Aligning Flash TextField instances visually correct

I was looking for an easy way to align TextField instances with different font sizes visually correct. I really thought this wouldn’t take much time but it turned out to become really frustrating.

So think about a simple scenario: Try to align two TextField instances with different font sizes side by side. If you just set the TextField.y property to the same value you will recognise that different font sizes have different top margins. Well, you might fix that by hand if you have a static layout but what if you don’t know what kind of Text will be displayed? In my case I needed to align text always on top with the same margin regardless of the headline font size.

I tried hard to get this done by using different methods provided by the TextField class. Then I tried to work with the TextLineMetrics class as well. Nothing worked properly for me. I needed to work with CSS formatted HTML text so I was looking for a margin-top style or something similar. Not available. Hm.

Then I remembered my solution about finding the alpha bounds within external loaded PNG files and used that. Well, the main downside is that I need to create a BitmapData instance to determine the exact text bounds but otherwise it worked out very well.

It all comes down to two simple methods that will slip into my library. At the end you will receive a rectangle representing the bounds on the TextField instance.

If you know a different way to obtain the same exact result please leave me a comment!

Here’s my solution:

function getDisplayObjectAlphaBounds( displayObject : DisplayObject, smoothing : Boolean = true ) : Rectangle
	var bitmapData : BitmapData = new BitmapData( displayObject.width, displayObject.height, true, 0 );
		bitmapData.draw( displayObject, null, null, null, null, smoothing );
	var alphaBounds : Rectangle = bitmapData.getColorBoundsRect( 0x01000000, 0x01000000 );
	return alphaBounds;
function getTextFieldTextBounds( textField : TextField, smoothing : Boolean = true ) : Rectangle
	var background : Boolean = textField.background;
	var backgroundColor : uint = textField.backgroundColor;
	var border : Boolean = textField.border;
	var borderColor : uint = textField.borderColor;
	var opaqueBackground : Object = textField.opaqueBackground;
	textField.background = false;
	textField.border = false;
	opaqueBackground = null;
	var textBounds : Rectangle = getDisplayObjectAlphaBounds( textField, smoothing );
	textField.background = background;
	textField.backgroundColor = backgroundColor;
	textField.border = border;
	textField.borderColor = borderColor;
	textField.opaqueBackground = opaqueBackground;
	return textBounds;
var textFormat : TextFormat = new TextFormat();
	textFormat.align = TextFormatAlign.CENTER;
	textFormat.color = 0x0000FF;
	textFormat.font = "Arial";
	textFormat.size = 30;
var textField : TextField = new TextField();
	textField.border = true;
	textField.borderColor = 0x0000FF;
	textField.background = true;
	textField.backgroundColor = 0x000022;
	textField.defaultTextFormat = textFormat;
	textField.height = 260;
	textField.text = "\nThis text\ncan be\naligned\nproperly!";
	textField.width = 300;
	textField.x = 30;
	textField.y = 30;
addChild( textField );
// Get bounds
var textBounds : Rectangle = getTextFieldTextBounds( textField );
// Draw bounds
var shape : Shape = new Shape();
	shape.x = textField.x;
	shape.y = textField.y;
var g : Graphics =;
	g.lineStyle( 1, 0x00FFFF );
	g.drawRect( textBounds.x, textBounds.y, textBounds.width, textBounds.height );
addChild( shape );

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