Digikam/CMake Documentation(Frameworks)

Introduction

CMake configuration files were rewritten by Veaceslav Munteanu <veaceslav dot munteanu90 at gmail dot com> at 10 June 2014. The aim of new configuration was to reduce the linking overhead and improve CPU utilization while still keeping the modular design implemented by Teemu Rytilahti

CMake Structure

Independent Cmake configuration is presents in following folders:

digikam-software-compilation
core
extra
docs

The rewrite touched mostly the core folder.

CMake executables for core

Core cmake will link the following executable:

digikam
showfoto
digikam database server - if compilation is enabled in cmake files
various test executables - if testing is enabled

each of them depend on various sources which must be compiled before.

CMake Implementation Details

Shared Libraries

To avoid linking overhead and make a better use of sources there are some dynamic libs.

digikamcore - core components used by almost all executables
digikamdatabase - database components, also used together with digikamcore
imageplugins - image plugin implementation
kio modules - soon to be deprecated

Warning

Please add sources to digikam core or digikam database only if they don't depend on any big component from digikam main executable. These two shared libs must be kept small because they link in a lot of places

Static Libraries

Currently cmake configuration features 4 shared libs:

queuemanager
advancedrename
importui
baloowrap

This libs are linked in digikam main executable and some tests

Warning

Avoid making static libs, use OBJECT libraries instead. Only make STATIC libraries which does not depend on other digikam code. Also make sure you put the PRIVATE parameter when setting the target_link_libraries.

target_link_libraries(digikamcore
                      PRIVATE
                      Qt5::Core
                      Qt5::Gui
                      Qt5::Widgets
)

Object Libraries

While static libraries are still collection of objects, CMake offer a better approach by allowing to specify an OBJECT library:

set(libslideshow_SRCS
    slidetoolbar.cpp
    slideosd.cpp
    slideproperties.cpp
    slideimage.cpp
    slideerror.cpp
    slideend.cpp
    slideshow.cpp
    slidehelp.cpp
    slideshowsettings.cpp
)

add_library(slideshow_src OBJECT ${libslideshow_SRCS})

OBJECT library is a cmake internal implementation feature and allow to easily manage sources. Here is an example of how to make a shared lib using OBJECT libraries:

add_library(digikamcore
            SHARED
            $<TARGET_OBJECTS:slideshow_src> # the lib we made  few lines above
            $<TARGET_OBJECTS:digikamdatabasecore_src>
            $<TARGET_OBJECTS:dimg_src>
           ....
)

Final Words

Remember
Please follow the guidelines when adding sources to CMakeFiles: Use OBJECT libraries Avoid using STATIC libraries Use PRIVATE parameter on target_link_libraries Keep digikamcore and digikamdatabase libraries small