ReTargetable Graphics

Retargetable graphics (abbreviated as RTG) is a device driver API mainly used by third-party graphics hardware to interface with AmigaOS via a set of libraries. The software libraries may include software tools to adjust resolution, screen colors, pointers, and screenmodes. It will use available hardware and will not extend the capabilities in any way.

The Amiga OS 3.x intuition.library is limited to 8-bit display depths, but RTG libraries make it possible to handle higher depths such as 24 bits; on Amiga there are two common APIs: Picasso 96 and CyberGraphX, which are almost compatible with each other. Both Picasso 96 and CyberGraphX require at least 4 MB RAM and a 68020 CPU to operate.

Although Commodore planned to introduce retargetable graphics in future version of AmigaOS (4.0), the company was not able to deliver such solution before its demise. Third-party graphics card manufacturers were thus forced to create their own software layers on top of AmigaOS, incompatible with each other. Most of these early Amiga graphics card drivers shared common limitations: compatibility with current applications was maintained by opening Workbench (or also other application screens, also known as "Workbench emulation") on the graphics card—usually in 16 (under AmigaOS 2.x) or 256 colours (under AmigaOS 3.x); full graphics card features like high-colour (15- or 16-bit) and true-colour (24- or 32-bit) display could be used only by applications directly programmed for such driver software. Earliest of these solutions like Grafexa and SAGE libraries were able to display only their own applications on the graphics card without any support for "Workbench emulation". Examples of other drivers are EGS, Merlin/Domino, Omnibus, Retina (which should be able even to display Workbench in 24 bit colour), Graffity, Picasso, and ProBench. Of these, Picasso offered good compatibility with older applications, because most OS-compliant programs could be promoted to graphics card display, and relatively strong software support. ProBench (by ProDev) was released as a new "Workbench emulator" for the old Merlin graphics card in 1994, and version 3 (1996) introduced 16 bit colour depth and compatibility with CyberGraphX.

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