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How to cross-compile Qt for WebOS

History:

  • 08.02.2012: first version

Qt and QML on WebOS devices

This document explains how to set-up Qt 4.8 (Trolltech/Nokia's cross-platform application and UI framework) on WebOS devices, and then how to cross-compile Qt or QML apps.

This guide assumes:

  • a Linux development environment (here Kubuntu 11.10 running in virtualbox on a win7 host)
  • Qt 4.8 (the process for Qt 4.7.x is mostly identical; no idea for Qt 5)
  • OpenSSH running on the webos device to scp files to it
  • The reasonable development tools

The steps include:

  1. Getting and setting-up the Palm PDK
  2. Optionally: completing the PDK with some missing includes
  3. Getting Qt 4.8, setting it up for cross-compilation
  4. Cross-compilation of Qt 4.8
  5. Updated webos port of Qt
  6. Application tweaks to look for libs in the right places

1. Getting and setting up the Palm PDK

Qt is cross-compiled with the official Palm PDK. The PDK plays nice: it can be installed alongside the webos internals WIDK without conflicts; there is no need to modify paths or environment variables.

Note that I haven't "fully" installed the PDK. In particular I haven't set-up the emulator. The basic stuff needed are: the arm gcc toolchain, and novacom to communicate with the device. VirtualBox can be skipped. Java may be necessary.

  1. Read about the Palm SDK 3.05 and the installation procedure. Follow the instructions on there. But essentially this boils down to:
  2. Download novacom from that page
  3. Download the SDK from that page
  4. Install novacom and the SDK following the instructions. I.e.:
    1. sudo dpkg -i palm-sdk_3.0.5-svn528736-pho676_i386.deb
    2. sudo dpkg -i palm-novacom_1.0.80_i386.deb
  1. The SDK is now in /opt/PalmPDK

When you're running 64 bits Linux please make sure to also install ia32-libs by running: (otherwise you'll get the error that "arm-none-linux-gnueabi-g++ cannot be found"!)

  1. sudo apt-get install ia32-libs


You may check that all is fine so far (or skip this - this is simply to step-by-step see if all is ok):

  1. You can invoke gcc or g++ from the PDK arm toolchain to compile some test program. E.g. /opt/PalmPDK/arm-gcc/bin/arm-none-linux-gnueabi-g++ hello.cpp -o hello
  2. You can copy this file to the usb drive on the device: scp hello root@ip.address.of.device:/media/internal
  3. You can go log on the device with novaterm: novaterm
  4. You can run your test program: /media/internal/hello

If that works then on to the next steps.

2. Optional: completing the PDK with some missing includes

The Palm PDK contains an arm toolchain which can be used as-is to cross-compile Qt. This step can be skipped, unless you want maximum performance with JavaScript in WebKit.

There is one issue with the Palm PDK. The Qt configuration script relies on the existence of one include file - /opt/PalmPDK/include/asm/hwcap.h (actually more includes in the /opt/PalmPDK/include/asm directory are needed) - to know whether programs can identify the characteristics of the CPU, such as the availability of Neon instructions.

Without these includes, Qt will cross-compile and work, but the just-in-time JavaScript compiler in WebKit will be deactivated. This decreases JavaScript performance by a factor ~3.

Therefore the recommended approach is to provide the missing include files. These files can be found in the CodeSourcery arm toolchain.

  1. Download the arm toolchain "Sourcery G++ Lite 2009q3-67 for ARM GNU/Linux" from Mentor Graphics' website. You need to register to download, but it's free. Make sure you get the ARM GNU/Linux Release (not the ARM EABI release!). The file you get should be called arm-2009q3-67-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
  2. Untar this file: tar xvfj arm-2009q3-67-arm-none-linux-gnueabi-i686-pc-linux-gnu.tar.bz2
  3. Copy the entire include/asm directory to the PalmPDK: cp -r arm-2009q3/arm-none-linux-gnueabi/libc/usr/include/asm /opt/PalmPDK/include
  4. Copy the files int-l64.h and int-ll64.h from include/asm-generic directory to the PalmPDK: cp -r arm-2009q3/arm-none-linux-gnueabi/libc/usr/include/asm-generic/int* /opt/PalmPDK/arm-gcc/sysroot/usr/include/asm-generic
  5. Various SDL include files are in the "wrong location". Instead of editing various files to point to the SDL directory, lets just copy them all over to the regular include directory cp -r /opt/PalmPDK/include/SDL/* /opt/PalmPDK/include/

You're set!

3. Getting Qt 4.8, setting it up for cross-compilation

This step gets the Qt 4.8 sources, and sets-up Qt for cross-compilation using the Palm PDK.

3.1 Get the Qt sources

  1. Cd to your home directory: cd ~
  2. Get the Qt 4.8 sources: http://get.qt.nokia.com/qt/source/qt-everywhere-opensource-src-4.8.0.tar.gz
  3. Untar: tar xvfz qt-everywhere-opensource-src-4.8.0.tar.gz

3.2 Qt mkspecs for WebOS

We set-up the mkspecs for WebOS (compiler parameters required for cross-compilation):

  1. Cd to the qws mkspecs: cd ~/qt-everywhere-opensource-src-4.8.0/mkspecs/qws
  2. The WebOS mkspecs are mostly the same as the linux-arm-gnueabi-g++ mkspecs. So we copy them and modify them afterwards: cp -r linux-arm-gnueabi-g++ linux-webos
  3. Edit the linux-webos mkspecs to set-up the cross-compiler path and other build parameters. E.g. vi ~/qt-everywhere-opensource-src-4.8.0/mkspecs/qws/linux-webos/qmake.conf. This file must look like this:


 
#
# qmake configuration for WebOS builds with arm-linux-g++
#

#for 4.7.4:
#include(../../common/g++.conf)
#include(../../common/linux.conf)
#include(../../common/qws.conf)

# for 4.8
include(../../common/linux.conf)
include(../../common/gcc-base-unix.conf)
include(../../common/g++-unix.conf)
include(../../common/qws.conf)

# modifications to g++.conf
#Toolchain

#Base directory of gcc toolchain

GCCBASE                 = /opt/PalmPDK/arm-gcc/bin
TSLIB_INCDIR            = /opt/PalmPDK/include
TSLIB_LIBDIR            = /opt/PalmPDK/device/lib


#Compiler Flags to take advantage of the ARM architecture
QMAKE_CFLAGS_RELEASE    = -O2 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=softfp -ftree-vectorize
QMAKE_CFLAGS_DEBUG      = -O0 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=softfp

QMAKE_CXXFLAGS_RELEASE  = -O2 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=softfp -ftree-vectorize
QMAKE_CXXFLAGS_DEBUG    = -O0 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=softfp

# For official pdk
QMAKE_CC                = $$GCCBASE/arm-none-linux-gnueabi-gcc
QMAKE_CXX               = $$GCCBASE/arm-none-linux-gnueabi-g++
QMAKE_LINK              = $$QMAKE_CXX
QMAKE_LINK_SHLIB        = $$QMAKE_CXX
QMAKE_RANLIB            = $$GCCBASE/arm-none-linux-gnueabi-ranlib

# modifications to linux.conf
QMAKE_AR                = $$GCCBASE/arm-none-linux-gnueabi-ar cqs
QMAKE_OBJCOPY           = $$GCCBASE/arm-none-linux-gnueabi-objcopy
QMAKE_STRIP             = $$GCCBASE/arm-none-linux-gnueabi-strip


QMAKE_INCDIR = $$TSLIB_INCDIR 
QMAKE_LIBDIR = $$TSLIB_LIBDIR 
QMAKE_LIBS   += -lrt -lz 

QMAKE_LFLAGS += -Wl,--allow-shlib-undefined 

load(qt_config)


3.3 gfxdrivers plugin for WebOS

Qt embedded needs a gfxdrivers plugin which allows Qt to show things on a screen, get keyboard input and mouse events. This step gets the WebOS Qt gfxdrivers plugin.

The initial plugin version was written by Darron Black [1,2] and it uses SDL for graphics. With the changes in WebOS 2.x, that plugin doesn't work anymore: it uses root access to read the keyboard, but recent PDK apps are not running as root anymore but in jails. Therefore an extended version is required that handles keyboard input for "non-root" users. That version is available from Qt gfxdrivers plugin for WebOS on Google Code. It has also tentative support for screen rotation.

  1. Cd to the Qt gfxdrivers directory: cd ~/qt-everywhere-opensource-src-4.8.0/src/plugins/gfxdrivers
  2. Get the WebOS gfxdrivers plugin from the svn repository: svn checkout http://qt-webos.googlecode.com/svn/trunk/ webos
  3. Edit ~/qt-everywhere-opensource-src-4.8.0/src/plugins/gfxdrivers/gfxdrivers.pro to add the line: contains(gfx-plugins, webos)  :SUBDIRS += webos
  4. In order to support screen rotation we need to patch the "transformed" screen driver. This driver is provided by Qt to do screen rotation or offsetting and it uses as back-end the driver doing the actual access to the pixels (that would be our webos qgfxdrivers). Unfortunately the transformed driver doesn't allow to "notify" SDL when pixels are changed. A quick hack is to patch ~/qt-everywhere-opensource-src-4.8.0t/src/gui/embedded/qscreentransformed_qws.cpp. In this patch we hijack the functionality of the "blank" method (which is supposed to blank the screen) to notify the WebOS gfxdrivers before and after pixels are modified. So edit qscreentransformed_qws.cpp around lines 430 and add the two lines marked with the comments below:
.
.
.
    screen()->blank(true);                        // ADD THIS FOR WEBOS
    QWSDisplay::grab();
    for (int i = 0; i < rects.size(); ++i) {
        const QRect r = rects.at(i) & bound;

        QPoint dst;
        switch (trans) {
        case Rot90:
            dst = mapToDevice(r.topRight(), QSize(w, h));
            break;
        case Rot180:
            dst = mapToDevice(r.bottomRight(), QSize(w, h));
            break;
        case Rot270:
            dst = mapToDevice(r.bottomLeft(), QSize(w, h));
            break;
        default:
            break;
        }
        func(this, image, r.translated(-topLeft), dst);
    }
    QWSDisplay::ungrab();
    screen()->blank(false);                       // ADD THIS FOR WEBOS
.
.
.


3.4 Cross-compile

Now we can configure and cross-compile Qt. The lines below configure Qt to install in ~/qte-48:

  1. cd ~/qt-everywhere-opensource-src-4.8.0
  2. ./configure -v -prefix ~/qte-48 -embedded arm -platform qws/linux-x86-g++ -xplatform qws/linux-webos -depths 16,24,32 -no-multimedia -no-audio-backend -no-phonon -no-phonon-backend -no-nis -no-iconv -no-dbus -no-cups -no-largefile -no-accessibility -no-gtkstyle -no-qt3support -qt-gfx-vnc -plugin-gfx-vnc -no-glib -qtlibinfix 48 -xmlpatterns -exceptions -opensource -make libs -nomake tools -nomake demo -nomake examples -nomake docs -webkit -javascript-jit -script -scripttools -declarative -openssl -qt-gfx-transformed
  3. make -j4
  4. make install

The WebOS gfxdrivers plugin must be compiled manually:

  1. cd ~/qt-everywhere-opensource-src-4.8.0/src/plugins/gfxdrivers/webos
  2. make

This builds and copies the plugin into ~/qte-48/plugins/gfxdrivers


Hopefully you've made it so far without problems! You now have Qt in ~/qte-48.

4. Compiling Qt apps

We see here how to compile a Qt app for Qt on WebOS. We look at two examples that are directly taken from the Qt distribution.

  1. fancybrowser: this is a Qt-widget-based example browser. It is available in QTSDKDIR/Examples/4.8/webkit/fancybrowser. Download the source with the modifications here
  2. webbrowser: this is a Qt-QML-based example browser. It is available in QTSDKDRIR/Demos/4.8/declarative/webbrowser. Since this is a QML app, a QmlApplicationViewer must be used to run the QML files. Download the source with the modifications here

The binaries are available on the WebOS homebrew app repository [www.webosnation.com/a-browser-qt-test here] and [www.webosnation.com/a-browser-qml-test here].


The way compilation of the apps is mostly identical, but the QML-based project has a few extra complexities so we'll see first the widget-based project.

4.1 Qt-widget app

We assume a copy of QTSDKDIR/Examples/4.8/webkit/fancybrowser in your working directory, e.g. ~/fancybrowser

Two things must be modified in the project:

  • fancybrowser.pro: this is the project file, it must be modified to include the proper libraries
  • main.cpp: this is the file in which the QApplication object is instanciated. We must do some setup to indicate to the application:
    • where to find system fonts,
    • to start the application as a GUI server application
    • to use the WebOS gfxdrivers plugin, or to use the transformed gfxdrivers plugin in combination with the WebOS gfxdrivers plugin to support screen rotation.

Note that one could avoid modifying main.cpp altogether because the same results can be achieved by environment variables and by command line arguments. Therefore a script could set the environment variables and call the executable with the appropriate parameters. However we go through the self-contained solution, which is a bit more complex but may seen as more clean.

Modifications to the .pro file

The pro file must be modified to link the PDL and SDL libs, and also to look for the Qt libraries at the right location at runtime. Here we assume that the Qt libs are in a subdirectory called 'qt' below the directory where the application is deployed.

Modify fancybrowser.pro and add this at the end:

!win32: {
message(assume qws)
# Set the runtime path to a relative directory w.r.t. the location of the executable
LIBS += -Wl,-rpath,"'\$$ORIGIN/qt'" -L/opt/PalmPDK/device/lib -lpdl -lSDL
INCLUDEPATH += /opt/PalmPDK/include/SDL
}

Note that !win32:{...} sets these parameters for any "non windows build" (I happen to build the desktop app on Windows and the WebOS app on Linux). Ideally we would rather have something for webos (webos:{...}) but I did not investigate how to do enable that - if somebody knows, feel free to share.

Modifications to the main file

There are modifications to main.cpp in three categories.

When instanciating a QApplication object the fonts are search in the directory specified by the QT_QWS_FONTDIR environment variable. To my knowledge this cannot be specified to QApplication in another way. Therefore we set programmatically QT_QWS_FONTDIR to where we have our fonts. There are two possibilities: we can deploy the fonts of Qt, or we can use the fonts already available on the WebOS device. Using the fonts of the WebOS device is fine so we use this. See the commented-out line for the alternative approach.

When instanciating the QApplication object we want to start the application as a GUI server application. This is achieved by passing QApplication::GuiServer in the QApplication constructor. The alternative approach is to call the program with -qws on the command line.

The gfxdrivers plugin must be specified. This can be done with the -display command line argument. Here we programmatically set this command line argument. We have two alternatives. We can use directly the WebOS gfxdrivers plugin. This does not allow for screen rotation. The command line would then be '-display PalmPreSDLFb:nnn. Alternatively, we can use the transformed gfxdrivers in combination with the WebOS gfxdrivers plugin. This allows for screen rotation. The command line would then be -display Transformed:PalmPreSDLFb:nnn.

nnn is a number which you must set to identify the display driver. In a normal embedded system only a single GUI server application would run at any time, and this number can be the same for all applications (or even left out, QApplication assumes number 0 then). This number is used by Qt to create a temporary directory (/tmp/qtembedded-nnn) that contains, among others, a font cache.

However, on WebOS each running Qt applications is a GUI server. Each application will thus create a /tmp/qtembedded-nnn directory. Therefore nnn must be unique for each Qt application. (maybe we need a convention to avoid conflicts - might be enough to use some randomly generated number for each app).

main.cpp can be modified as follows:

int main(int argc, char * argv[])
{
    int rv;

#ifdef Q_WS_QWS
#warning "Hacks for QWS"
    // ------------------------------------------------------------------------
    // FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP
    // Get the path to the exe...
    // Ideally we should use QApplication::applicationDirPath, but instanciating that
    // one attempts to load the fonts... which aren't defined yet
    char pathexe[1024];
    rv = readlink("/proc/self/exe", pathexe, sizeof(pathexe));
    if(!(rv>0 && rv<sizeof(pathexe)))
    {
        printf("Couldn't get the exe path - terminating\n");
        return -1;
    }
    pathexe[rv]=0;
    printf("path to exe: %s\n",pathexe);
    *strrchr(pathexe,'/')=0;    // Eliminate the application name
    QString fontpath = QString(pathexe)+"/fonts";
    //if(!qputenv("QT_QWS_FONTDIR",fontpath.toAscii()))              // USE THIS IF YOU DEPLOY YOUR OWN FONTS
    if(!qputenv("QT_QWS_FONTDIR","/usr/share/fonts"))                // USE THIS IF YOU USE THE WEBOS FONTS
    {
        printf("Can't set font path");
    }
    //
    // FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP
    // ------------------------------------------------------------------------

    // Hack setting the the display driver
    int argc2 = argc+2;
    char **argv2 = new char*[argc2];
    for(int i=0;i<argc;i++)
    {
        argv2[i] = new char[strlen(argv[i])+1];
        strcpy(argv2[i],argv[i]);
    }
    //char *display[]={"-display","PalmPreSDLFb:100"};              // USE THIS FOR THE WEBOS GFXDRIVERS PLUGIN W/O ROTATION
    char *display[]={"-display","Transformed:PalmPreSDLFb:100"};    // USE THIS FOR THE WEBOS GFXDRIVERS PLUGIN AND ROTATION
    argv2[argc] = display[0];
    argv2[argc+1] = display[1];

    // QApplication::GuiServer is akin to passing -qws on the command line
    // Passes argv2 / argc2 which stays alive for the entire duration of QApplication
    QApplication app(argc2, argv2,QApplication::GuiServer);  

#else
#warning "No QWS - business as usual"
    QApplication app(argc, argv,QApplication::GuiServer);
#endif

.
.
.
.

    rv = app.exec();
    return rv;

}

Compilation

Generate the makefile and compile:

  1. ~/qte-48/bin/qmake fancybrowser.pro
  2. make

Now the app is compiled. The Qt libs must also be deployed on the device. See the deployment section below for how to lay-out the files.

4.2 Qt-QML app

We assume a copy of QTSDKDIR/Demos/4.8/declarative/webbrowser in your working directory, e.g. ~/webbrowser

Essentially the same modifications must be made to the Qt-QML project as for the Qt-widget project, with some additions to the main file.

Modifications to the .pro file

Same as for the Qt-widget app.

Modifications to the main file

Same as for the Qt-widget app, and in addition we must set the path where the QML imports can be found. This can be specified with the QML_IMPORT_PATH environment variable. We set-it up programmatically here.

The file main.cpp looks like this:


int main(int argc, char * argv[])
{
    int rv;

#ifdef Q_WS_QWS
#warning "Hacks for QWS"
    // ------------------------------------------------------------------------
    // FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP
    // Get the path to the exe...
    // Ideally we should use QApplication::applicationDirPath, but instanciating that
    // one attempts to load the fonts... which aren't defined yet
    char pathexe[1024];
    rv = readlink("/proc/self/exe", pathexe, sizeof(pathexe));
    if(!(rv>0 && rv<sizeof(pathexe)))
    {
        printf("Couldn't get the exe path - terminating\n");
        return -1;
    }
    pathexe[rv]=0;
    printf("path to exe: %s\n",pathexe);
    *strrchr(pathexe,'/')=0;    // Eliminate the application name
    QString fontpath = QString(pathexe)+"/fonts";
    //if(!qputenv("QT_QWS_FONTDIR",fontpath.toAscii()))              // USE THIS IF YOU DEPLOY YOUR OWN FONTS
    if(!qputenv("QT_QWS_FONTDIR","/usr/share/fonts"))                // USE THIS IF YOU USE THE WEBOS FONTS
    {
        printf("Can't set font path");
    }
    //
    // FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP    FONT SETUP
    // ------------------------------------------------------------------------

    // ------------------------------------------------------------------------
    // QML SETUP    QML SETUP    QML SETUP    QML SETUP    QML SETUP    QML SETUP
    QString qmlpath = QString(pathexe)+"/imports";
    if(!qputenv("QML_IMPORT_PATH",qmlpath.toAscii()))
    {
        printf("Can't set qml path");
    }

    // Hack setting the the display driver
    int argc2 = argc+2;
    char **argv2 = new char*[argc2];
    for(int i=0;i<argc;i++)
    {
        argv2[i] = new char[strlen(argv[i])+1];
        strcpy(argv2[i],argv[i]);
    }
    //char *display[]={"-display","PalmPreSDLFb:100"};              // USE THIS FOR THE WEBOS GFXDRIVERS PLUGIN W/O ROTATION
    char *display[]={"-display","Transformed:PalmPreSDLFb:100"};    // USE THIS FOR THE WEBOS GFXDRIVERS PLUGIN AND ROTATION
    argv2[argc] = display[0];
    argv2[argc+1] = display[1];

    // QApplication::GuiServer is akin to passing -qws on the command line
    // Passes argv2 / argc2 which stays alive for the entire duration of QApplication
    QApplication app(argc2, argv2,QApplication::GuiServer);  

#else
#warning "No QWS - business as usual"
    QApplication app(argc, argv,QApplication::GuiServer);
#endif

.
.
.
.

    rv = app.exec();
    return rv;

}

Compilation

Same as for Qt-widget apps.

4.3 Deployment

We can now test the application, and create an IPK which can be uploaded to the HP or homebrew app repository.

In order to test the app, it must be copied to the device together with Qt libs. The device directory structure, assuming the app is in APPDIR, must be as follows:

APPDIR:                  the application is here
APPDIR/qt:               qt libs. Copy ~/qte-48/lib/*.so.4 here)
APPDIR/fonts:            fonts (not needed if the WebOS fonts are used). Copy ~/qte-48/lib/fonts/* here
APPDIR/gfxdrivers:       gfxdrivers plugins. Copy ~/qte-48/plugins/gfxdrivers/* here
APPDIR/imageformats:     imageformats plugins. Copy ~/qte-48/plugins/imageformats/* here
APPDIR/imports:          QML stuff (not needed for Qt-widget). Copy ~/qte-48/imports/* here

You can deploy these files in /media/internal/APPDIR for testing and run the application from the command line.

To create an IPK file you need in addition an appinfo.json file. For example:

{
	"title": "A-Browser Qml (test)",
	"type": "pdk",
	"main": "abrowse-qml",
	"id": "net.danielroggen.abrowseqml",
        "version": "0.2.0",
	"vendor": "danielroggen",
	"icon":     "icon.png" 
}

Now create a STAGING directory which contains:

  • the application
  • the Qt stuff (keeping the directory structure mentionned above)
  • the icon
  • the appinfo.json
  • any other required file

And run palm-package STAGING. This will create an .ipk ready for distribution. Before distributing, try to install it on the device with Preware: copy the ipk to the device, run Preware and select the option to install ipk packages from the menu, and check that your app works.


5. Limitations

  • No virtual keyboard so far


A. Links

[1] Qt on the Palm Pre

[2] Qt port to webOS by Darron Black on gitorious

[3] A-Browser QML source and binary

[4] A-Browser Qt source and binary

[5] Updated WebOS gfxdrivers plugin

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