TL;DR

Do not use eglfs with Qt if you're using QWidgets. QWidgets use the software renderer (writing this as of Qt 5.6.1). If you use eglfs, Qt renders them first to an image and then uses OpenGL ES to render that to the display. As I found out below, using linuxfb worked much better since it didn't have to do the OpenGL ES step. The xcb plugin for X11 also worked fine.

See Qt's embedded Linux guide and specifically the 2nd paragraph of the EGLFS section.

qt-rectangles

This is a simple test program to demonstrate performance differences on the Raspberry Pi.

To run:

qmake qt-rectangles.pro
make
./qt-rectangles

Measurements

Key:

• xcb = X11 w/ OpenGL ES
• eglfs = Full screen OpenGL ES (no X11)
• linuxfb = Full screen software rendered
• noalpha = No alpha blending of rectangles
• gl = Use QOpenGLWidget version

See http://doc.qt.io/qt-5/embedded-linux.html for more information on xcb, eglfs, and linuxfb.

16x16 rectangles (8100 total)

120x120 rectangles (144 total)

1920x1080 rectangle (1 total)

Notes to self

Compiling the eglfs version of Qt 5

1. Download qtbase-opensource-src-5.6.1-1.tar.xz and untar it on the Raspberry Pi.

2. Copy qmake.conf to $QT/mkspecs/linux-g++

3. Uninstall any X11 dev libraries. They seemed to confuse Qt's ./configure script and since I didn't want them to link in anyway, I removed them. This was a manual process of running apt list --installed | grep -- -dev, looking for the X11 ones and then uninstalling them.

4. Run ./configure -eglfs -no-xcb -no-xcb-xlib -no-nis -opensource -confirm-license -no-qml-debug -no-linuxfb -no-gif -opengl es2 -no-pch (See log at bottom)

5. Run make

6. Come back tomorrow

Running

Make sure that the paths are right to the proper Qt versions. The easy way is to compile one version of Qt with only eglfs support and the other version with only xcb support. Then if you get the wrong library at runtime, the -platform argument will result in an error. I.e., do this:

QT_PLUGIN_PATH=/qt-eglfs/plugins LD_LIBRARY_PATH=/qt-eglfs/lib ./qt-rectangles -platform eglfs

To get an xcb version of Qt5 quickly, run sudo apt-get install qt5-default

Qt's ./configure log for enabling eglfs

$ ./configure  -eglfs -no-xcb -no-xcb-xlib -no-nis -opensource -confirm-license
-no-qml-debug -no-linuxfb -no-gif -opengl es2 -no-pch

This is the Qt Open Source Edition.

You are licensed to use this software under the terms of
the Lesser GNU General Public License (LGPL) versions 2.1.
You are also licensed to use this software under the terms of
the GNU Lesser General Public License (LGPL) versions 3.

You have already accepted the terms of the Open Source license.

Running configuration tests (phase 1)...
Done running configuration tests.
Creating qmake...
.............................................................................Done.
Running configuration tests (phase 2)...
Done running configuration tests.

   Configure summary

Build type:    linux-g++ (arm, CPU features: none detected)
Platform notes:

            - Also available for Linux: linux-clang linux-kcc linux-icc
              linux-cxx

Build options:
  Configuration .......... accessibility audio-backend c++11 c++14 clock-gettime
clock-monotonic compile_examples concurrent dbus dbus-linked egl eglfs
eglfs_brcm enable_new_dtags evdev eventfd fontconfig full-config getaddrinfo
getifaddrs harfbuzz iconv icu inotify ipv6ifname large-config largefile libudev
medium-config minimal-config mremap no-gif no-qml-debug opengl opengles2 openvg
pcre png posix_fallocate qpa qpa reduce_exports release rpath shared
small-config system-freetype system-jpeg system-png system-zlib
threadsafe-cloexec use_gold_linker
  Build parts ............ libs tools examples
  Mode ................... release
  Using sanitizer(s)...... none
  Using C++ standard ..... c++14
  Using gold linker....... yes
  Using new DTAGS ........ yes
  Using PCH .............. no
  Using LTCG ............. no
  Target compiler supports:
    Neon ................. no

Qt modules and options:
  Qt D-Bus ............... yes (linked to dbus-1)
  Qt Concurrent .......... yes
  Qt GUI ................. yes
  Qt Widgets ............. yes
  Large File ............. yes
  QML debugging .......... no
  Use system proxies ..... no

Support enabled for:
  Accessibility .......... yes
  ALSA ................... no
  CUPS ................... no
  Evdev .................. yes
  FontConfig ............. yes
  FreeType ............... yes (system library)
  Glib ................... no
  GStreamer .............. no
  GTK theme .............. no
  HarfBuzz ............... yes (bundled copy)
  Iconv .................. yes
  ICU .................... yes
  Image formats:
    GIF .................. no
    JPEG ................. yes (plugin, using system library)
    PNG .................. yes (in QtGui, using system library)
  libinput................ no
  Logging backends:
    journald ............... no
    syslog   ............... no
  mtdev .................. no
  Networking:
    getaddrinfo .......... yes
    getifaddrs ........... yes
    IPv6 ifname .......... yes
    libproxy.............. no
    OpenSSL .............. no
  NIS .................... no
  OpenGL / OpenVG:
    EGL .................. yes
    OpenGL ............... yes (OpenGL ES 2.0+)
    OpenVG ............... yes-auto
  PCRE ................... yes (bundled copy)
  pkg-config ............. yes
  PulseAudio ............. no
  QPA backends:
    DirectFB ............. no
    EGLFS ................ yes
      EGLFS i.MX6 ........ no
      EGLFS i.MX6 Wayland. no
      EGLFS EGLDevice .... no
      EGLFS GBM .......... no
      EGLFS Mali ......... no
      EGLFS Raspberry Pi . yes
      EGLFS X11 .......... no
    LinuxFB .............. no
    Mir client............ no
    XCB .................. no
  Session management ..... yes
  SQL drivers:
    DB2 .................. no
    InterBase ............ no
    MySQL ................ no
    OCI .................. no
    ODBC ................. no
    PostgreSQL ........... no
    SQLite 2 ............. no
    SQLite ............... yes (plugin, using bundled copy)
    TDS .................. no
  tslib .................. no
  udev ................... yes
  xkbcommon-x11........... no
  xkbcommon-evdev......... no
  zlib ................... yes (system library)


NOTE: Qt is using double for qreal on this system. This is binary incompatible
against Qt 5.1.
Configure with '-qreal float' to create a build that is binary compatible with
5.1.

Qt is now configured for building. Just run 'make'.
Once everything is built, you must run 'make install'.
Qt will be installed into /usr/local/Qt-5.6.1

Prior to reconfiguration, make sure you remove any leftovers from
the previous build.