StageSizeScaleMode is a scaling mode which maintains the game's scene at a fixed size.
This will clip off the edges of the scene for dimensions which are too small.
However, unlike FixedScaleMode, this mode will extend the width of the current scene to match the window scale.
The result is that objects that would be offscreen on smaller window sizes will be visible in larger ones.
Note that compared with FixedScaleAdjustSizeScaleMode, this scale mode aligns with the top left of the game's screen.
The coordinates 0,0 are always located at the top left of your game window.
To enable it in your project, use FlxG.scaleMode = new StageSizeScaleMode();.