How to use the Feathers
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.
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
TextBlockTextRenderer does not support the simple subset of HTML that
TextFieldTextRenderer can display.
Advanced font styles
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
Advanced font styles may be customized by passing a
flash.text.engine.ElementFormat instance to the text renderer's
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.
ElementFormat allows you to customize font size, color, alpha, and more.
Text alignment is not included in the
FontDescription or the
ElementFormat. Instead, we can set the
textAlign property directly on the text renderer:
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
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
We didn't provide separate font styles for other states, like
ButtonState.DISABLED. When the
Button is in one of these states, the
TextBlockTextRenderer will fall back to using the value we passed to the
Using embedded fonts
To embed a TTF or OTF font for
[Embed] metadata, like this:
Here are the parameters:
sourceparameter is the path to the TTF or OTF font file.
fontFamilygives a name to the font. This name will be passed to the
fontWeightparameter controls which weight is embedded.
fontStyleparameter controls whether the font is italic or not.
mimeTypeparameter must be set to
embedAsCFFparameter must be set to
trueto 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
Be sure to set the
fontLookup property to