Development/Tutorials/Icons

    From KDE TechBase

    When you create your own KDE application you will probably want icons in it like this:

    These icons are called KIcons. This article shows you how to do this on the example of the software krep. In case of a cmake based project you will need to

    How to use icons in a qmake base project is discussed elsewhere.

    Your KDE project

    If you have a KDE project and want to use icons within it, and want that these icons install seamlessly, you will have to name the icons after the project. In the following we look at a project named krep. The important lines in CMakeLists.txt are the ones printed bold below:

    PROJECT( krep )
    FIND_PACKAGE( KDE4 REQUIRED )
    INCLUDE_DIRECTORIES( ${KDE4_INCLUDES} . )
    
    SET(krepSources main.cpp krep.cpp krep.h)
    
    qt4_add_dbus_adaptor( krepSources 
                          org.kde.krep.xml
                          krep.h
                          krep
                          mainadaptor
                          MainAdaptor )
    
    kde4_add_ui_files( krepSources krepui.ui )
    
    kde4_add_app_icon( krepSources "hi*-app-krep.png" )
    
    KDE4_ADD_EXECUTABLE( krep ${krepSources} )
    
    TARGET_LINK_LIBRARIES( krep ${KDE4_KPARTS_LIBS} )
    
    install( TARGETS krep ${INSTALL_TARGETS_DEFAULT_ARGS} )
    
    kde4_install_icons( ${ICON_INSTALL_DIR} )
    

    How to test it

    • delete a file
    rm /usr/local/share/icons/hicolor/22x22/apps/krep.png 
    
    • delete your cache
    rm -rf /var/tmp/kdecache-user/
    
    • relogin

    using this test case I could remove one icon after the other, 22x22, 64x64, 48x48, but when I removed 32x32, the icon disappeared from my application. This was the last icon that existed. Then I put in the 64x64 icon and the application carried an icon again. This means you can use any icon of 16x16, 22x22, 32x32, 48x48, 64x64, 128x128.

    The icon naming scheme

    Example for icon names:

    • hisc-apps-bla.svgz will be installed e.g. to /usr/local/share/icons/hicolor/scalable/apps/./bla.svgz. hi stands for "hicolor", sc for "scalable", apps for "applications", bla for the application's name and .svgz is the suffix for gzipped scalable vector graphic files.
    • hi128-app-ktimetracker.png will be installed e.g. to /usr/share/icons/hicolor/128x128/apps/ktimetracker.png. hi stands for "hicolor", 128 for a resolution of 128x128 pixels, app for "applications", ktimetracker for the application's name and .png is the suffix for portable network graphic files.

    example application

    In this chapter we will build an example application kicons that looks like this:

    You can obtain its source code as part of kdeexamples by calling

    git clone git://anongit.kde.org/kdeexamples
    

    It is based on the KAction example

    files

    The example application consists of

    Note the command clearAction->setIcon(KIcon("tutorial-kicon")); that sets the icon
    This is a file that defines our icon in (almost natural) english language. It is a scalable vector graphics. Before being used, it must be converted to a zipped scalable vector graphic file hisc-apps-tutorial-kicon.svgz, see below.
    sorry for the name, but there are naming conventions. Create this file with the command convert from the ImageMagick package convert world.svg hisc-apps-tutorial-kicon.svgz
    Note the commands kde4_install_icons(${ICON_INSTALL_DIR}) and kde4_update_iconcache() which integrate the icons.

    build it

    To compile, link and install the example application, do a

    cmake . && make && make install
    

    To run it, call

    tutorial-kicon
    

    Analyzing the KApplications

    Maybe you have already searched for yourself how a KDE application finds its icons. You will not be successful like this:

    # strace -e open ktimetracker 2>&1 | grep icon
    open("/usr/lib64/libkemoticons.so.4", O_RDONLY) = 3
    #
    

    You see, a KDE application (in this case ktimetracker) does not open icon files or even look for them. However, it spawns a process to look for these icons:

    linux-qgla:~/repos/kdepim/ktimetracker # strace -ffe open ktimetracker 2>&1 | grep icon
    open("/usr/lib64/libkemoticons.so.4", O_RDONLY) = 3
    [pid  3457] open("/root/.icons/DMZ/cursors/left_ptr", O_RDONLY) = -1 ENOENT (No such file or directory)
    [pid  3457] open("/root/.icons/DMZ/index.theme", O_RDONLY) = -1 ENOENT (No such file or directory)
    [pid  3457] open("/usr/share/icons/DMZ/cursors/left_ptr", O_RDONLY) = 10
    [pid  3457] open("/var/tmp/kdecache-root/icon-cache.kcache", O_RDWR|O_CREAT|O_CLOEXEC, 0666) = 10
    [pid  3457] open("/var/tmp/kdecache-root/kpc/kde-icon-cache.data", O_RDONLY|O_CLOEXEC) = 10
    [pid  3457] open("/var/tmp/kdecache-root/kpc/kde-icon-cache.index", O_RDONLY|O_CLOEXEC) = 10
    [...]
    

    See also