A widget in the top-right corner of every screen allows screens to be cycled through. Screens can be overlaid by dragging each up or down by their title bars. AmigaOS 4 introduced screens that are draggable in any direction. Workbench is the native graphical file manager and desktop environment of AmigaOS. Though the term Workbench was originally used to refer to the entire operating system, with the release of AmigaOS 3.1 the operating system was renamed AmigaOS and subsequently Workbench refers to the desktop manager only. As the name suggests, the metaphor of a workbench is used, rather than that of a desktop; directories are depicted as "drawers", executable files are "tools", data files are "projects" and GUI widgets are "gadgets". In many other aspects the interface resembles Mac OS, with the main desktop showing icons of inserted disks and hard drive partitions, and a single menu bar at the top of every screen. Unlike the Macintosh mouse available at the time, the standard Amiga mouse has two buttons – the right mouse button operates the pull-down menus, with a "release to select" mechanism. Until the release of version 3, AmigaOS only natively supported the native Amiga graphics chipset, via "graphics.library", which provides an API for geometric primitives, raster graphic operations and handling of sprites. As this API could be bypassed, some developers chose to avoid OS functionality for rendering and directly program the underlying hardware for gains in efficiency. Third-party graphics cards were initially supported via proprietary unofficial solutions. A later solution where AmigaOS could directly support any graphics system, was termed "retargetable graphics" (RTG). With AmigaOS 3.5, some RTG systems were bundled with the OS, allowing the use of common hardware cards other than the native Amiga chipsets. The main RTG systems are CyberGraphX, Picasso 96 and EGS. Some vector graphic libraries, like Cairo and Anti-Grain Geometry, are also available. Modern systems can use cross-platform SDL (simple DirectMedia Layer) engine for games and other multimedia programs. The Amiga did not have any inbuilt 3D graphics capability, and so had no standard 3D graphics API. Later, graphics card manufacturers and third-party developers provided their own standards, which included MiniGL, Warp3D, StormMesa ("agl.library") and CyberGL. The Amiga was launched at a time when there was little support for 3D graphics libraries to enhance desktop GUIs and computer rendering capabilities.