RaspberryPi2EGLFS

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A modern guide for cross-compiling Qt for HW accelerated OpenGL with eglfs on Raspbian and setting up Qt Creator

Initial notes
  • This is not intended for running desktop-style, windowed Qt apps under X11, but rather for the real embedded/device creation use case where the Qt app runs fullscreen on top of dispmanx/EGL using the Broadcom drivers.
  • For detailed, generic information about eglfs and Qt on Embedded Linux check the Qt documentation.
Tested Configurations
  • Qt 5.6 with Raspbian Wheezy / Jessie
  • Qt 5.9.1 with Raspbian Stretch on Raspberry 3 model B

Step by step

  1. Get old raspbian images from here or latest raspbian image from here.
  2. Follow an official installation guideto boot it up or: Unzip and write it to a memory card. Replace ... with the SD card device (check with lsblk or dmesg eg. mmcblk0)
    sudo dd if=2015-09-24-raspbian-jessie.img of=... bs=4M
    
  3. [on RPi] (optional) Run raspi-config, change it to boot to the console instead of X, change the GPU memory to 256 MB.
    sudo raspi-config
    
  4. [on RPi] For Raspbian Stretch you need also to update your RPi:
    sudo rpi-update
    reboot
    
  5. [on RPi] Install a bunch of development files (for simplicity we use build-dep, not everything is really needed, but it is easier this way).
    1. Edit sources list in /etc/apt/sources.list with use of your favorite editor (nano / vi) and uncomment the deb-src line:
      sudo nano /etc/apt/sources.list
      
    2. Update your system and install required libraries:
      sudo apt-get update
      sudo apt-get build-dep qt4-x11
      sudo apt-get build-dep libqt5gui5
      sudo apt-get install libudev-dev libinput-dev libts-dev libxcb-xinerama0-dev libxcb-xinerama0
      
  6. [on RPi] Prepare our target directory
    sudo mkdir /usr/local/qt5pi
    sudo chown pi:pi /usr/local/qt5pi
    
  7. [on host PC] Create our working directory and get a toolchain:
    mkdir ~/raspi
    cd ~/raspi
    git clone https://github.com/raspberrypi/tools
    
  8. [on host PC] Create a sysroot. Using rsync we can properly keep things synchronized in the future as well. Replace raspberrypi.local with the address of the Pi.
    mkdir sysroot sysroot/usr sysroot/opt
    rsync -avz pi@raspberrypi.local:/lib sysroot
    rsync -avz pi@raspberrypi.local:/usr/include sysroot/usr
    rsync -avz pi@raspberrypi.local:/usr/lib sysroot/usr
    rsync -avz pi@raspberrypi.local:/opt/vc sysroot/opt
    
  9. [on host PC] Adjust symlinks to be relative. Use provided script, because the old fixQualifiedLibraryPaths is not working properly:
    wget https://raw.githubusercontent.com/riscv/riscv-poky/master/scripts/sysroot-relativelinks.py
    chmod +x sysroot-relativelinks.py
    ./sysroot-relativelinks.py sysroot
    
  10. [on host PC] Get qtbase and configure Qt. The target directory is /usr/local/qt5pi on the Pi, the host tools like qmake will go to ~/raspi/qt5, while make install will target ~/raspi/qt5pi (this is what we will sync to the device). Don't forget to adjust paths if you changed that. For some reason the ~/ in the paths may not work, if this the case just use full paths. You need to change <qt-version> with a proper Qt version (for example 5.6, or 5.9.1; note that version 5.9.1 is a tag not a branch, so you may want to create a local branch with it). You need to change <rpi-version> with a proper Raspberry Pi version. Use: linux-rasp-pi-g++ for RPi, linux-rasp-pi2-g++ for RPi2 and linux-rasp-pi3-g++ for RPi3. If your system is 64 bit you may also edit device option to:
    -device-option CROSS_COMPILE=~/raspi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-
    
    For higher Qt version (like 5.9.1) you may also need to add
    -no-use-gold-linker
    
    option. You probably also want to add -jn option to make command, where n is a number of cores you like to use for the complication.
    git clone git://code.qt.io/qt/qtbase.git -b <qt-version>
    cd qtbase
    ./configure -release -opengl es2 -device <rpi-version> -device-option CROSS_COMPILE=~/raspi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf- -sysroot ~/raspi/sysroot -opensource -confirm-license -make libs -prefix /usr/local/qt5pi -extprefix ~/raspi/qt5pi -hostprefix ~/raspi/qt5 -v
    
    make
    make install
    
    If you failed, you can clear everything with:
    git clean -dfx
    
  11. [on host PC] Deploy Qt to the device. We simply sync everything from ~/raspi/qt5pi to the prefix we configured above.
    rsync -avz qt5pi pi@raspberrypi.local:/usr/local
    
  12. [on host PC] Build an example up to test if everything went well. After proper build, copy an executable to the device.
    cd qtbase/examples/opengl/qopenglwidget
    ~/raspi/qt5/bin/qmake
    make
    
    scp qopenglwidget pi@raspberrypi.local:/home/pi
    
  13. [on RPi] Update the device to let the linker find the Qt libs:
    echo /usr/local/qt5pi/lib | sudo tee /etc/ld.so.conf.d/qt5pi.conf
    sudo ldconfig
    
    If you're facing issues with running the example, try to use 00-qt5pi.conf instead of qt5pi.conf, to introduce proper order.
  14. [on RPi] Fix the EGL/GLES libraries. The device may have the Mesa version of libEGL and libGLESv2 in /usr/lib/arm-linux-gnueabihf, resulting Qt apps picking these instead of the real thing from /opt/vc/lib. This may be fine for X11 desktop apps not caring about OpenGL performance but is totally useless for windowing system-less, fullscreen embedded apps. You may want to save the originals somewhere, just in case.
    sudo mv /usr/lib/arm-linux-gnueabihf/libEGL.so.1.0.0 /usr/lib/arm-linux-gnueabihf/libEGL.so.1.0.0_backup
    sudo mv /usr/lib/arm-linux-gnueabihf/libGLESv2.so.2.0.0 /usr/lib/arm-linux-gnueabihf/libGLESv2.so.2.0.0_backup
    sudo ln -s /opt/vc/lib/libEGL.so /usr/lib/arm-linux-gnueabihf/libEGL.so.1.0.0
    sudo ln -s /opt/vc/lib/libGLESv2.so /usr/lib/arm-linux-gnueabihf/libGLESv2.so.2.0.0
    
    Please make sure to also add missing symbolic links:
    sudo ln -s /opt/vc/lib/libEGL.so /opt/vc/lib/libEGL.so.1
    sudo ln -s /opt/vc/lib/libGLESv2.so /opt/vc/lib/libGLESv2.so.2
    
  15. [on RPi] Run example, that we've built before. At this point it should just work at fullscreen with 60 FPS and mouse, keyboard, and possibly touch support.
  16. [on host PC] Build other Qt modules as desired, the steps are always the same (you need to adjust <qt-module> and <qt-version>):
    git clone git://code.qt.io/qt/<qt-module>.git -b <qt-version>
    cd <qt-module>
    
    ~/raspi/qt5/bin/qmake -r
    make
    make install
    
    Then deploy new files by running:
    rsync -avz qt5pi pi@raspberrypi.local:/usr/local
    

Additional notes

Frequently asked question: I only get a low resolution like 640x480 or even 576x416 with black boxes. How to fix this?

As a quick fix, try adding disable_overscan=1 to /boot/config.txt and after a reboot check with /opt/vc/bin/tvservice what modes are available. For example, to switch to 1024x768:

$ /opt/vc/bin/tvservice -m DMT
Group DMT has 4 modes:
           mode 4: 640x480 @ 60Hz 4:3, clock:25MHz progressive 
           mode 9: 800x600 @ 60Hz 4:3, clock:40MHz progressive 
           mode 16: 1024x768 @ 60Hz 4:3, clock:65MHz progressive 
           mode 35: 1280x1024 @ 60Hz 5:4, clock:108MHz progressive 

$ /opt/vc/bin/tvservice -e "DMT 16 HDMI"
$ fbset -xres 1024 -yres 768

Troubleshooting

Enabling the logging categories under qt.qpa is a good idea in general. This will show some debug prints both from eglfs and the input handlers.

export QT_LOGGING_RULES=qt.qpa.*=true
./qopenglwidget

A typical output would like like this:

qt.qpa.egldeviceintegration: EGL device integration plugin keys: ("eglfs_brcm", "eglfs_kms")
qt.qpa.egldeviceintegration: EGL device integration plugin keys (sorted): ("eglfs_brcm", "eglfs_kms")
qt.qpa.egldeviceintegration: Trying to load device EGL integration "eglfs_brcm"
qt.qpa.egldeviceintegration: Using EGL device integration "eglfs_brcm"
Unable to query physical screen size, defaulting to 100 dpi.
To override, set QT_QPA_EGLFS_PHYSICAL_WIDTH and QT_QPA_EGLFS_PHYSICAL_HEIGHT (in millimeters).
qt.qpa.input: libinput: input device 'Logitech Optical USB Mouse', /dev/input/event0 is a pointer caps = relative-motion button
qt.qpa.input: libinput: input device 'Apple Inc. Apple Keyboard', /dev/input/event1 is a keyboard
qt.qpa.input: libinput: input device 'Apple Inc. Apple Keyboard', /dev/input/event2 is a keyboard
qt.qpa.input: libinput: input device 'Raspberry Pi Sense HAT Joystick', /dev/input/event3 is a keyboard
qt.qpa.input: Using xkbcommon for key mapping

Verify that eglfs_brcm is in use and that input devices are correctly found.

When using a touchscreen, setting the correct physical screen size may be essential to get properly scaled, finger friendly user interface elements with Qt Quick Controls. When using ordinary monitors via HDMI, the default 100 dpi may be acceptable.

It is also wise to carefully check the output of configure (saved as config.summary) before proceeding to build qtbase. Check that the following are marked as 'yes':

Support enabled for:
  ...
  Evdev .................. yes
  FontConfig ............. yes
  FreeType ............... yes (system library)
  ...
  libinput................ yes
  ...
  OpenGL / OpenVG: 
    EGL .................. yes
    OpenGL ............... yes (OpenGL ES 2.0+)
  QPA backends: 
    EGLFS ................ yes
      ...
      EGLFS Raspberry Pi . yes
    ...
    LinuxFB .............. yes
    ...
  udev ................... yes
  xkbcommon-evdev......... yes

Regarding keyboard input

By default Qt attempts to disable the keyboard and hide the cursor on application startup. This is very handy since this way keystrokes will not go to the console (which is enabled by default in a normal Raspbian image) "underneath". However, at the moment this will all silently fail when starting an application remotely via ssh. This is the explanation for the (harmless) 9;15] and similar prints and the keyboard input unexpectedly going to the console as well. As a workaround, start apps directly on the console. Alternatively, you could experiment with getting rid of the first TTY by doing sudo systemctl disable getty@tty1.service and reboot. (tty2 and others remain usable)

Qt Creator

Once Qt is on the device, Qt Creator can be set up to build, deploy, run and debug Qt apps directly on the device with one click.

Go to Options -> Devices
  Add
    Generic Linux Device
    Enter IP address, user & password
    Finish
Go to Options -> Compilers
  Add
    GCC
    Compiler path: ~/raspi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf-g++
Go to Options -> Debuggers
  Add
    ~/raspi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-gdb
Go to Options -> Qt Versions
  Check if an entry with ~/raspi/qt5/bin/qmake shows up. If not, add it.
  
Go to Options -> Build & Run
  Kits
    Add
      Generic Linux Device
      Device: the one we just created
      Sysroot: ~/raspi/sysroot
      Compiler: the one we just created
      Debugger: the one we just created
      Qt version: the one we saw under Qt Versions
      Qt mkspec: leave empty

Done. At this point you should be able to start a new project with the new kit, build and deploy it, etc.

Note: While things will usually just work for applications, developing libraries and in particular, Qt modules may be problematic when it comes to deployment. The per-project Run tab under Projects -> Build & Run is your friend. In some cases the target deployment paths will just be wrong. Life is too short for worrying about all the intricate details of Creator and the build system. Therefore, if all else fails, use Add Deploy Step ("Make" and "Custom Process Step" are extremely handy, anything can be made working with a combination of make install, rsync and scp) and change Run configuration to Custom Executable.

Sense HAT

To access the sensors and leds on the Sense HAT, you can use the unofficial Qt Sense HAT module on qt-labs. Check it out via git and build it like any other Qt module.

The joystick shows up as an ordinary evdev device providing key events so it will just work. Regarding the leds and sensors, see the README.

Qt Multimedia

Unfortunately the GStreamer-based multimedia stuff is not quite usable at the time of writing - accelerated video works only sometimes (and with glitches), while the camera is just broken.

As an alternative to Qt Multimedia, try using OpenMAX directly. For an open implementation refer to this project. For the Raspberry Pi Camera Module take a look at the raspistill application sources for an example on how to get the camera preview image into an OpenGL texture.

If you wish to experiment with Qt Multimedia, try the following:

Before building Qt Multimedia 5.6, make sure the following are installed:

sudo apt-get install gstreamer1.0-omx libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev

Do not forget to sync the headers and libs back to the sysroot on the host PC and re-run the sysroot-relativelinks.py script.

Once the GStreamer 1.0 dependencies are in place, make sure Qt Multimedia is built with 1.0 support:

~/raspbi/qt5/bin/qmake -r GST_VERSION=1.0

To verify that the accelerated OpenMAX path is used for H.264 videos, do export GST_DEBUG=omx:4 before running a video playback app like the qmlvideofx example.