Cooking with OpenEmbedded

For that matter, it happen that you are interested in Qt for embedded application, and you are using OpenEmbedded to build a nice custom distribution.
It would be great if your Qt application could be that image. Hopefully, we can sure build a recipe do to so.

Go to your OpenEmbedded repository, and then to the recipes/ directory.
Create a subfolder, called “helloworldqt” for example. Try to respect the name policy: lower cases, no spaces, no weird char (avoid _ especially).

Create a file, a usual template is {project}_{version}.bb, in our case helloworldqt_1.0.0.bb.
This is a recipe, here is a simple content for our project (download it here):

DESCRIPTION = "Small Qt Hello World!"
LICENSE = "GPL"
PR = "r0"

S = "${WORKDIR}/${P}"

SRC_URI = "file://HelloWorldQt.tar"

FILES_${PN} = "${libdir}/qt4"

inherit qt4e cmake

EXTRA_OECMAKE = "-DQT_LIBRARY_DIR=${OE_QMAKE_LIBDIR_QT} \
                 -DQT_INSTALL_LIBS=${OE_QMAKE_LIBDIR_QT} \
                 -DQT_INCLUDE_DIR=${OE_QMAKE_INCDIR_QT} \
		 -DQT_HEADERS_DIR=${OE_QMAKE_INCDIR_QT} \
                 -DQT_MOC_EXECUTABLE=${OE_QMAKE_MOC} \
                 -DQT_UIC_EXECUTABLE=${OE_QMAKE_UIC} \
                 -DQT_UIC3_EXECUTABLE=${OE_QMAKE_UIC3} \
                 -DQT_RCC_EXECUTABLE=${OE_QMAKE_RCC} \
                 -DQT_QMAKE_EXECUTABLE=${OE_QMAKE_QMAKE} \
                 -DQT_QTCORE_INCLUDE_DIR=${OE_QMAKE_INCDIR_QT}/QtCore \
                 -DQT_DBUSXML2CPP_EXECUTABLE=/usr/bin/qdbusxml2cpp \
                 -DQT_DBUSCPP2XML_EXECUTABLE=/usr/bin/qdbuscpp2xml \
		 -DQT_MKSPECS_DIR=${QMAKESPEC}/../ \
                "

OECMAKE_SOURCEPATH = "../HelloWorldQt"

# Adding our bin file to the main package
FILES_${PN} = "${bindir}/*"

The final architecture for your project in OE should be something like this:

helloworldqt/
helloworldqt/files/HelloWorldQt.tar
hellowroldqt/helloworldqt_1.0.0.bb

Here is a tricky part, CMake is using a file called FindQt4.cmake to look for Qt4 libraries, while it would work with the qt4x11 of Qt, Qt4-embedded produce libraries that end with an E, making it inefficient only because of that missing E.
Since the problem has been corrected in a more recent version of cmake, another cleaner solution is to download the last version of the FindQt4.cmake file here and to replace yours. This will also work if you have a native cmake (as long as your version is recent enough to handle stuff in that .cmake file).

Otherwise, you can change add the E manually (dirty). If you use a cmake from OE (ie you didn’t ASSUME cmake-native in your local.conf), just edit the file /oetmp/staging/i686-linux/usr/share/cmake-2.6/Modules/FindQt4.cmake.
Line 696, add ${QT_MODULE}E, it should look something like this:

NAMES ${QT_MODULE} ${QT_MODULE}4 ${QT_MODULE}E

Then the module should work fine.