Building Qt Virtual Keyboard

Overview

This document describes how to build the Qt Virtual Keyboard plugin.

The project is split into the following subprojects:

The input methods are implemented either in C++ or QML. Qt Virtual Keyboard provides implementations of PlainInputMethod, MultitapInputMethod and HunspellInputMethod. The MultitapInputMethod is implemented in QML while the others are implemented in C++.

Build Instructions

The Qt Virtual Keyboard can be built for Linux Desktop/X11, Windows Desktop or Boot2Qt targets. The target is automatically detected by QMAKE and requires no special configuration parameters.

Qt Creator is the preferred build environment for Qt Virtual Keyboard as you can then leverage the shadow build functionality and rapidly switch between build targets.

Configuration Options

The table below contains the top-level options for configuring the virtual keyboard features.

These options can be passed to configure when doing a full build of Qt. Alternatively, when building only the Qt Virtual Keyboard, you can configure the keyboard using the following command (where SRCDIR points to the source directory of QtVirtualKeyboard):

qmake $SRCDIR -- [options]

Building Documentation

Hunspell Integration

By default, HunspellInputMethod will not be available unless the Hunspell library and development headers are found. For Linux/X11 targets, the Hunspell library can be provided by installing the libhunspell-dev package. Alternatively, the Hunspell sources can be extracted into the src/plugins/hunspell/3rdparty/hunspell directory. The sources are automatically detected by the qmake and the project will be configured to use the local Hunspell. If Hunspell sources are used, then the dictionary files must also be copied into the src/plugins/hunspell/3rdparty/hunspell/data directory.

An example of how the directory structure should look after copying in the Hunspell sources and dictionary files is listed below:

3rdparty
└── hunspell
    ├── data
    │   ├── en_GB.aff
    │   └── en_GB.dic
    ├── hunspell.pro
    └── src
        └── hunspell
            ├── affentry.cxx
            ├── affentry.hxx
            (etc.)

Cerence Handwriting Integration

Cerence Handwriting integration supports the Alphabetic and CJK (Chinese Japanese Korean) engines. Both engines are integrated via T9WriteInputMethod. The input method is initialized with one engine at the time. The engine selection happens automatically based on the current input locale.

Cerence Handwriting Compatibility

Qt Virtual Keyboard is compatible with Cerence Handwriting v8.7 or later.

Cerence Handwriting Build Preparations

The contents of the SDK must unpacked using the unpack.py script located in the cerence directory. This ensures the correct directory structure for CMake to find the content.

$ cd src/plugins/cerence/
$ python unpack.py filename.zip

This will unpack the contents to the src/plugins/cerence/sdk directory, where the CMake can pick it up automatically.

Alternatively, you can unpack to any other directory by adding extra parameter to the command line. In this case, the location of the SDK must be passed to the configure script.

configure ... -vkb-cerence-sdk /path/to/cerence/sdk

Layout of the Cerence SDK

The extracted content of the SDK looks like this:

sdk
├───t9write
│   ├───api
│   ├───data
│   │   ├───arabic
│   │   ├───hebrew
│   │   └───thai
│   └───lib
│       ├───linux
│       │   ├───arm64
│       │   │   ├───shared
│       │   │   │   ├───alphabetic
│       │   │   │   └───cjk
│       │   │   └───static
│       │   │       ├───alphabetic
│       │   │       └───cjk
│       │   └───x86_64
│       │       ├───shared
│       │       │   ├───alphabetic
│       │       │   └───cjk
│       │       └───static
│       │           ├───alphabetic
│       │           └───cjk
│       └───win32
│           ├───x86
│           │   ├───shared
│           │   │   ├───alphabetic
│           │   │   └───cjk
│           │   └───static
│           │       ├───alphabetic
│           │       └───cjk
│           └───x86_64
│               ├───shared
│               │   ├───alphabetic
│               │   └───cjk
│               └───static
│                   ├───alphabetic
│                   └───cjk
└───xt9
    ├───api
    ├───data
    └───lib
        ├───linux
        │   ├───arm64
        │   │   ├───shared
        │   │   └───static
        │   └───x86_64
        │       ├───shared
        │       └───static
        └───win32
            ├───x86
            │   ├───shared
            │   └───static
            └───x86_64
                ├───shared
                └───static

Where the contents of each directory are:

The Cerence Handwriting and XT9 integration code is automatically activated when the Cerence SDK is detected.

All other extensions should be cleaned from the [qtbase]/plugins/virtualkeyboard directory before building the Cerence extensions to avoid conflicting behavior at runtime. The Cerence extensions do not require any other virtual keyboard plugin to function.

Handwriting databases and language databases for XT9 are installed in the [qtbase]/qtvirtualkeyboard/cerence directory. In addition, there are two other alternatives for locating these files:

• A custom runtime location defined by Environment Variables
• The -vkb-bundle-cerence command line option to embed resources in the plugin binaries

MyScript Text SDK Integration

MyScript Text is designed for building applications that enable the recognition of handwritten text. MyScript Text supports the recognition of isolated characters, cursive, print and superimposed writing. MyScript superimposed writing is integrated into Qt Virtual Keyboard. It enables the recognition of letters, words or parts of words written one over the other, without any explicit separation between consecutive fragments. It is capable of running on memory and CPU constrained devices.

Input handwriting styles of MyScript Text SDK

The end-user can write one word fragment over the other, or one character over the other, as depicted below. Space between two written words are automatically added, so that there is no need for an explicit gesture.

Language coverage of MyScript Text SDK

MyScript Superimposed supports 72 languages.

MyScript Text SDK Packages Installation

The MyScript delivery team can provide you the packages with various .zip archives. To access all the code, tools, and resources needed for building your own handwriting application, extract all the packages in the same destination folder as src/plugins/myscript/sdk, where the CMake can pick it up automatically.

Alternatively, you can extract the packages to any other directory. In this case, the location of the SDK must be passed to the configure script.

configure ... -vkb-myscript-sdk /path/to/myscript/sdk

The file hierarchy should look like below:

myscript
└── sdk
    ├─── conf
    ├─── doc
    ├─── edk
    ├─── engine
    │   └─── bin
    │       ├─── lin-arm64
    │       │   └─── *.so
    │       ├─── lin-armv7
    │       │   └─── *.so
    │       ├─── lin-armv7hf
    │       │   └─── *.so
    │       ├─── lin-x64
    │       │   └─── *.so
    │       ├─── lin-x86
    │       │   └─── *.so
    │       ├─── win-x64
    │       │   └─── *.dll
    │       ├─── win-x86
    │       │   └─── *.dll
    │       (etc.)
    ├─── rdk
    ├─── resources
    │   ├─── ar
    │   │   └─── *.res
    │   ├─── en_GB
    │   │   └─── *.res
    │   ├─── ja_JP
    │   │   └─── *.res
    │   ├─── ko_KR
    │   │   └─── *.res
    │   ├─── zh_CN
    │   │   └─── *.res
    │   (etc.)
    ├─── tools
    └─── voim
        ├─── api
        ├─── bin
        │   ├─── lin-arm64
        │   │   └─── *.so
        │   ├─── lin-armv7
        │   │   └─── *.so
        │   ├─── lin-armv7hf
        │   │   └─── *.so
        │   ├─── lin-x64
        │   │   └─── *.so
        │   ├─── lin-x86
        │   │   └─── *.so
        │   ├─── win-x64
        │   │   └─── *.dll
        │   ├─── win-x86
        │   │   └─── *.dll
        │   (etc.)
        └─── conf

The description for the contents of each directory are:

Setting the Certificate of MyScript Text SDK

A valid certificate is mandatory to use the MyScript Text SDK. This is a security measure that uniquely identifies you as a legitimate customer of MyScript technologies. The certificate helps MyScript trace customers' identify and the products that have been purchased.

The certificate is delivered in the [your_login].vo.zip package. When you unzip this package, the certificate is automatically put in the appropriate location. This ensure that the certificate is instantly working within the services and code samples that you have been provided with.

How to build Qt Virtual Keyboard with MyScript Text SDK

The MyScript integration code is automatically activated when the MyScript Text SDK is detected.

Language resources for MyScript Text SDK are installed in the [qtbase]/qtvirtualkeyboard/myscript directory.

Static builds

The virtual keyboard can be built and linked statically against the application. This implies that Qt is also built statically (using the -static option in the configure command line).

Static builds of the virtual keyboard are enabled by adding CONFIG+=static to the qmake command line and then rebuilding.

Some third party modules used by the virtual keyboard are always built as shared libraries (e.g. Hunspell).

Using the static plugin

The following section should be added to the application project file that uses the statically built virtual keyboard.

static {
    QTPLUGIN += qtvirtualkeyboardplugin
    QT += svg
}

QTPLUGIN causes qmake to pull linker dependencies for the virtual keyboard plugin. The SVG module is required as an extra dependency for Qt, since the SVG format is required by the default styles.

From here on, using a statically built virtual keyboard is no different from the normal case.

Deployment

Desktop Targets

Add a Deploy Step that executes the make install command, then deploy using the Deploy All command.

Boot2Qt Targets

The installation is done by copying the necessary files to the memory card, or by using the adb push command.