Creating custom Feathers themes

Many apps, including games, require heavy branding that involves styling every Feathers component with custom skins and fonts. In these cases, the example themes included with Feathers won't offer enough customization options to match the designer's vision. We will need a custom theme, built from scratch.

Creating a theme class

Let's create a new theme from scratch. We'll create a subclass of StyleNameFunctionTheme:

package
{
    public class CustomTheme extends StyleNameFunctionTheme
    {
        public function CustomTheme()
        {
            super();
        }

        private function initialize():void
        {

        }
    }
}

We've added a function named initialize(). We'll soon fill this function with calls to other functions that get different parts of the theme ready to use. However, before we can call initialize(), we need to decide how we're going to manage our assets like textures and fonts. We don't want to call this function until all assets are fully loaded.

Managing assets

There are two ways to include assets with a theme. Each has its own advantages and disadvantages, and we'll need to pick which one works best for the specific app that we're building.

Embedded assets

The simplest way to include assets to embed the assets at compile time. This approach lets us simply instantiate the classes when they are needed, and we don't need to wait for an event to indicate that they are ready. However, embedding files will increase the memory that our app requires at runtime. On mobile, memory can be limited, and this approach will restrict how many textures that we can keep in memory simultaneously. For a small set of assets, that may be a small price to pay for convenience. For multiple texture atlases, using up memory that we might need at runtime is often unacceptable.

Let's start by embedding a texture atlas in our CustomTheme class:

[Embed(source="/../assets/images/atlas.png")]
private static const ATLAS_BITMAP:Class;

[Embed(source="/../assets/images/atlas.xml",mimeType="application/octet-stream")]
private static const ATLAS_XML:Class;

A texture atlas requires of two files, an image and an XML file. Let's add a member variable to our theme to hold the TextureAtlas once it is created:

private var atlas:TextureAtlas;

Now, we'll add a function named createTextureAtlas() that will instantiate the TextureAtlas using our embedded assets:

private function createTextureAtlas():void
{
    var atlasTexture:Texture = Texture.fromEmbeddedAsset( ATLAS_BITMAP );
    var atlasXML:XML = XML( new ATLAS_XML() );
    this.atlas = new TextureAtlas( atlasTexture, atlasXML );
}

In the CustomTheme constructor, we'll call createTextureAtlas(), and then we can immediately call initialize():

public function CustomTheme()
{
    super();
    this.createTextureAtlas();
    this.initialize();
}

If our theme requires other embedded assets, such as bitmap fonts or additional texture atlases, we simply need to instantiate these assets before we call initialize().

Loading assets at runtime

Another approach to including assets with a theme is to load them from external files at runtime. Starling's AssetManager supports loading a set of multiple files at runtime, and it provides conveniences like automatically converting bitmaps to textures and registering bitmap fonts. Once everything is loaded, our assets will use less memory than if they were embedded, meaning that we can pack in more textures and things. Loading assets doesn't happen instantaneously, though, and we cannot initialize the theme until the AssetManager finishes loading our assets. Additionally, our app will need to wait before it can instantiate Feathers components.

Similar to the previous example that used embedded assets, we want to load a texture atlas to be used by our CustomTheme class. We'll need two files for the texture atlas, we'll call them atlas.png and atlas.xml.

Let's define a couple of member variables, one for the texture atlas, and one for the AssetManager that will load the required files:

private var atlas:TextureAtlas;
private var assets:AssetManager;

Now, we'll add a function named loadAssets() that will instantiate the AssetManager and enqueue the asset files:

private function loadAssets():void
{
    this.assets = new AssetManager();
    this.assets.enqueue( "atlas.png" );
    this.assets.enqueue( "atlas.xml" );
    this.assets.loadQueue( this.assets_onProgress );
}

At the end, we call loadQueue() on the AssetManager to load our assets. We need to pass a callback to this function so that we know when the assets finish loading. The callback accepts a single parameter, a variable with a value between 0.0 and 1.0. Once this value is equal to 1.0, our assets have fully loaded:

private function assets_onProgress( progress:Number ):void
{
    if( progress < 1.0 )
    {
        return;
    }
    this.atlas = this.assets.getTextureAtlas( "atlas" );
    this.initialize();
    this.dispatchEventWith( Event.COMPLETE );
}

If the assets aren't loaded, we simply return. Once the assets are ready, we can access the TextureAtlas from the AssetManager. We pass the name of the texture atlas to the getTextureAtlas() function. The name of a texture atlas is the image's file name, without the extension. In this case, our file is named atlas.png, so we pass "atlas" to getTextureAtlas().

Once we've set the atlas member variable, we can call initialize(). If our custom theme needed to load more assets, we'd want to get them all from the AssetManager before calling initialize().

Finally, we want to inform the rest of our app that it can proceed, so we'll dispatch Event.COMPLETE. The app can listen for this event very easily:

this.theme = new CustomTheme();
this.theme.addEventListener( Event.COMPLETE, theme_completeHandler );

Once the listener is called, the app is free to start instantiating components, and the theme will style them automatically.

Styling components

Once our assets are loaded, we can start setting up the functions called to style each component in our app. Inside one of these functions, styling is simply a matter of directly setting a component's properties. It's the same type of styling you would do if you were using Feathers without a theme. For example, we might set some styles on a Button:

private function setButtonStyles( button:Button ):void
{
    button.defaultSkin = new Image( this.atlas.getTexture( "button-up" ) );
    button.downSkin = new Image( this.atlas.getTexture( "button-down" ) );

    button.padding = 20;
    button.gap = 15;

    button.fontStyles = new TextFormat( "_sans", 18, 0x333333 );
}

In our initialize() function, let's call a new function that we'll create in a moment, named initializeStyleProviders():

private function initialize():void
{
    this.initializeStyleProviders();
}

Now, let's create initializeStyleProviders() and set up our first style provider, the one for the Button class:

private function initializeStyleProviders():void
{
    // button
    this.getStyleProviderForClass( Button ).defaultStyleFunction = this.setButtonStyles;
}

getStyleProviderForClass() returns a StyleNameFunctionStyleProvider.

StyleNameFunctionStyleProvider has two main capabilities. Its defaultStyleFunction property sets the function that will be called for the most common variation of a particular component. Using the code above, if we create regular old button, we want our setButtonStyles() function to be called.

However, it's common for different variations of the same component to exist together in one app. For instance, some buttons may be visually highlighted in red to indicate that something potentially dangerous is about to happen, like deleting some data. The Button.ALTERNATE_STYLE_NAME_DANGER_BUTTON constant is defined by Feathers to help differentiate this variation of a button. You can add this style name to the component to tell the theme that it should be styled differently:

button.styleNameList.add( Button.ALTERNATE_STYLE_NAME_DANGER_BUTTON );

Inside our theme, we can add a new function for this button variation. We'll name it setDangerButtonStyles():

private function setDangerButtonStyles( button:Button ):void
{
    button.defaultSkin = new Image( this.atlas.getTexture( "danger-button-up" ) );
    button.downSkin = new Image( this.atlas.getTexture( "danger-button-down" ) );

    button.padding = 20;
    button.gap = 15;

    button.fontStyles = new TextFormat( "_sans", 18, 0x333333 );
}

Now, we can use the setFunctionForStyleName() on the StyleNameFunctionStyleProvider:

this.getStyleProviderForClass( Button )
    .setFunctionForStyleName( Button.ALTERNATE_STYLE_NAME_DANGER_BUTTON, this.setDangerButtonStyles );

If a component has this style name, the default setButtonStyles() function won't be called. Instead, setDangerButtonStyles() will be called.

Styling sub-components

Some components have sub-components that need to be skinned too. For instance, the Slider component has a thumb that is a Button. These sub-components may be skinned using style names provided by their parent component. For instance, we can use Slider.DEFAULT_CHILD_STYLE_NAME_THUMB to skin the thumb of a slider.

this.getStyleProviderForClass( Button )
    .setFunctionForStyleName( Slider.DEFAULT_CHILD_STYLE_NAME_THUMB, this.setSliderThumbStyles );

Components usually provide a way to customize a sub-component's style name, in case something other than the default is needed. For a Slider, we can set the customThumbStyleName property:

slider.customThumbStyleName = "custom-thumb";

Then, we can use that custom style name just like we would for other variations of a component:

this.getStyleProviderForClass( Button )
    .setFunctionForStyleName( "custom-thumb", this.setSliderThumbStyles );

Setting global defaults

Certain global properties are frequently set by a theme. For instance, we might want to set FeathersControl.defaultTextRendererFactory and FeathersControl.defaultTextEditorFactory in our custom theme, depending on how we prefer to render text or edit it in a TextInput.

Let's create an initializeGlobals() function:

private function initializeGlobals():void
{
    FeathersControl.defaultTextRendererFactory = function():ITextRenderer
    {
        return new TextBlockTextRenderer();
    };

    FeathersControl.defaultTextEditorFactory = function():ITextEditor
    {
        return new StageTextTextEditor();
    };
}

We can call this function before the call to initializeStyleProviders() in initialize():

private function initialize():void
{
    this.initializeGlobals();
    this.initializeStyleProviders();
}