The theme management system for the GNUstep GUI is based
around the
GSTheme
class, which provides support for loading of theme
bundles and methods for drawing common user interface
elements. The theme system works in
conjunction with a variety of other GUI classes
and is intended to eventually allow for very major
changes in GUI appearance and behavior.
Various design imperatives apply to the theme system,
but probably the key ones are:
It should allow designers and other non-technical users
to easily develop new and interesting GUI styles likely
to attract new users to GNUstep.
Using and switching between themes should be an easy
and pleasant experience... so that people are not put
off when they try using themes.
It should eventually permit a GNUstep application to
appear as a native application on ms-windows and
other systems.
To attain these aims implies the recognition of some more
specific objectives and some possible technical
solutions:
We must have as simple as possible an API for the
functions handling the way GUI elements work and
the way they draw themselves. The standard
OpenStep/MacOS-X API provides mechanisms
for controlling the colors used to draw controls (via
NSColor
and
NSColorList
) and controlling the way controls behave
(NSInterfaceStyleForKey() and
[NSResponder -interfaceStyle]
), but we need to extend that with methods to draw controls entirely differently if required.
We must have a GUI application for theme
development. It is not sufficient to
provide an API if we want good graphic
designers and user interface specialists to
develop themes for us.
It must be possible for an application to
dynamically change the theme in use while
it is running and it should be easy for a user to
select between available themes. This
implies that themes must be loadable bundles
and that it must always be possible to unload a
theme as well as loading one. It suggests
that the theme selection mechanism should be in
every application, perhaps as an extension to an
existing panel such as the info panel.
There are various aspects of theming which can be
treated pretty much separately, so there is no
reason why a theme might not be created which
just employs one of these mechanisms.
System images
Possibly the simples theme change... a theme
might supply a new set of system images used
for arrows and other icons that the GUI decorates
controls with.
System colors
A theme might simply define a new system color
list, so that controls are drawn in a new color
range, though they would still function the
same way. Even specifying new colors can make
the GUI look quite different though.
Beyond system colors, the theming API also
provides a mechanism for specifying colors
for particular parts of GUI controls.
Image tiling
Controls might be given sets of images used
as tiling to draw themselves rather than using the
standard line drawing and color fill
mechanisms.
Interface style
A theme might supply a set of interface style keys
for various controls, defining how those controls
should behave subject to the limitation of the
range of behaviors coded into the GUI library.
Method override
A theme might actually provide code, in the form of
a subclass of
GSTheme
such that drawing methods have completely
custom behavior.
While many themes can be created without
subclassing GSTheme, there are some cases
where writing code is necessary (most notably
when interfacing to a native theming engine for
some platform in order to make a GNUstep app
have a native look). In these cases the
subclass should follow certain rules in
order to operate cleanly and efficiently:
Stability
Theme operation should remain consistent
while it is in use, particularly in the
provision of resources such as images and
colors. If a theme needs to change a
resource (such as an image) then it should
do so by calling
-deactivate
, making the change, and then calling
-activate
. This sequence ensures that the GUI library is
made aware of any changes and can redraw the
screen. The deactivation/activation
sequence is expensive, so the subclass
should attempt to combine multiple resource
updates into a group rather than performing
the deactivation/activation for each resource
individually.
Activation
The standard
-activate
method replaces existing system images,
colors, interface style settings and other
user defaults settings with versions stored in
the theme bundle. If a subclass wishes
to dynamically provide these resources rather
than supplying them as static information in
the bundle, it may update the in-memory
information after the normal operation
has taken place. This should be done by the
theme registering itsself as an observer of
GSThemeWillActivateNotification
and adding the resources just before the theme
becomes active. Cleanup may be done
in response to a
GSThemeWillDeactivateNotification
(called before the default cleanup) or a
GSThemeDidDeactivateNotification
(called after the default cleanup).
Versioning
With a theme which contains only static
resources, versioning is not much of an
issue, but with a code-based theme (ie where
you subclass GSTheme) versioning does become
very important. This is because, while you can
load code from a bundle, you can't unload it
again... so if you have two versions of a
theme where the subclass has the same name,
then you have a conflict and can't load both
and swap between the two. Thematic.app
solves this problem my incorporating a
version number into the name of the GSTheme
subclasses it creates, but that's not
the only consideration... You must also
ensure that either you do not define any
other classes in your theme or that, if you
do define them you make sure that each of them
incorporates the theme version number.
A similar consideration would apply
to any categories, however category conflicts
are far more difficult to resolve since even
with different version names of the
categories, the categories all effect
the same class/methods. In fact this issue is
so tricky to deal with that you should simply
not use categories within your theme code.
To work around this limitation, the
GSTheme class supports overriding of the
methods of any other class while the theme
is active. See the
-overriddenMethod:for:
method for more information.
Image override
System images (those returned by the
[NSImage +imageNamed:]
method) are handled by the default theming mechanism, for each system image supplied in the theme bundle, the image is loaded from the bundle and used while the theme is active. Any pre-existing in-memory image is saved on theme activation and restored on theme deactivation. A theme subclass may override the -imageClass
method to change the class used to load each image from the bundle... thus allowing customisation of not just the images but also of the image behavior in the (very rare) cases where this is desirable. Finally, a theme may provide application specific images which are loaded in preference to named images from the application's own bundle. These images are simply stored in a subdirectory whose name is the same as the application's bundleIdentifier.
This interface is HIGHLY unstable
and incomplete at present.
This is a class used for 'theming', which is mostly a
matter of encapsulating common drawing behaviors so
that GUI appearance can be easily modified, but also
includes mechanisms for altering some GUI behavior
(such as orientation and position of menus).
Methods in this class standardize drawing of
buttons, borders and other common GUI elements, so
that all other classes within the GUI will provide a
consistent appearance by using these methods.
The default implementation uses the standard
configurable colors defined in NSColor, such
as controlLightHighlightColor,
controlShadowColor and
controlDarkShadowColor. Themes
are expected to override the default system color list
with their own versions, and this class cooperates
with
NSColor
and
NSColorList
to establish the correct system color list when a
theme is activated.
The class provides a mechanism for automatic
loading of theme bundles consisting of
resources used to define how drawing is done,
plus an optional binary subclass of this class (to
replace/extend the drawing methods this
class provides).
In future this class should provide mechanisms to
draw controls by tiling of images, and provide
control over GUI behavior by controlling the
values returned by
NSInterfaceStyleForKey()
so that controls use the appropriate behavior.
Loads a theme from a theme bundle of the specified
name, which may be either a full path name of the
theme bundle, or a simple theme name (in which case
the standard directories are searched for it) or
nil (in which case the default GNUstep
theme is returned). Returns the loaded theme
but does not make it the current theme, to do that you
will need to call the
+setTheme:
method.
Set the currently active theme to be the
instance specified. You do not normally
need to call this method as it is called automatically
when the user default which specifies the current
theme (GSTheme) is updated.
Returns the currently active theme instance. This
is the value most recently set using
+setTheme:
or (if none has been set) is a default instance of the
base class.
This method is called automatically when the
receiver is made into the currently active theme
by the
+setTheme:
method. Subclasses may override it to perform
startup operations, however, the method is not
really intended to be overridden, and subclasses
should generally handle activation work in
response to the GSThemeWillActivatenotification
posted by this method.
The base implementation handles setup and caching of
the system color list, standard image information,
tiling information, and user defaults. It
then sends a GSThemeWillActivateNotification to
allow subclasses to perform further activation
work, and a GSThemeDidActivateNotification to allow
other parts of the GUI library to update themselves
from the new theme.
Finally, this method marks all windows in the
application as needing update... so they will
draw themselves with the new theme information.
NB. If a GSTheme subclass is integrating to an
external native theming mechanism in order to
make GNUstep apps look like native apps, then the
external theme may change dynamically and the
GSTheme subclass may need to change the GNUstep
application to reflect this change. When this
happens, the update should be handled by the
subclass calling
-deactivate
and then
-activate
to make the changes 'live'.
Returns the class used by the theme for loading
color lists. The default implementation returns the
NSColorList class, but a subclass may override
this to return a color list class whose values change
dynamically in response to changes of a native
theming API for instance. The class returned
by this method should be NSColorList or one of its
subclasses. Subclasses should note that GSTheme
will initialise the instances of the class using the
[NSColerList -initWithName:fromFile:]
method.
Removes the name from the color cache forcing it to
be re-created next time the named color is required.
Passing nil for aName
removes all named colors. Passing a negative
value for elementState applies to all
caches.
This returns the color for drawing the item whose name
is aName in the specified state. If
aName is nil or if there is
no color defined for the particular combination of item
name and state, the method returns nil.
The standard names used for the parts of
various controls are declared in GSTheme.h
See also the
-tilesNamed:state:
method.
Returns the system color list defined by the
receiver. The default implementation
returns the color list provided in the theme bundle
(if any) or the default system color list.
This method is called automatically when the
receiver is stopped from being the currently
active theme by the use of the
+setTheme:
method to make another theme active. Subclasses
may override it to perform shutdown operations, but
it is preferred for subclasses to perform their own
deactivation in response to a
GSThemeWillDeactivateNotification.
The base implementation sends a
GSThemeWillDeactivateNotification
to allow subclasses to perform cleanup, then restores
image, color and default information to the state
before the theme was activates, and finally sends
a GSThemeDidDeactivateNotification to allow other parts
of the GUI library to update themselves.
NB. If a GSTheme subclass is integrating to an
external native theming mechanism in order to
make GNUstep apps look like native apps, then the
external theme may change dynamically and the
GSTheme subclass may need to change the GNUstep
application to reflect this change. When this
happens, the update should be handled by the
subclass calling
-deactivate
and then
-activate
to make the changes 'live'.
Returns the class used by the theme for loading
images. The default implementation returns the
NSImage class, but a subclass may override this to
return an image class whose instances dynamically
alter what they draw in response to changes of a
native theming API for instance. This method
must return the NSImage class or one of its
subclasses. Subclass implementations should
note that instances will be initialised using the
[NSImage -initWithContentsOfFile:]
method and will use the [NSImage -imageFileTypes]
method to determine which image files can be loaded.
Returns the info dictionary for this theme. In
the base class implementation this is simply the info
dictionary of the theme bundle, but subclasses
may override this method to return extra or different
information.
Keys found in this dictionary include:
GSThemeDomain
A dictionary whose key/value pairs are used to set up
new values in the GSThemeDomain domain of the user
defaults system, and hence define values for
these unless overridden by values set explicitly
by the user.
GSThemeTiles
A dictionary keyed on tile names and containing the
following:
FileName
Name of the file (within the GSThemeTiles
directory in the bundle) in which the
image for this tile is stored.
HorizontalDivision
The offset along the X-axis used to divide the
image into columns of tiles.
VerticalDivision
The offer along the Y-axis used to divide the
image into rows of tiles.
Initialise an instance of a theme with the
specified resource bundle. You
don't need to call this method directly, but if you
are subclassing you may need to override this to
provide additional initialisation.
Returns the name used to locate theming resources
for a particular GUI element. If no name has been set
for the particular object this method returns
nil.
Returns the original implementation of a method
overridden by this theme, or zero if the
method was not overridden.
A theme may override a method of another class by
implementing a method whose name is
'_overrideXXXMethod_YYY' where
'XXX' is the name of the class whose method is to
be overridden, and 'YYY' is the normal name of the
method in that class. eg.
_overrideNSScrollerMethod_drawRect:
NB. The overriding method may not access instance
variable directly and must cast all uses of
'self' to be the correct class.
Set the name that is used to identify theming resources
for a particular control or other GUI element. This is
used so that where an element is part of a control it
can be displayed differently from the same class of
element used outside that control. Supplying
a nil value for aString simply
removes any name setting for anObject.
Supplying nil for
anObject is illegal (raises an exception)
unless the value of aString is also
nil (and the method does nothing).
Any control which uses this method to set
names for subsidiary elements must also make sure to
remove the name mapping before that element is
deallocated, unless the
takeOwnership option is YES,
in which case anObject is retained, the name
mapping lasts only until the receiver is
deactivated, and at that point
anObject is released.
Provides a standard inspector window used to
display information about the receiver. The
default implementation displays the icon, the
name, and the authors of the theme.
The code managing this object (if any) must be
prepared to have the content view of the window
re-parented into another window for display
on screen.
Removes the name tile images from cache, forcing
re-creation next time the named tiles are
required. Passing nil for
aName removes all named tiles.
Passing a negative value for
elementState applies to all caches.
Returns the tile image information for a particular
image name, or nil if there is no such
information or the name is nil.
The standard names used for the parts of
various controls are declared in GSTheme.h
The GUI library uses this internally to handling tiling
of image information to draw user interface elements.
The tile information returned by this method can be
passed to the
-fillRect:withTiles:background:fillStyle:
method. The elementState argument specifies the state for which tiles are requested. See the -colorNamed:state:
method for determining colors to be used for drawing specific GUI elements.
Theme drawing methods. Methods which return
information/resources are generally
expected (ie unless explicitly documented otherwise)
to be returning something which persists until the method
is called again or until the current theme is deactivated
(whichever comes first). This means that
drawing code should not need to
retain/release any returned object (the theme
is responsible for retaining the object), and should also
be able to cache size information etc for later drawing.
This simple rule means that drawing code can be
written to be as efficient as possible while keeping
caching strategies simple and uniform. To
facilitate this within the theme code itsself, it
is recommended that you make use of the
-setName:forElement:temporary:
method to retain any vended object until deactivation.
Creates and returns the cell to be used to draw a
scroller arrow of the specified type and
orientation. The theme instance is
responsible for ensuring that the cell
continues to exist until the theme is deactivated
(the default implementation does this by naming the
cell using the
-setName:forElement:temporary:
method, which also provides a name for the cell
color and image).
Creates and returns the cell to be used to draw a
scroller knob of the specified orientation.
The theme instance is responsible for ensuring that the
cell continues to exist until the theme is deactivated
(the default implementation does this by naming the
cell using the
-setName:forElement:temporary:
method).
Creates and returns the cell to be used to draw a
scroller slot of the specified orientation.
The theme instance is responsible for ensuring that the
cell continues to exist until the theme is deactivated
(the default implementation does this by naming the
cell using the
-setName:forElement:temporary:
method).
Returns the width which should be allowed for a
scroller within the current theme. Drawing code is
entitled to assume that this value will remain
constant until the theme is deactivated.
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
Returns the color used to draw a menu item
background.
The menu item background is drawn atop the menu
background.
By default, looks up the color named
menuItemBackgroundColor, otherwise returns
the control background color. When selected or
highlighted, the background color is
provided by
[NSColor +selectedMenuItemColor]
.
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
Can be overridden in subclasses to return a custom
color, but generally should not. Instead themes
should provide default colors in the GSThemeDomain
(in their Info.plist).
If YES, instructs NSScrollView to make the
scrollers overlap the border. The scroll view
border is drawn using the NSScrollView part, which
must be provided by the theme if this method returns
YES. Controlled by user default
GSScrollViewScrollersOverlapBorders;
default NO;
If YES, instructs NSScrollView to leave an
empty square space where the horizontal and vertical
scrollers meet. Controlled by user default
GSScrollViewUseBottomCorner;
default YES.
Return YES if the scroller arrows are
at the same end. Return NO to get one
scroller arrow at each end of the scroller. The
default implementation first checks the default
GSScrollerArrowsSameEnd and if that
is not set, delegates to the NSInterfaceStyle.
Returns YES if clicking in the
scroller slot should scroll by one page,
NO if the scroller should jump to the
location clicked. The default implementation first
checks the default GSScrollerScrollsByPage and if
that is not set, delegates to the NSInterfaceStyle.
Returns the class used to create the title bar in
the given menu view. By default, returns GSTitleView.
A subclass can be returned to customize the
title view look and behavior.
Method to tile the supplied image to fill
the horizontal rectangle. The rect
argument is the rectangle to be filled. The
image argument is the data to fill with.
The source argument is the
rectangle within the image which is
used. The flipped argument
specifies what sort of coordinate system is in
use in the view where we are drawing.
Tile rect with image. The tiling
starts with the origin of the first copy of the
image at the bottom left corner of the
rect unless center is
YES, in which case the image
is centered in rect and tiled outwards from
that.
Method to tile a rectangle given a group of up to
nine tile images. The GSDrawTiles object
encapsulates the tile images and information
about what parts of each image are used for tiling.
This draws the left, right, top and bottom
borders by tiling the images at left, right, top
and bottom. It then draws the four corner images and
finally deals with the remaining space in the
middle according to the default style set for the
GSDrawTiles object used. The background
color specified is used to fill the center
where style is FillStyleNone. The return value
is the central rectangle (inside the border images).
Method to tile a rectangle given a group of up to
nine tile images. The GSDrawTiles object
encapsulates the tile images and information
about what parts of each image are used for tiling.
This draws the left, right, top and bottom
borders by tiling the images at left, right, top
and bottom. It then draws the four corner images and
finally deals with the remaining space in the
middle according to the specified style.
The background color specified is
used to fill the center where style is
FillStyleNone. The return value is
the central rectangle (inside the border images).
Method to tile the supplied image to fill
the vertical rectangle. The rect
argument is the rectangle to be filled. The
image argument is the data to fill with.
The source argument is the
rectangle within the image which is
used. The flipped argument
specifies what sort of coordinate system is in
use in the view where we are drawing.
Modifies the given NSRect for use by NSMenu to
position and size the displayed menu. The default
implementation simply returns the original
NSRect unmodified.
Used by the theme to organize the main menu
. The default implementation organizes the main
menu in the same way that NSMenu's old
default behaviour did, generating an "app name"
menu for horizontal display.
This method sets the menu for the
window using the current theme In the
default theme this calls the setMenu: method on the
window giving the menu
parameter as the argument.