clearPicture

No picture plays any more, so the one on screen must go.

The engine calls this when a picture stops and nothing takes its place: the picture is turned off while the sound plays, an item with no picture opens, an open fails, the player stops, or this renderer is attached while no picture plays. The renderer forgets the frame it shows and any frame it accepted but has not drawn yet, and shows its background from then on, with the subtitle overlay still drawn over it, until the next present brings a picture back. An item that ended, or failed while it played, is not told, so its last picture stays, as in other players.

Never called while a present is running. Defaulted so an existing renderer keeps compiling; such a renderer keeps its last picture on screen, which is what every renderer did before this existed.