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Architecture

# Overview

Maliit is an input method framework with a client-server architecture. The server hosts an UI for text input. The client receives the text input and displays it in the application. The Framework uses D-Bus for IPC (can be replaced with something else by re-implementing the communication class) and Qt's input method support, together with a Maliit input context backend.

Server and client (that is, the application) run in different processes. The server runs as a single-instance process for each user session.

Whenever the server handles a client request (eg. when text entry is tapped, thus becoming the focus widget), the server projects a translucent fullscreen overlay onto the screen, effectivly capturing all input events. Maliit plugins then render their UI into the overlay, propagating the consumed input method area to the server. The fullscreen overlay is transient to the application window, that is, if the application window goes away, so does the fullscreen overlay.

The system compositor composes the remaining translucent background area with the application UI's rendering output. Except for touch and mouse events targeting the active plugin's propagated input method area, all input events are forwarded to the underlying application window.

Maliit can run in a self compositing mode, which bypasses the system compositor and instead composes the application UI's rendering output in the Maliit server process. In this mode, no system compositor is required.

In Harmattan and MeeGo, MCompositor takes the role of a compositing window manager. MCompositor serves as a reference window manager for Maliit.

The Framework provides interfaces which are implemented by the plugins. Plugins provide the input method's UI and are also responsible for input method engine integration. A typical plugin use-case is the implementation of a virtual keyboard with error correction and word prediction support. Plugins handle text composition and send the result to the application via the server, using either preedit or commit strings. The latter are considered the final text input, whereas the former can still be modified by plugins. Preedit strings can be used to show the would-be result to users.

Each application creates its own input context, which acts as the application's client that connects to the Maliit server. The input context receives text composed by input methods and forwards it to the application's focus widget (usually a text entry). Maliit's input context backend supports Qt application. Support for GTK+ applications is provided through Maliit's input method bridges.

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