After the two earlier systems, SCFOR and GROATS, at the Atlas Computer Laboratory, a new system with an interactive front-end based on the PDP15 was defined on the ICL 1906A and IBM360/195. The output system was changing from the SC4020 to the FR80 with its ability to define high quality colour output with synchronised sound tracks from the EMS VC3 synthesiser attached to the DEC PDP15. The new system was called SPROGS for SC4020, PDP15 Rapid Output of Graphics System. (GROATS is a very small unit of UK currency and a SPROG is a raw recruit in the UK army ;-) ).
SPROGS was a Fortran-based system but it had a front-end system defined in TREE-META that made the code that was actually written much more user friendly than Fortran IV.
The region concept in GROATS was extended so that each region could act as a mask, a clipping region, or a changing the visibility of a drawing facility. This allowed a whole set of animation effects to be achieved.
The picture store concept in GROATS was extended so that pictures became the major unit of graphical display.
A new feature was the film file which was effectively a parameterised definition of an object and its action over a sequence of frames (a man walking, a ball bouncing, a viewpoint changing).
A sequence of film files could be defined with some having the same or overlapping times and one film file could modify the action of another. A simple example is the case of a film file that defines the motion of a ball bouncing between two walls. Two further film files could be added so that the walls moved backwards and forwards and the ball continued to bounce between the walls whatever the position when it arrives.
A full description of the system is given in the SPROGS User Manual.