$18(Example V: Dual buffering)
$p1
The system assumes the use of a dual buffering technique for most
of the applications, where a new image is being created outside the currently
visible area of the framestore, and upon completion is swopped onto the
screen during the nearest vertical flyback. The technique assumes 
framestore memory size to be at least twice the size of the amount
required to support one visible frame.
There are different methods of partitioning such memory: geometrically
in X or Y through framestore offset registers,
or by mapping different sets of planes into the video output.
$b1
$z0.03"$x+7"$y+4.8"$x-7"$y-4.8"$z0$y+4.8"
$p1
In the example two 768x512 pixel buffers are fitted one above the other
in a 1024x1024 framestore.
Top $22[SetXY](baseX,baseY) node of the structure places the absolute
evaluation coordinates (workX,workY) in relative (0,0) coordinates
of one of the frames. A $22[Clip](768,512) node below it protects
the neighbouring, displayed frame and points vertically to the image
definition graph.
Having completed evaluating the main graph, a $22[FlybackY] node
witholds the continuation to the right until the nearest frame
vertical flyback, when the $22[Pan](baseX,baseY) through
framestore offset registers puts the display area over the newly evaluated
frame. $22[SetXY] and $22[Pan] nodes indirect into a 2-element offset
definition, where location X remains at 0 and Y is alternatively swapped
between 0 and 512.
$n
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