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🔥 Creating a new Effect for Burn-My-Windows

The extension is very modular and with a bit of creativity and GLSL knowledge, you can easily create your own effects. If you are happy with your results, please open a pull request so that we can include your effect in the next version of Burn-My-Windows!

⚠️ For now, this guide is only for GNOME Shell (and not for KWin). As soon as the API for KWin is more stable, this guide will be updated.

Before you Start

First you should fork the repository and clone it to your PC. Afterwards, use a terminal in the directory of the cloned repository to install the extension.

make install

ℹ️ Whenever you changed something in the source code, you will have to call this command and restart GNOME Shell with Alt + F2, r + Enter. Or logout / login if you are on Wayland to see the changes.

Debugging

Debugging GNOME Shell extensions is a bit difficult. Most of the time, you will print messages to a log in order to understand what is going on. To make this a bit more convenient, Burn-My-Windows includes the method utils.debug("Hello World"). With this, each line will be prefixed with the extension's name, which will make spotting log messages more easy. You can use the following command to watch the log output; it will highlight all messages from Burn-My-Windows:

journalctl -f -o cat | grep -E 'burn-my-windows|'

Adding a new Effect

For the sake of this tutorial, we will create a "Simple Fade" effect. Of course, you can replace any occurrence of this name and its nick simple-fade with your custom effect name.

Three simple steps are required to create a new effect. You will have to ...

  1. add preferences keys for enabling the effect,
  2. create an additional effects class, and finally
  3. register the new effect in two places.

1. Expanding the Schema

For enabling the new effect, the boolean settings keys simple-fade-enable-effect and simple-fade-animation-time are required. In this example, we also add a floating point value for storing another property of the effect - we will use them later in the tutorial. Just copy the XML code below to the file schemas/org.gnome.shell.extensions.burn-my-windows-profile.gschema.xml. Just remember to replace simple-fade with your custom name!

<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<!-- Simple Fade Effect Options                                                    -->
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->

<key name="simple-fade-enable-effect" type="b">
  <default>false</default>
  <summary>Simple Fade Enable Effect</summary>
  <description>Use the Simple Fade effect.</description>
</key>

<key name="simple-fade-animation-time" type="i">
  <default>1500</default>
  <summary>Simple Fade Animation Time</summary>
  <description>The time the Simple Fade effect takes.</description>
</key>

<key name="simple-fade-width" type="d">
  <default>0.1</default>
  <summary>Simple Fade Width</summary>
  <description>Width of the fading effect.</description>
</key>

2. Creating the Effect Class

You will have to create a new GLSL file called resources/shaders/simple-fade.frag and a new JavaScript source file called src/effects/SimpleFade.js. Simply paste the following source code to the respective file. Please study this code carefully, all of it is explained with inline comments.

Expand this to show the GLSL code. 
//////////////////////////////////////////////////////////////////////////////////////////
//          )                                                   (                       //
//       ( /(   (  (               )    (       (  (  (         )\ )    (  (            //
//       )\()) ))\ )(   (         (     )\ )    )\))( )\  (    (()/( (  )\))(  (        //
//      ((_)\ /((_|()\  )\ )      )\  '(()/(   ((_)()((_) )\ )  ((_)))\((_)()\ )\       //
//      | |(_|_))( ((_)_(_/(    _((_))  )(_))  _(()((_|_)_(_/(  _| |((_)(()((_|(_)      //
//      | '_ \ || | '_| ' \))  | '  \()| || |  \ V  V / | ' \)) _` / _ \ V  V (_-<      //
//      |_.__/\_,_|_| |_||_|   |_|_|_|  \_, |   \_/\_/|_|_||_|\__,_\___/\_/\_//__/      //
//                                 |__/                                                 //
//////////////////////////////////////////////////////////////////////////////////////////

// SPDX-FileCopyrightText: Your Name <your@email.com>
// SPDX-License-Identifier: GPL-3.0-or-later

// The content from common.glsl is automatically prepended to each shader effect. This
// provides the standard input:

// vec2  iTexCoord:     Texture coordinates for retrieving the window input color.
// bool  uIsFullscreen: True if the window is maximized or in fullscreen mode.
// bool  uForOpening:   True if a window-open animation is ongoing, false otherwise.
// float uProgress:     A value which transitions from 0 to 1 during the animation.
// float uDuration:     The duration of the current animation in seconds.
// vec2  uSize:         The size of uTexture in pixels.
// float uPadding:      The empty area around the actual window (e.g. where the shadow
//                      is drawn). For now, this will only be set on GNOME.

// Furthermore, there are two global methods for reading the window input color and
// setting the shader output color. Both methods assume straight alpha:

// vec4 getInputColor(vec2 coords)
// void setOutputColor(vec4 outColor)

// The width of the fading effect is loaded from the settings.
uniform float uFadeWidth;

void main() {
  // Get the color from the window texture.
  vec4 oColor = getInputColor(iTexCoord.st);

  // Radial distance from window edge to the window's center.
  float dist = length(iTexCoord.st - 0.5) * 2.0 / sqrt(2.0);

  // This gradually dissolves from [1..0] from the outside to the center. We
  // switch the direction for opening and closing.
  float progress = uForOpening ? 1.0 - uProgress : uProgress;
  float mask = (1.0 - progress * (1.0 + uFadeWidth) - dist + uFadeWidth) / uFadeWidth;

  // Make the mask smoother.
  mask = smoothstep(0, 1, mask);

  // Apply the mask to the output.
  oColor.a *= mask;

  setOutputColor(oColor);
}
Expand this to show the JavaScript code. 
//////////////////////////////////////////////////////////////////////////////////////////
//          )                                                   (                       //
//       ( /(   (  (               )    (       (  (  (         )\ )    (  (            //
//       )\()) ))\ )(   (         (     )\ )    )\))( )\  (    (()/( (  )\))(  (        //
//      ((_)\ /((_|()\  )\ )      )\  '(()/(   ((_)()((_) )\ )  ((_)))\((_)()\ )\       //
//      | |(_|_))( ((_)_(_/(    _((_))  )(_))  _(()((_|_)_(_/(  _| |((_)(()((_|(_)      //
//      | '_ \ || | '_| ' \))  | '  \()| || |  \ V  V / | ' \)) _` / _ \ V  V (_-<      //
//      |_.__/\_,_|_| |_||_|   |_|_|_|  \_, |   \_/\_/|_|_||_|\__,_\___/\_/\_//__/      //
//                                 |__/                                                 //
//////////////////////////////////////////////////////////////////////////////////////////

// SPDX-FileCopyrightText: Your Name <your@email.com>
// SPDX-License-Identifier: GPL-3.0-or-later

"use strict";

import * as utils from "../utils.js";

// We import the ShaderFactory only in the Shell process as it is not required in the
// preferences process. The preferences process does not create any shader instances, it
// only uses the static metadata of the effect.
const ShaderFactory = await utils.importInShellOnly("./ShaderFactory.js");

const _ = await utils.importGettext();

//////////////////////////////////////////////////////////////////////////////////////////
// This effect ...                                                                      //
// <- Please add a description of your effect here ->                                   //
//////////////////////////////////////////////////////////////////////////////////////////

// The effect class can be used to get some metadata (like the effect's name or supported
// GNOME Shell versions), to initialize the respective page of the settings dialog, as
// well as to create the actual shader for the effect.
export default class Effect {
  // The constructor creates a ShaderFactory which will be used by extension.js to create
  // shader instances for this effect. The shaders will be automagically created using the
  // GLSL file in resources/shaders/<nick>.glsl. The callback will be called for each
  // newly created shader instance.
  constructor() {
    this.shaderFactory = new ShaderFactory(Effect.getNick(), (shader) => {
      // Store uniform locations of newly created shaders.
      shader._uFadeWidth = shader.get_uniform_location("uFadeWidth");

      // Write all uniform values at the start of each animation.
      shader.connect("begin-animation", (shader, settings) => {
        shader.set_uniform_float(shader._uFadeWidth, 1, [
          settings.get_double("simple-fade-width"),
        ]);
      });
    });
  }

  // ---------------------------------------------------------------------------- metadata

  // The effect is available on all GNOME Shell versions supported by this extension.
  static getMinShellVersion() {
    return [3, 36];
  }

  // This will be called in various places where a unique identifier for this effect is
  // required. It should match the prefix of the settings keys which store whether the
  // effect is enabled currently (e.g. '*-enable-effect'), and its animation time
  // (e.g. '*-animation-time'). Also, the shader file and the settings UI files should be
  // named likes this.
  static getNick() {
    return "simple-fade";
  }

  // This will be shown in the sidebar of the preferences dialog as well as in the
  // drop-down menus where the user can choose the effect.
  static getLabel() {
    return _("Simple Fade Effect");
  }

  // -------------------------------------------------------------------- API for prefs.js

  // This is called by the preferences dialog whenever a new effect profile is loaded. It
  // binds all user interface elements to the respective settings keys of the profile.
  static bindPreferences(dialog) {
    // Empty for now... Code is added here later in the tutorial!
  }

  // ---------------------------------------------------------------- API for extension.js

  // The getActorScale() is called from extension.js to adjust the actor's size during the
  // animation. This is useful if the effect requires drawing something beyond the usual
  // bounds of the actor. This only works for GNOME 3.38+.
  static getActorScale(settings, forOpening, actor) {
    return { x: 1.0, y: 1.0 };
  }
}

3. Registering the new Effect

You will have to register the new effect in two files. Both, extension.js and prefs.js define an array in the beginning where you have to add an import to your new effect. Like this:

import SimpleFade from './src/effects/SimpleFade.js';

...

const ALL_EFFECTS = [
  ...
  new SimpleFade(),
  ...
];

Testing your Effect

Now you can call make install and restart GNOME Shell with Alt + F2, r + Enter. Or logout / login if you are on Wayland. You can open the extension's preferences and choose the new effect! However, there are no configuration options yet. It is also not possible to adjust the animation time setting.

gnome-extensions prefs burn-my-windows@schneegans.github.com

Adding a Preferences Page

There should be two sliders in this example: The animation duration and the width of the fading gradient. Just save the code below to resources/ui/adw/simple-fade.ui. Remember to replace any occurrence of simple-fade with your effect's nick-name!

Expand this to show the UI code. 
<?xml version="1.0" encoding="UTF-8"?>

<!--
SPDX-FileCopyrightText: Your Name <your@email.com>
SPDX-License-Identifier: GPL-3.0-or-later
-->

<interface domain="burn-my-windows">

  <object class="GtkAdjustment" id="simple-fade-animation-time">
    <property name="upper">3000</property>
    <property name="lower">100</property>
    <property name="step-increment">10</property>
    <property name="page-increment">100</property>
  </object>

  <object class="GtkAdjustment" id="simple-fade-width">
    <property name="upper">1</property>
    <property name="lower">0</property>
    <property name="step-increment">0.01</property>
    <property name="page-increment">0.1</property>
  </object>

  <object class="AdwExpanderRow" id="simple-fade-prefs">

    <child>
      <object class="AdwActionRow">
        <property name="title" translatable="yes">Animation Time [ms]</property>
        <child>
          <object class="GtkScale">
            <property name="valign">center</property>
            <property name="draw-value">1</property>
            <property name="digits">0</property>
            <property name="value-pos">left</property>
            <property name="width-request">300</property>
            <property name="adjustment">simple-fade-animation-time</property>
          </object>
        </child>
        <child>
          <object class="GtkButton" id="reset-simple-fade-animation-time">
            <property name="icon-name">edit-clear-symbolic</property>
            <property name="valign">center</property>
            <property name="tooltip-text" translatable="yes">Reset to Default Value</property>
            <style>
              <class name="flat" />
            </style>
          </object>
        </child>
      </object>
    </child>

    <child>
      <object class="AdwActionRow">
        <property name="title" translatable="yes">Fade Width</property>
        <child>
          <object class="GtkScale">
            <property name="valign">center</property>
            <property name="draw-value">1</property>
            <property name="digits">2</property>
            <property name="value-pos">left</property>
            <property name="width-request">300</property>
            <property name="adjustment">simple-fade-width</property>
          </object>
        </child>
        <child>
          <object class="GtkButton" id="reset-simple-fade-width">
            <property name="icon-name">edit-clear-symbolic</property>
            <property name="valign">center</property>
            <property name="tooltip-text" translatable="yes">Reset to Default Value</property>
            <style>
              <class name="flat" />
            </style>
          </object>
        </child>
      </object>
    </child>

  </object>

</interface>

Loading the Preferences Page

In order to load the above *.ui file, add the following code to your effect's bindPreferences() method.

static bindPreferences(dialog) {
  // These connect the settings to the UI elements. Have a look at prefs.js
  // on how to bind other types of UI elements.
  dialog.bindAdjustment('simple-fade-animation-time');
  dialog.bindAdjustment('simple-fade-width');
}

Once this is in place, you can kill the extension-preferences process and re-open the settings. It is not required to reload GNOME Shell for developing the preferences dialog! Here's a handy one-liner to do this:

make install && pkill -f '.Extensions' && sleep 2 ; gnome-extensions prefs burn-my-windows@schneegans.github.com

Summing Up

That's it! If you have any questions, feel free to ask them on the discussions board. If you are happy with your effect, submit a pull request, and it may get included in the next version!