libplasma provides the Theme class so Plasma elements and other applications, such as KRunner, that need to graphically hint or theme interface elements. This is not a replacement for QStyle, but rather provides standard elements for things such as box backgrounds.
This allows for easy re-theming of the desktop while also keeping elements on the desktop more consistent with each other.
See also Creating a Plasma Theme.
Theme Location, Structure and Definition
Themes are stored in share/apps/desktoptheme. A theme is described by a .desktop file in share/apps/desktoptheme. The contents of which might look like this:
Comment=Theme done in the Oxygen style
X-KDE-PluginInfo-Author=The Oxygen Project
The X-KDE-PluginInfo-Name entry must contain the name of the subdirectory in share/apps/desktoptheme where the SVG files for this theme exist.
Beneath this directory one will find the following file structure:
- colors: optional a configuration file defining a colorscheme that blends well with the images
- dialogs/': images for dialogs
- wallpapers/: wallpaper packages
- widgets/: images for widgets
- opaque/: optional directory containing images appropriate for non-compositing environments
- locolor/: optional directory containing images appropraite for locolor (e.g. 8 bit color) environments
Theme elements are accessed by path. Whether this maps to literal paths on disk or not is not guaranteed and considered an implementation detail of Plasma::Theme.
Therefore, to access the dialog background, one might create an svg in this manner:
It is generally recommended to use Plasma::Svg instead of QSvgRenderer directly, however. Remember to call resize() on the Plasma::Svg before painting with it!
Themes may optionally provide wallpapers to be used with the theme. These wallpapers must appear in the wallpapers/ directory within the theme.
A theme may also define a default wallpaper, wallpaper size and wallpaper file extension to be used in conjunction with the theme. The default wallpaper may either be installed in the standard location for wallpapers or may be shipped with the theme itself. The default wallpaper settings should appear in the theme's metadata.desktop file and contain the following entries:
defaultTheme=<name of default wallpaper package>
defaultFileSuffix=<wallpaper file suffix, e.g. .jpg>
defaultWidth=<width in pixels of default wallpaper file>
defaultHeight=<height in pixels of default wallpaper file>
Reaction to Theme Changes
If you use Plasma::Svg, changes to the theme are automatically picked up. Otherwise, you can connect to the changed() signal in the Plasma::Theme class. This signal is emitted whenever the theme is changed, which may be triggered by the user switching the theme used or system changes such as a composite manager becoming available.
All background svg's (except for desktop wallpapers) must have the following named elements, all of which will be painted at the native size (and can therefore be bitmaps), except for the center which will be scaled:
- topleft: the top left corner
- topright: the top right corner
- bottomleft: the bottom left corner
- bottomright: the bottom right corner
- top: the top bar between the two top corners
- left: the left bar between the two left corners
- right: the right bar between the two right corners
- bottom: the bottom bar between the two bottom corners
- center: the center fill; will be scaled so should be an actual SVG element
Some plasma components may use the above named elements with prefixes. For example the panel placed on the left side of the screen uses the "west" prefix (west-topleft, west-topright, etc.).
Additionally, the following elements can be used to control the rendering of the backgrounds:
- hint-stretch-borders: if it exists, the borders will not be tiled but rather will be stretched to fit
- hint-tile-center: if it exists, the center will not be scaled but rather will be tiled to fit. (Optional, from 4.1 and later)
- hint-no-border-padding: If this element exists, padding will not be added for the borders, and content will therefore be able to use the entire area.
- hint-apply-color-scheme: If this element exists, the svg will be colorized using the color scheme colors. Colorization is applied at 100%, and tapers off on either side, of an HSV color value/intensity of 127. (Optional, From KDE 4.1 and later)
- [prefix]-hint-margin-[direction]: Use this optional hints if you want different margins than the borders size. The [prefix]- part is optional and identifies the prefix of the panel you want to specify the margins. [direction] can be either top, bottom, left or right and indicates the border you want to configure. (Optional, From KDE 4.2 and later)
Current Theme Elements
Themes get installed to share/apps/desktoptheme. Each theme is stored in a subdirectory with the following file structure
- /dialogs: elements for dialogs
- /background.svg: generic dialog background used by the sceensaver password dialog, etc. See the section on backgrounds above for information on the required elements in this file.
- /krunner.svg: dialog background, used by the Run Command. See the section on backgrounds above for information on the required elements in this file.
- /shutdowndlg.svg: background and buttons for the log out dialog
- background: background for the logout dialog
- button-normal: button background
- button-hover: button background on cursor hover
- button-small-normal: small button background
- button-small-hover: small button background on cursor hover
- /widgets: generic desktop widget background
- /background.svg: a background image for plasmoids. See the section on backgrounds above for information on the required elements in this file.
- /translucentbackground.svg: a standard background image for plasmoids that for their nature are bigger and with not much text. In this case a translucent background looks better. It needs the same elements of background.svg in it. If this file is not present, the plasmoids that uses this will use background.svg instead.
- /tooltip.svg: background for tooltips used for instance in the taskbar and with icons. See the section on backgrounds above for information on the required elements in this file.
- /clock.svg: an analog clock face. it must have the following named elements:
- ClockFace: the background of the clock, usually containing the numbers, etc
- HourHand: the hour hand, pointing down in the svg
- MinuteHand: the minute hand, pointing down in the svg
- SecondHand: the second hand, pointing down in the svg
- HourHandShadow, MinuteHandShadow and SecondHandShadow: drop shadows for the hands (optional, KDE 4.1 and later)
- HandCenterScrew: the "pin" that holds the hands together in the center
- Glass: a final overlay which allows for things such as the appearance of glass
- hint-square-clock: if present the shape of the clock will be square rather than round
- In the svg the hands must be placed in a position that indicates the time 6:30:30 and the y-axis position is the one they will have in the rendered applet
- /iconbutton.svg: backgrounds and overlays for icons that are clickable. can have any of the following named elements:
- minibutton: the default appearance of the top-left button
- minibutton-hover: the appearance of the top-left button when is hovered
- minibutton-pressed: the appearance of the top-left button when is pressed
- background: the default background, painted beneath the icon
- background-hover: background when the mouse hovers the icon
- background-pressed: background when the icon is pressed
- foreground the default foreground, painted on top of the icon
- foreground-hover: foreground when the mouse hovers the icon
- foreground-pressed: foreground when the icon is pressed
- selection-rect: displayed when the icon is selected
- /panel-background.svg: the default background image for panels. See the section on backgrounds above for information on the required elements in this file.
- If you want to create different background for panels located at the top, bottom, left or right, then also create sets of background elements with the following prefixes: north, south, west and east respectively. For example the center element of the left positioned panel's background should be named west-center. (KDE 4.1 and later)
- /plot-background.svg: a background for plotter (graph) widgets, such as the plots in ksysguard
- /toolbox-button.svg: the background for the desktop configuration toolbox button that sites at the edge of the desktop
- /tasks.svg: task item backgrounds for tasks (KDE 4.1 and later). See the section on backgrounds above for information on the required elements in this file. The following element prefixes are required:
- focus: background of focused task item
- hover: background when the pointer hovers the task item
- attention: background when tasks item is trying to get attention
- normal: background of normal, unfocused task item
- minimized: background for minimized tasks
- The svg should contain elements of all five prefixes, if a prefix is missing that element will be not be drawn.
- /systemtray.svg: a background for the system tray (KDE 4.1 and later). See the section on backgrounds above for information on the required elements in this file.
- /containment-controls.svg: handles for the control used to resize the panel (KDE 4.1 and later). The following elements are required.
- maxslider maximum size slider, south position
- minslider minimum size slider, south position
- offsetslider positioning slider, south position
- Each of the above elements must be present with north, south, east and west prefixes for each panel position.
- There are also four backgrounds (north, south, east and west orientations) for the ruler widget itself in the "Backgrounds format", since the width of the widget is 100% the elements of left and right (or north and bottom if vertical) are not needed
- /button.svg: graphics elements for a button widget (KDE 4.2 and later), it needs the followin prefixes:
- normal normal button
- pressed pressed button
- active button under mouse
- focus keyboard focus rectangle superimposed to the button graphics
- /dragger.svgz: drag handle for extenders (like the popup date of clock applets, KDE 4.2 and later)
In the folder share/apps/desktoptheme/opaque the same hierarchy can be found: when compositing is disabled files in this folder are preferred over the corresponding ones listed above. Only background for top level windows are appropriate to go in this folder.
Since top-level windows will be shaped according to the transparency of the svg and window shapes don't support alpha-blending, if the svg has rounded borders they should have a shape that don't require antialiasing, like the following example.