I think performance in flash is pretty bad in general. I tried some of the flixel demos in flash on macOS and the performance for those isn't great either if you up the resolution. Is your goal to make a flash game? It is probably better to move to html5 for web games.
Ok after loosing hairs with openfl or lime api and being unsuccesfull.
Here is a pure html5 workaround (for some that would stumble upon this post)
// some were in your state initialisation
var myInput = new FlxUIInputText();
add( myInput );
then the listeners
function onPaste(e: ClipboardEvent):Void
myInput.text = e.clipboardData.getData("text/plain");
function onCopy(e: ClipboardEvent):Void
After some debugging I have found that advanced-layout uses a default scale setting where it sets the reference screen size to 800x600 no matter what window size you set for your game. The solution is to create a new instance of Layout and Scale with proper width and height, then set the layout to our custom one. It didn't take me very long time to figure that out but I wish there was a thing about it in advanced-layout documentation so I could spend that time more productively.
I figured out a way to make it happen that works pretty nicely. Hopefully this little code chunk helps someone else out. It composes two polygons with a number of segments, flips the second array to make it easy to connect the two vertex lists together, creates polygons from the simplifications, then uses nape's GeomPoly to simplify the solids into simpler shapes. Then we add it to the NapeSprite.
public function createRingBody(radius:Float = 16):Void
var segments = 200;
if (body != null)
setBody(new Body(BodyType.STATIC, Vec2.weak(x, y)));
// Create a poly object
var p1 = Polygon.regular(radius, radius+30, segments);
var p2 = Polygon.regular(radius-10, radius-10+30, segments);
var gPoly = new GeomPoly();
for (p in p1)
for (p in p2)
var verts = new Array<Vec2>();
var it = gpoly.iterator();