
private:
std::unique_ptr<WidgetsForm> m_window;
};
// widgetFormHandler.cpp
#include "widgetFormHandler.h"
#include "widgetForm.h"
WidgetFormHandler::WidgetFormHandler(QObject *parent)
: QObject(parent)
, m_window(std::make_unique<WidgetsForm>())
{
// Hide window by default
m_window->setVisible(false);
}
WidgetFormHandler::~WidgetFormHandler() = default;
const bool WidgetFormHandler::isVisible()
{
return m_window->isVisible();
}
void WidgetFormHandler::setVisible(bool visible)
{
m_window->setVisible(visible);
emit visibleChanged();
}
To make this bi-directional, set NOTIFY to a signal that allows the property to be updated in QML after it being emitted and emit the signal where applicable. We emit it from setVisible in this class, however if QWidget
had a signal that emitted when its visible state changed, I would also make a connection between that signal and that of our handler’s visibleChanged
. However, that isn’t the case, so we have to make sure to emit it ourselves.
Develop the widget window as you would any other widget. If you use UI forms, go to the header file and create a signal for each action that you wish to relay over to QML.
In this example we'll relay a button press from the UI file, so we'll create a button named pushButton in our ui file:
Qt Designer shows UI file with a button named pushButton, in camel case.
Now add a buttonClicked
signal to our header:
// widgetsForm.h
#pragma once
#include <QWidget>
namespace Ui
{
class WidgetsForm;
}
class WidgetsForm : public QWidget
{
Q_OBJECT
public:
explicit WidgetsForm(QWidget *parent = nullptr);
~WidgetsForm();
signals:
void buttonClicked();
// Signal to expose button click from Widgets window
private:
std::unique_ptr<Ui::WidgetsForm> ui;
};
Once again, we use a unique pointer, this time to hold the ui object. This is better than what Qt Creator templates give us because it means C++ handles the memory management for us and we can avoid the need for a delete statement in the destructor.
In the window's constructor, we make a connection between the UI's button's signal and the one that we've created to relay the signal for exposure.
// widgetsForm.cpp
#include "widgetsform.h"
#include "ui_widgetsform.h"
WidgetsForm::WidgetsForm(QWidget *parent)
: QWidget(parent)
, ui(std::make_unique<Ui::WidgetsForm>())
{
ui->setupUi(this);
// Expose click
connect(ui->pushButton, &QPushButton::clicked, this, &WidgetsForm::buttonClicked);
}
WidgetsForm::~WidgetsForm() = default;
Before we connect the exposed signal to the QML interface, we need another signal on the interface to expose our event over to QML. Here I add qmlSignalEmitter
signal for that purpose:
// widgetFormHandler.h
[..]
signals:
void visibleChanged();
void qmlSignalEmitter(); // Signal to relay button press to QML
[..]
To complete all the connections, go to the interface layer’s constructor and make a connection between your window class’ signal and that of the interface layer. This would look as follows:
// widgetFormHandler.cpp
[..]
WidgetFormHandler::WidgetFormHandler(QObject *parent)
: QObject(parent)
, m_window(std::make_unique<WidgetsForm>())
{
QObject::connect(m_window, &WidgetsForm::buttonClicked, this,
&WidgetFormHandler::qmlSignalEmitter);
}
[..]
By connecting one emitter to another emitter we keep each classes' concerns separate and reduce the amount of boilerplate code, making our code easier to maintain.
Over at the QML, we connect to qmlSignalEmitter
using the on prefix. It would look like this:
import NameOfAppQmlModule // Should match qt_add_qml_module's URI on CMake
WidgetFormHandler {
id: fontWidgetsForm
visible: true // Make the Widgets window visible from QML
onQmlSignalEmitter: () => {
console.log("Button pressed in widgets") // Log QPushButton's click event from QML
}
}
I've prepared a demo app where you can see this technique in action. The demo displays text that bounces around the screen like an old DVD player's logo would. You change the text and font through two identical forms, one implemented in QML and the other done in Widgets. The code presented in this tutorial comes from that demo app.
Example code: https://github.com/KDABLabs/kdabtv/tree/master/Blog-projects/Widget-window-in-Qt-Quick-app
The moving text should work on all desktop systems except for Wayland sessions on Linux. That is because I'm animating the window's absolute position (which is restricted in Wayland for security reasons) rather than the contents inside a window. This has the benefit of not obstructing other applications, since the moving window that contains the text would capture mouse inputs if clicked, preventing those from reaching the application behind it.
The first time I employed this technique was in my FOSS project, QPrompt. I use it there to provide a custom font dialog that doubles as a text preview. Having a custom dialog gives me full control over formatting options presented to users, and for this app we only needed a preview for large text and a combo box to choose among system fonts. QPrompt is also open source, you can find the source code relevant to this technique here: https://github.com/Cuperino/QPrompt-Teleprompter/blob/main/src/systemfontchooserdialog.h
Thank you for reading. I hope you’ll find this useful. A big thank you to David Faure for suggesting the use of C++ unique pointers, and to him, Renato and my team for reviewing the code.
If there are other techniques that you’d like for us to try or showcase, let us know.
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