текст в bitmap программно

[Idalgo]

function createText(x,y, width:Number, height:Number, _txt:String):MovieClip {
    var depth:Number = this.getNextHighestDepth();
    var mc:MovieClip = this.createEmptyMovieClip("mc_" + depth, depth);
	mc._x = x;
	mc._y = y;

	txt = mc.createTextField('txt', mc.getNextHighestDepth(),0,0,width,height);
	txt.text = _txt;
	txt.type = "dynamic";
	txt.autoSize = false;
	txt.border = false;
	txt.background = false;
	txt.embedFonts = true;
	txt.wordWrap = true;
	txt.multiline = true;
	txt.selectable = false;
	myTextFormat = new TextFormat();
	myTextFormat.font = "MSS";
	myTextFormat.size = 22;
	txt.setTextFormat(myTextFormat);
	bmp = new BitmapData(txt._width, txt._height, true);
	
	mc.attachBitmap(bmp, mc.getNextHighestDepth(), 'auto', true);
	
	var matr:Matrix = new Matrix();
	var myColorTransform:ColorTransform = new ColorTransform(0, 0, 0, 1, 0, 0, 0, 0);
	var blendMode:String = "normal";
	var myRectangle:Rectangle = new Rectangle(0, 0, txt._width, txt._height);
	var smooth:Boolean = true;

	bmp.draw(txt);
	bmp.draw(txt, matr, myColorTransform, blendMode, myRectangle, smooth);

	txt.removeTextField();	
	
    return mc;
}

Получаю битмап с текстом на белом фоне.
Интересует с чисто теоретической стороны - где я не указал прозрачность