kwin/NOTES_4_0

KWin release notes for KDE4.0
=============================

= Introduction =

KWin, the standard KDE window manager, in KDE4.0 ships with the first version
of built-in support for compositing, making it also a compositing manager.
This allows KWin to provide advanced graphical effects, like for example with Compiz,
while also providing all the features from previous KDE releases (such as very good
intergration with the rest of KDE, advanced configurability, focus stealing prevention,
well-tested window manager, robust handling of misbehaving applications/toolkits, etc.).
Unlike Compiz, KWin still functions even when no system support for compositing is
available, with only compositing features not being available in such case.

Previous KWin versions in later KDE3.x releases included a standalone compositing
manager called kompmgr, based on the xcompmgr compositing manager. Kompmgr was only
loosely tied with KWin, used only XRender for rendering and provided only basic
features like transparency, shadows and fade in/out animations. Compositing manager
in KWin in KDE4.0 is integrated with the rest of KWin, can use either OpenGL or XRender
for rendering and has a framework for compositing effects, all these allowing KWin
to provide a much wider range of features.

Note, however, that compositing support in KWin in KDE4.0 is still considered experimental,
for several reasons. System support for compositing is often being problematic (various bugs
in X, drivers or other parts of the system), manual configuration of X may be required
for proper results (see below), some applications may not be prepared and work well
with compositing, the performance may not be adequate, and other problems.
Also, while KWin's compositing support is considered usable and reasonably stable, it
is relatively new code and has been tested only on a limited range of hardware.

Therefore, compositing support in KWin is disabled by default, and needs to be explicitly
enabled. If there will be any problems, you can disable it again (see below for troubleshooting)
and report a bug with all relevant information about the problem.


= Setting up =

Compositing support is enabled in KWin's configuration. Press Alt+F3 and select 'Configure Window
Behavior'. In the configuration module, select page 'Desktop Effects' and enable checkbox
'Enable desktop effects'. After accepting the changes, a dialog with a timeout will appear,
asking to confirm enabling of compositing support. If you do not confirm within the timeout,
compositing support will be disabled again, therefore, if enabling compositing triggers
any problems, it should be sufficient to wait several seconds before the changes are reverted.
Note that after enabling or disabling compositing it is recommended to restart your KDE
session in order to ensure that all applications detect the change.

If you cannot enable desktop effects, it may be because either your KDE is not built
with necessary support, or more probably because your system is not capable of providing
compositing support. See file
http://websvn.kde.org/*checkout*/trunk/KDE/kdebase/workspace/kwin/COMPOSITE_HOWTO
for some instructions on setting up your system. Note that there may be other factors
affecting whether you do or do not have compositing support.


= Usage =

A quick overview of features provided by compositing manager in KWin:

- Ctrl+F9 (and Ctrl+F10 for windows from all desktops) shows an overview of all windows
  and allows activating one of them. The feature can be also activated by moving the mouse
  into the top-left screen corner. A window can be activated by clicking it or by using arrows
  and Enter key. You can also type text to filter the list of windows.
- Ctrl+F8 shotcut activates a desktop grid - all your virtual desktops will be arranged
  on the screen (as an enlarged pager) - you can select and activate desktops using
  a number, a function key, by clicking on it or by using arrows and Enter key,
  you can move windows by dragging them or by right-clicking on them.
- The DesktopGrid effect also provides animations when switching between virtual desktops (can
  be turned off).
- The window switcher (Alt+Tab by default) provides live thumbnails of windows.
- Windows blocked by modal dialogs are dimmed.
- Screen can be zoomed in and out using Win+<equals>, Win+<minus> and reset using Win+0 (
  it is currently not possible to use mouse wheel, but this feature is planned). Note that
  because of input transformation not being yet available in X the zoomed screen has to move
  around to keep the mouse pointer at the same place like it would be when not zoomed.
- Screen can be shown with inverted colors by pressing Ctrl+Win+I (accessibility feature,
  Invert effect is not enabled by default).
- There are fade animations during login and logout.
- Windows fade in and out.
- Minimize animation to/from taskbar.
- Windows have shadows.

There are more features that are not enabled by default and need to be explicitly enabled
in the configuration.

There are various videos showing various compositing features of KWin. For example,
search for 'kwin_composite' at youtube.com (please keep in mind that many of those windows
are old and show testing or demo effects).


= Using KWin without KDE desktop =

Just like with older KWin versions it is possible to use KWin also with other desktop
environments or even as a standalone window manager, as long as required KDE libraries
are installed. Please note that KWin is a pure window manager and does not provide a panel
or handle desktop background like some window managers do. KWin's compositing features
work in the standalone mode, with some functionality missing (because of missing taskbar,
for example), and, while this has not been tested, it is expected that compositing
features will work also when running in other desktop environments, possibly with some
functionality missing again. Reports on using KWin with other desktop environments
are welcome.


= Performance =

Compositing internally works by redirecting window drawing to offscreen memory and composing
it on the screen in an additional drawing pass. This means that in general composited desktop
on average has worse performance that non-composited desktop (although in some cases it
may perform better, be that real improvement or just perceived one due to animations, better
synchronization or similar factors). For example, binding window pixmaps to OpenGL textures
(that is, preparing window contents for drawing) can be a relatively costly operation
with large windows, making things like animations in Plasma desktop window or page scrolling
in a maximized browser window jerky. Heavy system load can also cause the compositing manager
not repaint often enough, resulting in lagging or jerky screen redrawing.

KWin in KDE4.0 is also relatively new code and has not been extensively optimized yet,
therefore its performance may not be in some areas comparable with performance of other
compositing managers. In such cases performance should be improved with newer versions.

Note that current XRender implementations (in X/drivers) often perform rather poorly and
therefore the OpenGL mode usually should have much better performance. See below for notes
on XRender mode.

Tip: Performance/smoothness with nVidia cards: Smoothness of KWin rendering
can be improved by setting env.variable KWIN_NVIDIA_HACK to 1 (e.g. append
"export KWIN_NVIDIA_HACK=1" to your ~/.profile file). This sets __GL_YIELD=NOTHING
for KWin, letting KWin use more CPU time for OpenGL operations, however
at the expense of affecting performance of other applications. This is
therefore disabled by default. This setting may be removed in the future
if the negative impact becomes insignificant. See section "OPENGL YIELD BEHAVIOR"
in README.txt for nVidia cards.


= Troubleshooting =

As already said, compositing support in KWin is considered usable and reasonably stable,
but due to several reasons it may not work properly for you.

If there are any problems with compositing support, the simplest option is to disable
it again. KWin will normally continue functioning, only not providing compositing features.
If you cannot normally turn off compositing support (for example because the screen
is corrupted), you can turn it off using one of these ways:
- run command 'kwriteconfig --file kwinrc --group Compositing --key Enabled false' from
  the command line
- set environment variable 'KWIN_COMPOSE' to 'N' (append 'export KWIN_COMPOSE=N' at the end
  of your ~/.profile), this affects compositing only temporarily
You will probably need to switch to text mode or start failsafe session from KDM to be
able to perform this.

See file http://websvn.kde.org/*checkout*/trunk/KDE/kdebase/workspace/kwin/COMPOSITE_HOWTO
for some issues with various graphics cards.


= XRender mode =

It is possible to use XRender for compositing instead of the default OpenGL.
XRender mode in general has less features, however at the moment it is also considered
unstable - it has not received as much testing as OpenGL mode, some features may be incomplete
and it is recommended to use the OpenGL mode if possible. Also note that current XRender
implementations (in X/drivers) often perform rather poorly.


= Developers =

KWin provides support for writing compositing effects that may be loaded into KWin as
plugins. These effects communicate with KWin core using C++ API specially designed for this
purpose, making effects not directly dependent on KWin core and changes in it.

At the time of the KDE4.0 release, since compositing support is still under heavy development,
this API is considered unstable and subject to change. If you write your own effect plugin,
you may need to recompile it after KWin update. KWin will however detect incompatible
versions and will not load such plugins (automatic, you do not need to provide any code for it).
As the compositing support will become more stabilized, this API will be kept backwards and
binary compatible, just like with other KDE libraries.

At the time of the KDE4.0 release, API for compositing effects is unfortunately only sparsely
documented. Developers interested in writing compositing effects for KWin are suggested
to use source code of effects shipped with KWin (the Howto effect as the starting point)
and/or ask on the KWin mailing list.

Links to various KWin-related documents are available at http://techbase.kde.org/Projects/KWin .

= FAQ =

== Why not Compiz? ==

It is possible to use Compiz instead of KWin with KDE, however KWin remains the default window manager.
The option of replacing KWin with Compiz had been evaluated before work on compositing features
of KWin started and the conclusion was, in short, that it would lead to a lot of work and duplicated
effort.

To answer in more detail, several technical things need to be explained. Both KWin and Compiz
are a combined window manager and compositing manager. Window manager functionality takes care
of all aspects of handling windows, such as their placement, selecting the active one as so on.
This functionality is crucial for a desktop - without a window manager it would be very difficult
to perform most operations with windows. Compositing manager functionality, on the other hand,
can be considered optional - while it brings many new features, it is still possible very well
to use a desktop (such as with KWin in KDE3).

The reasons to add compositing support to KWin instead of using Compiz include:

- Compiz at the present time is very likely the most advanced compositing manager with many features,
with a headstart when compared with KWin, however, this cannot be said about Compiz as the window manager,
where KWin has the advantage of being a much more tested codebase, providing more stable, well-tested
and robust window manager, with many features. Given that, as said above, window manager functionality
is considered to be more important, it would be unwise to force all KDE users to a change that
would likely mean regressions in many aspects.

These regressions would include lesser integration with KDE, visual and behavioral changes
(the 'KDE window decorator' shipped with Compiz only mimics the look of KWin's decorations,
but does not provide the same functionality, even the Alt+F3 popup menu visibly differs),
possible introduction of problems that have already been fixed in KWin, missing features
that have already been implemented in KWin, and so on. Developing, testing and bugfixing a window
manager can be a very demanding work and repeating all the work done on KWin again for Compiz would
presumably require a lot of effort. As such, claims that KWin is 'reinventing the wheel' are missing
the point, since Compiz, being a relatively new window manager, is reinventing at least as much,
if not more, from other window managers including KWin,

Also, given that there can be only one window manager and one compositing manager at a time,
there would not be possibly a way to remedy these problems by somehow running Compiz and KWin together.

- Compiz currently does not work at all when compositing is not possible, thus requiring a fallback
window manager for such case. This in practice would mean that KDE developers would be required
to work on improving Compiz and would have to keep KWin at least for maintenance as the fallback
for Compiz, thus having two window managers for KDE. Besides the developer work of taking care
of two window managers this would also bring many user problems resulting from two different
window managers, with differences in the look and feel, feature sets and bugs.

It should be also noted that Metacity, GNOME's window manager, has not been dropped in favour of Compiz
either, but is still, to our knowledge, under development and adding compositing features to it
is a work in progress.


== Why not use plugins from Compiz? ==

This option was considered in the past as well. After examination of Compiz code the conclusion was
that this is technically almost impossible. Compiz plugins appear to be merely parts of Compiz
that are separated from its core, but which still heavily depend on it - there are even plugins
that appear to copy and paste parts of Compiz core and modify it. Making it possible to use such
plugins from KWin would essentially require KWin to become Compiz.


== Why add compositing support to KWin when Compiz is better ? ==

There can be different ideas about what better means, but regardless of that, the main aim of KWin
is not to replace Compiz. Many users have asked for compositing support in KDE, and, as explained
in 'Why not Compiz?', the best way to achieve that is considered to be adding compositing
support to KWin. KWin aims to provide compositing support, focusing on providing useful compositing
features and basic visual effects, while keeping its other strengths.