How to use the Feathers BitmapFontTextEditor component

The BitmapFontTextEditor class renders text using bitmap fonts. This text editor is fully integrated with the Starling display list, which means that nothing appears as an overlay when the text editor is focused.

Advantages and disadvantages

Due to limitations in the Adobe AIR runtime, this text editor cannot be used on mobile. Adobe AIR does not offer an API for displaying the soft keyboard on iOS when the text editor receives focus. This text editor should only be used in desktop apps.

Bitmap fonts separate each character into sub-textures inside an atlas. These sub-textures are displayed as images placed next to each other to form words and paragraphs. If the text has a particularly stylized appearance, such as gradients and outlines, bitmap fonts provide the best performance because the styles can be calculated at design time rather than runtime.

While the English language has only 26 letters in the alphabet (in addition to any punctuation and other supporting characters that you might need), some languages require many hundreds of characters. A texture that contains all of those characters may be impossible to use with bitmap fonts because it hits texture memory limits imposed by the Flash runtime or the GPU. In these situations, you may have no choice but to use device fonts.

Bitmap fonts may be scaled, but because they use bitmaps, only scaling down is recommended. Even then, you may lose out on text hinting that would make vector fonts more readable at smaller sizes. It's common to include separate font sizes as separate textures for bitmap fonts to achieve the best looking results, and that can require a lot of memory.

BitmapFontTextEditor does not support multiple font styles. A BitmapFontTextEditor must use a single bitmap font to render its entire text.

Advanced font styles

To use bitmap fonts with TextInput, create a BitmapFontTextEditor class in the appropriate factory exposed by the parent component. In the following example, we'll use the textEditorFactory of a TextInput component:

var input:TextInput = new TextInput();
input.textEditorFactory = function():ITextEditor
    var textEditor:BitmapFontTextEditor = new BitmapFontTextEditor();
    textEditor.styleProvider = null;
    //set advanced font styles here

    return textEditor;

Font styles may be customized by passing a BitmapFontTextFormat instance to the text editor's textFormat property.

var format:BitmapFontTextFormat = new BitmapFontTextFormat( "FontName" );

Pass the font to display to the BitmapFontTextFormat constructor. In the code above, we pass in the name of a font registered with TextField.registerCompositor(). We could also pass in a starling.text.BitmapFont instance that has not been registered.

The tint of the text can be customized with the color property:

format.color = 0xc4c4c4;

The RGB values of the tint color are multiplied with the RGB values of each of the font texture's pixels, similar to starling.display.BlendMode.MULTIPLY.

The alignment of the text can be customized with the align property:

format.align = TextFormatAlign.CENTER;

Bitmap fonts have one primary font size. They may be scaled, but scaled bitmap fonts may not render as nicely as scaled vector fonts. However, if needed, we can use the size property:

format.size = 18;

In most cases, it's not necessary to set the size property. The primary font size will be detected automatically.

BitmapFontTextEditor provides a number of other advanced properties that may be customized, but aren't included in this quick introduction. For complete details about available properties, please take a look at the BitmapFontTextEditor API reference and the BitmapFontTextFormat API reference.

How to change advanced font styles when a parent component has multiple states

TextInput has multiple states, and it's possible to pass a different BitmapFontTextFormat to the BitmapFontTextEditor for each state. When the parent component's state changes, the font styles of the text editor will update automatically.

For instance, we can provide a different font style for the focused state of a TextInput by calling setTextFormatForState():

var defaultFormat:BitmapFontTextFormat = new BitmapFontTextFormat( "FontName", 20, 0xc4c4c4 );
textEditor.textFormat = defaultFormat;

var focusedFormat:BitmapFontTextFormat = new BitmapFontTextFormat( "FontName", 20, 0x343434 );
textEditor.setTextFormatForState( TextInput.STATE_FOCUSED, focusedFormat );

We didn't provide separate font styles for other states, like TextInput.STATE_DISABLED. When the TextInput is in one of these states, the BitmapFontTextEditor will fall back to using the value we passed to the textFormat property.