Development/Tutorials/Icons

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

Error creating thumbnail: Unable to save thumbnail to destination

These icons are called KIcons. This article shows you how to do this using the software krep as an example. In case of a CMake-based project you will need to

• modify main.cpp (as it is typically called)
• modify CMakeLists.txt

How to use icons in QMake-based projects is discussed elsewhere.

Your KDE project

If you have a KDE project and want to use icons within it, and want these icons installed 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} )

Weitere Informationen:

• kde4_add_app_icon
• ICON_INSTALL_DIR

How to test it

The easy way is to define a custom cmake install prefix where you can simply insall the project without touching your system. Use following commands to setup this:

cd build
cmake -DCMAKE_INSTALL_PREFIX=$HOME/playground ../
make && make install

now the files should be deployed under

$HOME/playground/bin/krep
$HOME/playground/share/apps/krep
$HOME/playground/share/icons/hicolor/22x22/apps/krep.png

With this method you can easy see what you will get.

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-apps-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, apps 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 - on top of the KAction example - an example application kicons that looks like this:

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

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

files

The example application consists of

• main.cpp

just taken from the KAction example

• mainwindow.cpp

Note the command

clearAction->setIcon(KIcon("tutorial-kicon"));

that sets the icon

• mainwindow.h

just taken from the KAction example

• world.svg

This is a file that defines our icon in (almost natural) english language. It is a scalable vector graphic file. Before being used, it must be converted into a zipped scalable vector graphic named hisc-apps-tutorial-kicon.svgz, see below.

• tutorial-kiconui.rc

just taken from the KAction example

• hisc-apps-tutorial-kicon.svgz

sorry for the name, but there are naming conventions. Create this file with the convert command from the ImageMagick package

convert world.svg hisc-apps-tutorial-kicon.svgz

• CMakeLists.txt

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

mkdir build && cd build
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:

 # [http://www.linuxintro.org/wiki/Strace#Search_for_a_syscall 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
 [...]

Moving On

Now you can move on to how to place your application in the K-Menu using .desktop files.