How to use the TextBlockTextRenderer component (Starling version)

The TextBlockTextRenderer class displays text using Flash Text Engine, a software-based vector font renderer with many advanced features. Text may be rendered with either device fonts (the fonts installed on a user's operating system) or embedded fonts (in TTF or OTF formats). A flash.text.engine.TextBlock is drawn to BitmapData and converted to a Starling Texture to display as a snapshot within the Starling display list.

TextBlockTextRenderer is one of many different text renderers supported by Feathers. Since no method of rendering text on the GPU is considered definitively better than the others, Feathers allows you to choose the best text renderer for your project's requirements. See Introduction to Feathers text renderers for complete details about all of the text rendering options supported by Feathers.

Advantages and disadvantages

Flash Text Engine may render text using device fonts, which are the fonts installed on the user's operating system. For some languages with many glyphs and ligatures, device fonts may be the only option when embedded fonts would require too much memory.

Similarly, since embedded vector fonts often require less memory than embedded bitmap fonts, you may still be able to use embedded vector fonts when bitmap fonts would require too much memory.

Flash Text Engine has the best support for right-to-left languages and bi-directional text, which flash.text.TextField may not render correctly.

Changing vector-based text on the GPU is slower than with bitmap fonts because the text needs to be redrawn to BitmapData and then it needs to be uploaded to a texture on the GPU. However, once this texture is on the GPU, performance will be very smooth as long as the text doesn't change again. For text that changes often, the texture upload time may become a bottleneck.

Because each passage of vector text needs to be drawn to BitmapData, each separate renderer requires its own separate texture on the GPU. This results in more state changes and draw calls, which can create more work for the GPU, and it might hurt performance if you have many different instances of TextBlockTextRenderer on screen at the same time.

Flash Text Engine may render a bit slower than flash.text.TextField sometimes. In general, this performance difference is negligible, and the more advanced capabilities of FTE are often more compelling than a minor risk of reduced performance.

TextBlockTextRenderer optionally supports rich text, but it needs to be constructed manually adding multiple TextElement objects, each with different ElementFormat values, to a GroupElement object. You may pass the GroupElement to the text renderer's content property. TextBlockTextRenderer does not support the simple subset of HTML that TextFieldTextRenderer can display.

Advanced font styles

In general, you should customize font styles on the parent component of a text renderer using a starling.text.TextFormat object. For example, to customize the font styles on a Button component, you'd set the button's fontStyles property.

button.fontStyles = new TextFormat( "Helvetica", 20, 0xcc0000 );

However, starling.text.TextFormat object does not always expose every unique font styling feature that a text renderer supports. The next section demostrates how to set advanced font styles that may not be exposed through this class.

To render text with Flash Text Engine, create a TextBlockTextRenderer in the appropriate factory exposed by the parent component. In the following example, we'll use the labelFactory of a Button component:

var button:Button = new Button();
button.label = "Click Me";
button.labelFactory = function():ITextRenderer
	var textRenderer:TextBlockTextRenderer = new TextBlockTextRenderer();
	textRenderer.styleProvider = null;

	//set advanced font styles here

	return textRenderer;

You may need to remove the text renderer's style provider in the factory before changing font styles to avoid conflicts with the default styles set by a theme. That's why the styleProvider property is set to null in the code above.

Advanced font styles may be customized by passing a flash.text.engine.ElementFormat instance to the text renderer's elementFormat property:

var font:FontDescription = new FontDescription(
	"Source Sans Pro", FontWeight.BOLD, FontPosture.ITALIC );
textRenderer.elementFormat = new ElementFormat( font, 16, 0xcccccc );

The first parameter to the ElementFormat constructor is a FontDescription object. This class is provided by Flash Text Engine to handle font lookup, including name, weight (whether it is bold or normal), posture (whether it is italicized or not), and whether the font is embedded or installed on the device.

The ElementFormat allows you to customize font size, color, alpha, and more.

var format:ElementFormat = new ElementFormat( fontDescription );
format.fontSize = 20;
format.color = 0xc4c4c4;
format.alpha = 0.5;

Text alignment is not included in the FontDescription or the ElementFormat. Instead, we can set the textAlign property directly on the text renderer:

textRenderer.textAlign = TextBlockTextRenderer.TEXT_ALIGN_CENTER;

The TextBlockTextRenderer defines TEXT_ALIGN_CENTER and some other constants that the textAlign property accepts.

TextBlockTextRenderer 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 TextBlockTextRenderer API reference.

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

Some components, like Button and TextInput, have multiple states. It's possible to pass more than one ElementFormat to the TextBlockTextRenderer so that the font styles change when the parent component's state changes.

For instance, we can provide a different font style for the down state of a Button by calling setElementFormatForState()

var defaultFormat:ElementFormat = new ElementFormat( fontDescription, 20, 0xc4c4c4 );
textRenderer.elementFormat = defaultFormat;

var downFormat:ElementFormat = new ElementFormat( fontDescription, 20, 0x343434 );
textRenderer.setElementFormatForState( ButtonState.DOWN, downFormat );

We didn't provide separate font styles for other states, like ButtonState.HOVER or ButtonState.DISABLED. When the Button is in one of these states, the TextBlockTextRenderer will fall back to using the value we passed to the elementFormat property.

Using embedded fonts

To embed a TTF or OTF font for TextBlockTextRenderer, use [Embed] metadata, like this:

[Embed(source="my-font.ttf",fontFamily="My Font Name",fontWeight="normal",fontStyle="normal",mimeType="application/x-font",embedAsCFF="true")]
private static const MY_FONT:Class;

Here are the parameters:

  • The source parameter is the path to the TTF or OTF font file.
  • fontFamily gives a name to the font. This name will be passed to the FontDescription object.
  • The fontWeight parameter controls which weight is embedded.
  • The fontStyle parameter controls whether the font is italic or not.
  • The mimeType parameter must be set to application/x-font.
  • The embedAsCFF parameter must be set to true to use a font with Flash Text Engine.

To use an embedded font with TextBlockTextRenderer, pass the name specified in the fontFamily parameter of the [Embed] metadata to the FontDescription object.

var font:FontDescription = new FontDescription(
	"My Font Name", FontWeight.BOLD, FontPosture.ITALIC );
font.fontLookup = FontLookup.EMBEDDED_CFF;

Be sure to set the fontLookup property to FontLookup.EMBEDDED_CFF.

When setting font styles with starling.text.TextFormat, the TextBlockTextRenderer automatically detects if a font is embedded. The fontLookup property only needs to be set when using flash.text.engine.ElementFormat to provide advanced font styles.