1. The existing functionality is going to be moved into a library called libcowbell.  Very little will be changed at this point from what we already have.  (But there will be some extra tests.)
2. A release of the metacity-cowbell branch will be made that can use libcowbell.
3. A release of real Metacity will be made that can use either libcowbell or conventional themes.
4. Development of libcowbell can continue.  (I expect pseudoclasses to be among the first things added.)

More more cowbell. Iain has pointed out an existing GNOME-based project called cowbell.  I hope the fact that this project will be libcowbell will be enough to avoid confusion.

Feedback on feedback. Screwtape has reviewed the existing cowbell documentation in a web page here.  Here is my feedback on the feedback:

• §3: I did start out by showing the structure as pseudo-XML, but people commented as if the window borders were the result of rendering that XML (as if it were XUL, or something similar), so I think it may be misleading.
• §3: I dithered over using the ID or a class for this sort of thing for quite a while.  In the end I went with a class because we use classes for buttons (since they may repeat) and it seemed as well to use the same design for areas, and because you may have more than one content area visible at once, even if they are on separate windows.  But I may have been wrong, and I invite opposing opinions.
• §3: buttongroup: I really like this idea.  But AFAIK libccss doesn’t yet support last-child etc (see next…)
• §3.1: I want our CSS support to be up to level 3 wherever possible.  However, we are constrained partly by what libccss is currently capable of.  Of course we can patch libccss too!  Backgrounds and Borders is largely supported by libccss, though.
• §3.2: Unpainted areas are transparent (though if the frame is opaque, you’ll just see the frame through them).
• §3.3: font-size is important; what should the interaction be between the font size set in Metacity gconf and the font size in the theme?  Just use the theme font size for scaling as in v2?
• §3.3: button heights: I think I didn’t explain myself properly here.  You can (should) set height and width on buttons.  But these only serve to establish an aspect ratio.  The height is always calculated from the titlebar height at present.  Perhaps this is overly confusing.
• §3.5: :focus pseudoclass: perhaps this should be set on all elements in a focused window.  Or perhaps just the frame and we can use the descendant selector.
• §3.5: :disabled — hadn’t thought of this, good idea.  TMTOWTDI.
• §3.5: I’m not sure libccss supports :not() (but maybe it does!)  If so, yes, we should use it.  It’s far better to work the way people expect us to work.
• §3.7: I hope we support SVG too.  It would be extra nice if it could be styled with the same CSS somehow.
• §3.8: I really want mm and em as well as px.  I’m not certain libccss knows how to do this, but I will check.
• §4: Nobody’s really tried to put Dublin Core data in CSS before, and I’m probably not doing it the best way.  I worry that including a required custom XML file will be slipping back into using custom formats, though.  Maybe we should use an @rule.  Or specially-formatted comments.  Or maybe we should give up on the whole required metadata idea.
• §4: I like the idea of specifying alternative stylesheets, though metadata in the stylesheets themselves could also do this.
• §6.1: yes, we really need a default stylesheet.  I’m not sure what should go into it.  I will think about this and include it in the first libcowbell release.
• §6.2: okay, we’ll avoid data: URLs.
• §6.2: let’s implement the single file doctrine by allowing any file in ~/.themes/ThemeName/cowbell/ThemeName.tar to be treated as if it was in ~/.themes/ThemeName/cowbell/.  I think we can get that in the first libcowbell release too.
• §6.5: I really like Firebug.  Are you thinking we could use Firebug itself, or just copy its UI?
• §6.11: Maybe we could also modify hue/saturation/value directly in the URL thus: url(’file:fred.png?hue=#f00′)?
• §6.13: I was thinking of themes which, say, repeat a pattern an integral number of times on the otherwise empty part of the titlebar, scaled to fit; this wouldn’t be possible using border-images, but would work fine with filler.  On the other hand, perhaps this is overkill.

Feedback from everyone reading this, on the above and on the original document, is very welcome.

Maybe we need to take over a little piece of live.gnome.org to hash all this out.  Or maybe we need a mailing list.  I’ll wikify all this tonight and then post about it here.

Photo © Honza Soukup, cc-by.

Why? Some people have asked why anyone should be interested in CSS theming, given the existence of a stable and mature theme description format.  The answer is that there are perhaps a couple of hundred people in the world who understand the Metacity theme format, and its complexity presents a significant barrier to entry for anyone else attempting to learn it.  By contrast, millions upon millions of people have a basic understanding of CSS.

Efficiency. Some have pointed out that using CSS may cause great increase in memory footprint or execution time. Both of these are of primary importance to us. Furthermore, we know just how fast every theme renders using the standard engine. We are not prepared to introduce a new theme engine unless it is at least as efficient as the old one.

Mismatch. Some complain that the lists we gave of things we would need to ignore and things which would need to be added proved that there was a mismatch between CSS and what was needed.  This is based on a misunderstanding of CSS as a language to style HTML.  In fact CSS is a general-purpose styling language, and there are only a few places where it does not quite meet our needs.  Even in those places the design is flexible enough to accommodate us.

The balance of power. Ray asked whether the structure of the window should be under theme control, as well as the styling. Some ask how we decide what is under the control of the CSS.  We always need to find a balance between giving power to themes and giving power to users. Some things should be under theme control and some under user control, but it’s not trivial to decide which. Here are some examples:

• Justification of the text on the titlebar. Currently this is entirely under theme control; the user can’t change it. Some people would like this to change.
• The arrangement of buttons on the titlebar: which are on the left, which are on the right, and which aren’t shown at all. This is currently entirely under user control; the theme can’t change it. (This means that themes which attempt to look like OS X have to ask you to reorder your buttons so that close is on the left, since they can’t do it themselves.)
• The font on the titlebar. Currently this is entirely under user control; the theme can’t change it. This among other things is something we’d need to reexamine with a CSS theming engine.

(”Under user control” means set in GConf and, generally, modifiable in the control panel.  Some of these options cannot be set in the control panel at present, but that’s a separate problem.)

It may be true that windows should have a more flexible structure, and the ability to have the titlebar elsewhere is certainly something that’s been asked for from time to time. But assuming we should add such abilities, should the decision to use them be made by the theme, or should it be something selectable by the user in the control panel? These are deep questions.

Co-operation with GTK CSS theming. Yes: a good idea.  Whatever they’re doing, we should probably try to share in it.

Complexity. Some have said that CSS is a complex system, and that anything implementing it will therefore also be complex and difficult to implement.  This is an unwarranted assumption.  Take a look at the table of contents of the CSS specification and see how little of it actually applies to a fully-functional system for description of window borders:

• Syntax and basic data types; Selectors; Assigning property values, Cascading, and Inheritance; Media types:  all handled for us already by libcroco.
• Box model: we would need to implement this.  Not terribly complex because we have a simple and unchangeable layout model.
• Visual formatting model; Visual effects: these are complex, and we can ignore them entirely, since our layout needs are simple and unchangeable.
• Generated content, automatic numbering, and lists: we would need to implement basic generated content (the easy part); we have no content to be numbered, and no lists.
• Paged media: does not apply to us.
• Colors and Backgrounds: the most complex part which we would need to implement.
• Fonts; Text: partially applies to us (since some of it isn’t theme-controlled); mostly involves passing things into Pango.
• Tables: doesn’t apply to us; we have no tables.
• User interface: this is about setting cursors and things, and doesn’t apply to us.

Finally, we should probably reiterate that:

• this is still an experiment, and not an official direction which Metacity is taking;
• even if it ever happens, there’s certainly no decision to use WebKit.

Photo © johninbkk, cc-by.

It currently saves configuration data in a keyfile which contains one group per window, in this format:

[xlogo]
x=287
y=178
w=250
h=231

This isn’t necessarily how it will end up: we could use GConf or perhaps some database-like format. It uses a modified version of the system suggested by Hongli Lai: if WM_WINDOW_ROLE is set, we use that to recognise the window, otherwise we use the window title– otherwise programs like xclock wouldn’t be matchable. The role or title is currently represented by the group name in the keyfile.  The keyfile is saved at ~/.cache/metacity/matching.conf.

The system stores the position and size of every window at the moment it was closed.  There is no need to edit configuration files by hand.

There are inevitably some caveats:

• There is a bug such that when windows are restored they are offset by the size of the top-left hand corner of the frame.  (In other words, the coordinates are misinterpreted as the client window’s position, not the frame’s.)
• I haven’t tested this for scalability at all.  Keyfiles might be very inefficient when you have hundreds of records for all I know.
• It doesn’t know about workspaces, and it should; this will probably be the next thing I add.
• If your window was minimised or maximised, this will not be restored, and it should be.  This will probably be the next thing after that.
• It might not be the best idea to write out the keyfile on every window close.  Probably better to keep it in memory until the WM exits.
• It might be useful to have a switch on the window menu to lock the position and size so it restores the same way when you reload it, in case you move it.  On the other hand, this sounds like crack.

Should this branch be merged when the bugs are ironed out? Should it replace WM-based session files? These are good and interesting questions and ones we should discuss.  Tune in next time, gentle reader!  Or better, comment below.

Photo © Bob Fornal, cc-by-nc-sa.

Lots of happy buzz about window managers here at the desktop summit.  Some things people have said:

• Someone asked about implementing window matching.  It’s always been our policy that it should be done with an external tool, but policies can of course be rethought.  We might implement it in a branch and see whether anyone likes it.
• People are very excited about Mutter.
• Some concern was expressed by distros about whether enough machines will be capable of running gnome-shell: not just rather old machines but new ones which don’t have drivers yet.  Some interest in a version that uses software rendering.
• Owen Taylor’s work on the git migration and on gnome-shell got a standing ovation at the AGM.
• Several patches got reviewed and committed at last in hack sessions.
• Some discussion of the use of CSS in theming.
• Someone raised the idea of a generalised EWMH testing suite that can be used with Metacity or Mutter.  This sounds like a sterling idea.

In addition,

• the rpnparser branch (which is a simpler and faster theme expression parser) is still viable, but since the theme format for Mutter isn’t decided, it doesn’t really make sense to merge it.  But perhaps it still belongs in Metacity 2.  What are your thoughts, gentle reader?
• the squib of the day section in the blog only deals with enhancements, and since enhancements in Metacity are less likely and moving things to Mutter is more likely, this section may be on hiatus for a bit.

Photo © jcorrius, cc-by.

• How would you make a Prelude theme? Answered here and now floating around the net.
• Will the compositor ever be enabled by default? I’d like it to be.  There are apparently people it still doesn’t work for well, though.  Perhaps as newer hardware becomes more common this will become less likely.
• Will there be new features in the compositor? Possibly.  It seems to be working fine now, and I don’t want Metacity turning into a knock-off of Compiz.  But I can imagine some kind of plugin-based thing happening in a wild handwavy future, and in the meantime plenty of people are asking whether the shadows can become adjustable.
• What is Metacity’s role in GNOME Shell? GNOME Shell uses a fork of Metacity called Mutter (i.e. Metacity with Clutter).  Whether this will become the main Metacity in future, or whether the two will be developed in parallel, or whether it’ll be merged back upstream and have some way of controlling which control path is taken, is not yet decided.  I need to talk to the Mutter people more, anyway.
• How about window matching? Raise your voice about option 2 of this list.
• Can Metacity move the title bar from the tops of windows to the sides? Not in versions 1 or 2 of the theme format.  Maybe in version 3 this will be possible, if there was any use for it: it’d be a fairly simple change to the existing system.
• Why not merge Metacity and KWin and have one über-window-manager? Because choice is good.  That’s why we have EWMH, so you can run KWin with GNOME or Metacity with KDE if you really want.  Trying to reduce choice in window managers, or desktop environments, or whatever, really ends up with the choice of The Non-Free Market Leaders versus Everyone Else, which really isn’t much of a choice.  (But we do talk to Luboš and the other WM maintainers, and they’re all fine people, and we’re not attempting to sabotage one another’s work.  We’re even holding the conferences in the same place this year, you know…)

Photo © Nick Ford, cc-by-nc-nd.

A user writes:

At the moment i’m trying to make a theme for metacity but I have no idea how I can make the document icon drag-able and to interact with the desktop environment i.e. drag to the desktop to save or to the trash to delete.

Firstly, let me thank you for being willing to work on developing the desktop.

To begin with, this idea was based on “Window Experiments”.  desrt developed this idea into a program called icanhasedit back in August, which worked by taking over the responsibility of drawing window decorations from the window manager.  That’s certainly one way of going about solving the problem, but it brings a whole raft of problems of its own.  So let’s assume we want to keep the decorator in the window manager here.

Secondly, there is nothing in Metacity corresponding to “the document icon” as such.  It happens that most themes draw the icon of the current window on the menu button– the button which shows the window menu when you click it.  Some themes do it other ways, though: for example, Atlanta draws the icon on the titlebar next to the window’s name.  But let’s assume what we want is for the menu button to be draggable.

So you need to implement drag-and-drop from the widget representing that button.  Once that’s done, you need to have a way to tell what should actually happen when the button is dragged somewhere.  The trouble is that Metacity doesn’t know much about what’s actually in the window: it knows the name and the icon and a few other things, but the actual content is the business of the application.  So you need to invent a way for the WM to tell the application that a drag is happening, and for the application to tell the WM what the data being dragged is, and what its type is.  Then you need to argue it out on wm-spec-list and then you need to get applications actually to implement it so it’s useful.

So: this is possible, but it’s complicated and probably not an ideal first project.  If you want to try solving it, please go ahead and I’ll give you what help I can.  If you’d rather do something easier first and ramp up to this, I can help you with that too.

Do you think everyone who might possibly want to know about day-to-day Metacity life is reading the Metacity blog? If not, how could we tell them about it?