OpenFL fullscreen and resize example based on DisplayinABitmap sample.

gistfile1.hx

package;

import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.Sprite;
import openfl.Assets;

class Main extends Sprite {
	private static var full: Bool = false;

    public function new () {
            super ();
            
            var bitmap = new Bitmap (Assets.getBitmapData ("assets/openfl.png"));
            addChild (bitmap);
            
            bitmap.x = (stage.stageWidth - bitmap.width) / 2;
            bitmap.y = (stage.stageHeight - bitmap.height) / 2;

            for (mode in flash.system.Capabilities.screenModes) {
                    trace("w: " + mode.width + " h: " + mode.height + " refreshRate: " + mode.refreshRate);
            }

            stage.addEventListener(flash.events.KeyboardEvent.KEY_DOWN, keyDownHandler);
    }
    
    function resize(): Void {
            stage.resize(400, 400);
    }

    function resolution(): Void {
            if (full) {
                    stage.setFullscreen(false);
            }
            else {
                    stage.setFullscreen(true);
                    //stage.setResolution(800, 600);
                    var mode = new flash.system.ScreenMode();
                    mode.width = 800;
                    mode.height = 600;
                    mode.refreshRate = 60;
                    mode.format = flash.system.PixelFormat.BGRA8888;
                    stage.setScreenMode(mode);
            }
            full = !full;
    }

    function keyDownHandler(event: flash.events.KeyboardEvent): Void {
            //resize();
            resolution();
    }
}