Multi-process embedded systems with Qt for Device Creation and Wayland

Published Tuesday December 9th, 2014 | by

With the Qt 5.4 update for Qt for Device Creation it is now possible – on certain embedded systems – to run Qt applications on top of a Wayland compositor by relying only on the provided reference images without any additional modifications. While the stable and supported approach remains eglfs, the lightweight platform plugin that allows running fullscreen Qt applications on top of EGL and fbdev with the best possible performance, those who do not require any of the enhanced tooling but need to have multiple GUI applications running on the same screen can start experimenting with a Wayland-based system already today.

In this post we will take a look how this can be done on i.MX6 based systems, like for example the Sabre SD and BD-SL-i.MX6 boards.

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Posted in Embedded, Graphics, OpenGL

Qt Weekly #21: Dynamic OpenGL implementation loading in Qt 5.4

Published Thursday November 27th, 2014 | by

In Qt 5.4 there is a new configure option on Windows: -opengl dynamic. This, in addition to -opengl desktop and -opengl es2, changes the OpenGL implementation (and implicitly the window system interface API) that Qt is built against. However, unlike the previously existing flags, dynamic is something different. Enabling it ensures that neither the Qt libraries nor the applications link directly to an OpenGL implementation, meaning that neither opengl32.lib nor libEGL.lib + libGLESv2.lib are passed to the linker. Instead, Qt will, upon application startup, choose the implementation to load.

Starting with the Qt 5.4 release candidate the previously ANGLE-only pre-built packages are changed to be dynamic builds. It is therefore time to take a closer look at this feature.

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Posted in Graphics, OpenGL, Qt Quick, Windows

Qt Weekly #20: Completing the offering: QOpenGLWindow and QRasterWindow

Published Thursday November 20th, 2014 | by

Together with the introduction of QOpenGLWidget, Qt 5.4 adds two more classes: QOpenGLWindow and QRasterWindow. Let us now look at the list of native window classes and OpenGL container widgets. The list may look long and confusing at first glance, but it is all quite logical so everything will fall into place quickly:

  • QWindow: Represents a native window in the windowing system. The fundamental window class in Qt 5. Every top-level window, be it widget or Quick based, will have a QWindow under the hood. Can also be used directly, without widgets or Quick, both for OpenGL and software rendered graphics. Has no dependencies to the traditional QWidget stack.
  • QRasterWindow: Convenience wrapper over QWindow for software rendered graphics.
  • QOpenGLWindow: Convenience wrapper over QWindow for OpenGL graphics. Optionally backed by a framebuffer object, but the default behavior (and thus performance) is equivalent to QWindow.
  • QOpenGLWidget: The modern replacement for Qt 4’s QGLWidget. A widget for showing OpenGL rendered content. Can be used like any other QWidget. Backed by a framebuffer object.
  • QQuickWindow: A QWindow subclass for displaying a Qt Quick 2 (QML) scene.
  • QQuickView: Convenience wrapper for QQuickWindow for easy setup of scenes loaded from QML files.
  • QQuickWidget: The equivalent of QQuickView in the QWidget world. Like QOpenGLWidget, it allows embedding a Qt Quick 2 scene into a traditional widget-based user interface. Backed by a framebuffer object.

For completeness sake, it is worth noting two additional APIs:

  • QQuickRenderControl: Allows rendering Qt Quick 2 scenes into framebuffer objects, instead of targeting an on-screen QQuickWindow.
  • QWidget::createWindowContainer(): In Qt 5.1 & 5.2 the only way to embed Qt Quick 2 content (or in fact any QWindow) into a widget-based UI was via this function. With the introduction of QQuickWidget and QOpenGLWidget this approach should be avoided as much as possible. Its usage should be restricted to cases where it is absolutely neccessary to have a real native window embedded into the widget-based interface and the framebuffer object-based, more robust alternatives are not acceptable, or where it is known in advance that the user interface layout is such that the embedded window will not cause issues (for example because the embedded window does not care about input, is not part of complex layouts that often get resized, etc.).

We will now take a look at no. 2 & 3, the QWindow convenience wrappers.

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Posted in Graphics, OpenGL, QPA, Qt

Qt Weekly #19: QOpenGLWidget

Published Wednesday September 10th, 2014 | by

After Qt 5.3’s introduction of QQuickWidget, Qt 5.4 adds QOpenGLWidget, the long-awaited replacement for the legacy QGLWidget. This widget retains the familiar initializeGL/resizeGL/paintGL API, while enabling full interoperability with other widgets in complex user interfaces.

Internally QOpenGLWidget is built on the same technology as QQuickWidget. Unlike QGLWidget, it is not a native window and will not turn any siblings or ancestors into native either. This avoids stacking, clipping, focus and performance issues and is expected to behave identically across all supported platforms.

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Posted in Graphics, OpenGL, Qt

Bringing the magic of Qt to Windows Runtime

Published Tuesday March 25th, 2014 | by

We’ve been hard at work on the Windows Runtime (WinRT) port and it’s about time we share a bit with all of you. For Qt 5.3, we’re releasing the WinRT port as Beta quality, with most of the Qt Essentials modules in functional form (including QML & Quick). We also have preliminary tooling support, so you can get started on WinRT as quickly as you would on any other supported Qt platform.

An API for modern devices

As a reminder, Windows Runtime is a new API largely tied to Windows Store Apps, or applications which run within the Modern UI environment. It has C++ bindings (among other languages), and can be used on Windows 8, Windows Phone 8, and Windows RT – running the gamut from budget smartphones to high-end PCs. That’s a lot of devices.

One of the most important things for us (and many of you) has been getting Qt Quick working smoothly on the platform. As you might guess, there are some limitations to getting such a stack working here. For one, the memory APIs which are commonly used by just-in-time (JIT) compilers (such as in QtQml’s virtual machine engine) are restricted and cannot be used by apps in the Windows Store (this is, of course, for platform security reasons; the same restriction is in place on iOS). Fortunately, the V4 virtual machine which premiered in Qt 5.2 has solved this problem swimmingly, allowing WinRT to utilize the interpreted codepath for these types of operations (albeit at the cost of some less optimal code execution speed).
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Posted in cross-platform, integration, OpenGL, QPA, Qt Quick 2, Windows, WinRT

Qt Data Visualization 1.0 Beta

Published Thursday January 30th, 2014 | by

I’m happy to announce that we have now released the Qt Enterprise Data Visualization add-on 1.0 beta. The implementation has gone through quite many changes after we released the Technology Preview. We have been doing a lot of re-factoring both in the API and in the internals of the implementation so that we lay as solid foundation to further development as possible.

Datavisualization_Beta_Bars Datavisualization_beta_scatter2

Changes include:

  • Support for multiple series (surface not yet supported)
  • User modifiable themes
  • Improved input handling
  • Rotation of items in Scatter and Bar graphs
  • QML antialiasing support added
  • Added missing support for multiple graphs in same window
  • New examples
  • iOS support added

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Posted in Charts, Declarative UI, Graphics, OpenGL

New Scene Graph Renderer

Published Monday September 2nd, 2013 | by

Few phrases are more misused in software, whispered in social channels, promised over the negotiating table or shouted out loud in blogs, as the words “The next release will make everything better!”

So… I won’t say that.


Qt 5.2 introduces a new renderer to the Qt Quick Scene Graph.

When we set out to do the scene graph some three years ago, one of my visions was that we would be able to really take advantage of OpenGL and have game-like performance. The renderer we have in Qt 5.0 went a long way towards that goal. For opaque content, we sort based on state and render content front-to-back to minimize GPU overdraw. In the playground/scenegraph repository, we have a different renderer which batches similar primitives together to reduce the number of draw calls (which implicitly also reduces state changes).

The new renderer in Qt 5.2 combines both of these techniques and also tries to identify non-changing parts of the scene so they can be retained on the GPU. Qt 5.2 also adds the texture atlas support which was previously located in the playground/scenegraph’s customcontext. This greatly helps batching of textured content. I think that with Qt 5.2, we are now pretty close to that goal.

A new doc article explaining the renderer in more detail has been added for the more curious, though a deep understanding of the renderer is not needed to write well-performing applications. However, I suspect many people will still find it interesting.


There are still a lot of other ideas that could be employed for those who want to have a stab at it. If you have ideas, ping “sletta” on IRC or clone and start coding.

Now some numbers:

Three of the benchmarks are available here:

  • Extreme Table contains a large static table with some animated content on top. It shows the benefit of the GPU retention.
  • List Bench shows a number of simultaneously scrolling lists with an icon, alternating background color, and two texts per cell.
  • Flying Icons contains over 3000 images which are being animated with a unique animation per item.

I also included the front-page of the Qt Quick Controls gallery example and Samegame. Samegame is played in “Zen” mode while clicking to the rhythm of “Where Eagles Dare” by Iron Maiden. (I know… very scientific)

The number of OpenGL draw calls and amount of traffic is measured using apitrace, an awesome tool if you’re debugging OpenGL. As can be seen by the green numbers, we’ve managed to cut down the number of glXxx calls quite a bit, especially for the cases where we have plenty of re-occurrence, meaning lists, tables and grids.

The amount of traffic per frame is also significantly improved. The best examples are the “ExtremeTable” and “ListBench” which are sampled at a frame where no new delegates were being added or removed. I’m quite happy that the “ListBench” comes out as a zero-transfer frame. There is of course some traffic, the draw calls themselves and a couple of uniforms; but no vertex data and no texture data, which is what the tool measures. “FlyingIcons” changes the entire scene every frame so nothing can be retained, so minimal difference is expected. Controls Gallery is mostly static, but has an animated progress bar which needs a new texture every frame. This is the majority of the 20+kb transfer. Samegame comes out pretty high, primarily because of its extensive use of particle systems. A lesson learned is that if you are on a tiny memory bus, limit your particles.

These are theoretical numbers, but they give a good idea that the new renderer is on the right track. Let us look at numbers from running on hardware. I’ve created tables out of the cases where the new renderer had the most impact. The full table of numbers is at the very bottom.

Note, these benchmarks are run without the new V4-based QML engine. This is because the V4 engine also affects the results and I wanted to focus on rendering only.

The rendering time is measured with vsync enabled, but excluding the swap. So when we see that the MacBook spends 16ms rendering, it is actually being throttled while we are issuing OpenGL commands. When Iooked at this in Mac OS X’s Instruments, I saw that the driver was spending a lot of time in synchronous waiting, aka we have stalling in the pipeline. With the Qt 5.2 rendering, the synchronous waiting while drawing is gone. This is good news, as lists and list-like content is quite common in UIs.

In both the MacBook with Integrated chip and on the Nexus, the new renderer drastically reduces the time spent issuing OpenGL commands. It should also be said that the only reason the render times for the “ExtremeTable” did not go all the way to 0 is because of

“FlyingIcons” high CPU load is mostly primarily due to it running 3000+ animations in parallel, but as we can see from the time spent in the renderer, that there is still significant improvement.

Here are the rest of the numbers:

So this matches up pretty well with the theoretical results at the beginning. For reoccurring content, such as lists and grids, Qt 5.2 is quite an improvement over Qt 5.1. For those use cases we didn’t radically improve, we at least didn’t make them any worse.



Posted in Graphics, OpenGL, Qt Quick 2.0

Introducing QWidget::createWindowContainer()

Published Tuesday February 19th, 2013 | by

Qt 5 introduced a new set of OpenGL classes in Qt Gui and a new rendering pipeline for Qt Quick with the scenegraph. As awesome as these are, they were based on the newly introduced QWindow, making it very hard to use them in existing applications.

To remedy this problem, Qt 5.1 introduces the function QWidget::createWindowContainer(). A function that creates a QWidget wrapper for an existing QWindow, allowing it to live inside a QWidget-based application. Using QQuickView or QOpenGLContext together with widgets is now possible.

How to use

QQuickView *view = new QQuickView();

QWidget *container = QWidget::createWindowContainer(view);


How it works

The window container works by forcing the use of native child widgets inside the widgets hierarchy and will reparent the window in the windowing system. After that, the container will manage the window’s geometry and visibility. The rendering of the window happens directly in the window without any interference from the widgets, resulting in optimal performance.

As can be seen from the code-snippet above, the container can also receive focus.

Embedding the “Other Way”

This feature covers the use case where an application wants to either port an existing view to either Qt Quick or the new OpenGL classes in Qt Gui. What about the use case where an application’s mainview is written with widgets, say QGraphicsView, and the application wants to keep this and rewrite the surrounding UI with Qt Quick? Well, this is doable by keeping the main application QWidget-based and making each of the big UI blocks a QQuickView embedded in its own container.



Posted in OpenGL, Qt, Qt Quick 2.0

Graphics on Windows from a different angle

Published Wednesday October 24th, 2012 | by

With Qt 5 we are making the bold move of making OpenGL 2.0 a requirement for using  QtQuick2. There are several challenges with this new requirement, many of which have been discussed on the blogs and mailing lists already, but today I want to talk about one issue in particular and that’s OpenGL on Windows.

Microsoft has included OpenGL in Windows since Windows 98 (or earlier?), however the initial version was a software implementation and only supported version 1.1 of the API. Over time, the implementation has been improved so that today it is implemented as a wrapper on top of Direct3D. This is great, but unfortunately the version of the API that is supported has remained the same and that means it is not sufficient for running QtQuick2 or even Qt’s GL paint engine. You can insert your own conspiracy theory about why Microsoft has let OpenGL stagnate on Windows, but every theory will likely involve Direct3D. D3D is a component of DirectX that offers similar functionality to OpenGL. It is most commonly used by game developers to target desktop Windows and also XBox, but is also used by CAD applications.

Typically when a developer wants to run or develop something that requires OpenGL on Windows, the first place they go is to their hardware vendor’s website and download the latest drivers from Intel, NVidia, AMD or whoever.. This is fine, but can be somewhat inconvenient for end users of OpenGL applications. We wanted to avoid this problem with Qt applications so deployment would essentially be the same as with Qt 4 (but with possibly more DLLs). Luckily for us, we weren’t the first people to experience this problem. Most browsers these days (except IE) are supporting WebGL out of the box. WebGL is a 3D canvas API available through Javascript. The API is based on OpenGL ES 2.0 and the shader language is GLSL ES. So how can browsers offer an OpenGL 2 API without requiring new drivers? The solution is called the ANGLE (Almost Native Graphics Layer Engine) project.

ANGLE is a BSD licensed project that implements the OpenGL ES 2.0 API on top of DirectX 9.0c. In addition to this, it also implements the EGL API and contains a shader cross compiler that takes GLSL ES code and converts it to HLSL which is the shader language used in DirectX. So ANGLE allows us to essentially run the Qt Scene Graph on top of DirectX without modifying any of our code. Friedemann has already done most of the hard work by adding support for GLES2 and EGL into the Windows platform plugin and as a result it has been possible to use Qt 5 with ANGLE for quite some time now. However, to make this experience more painless, we are including ANGLE in Qt’s 3rdparty directory and making it the default OpenGL configuration on Windows.

For QML applications and lightweight OpenGL apps, you can use this new configuration to deploy your apps without requiring your end users to install new graphics drivers. On the other hand if your application requires full desktop OpenGL, then it’s simply a matter of configuring Qt with “-opengl desktop” and you get the same behavior as before.

One additional benefit of using ANGLE on Windows is that our graphics pipeline and multimedia pipeline are now based on the same underlying technology (DirectX) so we can take some shortcuts to get video frames into the Scene Graph more efficiently. Taking this one step further, Windows Vista introduced a new driver model called WDDM and one of the features here is that DirectX surfaces can now be shared across processes. This little feature will come in handy for our WebKit2 work which has seperate processes for the web renderer and the ui. All of this goodness might not make it into the 5.0 release, but it’s  all in progress so hopefully it makes an appearance soon!


Posted in Graphics, OpenGL, Qt, Windows

Qt 3D and Qt5 / Qt4 news and releases

Published Wednesday April 11th, 2012 | by

Well its taken 3+ years for Qt 3D to be an overnight success, but here it is: we are now part of Qt5 and we’ll be front and centre in the exciting picture that will be powering a new generation of QML enhanced apps on a whole range of platforms. As a Qt5 Essential Qt 3D will be running on all those supported Qt5 platforms providing OpenGL accelerated 3D content defined in QML. Its great news for us in the team, and good news for those of you using Qt 3D or planning on using it for your projects.

If you’re a Qt 3D fan and have been following the project for a while you’ll know that as a labs project we had to do our own releases, carefully making sure that packages we created matched the current supported versions of Qt 4. We have in the past released easy-to-use packages for Symbian^3, N900 and the N9 platforms, as well as for Windows desktop; and supported Linux and Mac with source packages. We got great feedback from those package releases, and saw some interesting projects built on Qt 3D.

As part of Qt5 the SDK team and release program will make Qt 3D available through official Qt5 release activities. This will free us up to spend more time on performance, bug-fixing and best of all the features that we’ve been asked for. This is fantastic news for us since packaging consumed quite a bit of our resources, and now we can focus that on improving Qt 3D.

Before we move away from Labs status we are making one more Qt 3D labs release: and this is it. This follows our Qt 3D TP1 and TP2 releases with a 1.0 release as part of our Qt 4.x programme. In this release are a number of important bug fixes, some new stuff like threaded texture and model loading, and the new Qt 3D Asset Viewer, which allows you to visually configure the models you load into your Qt 3D applications.

Today we announce our Qt 3D 1.0 for Qt 4.8.1 with only a small amount of fanfare: this will be our last 4.x major version release.

For Windows folks, you’ll need the Qt 4.8.1 Windows MSVC release which is available from the Qt downloads page.

The documentation is also available on-line on the Qt project site.

For N9 developers we no longer create a package. The publicly available Qt SDK can build these packages for you from our source download using the Qt 4.7.x Harmattan support, that is built right in to your SDK. Just follow the special N9 instructions in our build documentation. For Symbian likewise you will need to create your own packages. For folks using a MinGW based Qt on Windows, you will need to use the source package also.

Why are we not supplying N9 or Symbian packages for Qt 3D 1.0 against Qt 4.x? Since Qt 3D 1.0 for 4.x is a labs project, our previous device packages were not official Nokia system packages, and just functioned as a convenience to the developer. This is why we’re asking that you create your own packages to underscore the fact that Nokia does not supply Qt 3D system packages as part of Qt 4.x, and you’ll need to do your own work to include any Qt 3D functionality in your device apps. Apologies for this, but its the way it is for our 4.x labs status programme. Qt 3D team remains available on IRC and via our email lists (see below) to support you as far as possible when including Qt 3D in your apps, but unfortunately for Qt 4.x we cannot supply Nokia system packages for these platforms.

What about Qt5? That is where the excitement lies, with a vastly improved QML rendering engine, which has the benefit for Qt 3D of guaranteed OpenGL support. If you have QML2 then you have OpenGL and that means Qt 3D is ready to go on any Qt5 platform. We’d love you to try out Qt 3D on Qt5 – go and check out the Qt5 Alpha release which has just been announced, and tell us what you think. If you want to try out the bleeding edge, you can also get Qt 3D in Qt5 by building from Git.


Posted in OpenGL, Qt 3D

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