Theme development

In Pegasus themes can define the whole look and feel of the interface. There are no predefined views or layouts: you start with the whole screen as your canvas, and you can add your own views or elements in the kind of arrangement you wish. Pegasus merely provides the data, like the list of games and their assets. You can then use this data to build UI elements like a list of games, a screen for choosing platforms or a search panel for filtering games.

Compared to other frontends, this level of customization might produce a steeper learning curve initially, however in time it allows you to produce themes where the way games are presented and interacted with can be freely decided.


Themes are written in the QML language, a human readable text format. Each QML file describes a hierarchy of elements and their properties, representing a piece of the user interface. These smaller elements can then be combined to form larger or more complex elements, then eventually build up the theme itself.

// An example QML document
// Based on:

import QtQuick 2.0

Rectangle {
    id: canvas
    width: 250
    height: 200
    color: "blue"

    Image {
        id: logo
        source: "pics/logo.png"
        anchors.centerIn: parent


QML describes how elements look, arranged on screen and generally behave. When you want to tell what should happen, you can use JavaScript. In its simplest form this can be things like "if I press Enter then launch the game", but you can write any kind of complex logic if necessary.

Theme structure

Pegasus is looking for themes in the configuration directories, under a themes subdirectory (eg. ~/.config/pegasus-frontend/themes/). This directory might not exist by default, in this case you can just create it manually.

In this themes directory, each theme is located in its own folder, and the name of this folder should be unique. Two files are required for every theme:


The theme.cfg is a text file in the same format as Pegasus' metadata files. Currently the following options are recognized:

Every theme is required to have a theme.cfg file, with at least the name defined. Here is an example:

name: Tutorial
author: John Smith
version: 1.0
summary: A super cool theme!

Another one:

name: Tutorial 2
  John Smith <>
  Jane Doe <>
version: beta
summary: A super cool theme that
  should look really nice on big screens,
  like TVs
keywords: 10foot, retro


The theme.qml file is the entry point of your theme's UI structure. For example the following snippet could be used to check if everything works fine:

import QtQuick 2.0

FocusScope {

    Text {
        text: "Hello World!"
        color: "white"
        anchors.centerIn: parent


Themes should have a FocusScope as their root element, which is then set up by Pegasus to always fill the whole screen. (FocusScope itself is a special container in QML which is used for separating keyboard/gamepad input from other parts of the UI (eg. main menu).)


If you've created the theme.cfg and theme.qml files as described above, you should now see your entry in the list of available themes in Pegasus' settings menu.

After the theme is loaded, pressing the F5 key will make Pegasus reload its files, making it easier to try out changes.

Next steps

QML can be a quite large topic, so this documentation is grouped into the following main areas: