virtual RectF GetVisibleFrameRect() const = 0;
GetVisibleFrameRect obtains the currently visible rectangle. It is possible to retrieve the rectangle through ActionScript by using "Stage.visibleRect" property (ActionScript extensions should be turned on, see "ActionScript Extensions Reference").
This rectangle is changed when you change the aspect ratio and/or scale of Viewport and want to know which area is visible at the moment.
A RectF value describing the currently visible rectangle in pixels.