Last weekend was the GStreamer Hackfest in Staines, UK, in the Samsung’s premises, who also sponsored the dinners and the lunches. Special thanks to Luis de Bethencourt, the almighty organizer!
My main purpose was to sip one or two pints with the GStreamer folks and, secondarily, to talk about gstreamer-vaapi, WebKitGTK+ and the new OpenGL/ES support in gst-plugins-bad.
About gstreamer-vaapi, there were a couple questions about some problems shown in downstream (stable releases in distributions) which I was happy to announce that they are mostly fixed in upstream. On the other hand, Sebastian Drödge was worried about the existing support of GStreamer 0.10 and I answered him that its removal is already in the pipeline. He looked pleased.
In the WebKitGTK+ realm, I worked on a new functionality: to share the OpenGL context and the display of the browser with the GStreamer pipeline. With it, we could add gl filters into the pipeline. But honour to whom honour is due: this patch is a split of a previous patch done by Philippe Normand. The ultimate goal is to ditch the custom video sink in WebKit and reuse the glimagesink, with it’s new off-screen rendering feature.
Finally, on Sunday’s afternoon, I walked around Richmond and it is beautiful.
Thanks to Igalia, Intel and all the sponsors that make possible the hackfest and my attendance.
The last Friday 25 of July, National Day of Galicia, started very early because I had to travel to Strasbourg, official seat of the European Parliament, not for any political duty, but for the GNOME Users and Developers European Conference, the GUADEC!
My last GUADEC was in The Hague, in 2010, though in 2012, when it was hosted in Coruña, I attended a couple talks. Nonetheless, it had been a long time since I met the community, and it was a pleasure to me meet them again.
My biggest impression was the number of attendees. I remember the times in Turkey or in Gran Canaria where hundreds packed the auditoriums and halls. Nowadays the audience was smaller, but that is a good thing, since now you get in touch with the core of developers who drive and move the project easily.
We, Igalia, as sponsors, had a banner in the main room and a table in a corridor. Here is a picture of Juan to prove it:
Also I ran across with Emmanuele Bassi, setting up a booth to show up the Endless Mobile OS, based on GNOME 3. The people at GUADEC welcomed with enthusiasm the user experience provided by it and the purpose of the project. Personally, I love it. If you don’t know the project, you should visit their web site.
The first talk I attended what the classic GStreamer update by Sebastian Dröge and Tim Müller. They talked about the new features in GStreamer 1.4. Neat stuff in there. I like the new pace of GStreamer, rather of the old stagnated evolution of 0.10 version.
Afterwards, Jim Hall gave us a keynote about Usability in GNOME. I really enjoyed that talk. He studied the usability of several GNOME applications such as Nautilus (aka Files), GEdit, Epiphany (aka Web), etc., as part of his Masters’ research. It was a pleasure to hear that Epiphany is regarded as having a good usability.
After lunch I was in the main room hearing Sylvain Le Bon about sustainable business models for free software. He talked about crowd funding, community management and related stuff.
The next talk was Christian Hergert about his project GOM, an object mapper from GObjects to SQLite, which is used in Grilo to prevent SQL injection by some plugins that use SQLite.
The day closed with the GNOME Foundation’s teams reports.
Sunday came and I arrived to the venue for the second keynote: Should We Teach The Robot To Kill by Nathan Willis. In his particular style, Nathan, presented a general survey of GNU/Linux in the Automotive Industry.
Next, one of main talks from Igalia: Web 3.12: a browser to make us proud, presented by Edu. It was fairly good. Edu showed us the latest development in WebKitGTK+ and Epiphany (aka Web). There were quite a few questions at the end of the talk. Epiphany nowadays is actively used by a lot of people in the community.
After, Zeeshan presented his GNOME boxes, an user interface for running virtual machines. Later on Alberto Ruiz showed us Fleet Commander, a web application to handle large desktop deployments.
And we took our classic group photo:
That Sunday closed with the intern’s lighting talks. Cool stuff is being cooked by them.
On Monday I was in the venue when Emmanuele Bassi talked us about GSK, the GTK+ Scene Graph Kit, his new project, using as a starting point the lessons learned in Clutter. Its objective is to have a scene graph library fully integrated in GTK+.
After the lunch and the second part of the Foundation’s Annual General Meeting, Benjamin Otte gave an amusing talk about the CSS implementation in GTK+. Later, Jasper St. Pierre talked about the Wayland support in GNOME.
When the coffee break ended, the almighty Žan Doberšek gave the other talk from Igalia: Wayland support in WebKit2GTK+.
In the last day of the GUADEC, I attended Bastien Nocera’s talk: Hardware integration, the GNOME way, where he reviewed the history of his contributions to GNOME related with hardware integration and the goal of nicely support most of the hardware in GNOME, like compasses, gyroscopes, et cetera.
Afterwards, Owen Taylor talked us about the GNOME’s continuous integration performance testing, in order to know exactly why one release of GNOME is faster or slower than the last.
And the third keynote came: Matthew Garrett talked us about his experiences with the GNOME community and his vision about where it should go: to enhance the privacy and security of the users, something that many GNOMErs are excited about, such as Federico Mena.
Later on, David King talked about his plans for Cheese, the webcam application, turning it into a DBus service, using the current development of kdbus to sandbox the interaction with the hardware.
Afterwards Christian Hergert talked us about his plans for Builder, a new IDE for GNOME. Promising stuff, but we will see how it goes. Christian said that he is going to take a full year working on this project.
The GUADEC ended with the lighting talks, where I enjoyed one about the problems around the current encryption and security tools.
Finally, the next GUADEC host was unveiled: the Sweden Conspiracy: Gothenburg!
Some time ago I needed to jump into the fix-compile-test loop for WebKitGTK+, but in the armhf architecture, speaking in terms of Debian/Ubuntu.
To whom don’t know, WebKitGTK+ is huge, it is humongous, and it takes a lot of resources to compile. For me, at first glance, was impossible to even try to compile it natively in my hardware, which, by the way, is an Odroid-X2. So I setup a cross-compilation environment.
And I failed. I could not cross-compile the master branch of WebKitGTK+ using as root file system, a bootstrapped Debian. It is supposed to be the opposite, but all the multiarch thing made my old and good cross-compilation setup (based on scratchbox2) a bloody hell. Long story short, I gave up and I took more seriously the idea of native builds. Besides, Ubuntu and Debian does full native builds of their distributions for armhf, not to say that the Odroid-X2 has enough power for give it a try.
It is worth to mention that I could not use Yocto/OE or buildroot, though I would love to use them, because the target was a distribution based on Debian Sid/Ubuntu, and I would not afford a chroot environment only for WebKitGTK+.
With a lot of patience I was able to compile, in the Odroid, a minimalist configuration of WebKitGTK+ without symbols. As expected, it took ages (less than 3 hours, if I remember correctly)
Quickly an idea popped out in the office: to use distcc. I grabbed as many board based on ARMv7 I could find: another Odroid-X2, a couple Pandaboards, an Arndaleboard, and an IFC6410, installed in them a distcc compilation setup.
And yes, the compilation time went down, but not that much, though I don’t remember how much.
Many of the colleagues at the office migrated from distcc to icecream. Particularly, Juan A. Suárez told me about his experiments with icecc and his Raspberry pi. I decided to give it a shoot.
Icecream permits to do cross-compilation because the scheduler can deliver, into the compilation host, the required tool-chain by the requester.
First, you should have one or several cross tool-chains, one for each compilation tuple. In this case we will have only one: to compile in X86_64, generating code for armfh. Luckily, embdebian provides it, out of the box. Nevertheless you could use any other mean to obtain it, such as crosstool.
Second, you need the icecc-create-env script to create the tarball that the scheduler will distribute to the compilation host.
The output of this script is an archive file containing all the files necessary to setup the compiler environment. The file will have a random unique name like “ddaea39ca1a7c88522b185eca04da2d8.tar.bz2” per default. You will need to rename it to something more expressive.
Third, copy the generated archive file to board where your code will be compiled and linked, in this case WebKitGTK+.
For the purpose of this text, I assume that the board has already installed and configured the icecc daemon. Beside, I use ccache too. Hence my environment variables are more or less like these:
CCACHE_DIR=/mnt/hd/.ccache # /mnt/hd is a mounted hard disk through USB.
PATH=/usr/lib/ccache:.. # where Debian sets the compiler's symbolic links
Finally, the last pour of magic is the environment variable ICECC_VERSION. This variable needs to have this pattern
Where <native_archive_file> is the archive file with the native tool-chain. <platform> is the host hardware architecture. <cross_archive_file> is the archive file with the cross tool-chain. <target> is the target architecture of the cross tool-chain.
In my case, the target is not needed because I’m doing native compilation in armhf. Hence, my ICECC_VERSION environment variable looks like this:
Basically we can perceive a browser as an application for retrieving, presenting and traversing information on the Web.
For the composited video support, we are interested in the presentation task of the browser. More particularly, in the graphical presentation.
In WebKit, each HTML element on a web page is stored as a tree of Node objects called the DOM tree.
Then, each Node that produces visual output has a corresponding RenderObject, and they are stored in another tree, called the Render Tree.
Finally, each RenderObject is associated with a RenderLayer. These RenderLayers exist so that the elements of the page are composited in the correct order to properly display overlapping content, semi-transparent elements, etc.
It is worth to mention that there is not a one-to-one correspondence between RenderObjects and RenderLayers, and that there is a RenderLayer tree as well.
WebKit fundamentally renders a web page by traversing the RenderLayer tree.
What is the accelerated compositing?
WebKit has two paths for rendering the contents of a web page: the software path and hardware accelerated path.
The software path is the traditional model, where all the work is done in the main CPU. In this mode, RenderObjects paint themselves into the final bitmap, compositing a final layer which is presented to the user.
In the hardware accelerated path, some of the RenderLayers get their own backing surface into which they paint. Then, all the backing surfaces are composited onto the destination bitmap, and this task is responsibility of the compositor.
With the introduction of compositing an additional conceptual tree is added: the GraphicsLayer tree, where each RenderLayer may have its own GraphicsLayer.
In the hardware accelerated path, it is used the GPU for compositing some of the RenderLayer contents.
As Iago said, the accelerated compositing, involves offloading the compositing of the GraphicLayers onto the GPU, since it does the compositing very fast, releasing that burden to the CPU for delivering a better and more responsive user experience.
Although there are other options, typically, OpenGL is used to render computing graphics, interacting with the GPU to achieve hardware acceleration. And WebKit provides cross-platform implementation to render with
How does WebKit paint using OpenGL?
Ideally, we could go from the GraphicsLayer tree directly to OpenGL, traversing it and drawing the texture-backed layers with a common WebKit implementation.
But an abstraction layer was needed because different GPUs may behave differently, they may offer different extensions, and we still want to use the software path if hardware acceleration is not available.
This abstraction layer is known as the Texture Mapper, which is a light-weight scene-graph implementation, which is specially attuned for an efficient usage of the GPU.
It is a combination of a specialized accelerated drawing context (TextureMapper) and a scene-graph (TextureMapperLayer):
The TextureMapper is an abstract class that provides the necessary drawing primitives for the scene-graph. Its purpose is to abstract different implementations of the drawing primitives from the scene-graph.
One of the implementations is the TextureMapperGL, which provides a GPU-accelerated implementation of the drawing primitives, using shaders compatible with GL/ES 2.0.
There is a TextureMapperLayer which may represent a GraphicsLayer node in the GPU-renderable layer tree. The TextureMapperLayer tree is equivalent to the GraphicsLayer tree.
How does WebKitGTK+ play a video?
As we stated earlier, in WebKit each HTML element, on a web page, is stored as a Node in the DOM tree. And WebKit provides a Node class hierarchy for all the HTML elements. In the case of the video tag there is a parent class called HTMLMediaElement, which aggregates a common, cross platform, media player. The MediaPlayer is a decorator for a platform-specific media player known as MediaPlayerPrivate.
All previously said is shown in the next diagram.
In the GTK+ port the audio and video decoding is done with GStreamer. In the case of video, a special GStreamer video sink injects the decoded buffers into the WebKit process. You can think about it as a special kind of GstAppSink, and it is part of the WebKitGTK+ code-base.
And we come back to the two paths for content rendering in WebKit:
In the software path the decoded video buffers are copied into a Cairo surface.
But in the hardware accelerated path, the decoded video buffers shall be uploaded into a OpenGL texture. When a new video buffer is available to be shown, a message is sent to the GraphicsLayer asking for redraw.
Uploading video buffers into GL textures
When we are dealing with big enough buffers, such as the high definition video buffers, copying buffers is a performance killer. That is why zero-copy techniques are mandatory.
Even more, when we are working on a multi-processor environment, such as those where we have a CPU and a GPU, switching buffers among processor’s contexts, is also very expensive.
It is because of these reasons, that the video decoding and the OpenGL texture handling, should happen only in the GPU, without context switching and without copying memory chunks.
The simplest approach could be that decoder deliver an EGLImage, so we could blend the handle into the texture. As far as I know, the gst-omx video decoder in the Raspberry Pi, works in this way.
GStreamer added a new API, that will be available in the version 1.2, to upload video buffers into a texture efficiently: GstVideoGLTextureUploadMeta. This API is exposed through buffer’s metadata, and ought be implemented by any downstream element that deals with the decoded video frames, most commonly the video decoder.
For example, in gstreamer-vaapi there are a couple patches (which still are a work-in-progress) in bugzilla, enabling this API. In the low level, calling gst_video_gl_texture_upload_meta_upload() will call vaCopySurfaceGLX(), which will do an efficient copy of the vaAPI surface into a texture using a GLX extension.
This is an old demo, when all the pieces started to fit, but no the current performance. Still, it shows what has been achieved:
So far, all these bits are already integrated in WebKitGTK+ and GStreamer. Nevertheless there are some open issues.
gstreamer-vaapi et all:
GStreamer 1.2 is not released yet, and its new API might change. Also, the port of gstreamer-vaapi to GStreamer 1.2 is still a work in progress, where the available patches may have rough areas.Also, there are many other projects that need to be updated with this new API, such as clutter-gst and provide more feedback to the community.
Another important thing is to have more GStreamer elements implementing these new API, such as the texture upload and the caps features
The composited video task unveiled a major problem in WebKitGTK+: it does not handle the vertical blank interval at all, causing tearing artifacts, clearly observable in high resolutions videos with high motion.WebKitGTK+ composites the scene off-screen, using X Composite redirected window, and then display it at a X Damage callback, but currently, GTK+ does not take care of the vertical blank interval, causing this tearing artifact in heavy compositions.
At Igalia, we are currently researching for a way to fix this issue.
There is always room for performance improvement. And we are always aiming in that direction, improving the frame rate, the CPU, GPU and memory usage, et cetera.
So, keep tuned, or even better, come and help us.
Three weeks have passed since I wrote the last WebKit report, and they did so quick that it scares me. Many great things have happened since then.
Let’s start with my favorite area: multimedia. Phil landed a patch that avoids muting the sound if the audio pitch is preserved. And Calvaris finally landed his great new media controls. Now watching videos in WebKitGTK+ is a pleasure.
Claudio, besides his work in the snapshots API that we already commented, retook the implementation of the notifications API for WebKitGTK+. And, while implementing it, he fixed some crashers in WK2’s implementation. He has also given us an early screencast with the status of the notifications implementation: Check it out! (video).
Carlos García Campos, besides working hard on the stable and development releases of WebKitGTK+ library, has also landed a couple of fixes. Meanwhile, Dape removed some dependencies, making the code base more clean.
Claudio, whilst he waits for the review of his API to retrieve a snapshot, he retook the Notifications API work for WebKitGTK+, particularly for WebKit2. Also, and just for sake of landing something, he fixed a couple of minor compilationglitches.
The great WebKit hacker, Martin Robinson is exploring uncharted territory in the project: He’s trying to get away from port-specific things, by scratching in the core stuff, but the serendipity showed up, so he found some pretty serious port-specific bugs that have relatively straight-forward fixes.
In addition to all this work, Martin is working on a patch for mathvariant itself. The mathvariant attribute allows easily using the Mathematical Alphanumeric Symbols in MathML without having to type out XML entities. For instance this:
<mi mathvariant=”fraktur”>HI GUYZ!</mi>
will be rendered like this:
Carlos García Campos cooked a patch for fixing the WebKit2 GTK+ API by implementing the resources API, removed recently, using injected bundle. This is another effort to bring back WebKit2 into WebKitGTK+.
This a new weekly WebKit Igalia’s report. And the last week has been a shaky one.
Let’s start with a warm welcome to Žan Dobersek as collaborator student, who is working hard in a lot of cool matters: gardening the bots, cleaning up the Coverity run output, modifying the WebCoreTestSupport to decrease the dependency WebKit2 API, digging in a stack size problem in JSC, and much more fun stuff.
This weekly report project was supposed to start after the last WebKit hackfest, but my holidays got in between and now I’m recovering of them 😉
Here we go:
In summary, in these last three weeks we have had 15 commits and done 23 reviews.
Martin and Carlos have been working on the authentication mechanisms. Now they can be hooked ,through the web view API, by the applications, which could take control of the dialogues and credentials handling.
Martin has also been dealing with text rendering with complex layouts (such as Arabic). This effort leaded, finally, to the removal of Pango in favor of Harfbuzz.
Carlos, since the last year, has been working on his injected bundle patch, which offers a mean to support loading plugins in the web process using injected bundle. Hence, through DBus, an application could load a plugin to communicate, indirectly, with the Web process. This approach is supposed to be the milestone for the DOM bindings in WK2GTK, and also provides a mean to pre-fetch DNS registries. This patch has been happily pushed just recently, in the second week of January.
If this was not enough, Carlos also released the development version of WebKitGTK+ v1.11.4.
Now let us go to the multimedia realm, my favorite land.
Philippe finished the port of his patch for WebAudio support to GStreamer 1.0 as backend. And now he is porting the full-screen support in Gst 0.10 to Gst 1.0 in order to reuse ans share the same base code. Aligned with WebAudio, Philippe is developing a new audio source provider that gathers raw audio data from the MediaPlayer and pipe them into the AudioBus if it is required.
Xabier has been working to deliver a nice and neat HTML5 media controls, using stylable GTK+ controls. And myself, I’m still playing with the audio pitch preservation.
Another great landmark for us is a11y, and here Joanie has been working hard to bring back the accessibility tests on GTK to a sane state. And also keeps her efforts to enable an access to WebKit for Orca.
In other sort of things, Berto has been fighting against a bug on GtkLaunch, which was shown in Epiphany too when displaying only images. Meanwhile, Dape, lurked on spell checking support for Qt WebKit2. And Sergio enabled, by default, the WebP image handling.