Can I use CSS Box Alignment ?

As a member of the Igalia’s team implementing the CSS Grid Layout feature for Blink and WebKit rendering engines, I’m very proud of what we’ve achieved from our collaboration with Bloomberg. I think Grid is a very interesting feature for the Web Platform and we still can’t see all its potential.

One of my main assignments on this project is to implement the CSS Box Alignment spec for Grid. It’s obvious that alignment is an important feature for many cases in web development, but I consider it a key for a layout model like the one Grid provides.

We recently announced that the patch implementing the self-baseline alignment landed in Blink. This was the last alignment functionality pending to implement, so now we can consider that the spec is complete for Grid. However, implementing a feature like CSS Box Alignment has an additional complexity in the form of interoperability issues.

Interoperability is always a challenge when implementing any new specification, but I think it’s specially problematic for a feature like this for several reasons:

  • The feature applies to several layout models.
  • The CSS Flexible Box specification already defined some of the CSS properties and values.
  • Once a new layout model implements the new specification, Flexbox is forced to follow it as well.

I admit that the editors of this new specification document made a huge effort to keep backward compatibility with the Flexbox spec (which caused not so few implementation challenges). However, the current Flexbox implementation of the CSS properties and values that both specs have in common would become a Partial Implementation regarding the new spec.

Recently Florian Rivoal found out that this partial implementation of the CSS Box Alignment feature prevents the use of cascade or @support for providing customized fallbacks for the unimplemented Alignment properties.

What does Partial Implementation actually mean ?

As anybody can imagine, implementing a fancy web feature takes a considerable amount of time. During this period, the feature passes through several phases with different exposure to the end users. It’s precisely due to the importance of end user’s feedback that these new web features are shipped under experimental flags. This workflow is specially useful no only for browser devs but for the spec editors as well.

For this reason, the W3C CSS Working Group defines a general policy to manage Partial Implementations, which can be summarized as follows:

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported property values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

This policy is added to every spec as part of its Conformance appendix, so it is in the case of the CSS Box Alignment specification document. However, the interpretation of the Partial Implementation policy is far from trivial, specially for a feature like CSS Box Alignment. The most restrictive interpretation would imply the following facts:

  • Any new CSS property of the new spec should be declared invalid until is supported by all the layout models it applies to.
  • Any of the already existent CSS properties with new values defined in the new spec should be declared invalid until all these new values are implemented in all the layout models such property applies to.
  • Browsers shouldn’t ship (without experimental flags) any CSS property or value until it’s implemented in all the layout model it applies to.

When we discussed about this at Igalia we applied a less restrictive interpretation, based on the assumption that the spec actually defined several features which could be implemented and shipped independently, obviously avoiding any browsers interoperability issues. As it’s been always in the nature of the specification, keeping backward compatibility with Flexbox implementations has been a must, since its spec already defines some of the CSS properties now present in the new spec.

The issue filed by Florian was discussed during the Tokyo F2F Apr 19-21 2017 meeting, where it was agreed to add a new section in the CSS Box Alignment spec to clarify how implementors of this feature should manage Partial Implementations:

Since it is expected that support for the features in this module will be deployed in stages corresponding to the various layout models affected, it is hereby clarified that the rules for partial implementations that require treating as invalid any unsupported feature apply to any alignment keyword which is not supported across all layout modules to which it applies for layout models in which the implementation supports the property in general.

The new text added makes the Partial Implementation policy less restrictive and, even it contradicts our interpretation of independent alignment features per layout model, it affects only to models which already implement any of the CSS properties defined in the new spec. In this case, only Flexbox has to be updated to implement the new values defined for its alignment related CSS properties: align-content, justify-content and align-self.

Analysis of the implementation and shipment status

Before thinking on how to address the Partial Implementation issues, I decided to analyze what’s the status of the CSS Box Alignment feature in the different browsers. If you are interested in the full analysis, it’s available here. The following table shows the implementation status of the new spec in the Safary, Chrome and Firefox browsers, using a color code like unimplemented, only grid or both (flex and grid):

If you can try out some examples of these Partial Implementation issues, just try flexbox vs grid cases with some of these alignment values: align-items: center, align-self: left; align-content: start or justify-content: end.

The 3 major browsers analyzed have shipped most, if not all, the CSS Box Alignment spec implemented for CSS Grid Layout (since Chrome 57, Safari 10.1, Firefox 52). Firefox is the browser which implemented and shipped a wider support for CSS Flexible Box.

We can extract the following conclusions:

  • The 3 browsers analyzed have shipped Partial Implementations of the CSS Box Alignment specification, although Firefox is almost complete.
  • The 3 browsers have shipped a Grid feature that supports completely the new CSS Box Alignment spec, although Safari still misses the self-baseline values.
  • The 3 implementations of the new CSS Box Alignment specification are backward compatible with the CSS Flexible Box specification, even though it implements for some properties a lower level of the spec (e.g. self-baseline keywords)

Work in progress

Although we are still evaluating the problem together with the Blink and WebKit communities, at Igalia we are already working on improving the situation. We all agree on the damage to the Web Platform that these Partial Implementation issues are causing, as Florian pointed out initially, so that’s a good starting point. There are bug reports on both WebKit and Blink and we are already providing patches for some of them.

We are still discussing about the best approach, but our bet would be to request an intent-to-implement-and-ship for a CSS Box Alignment (for flexbox layout) feature. This approach fits naturally in our initial plans of implementing several independent features from the alignment specification. It seems that it’s what Firefox is doing, which already announced the implementation of CSS Box Alignment (for block layout)

Thanks to Bloomberg for sponsoring this work, as part of the efforts that Igalia has been doing all these years pursuing a better and more open web.

Igalia & Bloomberg logos

New shorthand properties for CSS Grid Layout

I’ve been working for a while already on the implementation of the CSS Grid Layout standard for the WebKit and Blink web engines. It’s a complex specification, indeed, like most of them, so I enjoyed a lot decrypting all the angles behind the language used to define the different CSS properties, their usage and limits, exceptions and so on.  It’s fair to start thanking the WebKit reviewers and Blink owners for their patient and support reviewing patches. It also worth mentioning that the E.D is still a live document with frequent changes and active discussions in the www-style mailing list, which is very active and supportive solving doubts and attending suggestions of the hackers working on the implementation.

Before continue reading, I’d strongly recommend reading the previous posts of my colleges Manuel and Sergio to understand the basic concepts of the CSS Grid Layout and its main features and advantages for the web.

I had the chance to land several patches in WebKit and Blink that improved the current implementation of the standard, both fixing bugs and adapting it to the latest syntax changes introduced in the spec, but perhaps the most noticeable improvements are, so far, the new grid-template and grid shorthands added recently.
 

The “grid-template” shorthand

 
Quoting the CSS Grid Layout specs:

The grid-template property is a shorthand for setting grid-template-columns, grid-template-rows, and grid-template-areas in a single declaration. It has several distinct syntax forms:

none | subgrid | <‘grid-template-columns’> / <‘grid-template-rows’> | [<’track-list’>/ ]? [<’line-names’>? <’string’> <’track-size’>?]+

It’s always easier if we have some examples at hand:

grid-template: auto 1fr auto / auto 1fr;
grid-template: 10px / "a" 15px;
grid-template: 10px / (head1) "a" 15px (tail1)
                      (head2) "b" 20px (tail2);
grid-template: (first) 10px repeat(2, (nav nav2) 15px) /       "a b c" 100px (nav)
                                                        (nav2) "d e f" 25px  (nav)
                                                        (nav2) "g h i" 25px  (last);

It’s important to notice that the subgrid functionality is under discussion to be postponed for the level 2 of the specification, hence  it was not implemented, for the time being,  in the shorthand either. This decision had the support of IE and Chromium browsers;   Mozilla partially agree on this, even though with some  doubts.

There was something special in the implementation of this shorthand property. Usually, the CSS property parsing methods are implemented straight forward, avoiding unnecessary or duplicated operations over the parsed value list. However, due to the ambiguity of the shorthand syntax, it’s not clear which form the expression belongs to until reaching the <string> clause. In order to reuse the <grid-template-{row, column}> parsing function, it was necessary to allow rewinding the parsedValue list in case of detecting the wrong form was being processed.

Another remarkable implementation detail was the change in the gridLineName parsing function, required to join the adjoining line names of the last and first columns (nav and nav2 in the example). See below the longhand equivalence of the last case in the previous example:

grid-template-columns: (first) 10px repeat(2, (nav nav2) 15px);
grid-template-rows: 100px (av nav2) 25px (nav nav2) auto (last):
grid-template-areas: "a b c" 
                     "d e f"
                     "g h i";

 

The “grid” shorthand

 
Quoting the CSS Grid Layout specs:

The grid property is a shorthand that sets all of the explicit grid properties (grid-template-rows, grid-template-columns, and grid-template-areas) as well as all the implicit grid properties (grid-auto-rows, grid-auto-columns, and grid-auto-flow) in a single declaration.

<‘grid-template’> | [<‘grid-auto-flow’> [<‘grid-auto-columns’>[/ <‘grid-auto-rows’>]?]?]

Even that the shorthand sets both implicit and explicit grid properties, it can be only specified either implicit or explicit grid properties; the missing properties will be set to the initial values. Now let’s see some examples:

grid: 15px / 10px;
grid: row 10px;
grid: column 10px / 20px;

The “grid” shorthand is the recommended mechanism even to define just the  the explicit shorthand, unless web authors are interested on cascade separately the impicit grid properties.
 

Current status and next steps

 
Both properties landed Blink trunk rencetly (revisions 170552 and 171143) and and they are waiting for the final review in WebKit, hopefully they will land soon. There are enough layout tests to cover the most common cases but perhaps some additional cases might be added in the future. As it was mentioned, there are certain ambiguities in both shorthands syntax and it’s also important to check out the www-style mailing list looking for changes that might require modifying the implementation, hence adding the proper test cases.

With the implemmentation of these two new shorthands, the properties implementation tasks are almost completed. We are working gonw on fixing bugs and implementing the alignment features. There is a quite important gap between the Blink and WebKit implementation, but we are working on porting patches as soon as possible, since we think it’s important to have both implementations synced.

I’ll attend the WebKit Contributors Meeting next week, so perhaps I could speed up the landing the patches for the shorthand properties. My main goal, though, will be to gather feedback from the WebKit community about the status of the CSS Grid Layout implementation, what features they miss the most, which bugs should have more priority and share with them our future plans at Igalia.

All this work was possbile thanks to the collaboration between Igalia and Bloomberg, We both are working hard to help and promote the wide adpoption of this standar, which will be shipped soon on IE and hopefully also in Chromimum. We are also following the efforts Mozila is doing, which give us the impresion that the interest of most of the browsers on this standar is quite high.

Improving selection in CSS Regions

I would like to introduce in this post the main problems we have detected in the Selection implementation of two of the most important web engines, such as Blink and WebKit. I’ve already described some of these issues, particularly for CSSRegions, but I’ll go a bit further now analyzing them and also introducing one of the proposal we have been working on at Igalia s part of the collaboration we have with Adobe.

Selection is a DOM Tree matter

At Igalia, we have been investigating how to adapt the selection to the new layout models which provide more complex ways of visualizing the content defined in the DOM Tree. Let’s consider the following basic example using CSSRegions layout:

base-case
Figure 1: base case

In the last post about this issue we have identified 4 main problems with selection in CSSRegions:

  • Selection direction
  • Highlighting and content mismatch
  • Incorrect block gaps filling
  • Clear the selection

I’ll describe some examples where these issues are present, where are the root causes and how they can be solved or, at least, improved. I’ll try as well to explain how the Selection works, starting from the mouse events the end user generates to perform a new selection, how those are mapped into a DOM Tree range and finally, how the rendering process produces the highlighting of the selected elements.

example-a1
Figure 2: Highlighting and selected content mismatch

I’ll use this first example (Figure 2) to briefly describe how the Selection is implemented and how all the involved components interact to generate both, the selected DOM Range and the corresponding highlighting by the RenderTree. Obviously the end user selects contents from the Visualized elements, in this case the content of two regular blocks (no regions involved). The mouse events are translated to VisiblePosition instances (Start and End)  in the DOM Tree using the positionForPoint method. Such VisiblePositions are then mapped into the corresponding RenderObjects in the Render Tree; these objects are the ones used to traverse the tree in the RenderView::setSelection method and mark the appropriated elements with one of the following flags: SelectionNone, SelectionStart, SelectionInside, SelectionEnd, SelectionBoth. These flags are also very important in the block gaps filling algorithm, implemented basically in the RenderBlock::selectionGaps method.

The algorithm implemented in the RenderVieww::setSelection method can be described, very simplified, as the following steps:

  • gathering information (RenderSelectionInfo and RenderblockSelectionInfo) of the old selection.
  • clearing the old selection (basically mark all the elements as SelectionNone)
  • updating the flags of the elements of the new selection.
  • gathering information of the new selection.
  • repainting old objects which might have changed.
  • painting the new selected objects.
  • repainting the old blocks which might have changed.
  • painting the new selected blocks.

The algorithm traverses the RenderTree, from the Start to the End using the RenderObject::nextInPreOrder function. Here is where the clear operation issues can appear. If not all objects can be reached by the pre-order traversal, the clear operation does not work properly. That’s why we introduced a way to traverse back the Tree (r155058) looking for elements which can be unreachable. One of the causes of this issue is the selection direction change.

This first example shows the highlighting and content mismatch issue, since the DOM Range considers the source (flow-into) element, while is not highlighted by the RenderTree.

The next example considers now selection from both regions and regular blocks and introduces also an interesting Selection topic: selection direction.

example-b1
Figure 3: Incorrect block gaps filling

As you can see in the diagram Figure 3, the user selected content upwards. In most of the cases the selection direction is not used at all, so Start  must be always above the End VisiblePosition in the DOM Tree. The VisibleSelection ensures that, but in this case, because of how the Source (flow-into) is defined according to the CSSRegions specification and where it was placed in the HTML code, the original Start and End position are not flipped. We will talk more about this in the next example. However,  the RenderObject associated to a DOM element with a flow-into property is located in the in the render tree under the RenderFlowThread object, which itself is placed at the end of normal render tree, thus causing the start render object to be below the end render object. This fact causes the highlighted content to be exactly the opposite to what the user actually selected.

This example illustrates also the issue of incorrect block gaps filling, since the element with the id content-1 is considered a block gap to be filled. This happens because of the changes introduced in the already mentioned revision  r155058  since the element with id content-2 and the body are flagged as SelectionEnd, the intermediate elements are considered as block gaps to be filled.

At this point is quite clear that the way the Render Tree is traversed is very important to produce a coherent selection rendering; notice that in this case, highlight and selected content match perfectly. The idea of using the Region DIV as container of the Source DIV content portion, which is rendered inside such region, looks like a promising approach. The next example will go further into this idea.

example-c1
Figure 4: Selection direction

In this example (Figure 4) the Start and End VisiblePosition instance have to be flipped by the generated VisibleSelection, since the DIV with the id content-1 is above the original Start element defined by the end user. By flipping both positions it makes the corresponding Start and End RenderObject instances to be consistent, that’s why there is no selection direction issue in this case. However, because of the position of the End element as child of the RenderFlowThread, the RenderElement with the id content-2  is selected, which, while being seamless from the user experience point of view, it does not match the selected content retrieved from the DOM Range.

The solution: Regions as containers

At this point is clear that the selection direction issues are one of the most important source of problems for the Selection with CSSRegions. The current algprithms, RenderView::setselection and RenderBlock::selectionGaps, require to traverse the RenderTree downwards from start to end. In fact, this is specially important for the block gaps filling algorithm.

It’s important to notice that the divergence of the DOM and Render trees when using CSSRegions comes from how these two concepts, the flow-into DOM element and the RenderFlowThread object, are managed and placed in each trees. Why not just using the region elements for the selection algorithms and considering both flow-into and RFT as “meta-elements” where the selected content is extracted from ?

Considering the steps defined previously for the selection algorithm the regions as containers approach could be described as follows:

  • Case 1: Start and Stop elements, either both or none, are children of the RenderFlowThread.
    • The current RenderView::setSelection algorithm works fine.
  • Case 2: Only Start is child of the RenderFlowThread.
    • First, determining the RenderElements range [RegionStart, RegionEnd] in the RenderFlowThread associated to the RenderRegion the Start element is rendered by.
    • Then, applying the current algorithm to the range of elements [Start, RegionEnd]
    • Finally, applying the current algorithm from the NextInPreOrder element of the RenderRegion until the Stop, as usual.
  • Case 3: Only Stop is child of the RenderFlowThread.
    • First, applying the current algorithm from the Start element to the RenderRegion the Stop element is rendered by.
    • Then, determining the RenderElements range [RegionStart, RegionEnd] in the RenderFlowThread associated to the RenderRegion the Stop element is rendered by.
    • Finally, applying the current algorithm to the range of elements [RegionStart, Stop]

Determining the selection direction, at VisibleSelection, is also affected by the structure of the RenderTree; even that the editing module in both WebKit and Blink is also using rendering info for certain operations, this is perhaps one of the weakest points of this approach. Let’s use one of the examples defined before to illustrate this situation.

example-b2
Figure 5: Block gaps filling issues solved

While traversing the RenderTree, once a RenderRegion is reached its corresponding range of RenderObjects is determined in the RenderFlowThread. The entire range will be traversed for the blocks flagged as SelectionInside. For the ones flagged as SelectionStart or SelectionEnd, the steps previously defined are applied.

The key of this new approach is that traversing is always downwards, from the Start to the End, which solves also the block gaps related issues.

Let’s considering now a more complex example (Figure 6), with several regions between a number of regular blocks. selection is more natural with this approach, coherent with what the user expects and also matching the DOM Tree range for most of the cases. This is, however, the biggest drawback of this approach, since it does not follow completely the Editing/Selection specs. I’ll talk  more about this in the last lines of this post.

example-d
Figure 6: Selection direction issues solved

The following video showcase our proposal on the WebKit MiniBrowser testing application using a real HTML example based on the Figure 6 diagram.

Even though selection is more natural an coherent, as I already mentioned, it does not follow completely the Editing/Selection specs. As I stated at the beginning of this post, selection is a DOM matter, defined by a Range of elements in the DOM Tree. This very simple case (Figure 7) is enough to describe this issue:

example-a
Figure 7: Regions as containers NON specs compliant

The regions as containers approach does not considers the Source (flow-into) elements as actual DOM elements, so they will never be part of the selection. This breaks the Editing/Selection specification, since those are regular DOM elements as they are defined in the CSS Region standard. This approach was our first try and perhaps too ambitious, providing a good user experience on selection with CSSRegions and specs compliant at the same time. Even that it was a good experience we can conclude that the problem is too complex and it requires a different strategy.

We had the opportunity to introduce and discuss our proposal during the last WebKitGtk+ Hackfest, where Rego, Mihnea and me had the chance to work hand in hand, carefully analyzing and digesting this proposal. Even that we finally discard it, we were able to design other approaches which some of them are really promising. Rego will introduce some of them shortly in a blog post. Hence, can’t end this post without thanking to Igalia and the GNOME Foundation for sponsoring such a productive and useful hackfest.

CSS Regions and Selection

Back in early June, Adobe and Igalia announced a collaboration to work on the CSS Regions and CSS Shapes W3C standards. Our first challenge has been to improve the Selection use cases when using complex layout models, like CSS Regions.

The CSS Regions model allows content to flow across multiple areas called Regions. This new approach offers web content designers a way to build richer and more complex layouts, mapping content with specific visual areas of a document. Defining different Flow Threads with multiple Regions, associating them to specific content, and applying different styles to a set of Regions is very powerful in terms of design and user experience. If you are interested, here you can find some examples of what is possible with CSS Regions.

But having this flexibility in web design requires overcoming quite a few technical challenges. The current implementation of CSS Regions in WebKit changes the way the Render Tree is created from the DOM Tree. This poses the challenge of making selection work with regions since selection is DOM based. Given its importance and frequent use, improving the interaction of selection and CSS Regions has been the main goal of our collaboration.

The W3C selection specification, which has not been updated since the last year, does not address the complexities introduced by new layout modules, like CSS Regions, CSS FlexBox and CSS Grid Layout module . We found out very quickly that selection had many issues, with respect to both visual appearance and selected content. We have created a tests suite to evaluate the different use cases of selection with CSS Regions.

test2
Selected content does not match the highlighted area.

test1
Selection direction issues

Let’s start with a very simple description of the concept of Selection Direction, which consist of the following points:

  • The WebCore::VisibleSelection class has two attributes called base and extent declared as dom::Position instances
  • Such positions refer respectively to the anchor and focus nodes in the DOM Tree.
  • Additionally, WebCore::VisibleSelection has two dom:Position attributes, start and end, which are used later during the rendering phase

Once the base and extent fields are set when instantiating a new VisibleSelection class, some adjustments and checks are performed to validate the selection. One of those checks is whether base position is before extent in the DOM Tree. Based on the result of this check, the start and end attributes will be set to either base or extent respectively.

In the first test, the selected content includes the entire region block, even when it was not selected by the user. The cause, as we will see in later, derives from the position of the source block in the DOM Tree, which in this case is defined between the two regular blocks.

The second example shows some selection direction related issues; in this case, what the user selected is precisely the content between the two highlighted areas. The problem here is that the base node of the original selection is below the extent node in the DOM Tree, so they are swapped in the selection logic. In addition, the CSS Regions implementation builds the Render Tree in a way that the source content defined by a RenderNamedFlowThread block is positioned below where it was defined in the DOM Tree. The consequence of this is that the start node is below the end node, so the highlighted area starts in the region block and continues from the root element (usually the body) until reaching the end node.

Our first approach was trying to provide a better user experience during selection with CSS Regions. We thought that adding multi-range capabilities to the DOM Selection API was the best way to go and we provided a patch. However, this approach was rejected by some Apple reviewers because multi-range selection introduces many problems, such as those detailed in the selection specification.

We have opened the debate again on the mailing list, though, because we think there might be some advantages to this approach, even without modifying the selection API. For instance, being able to handle independent Ranges and compose the expected selection will provide the flexibility needed to implement complex use cases. But, after some discussion with some of the Adobe Web Platform contributors, we have decided to focus on improving the selection following the current specification. While we feel this approach may lead to a non-optimal user experience for certain use cases, we expect implementing it will help us discover the problems inherent in the current selection specification. We have also been discussing these issues with some reviewers from Apple, Ryosuke Niwa and David Hyatt, and looking for alternatives to the multi-range approach.

We have posted additional patches, one to improve the selection behavior and another to revert the current limitation of selections related to including content from different Flow Threads. We think that this approach provides better integration of CSS Regions with HTML documents. Plus, it will allow us to properly evaluate the performance issues of selection with CSS Regions.

The other challenges we faced during this collaboration include:

  • changing how the selection rendering traverses the Render Tree in order to deal with the special RenderFlowThread blocks
  • adjusting the block gaps filling algorithm
  • clearing the selection
  • selection direction issues derived from the Render Tree and DOM Tree divergence

We detected a number of other issues,  such as how LayoutPoints are positioned in the DOM Tree when pointing to Region blocks, leading to an incorrect Selection extent node.  We are confident that we will ultimately have a fully-compliant selection specification implementation for CSS Regions, but the improvements using this approach are limited. Even after solving all the issues we have detected so far, selection might still seem weird and buggy from an end user perspective. Thus we think that the final solution, one which will provide the user with a more consistent experience, will be to complement the selection specification to consider not only the DOM Tree, but also how the Render Tree is built by the Layout Model.

GeoClue and Meego: QtMobility

As you probably know, GeoClue is part of the Meego architecture as the Geolocation component. However, current plans are using the QtMobility API for UI applications and defining GeoClue as one of the available backends.

The QtMobility software implements a set of APIs to ease the development of UI software focused on mobile devices. It provides some interesting features and tools for a great variety of mobile oriented development areas:

  • Contacts
  • Bearer (Network Management)
  • Location
  • Messaging
  • Multimedia
  • Sensors
  • Service Framework
  • System Information

All those software pieces are a kind of abstraction to expose easy and comprehensive API’s to be used in the UI application developments. In regard to Geolocation, lets describe in detail the Location component.

It was recently announced the first public implementation of a GeoClue based backend for the QtMobility Location API. The starting point to implement the GeoClue backend, as described in the QtMobility documentation, is the QGeoPositionInfoSource abstract class.  The implementation of this abstract class using GeoClue seems not too hard, however, the current GeoClue architecture has some limitations to fulfill the QtMobility specifications:

  • The QtGeoPositionInfo class, defined for storing the Geolocation data retrieved by the selected backend (GeoClue in this case) manages together global location, direction and velocity.
  • The GeoClue API has separated methods and classes for location, address and velocity. Independent signals are emitted whenever such parameters are changed.
  • The GeoClue Velocity interface is not implemented in the GeoClue Master provider.
  • Even though is not too hard to implement the abstract methods of the QGeoPositionInfoSource class, the start/stop updating methods are not very efficient in regard to battery and memory consumption. There is not easy or direct way to remove one provider when is not used.

As part of the Igalia’s plans on Meego, I’ve been working in the implementation of such GeoClue based backend for the Meego QtMobility framework. Now that part of my work has been already done, it’s time to share efforts and contribute to the public repository with some patches and performance reports I’ve got during the last months. Some work is still needed before releasing my work, but I hope I will be able to send something in the following weeks, so stay tunned.

Even though the code is not ready for being public, I could show a snapshots of the test application I implemented for the Meego Handset platform using the Meego Touch framework:

GeoClue test application for Meego Handset

The purpose of this application would be monitoring the DBus communication between the different location providers, creating some performance tests and evaluating the impact on a Mobile platform.

194412

QGeoPositionInfo Class Reference

GeoClue and Meego: Connman support

As promised, GeoClue now supports Connman as the connectivity manager module for acquiring network based location data.This step has been essential to complete the integration of GeoClue in the Meego architecture.

Check the patch if you want to know the details.

Thanks to Bastian Nocera for reviewing and pushing the commit, which is now part of the master branch of GeoCLue. Let see if it passes the appropriated tests before becoming part of some official release.

Network based positioning is one of the advantages of using GeoClue as Location provider. That’s obvious for Desktop implementations, where GPS and Cell Id based methods are not the most common use cases. On the other hand, Mobile environments could also get benefits from network based positioning, assisting the GPS based methods for improving the fix acquiring process; perhaps indicating where the closest satellite network is or showing a less accuracy location while the GPS fix is being established.

Finally, I would like to remark that my work is part of the Igalia’s bet for the Meego platform. I think the GeoClue project will be an important technology to invest in the future, since it’s relevant also for GNOME and Desktop technologies. In fact, GeoClue is also the Ubuntu’ s default Geolocation component.