$b2
$14(Id: Virtual coordinates and design inspection)
$p1
Having adopted the structured design approach the circuit designer is free
to concentrate on individual leaf cell creation. These leaf cells can
be quite large and complicated and in most cases extend
beyond the domain of the visible design workspace. By providing functions
such as panning and viewing the editor offers a much larger virtual design
workspace and uses the graphics screen only as a viewport into the design. 
$p1
The designer may then, during an editing session, view and edit sections of 
the layout at arbitrary design scales. 
Although each of the design subwindows can show sections of the same design 
in different scales, the whole of the design is represented and manipulated
in its virtual coordinates, here being equal to 1/8 lambda 
(a conventional design dimension unit where its mapping onto real dimensions
reflects the resolution of production technology).
$p1
In the example the background window shows a simple 8x4 memory array
reduced 4x, the next window with 2x reduction allows inspection
of RAM cells abbutment and the top window, with 1.5x enlargement shows
the alignment details on the right edge of the array.
$b1
#
$b1
$22[Deferred scaling]
$p1
A $22[Dscale](factorX,factorY) declares the environmental deferred scaling 
factors in X and Y for the subordinate subgraph. The operation is not
cummulative and there should be no more than one such node in each vertical
path in the graph.
The factors provide independent scaling in both axes, and do not take
effect immediately, allowing for unscaled composition of objects in their
virtual coordinates. They are applied only by the final drawing nodes
prior to creating them on the screen. Within these nodes clipping
is performed still in virtual coordinates.
For that reason the only immediate effect of 
declaring a deferred scaling, remapping of the clipping
environment from above into the virtual coodinates below.
$p1
An inspection viewport into a design is created by vertically composed
declarations of its position ($22[Move]), size ($22[Clip]) and viewing
scale ($22[Dscale]). The node $22[Move](-vX,-vY) below expresses in
designs virtual coordinates the positioning of the left bottom corner
of the viewport. All the viewports share the same global design structure.
Such "geometrical" viewing should be distinguished from "structured"
viewing, where the viewport can point at the selected subgraphs within the
design (the oblong window on previous page was in fact drawn by pointing
just below Y iteration loop in the global design of RAM array).
$p1
It is also worth noticing that the presented order of $22[Clip] and
$22[Dscale] nodes fixes the physical size of the viewport, decreasing
the amount of details as scaling factors increase.
Swopping of these two nodes would result in a constant amount of detail
and a growing viewport as the clipping would now be defined in the design's
virtual coordinates.
$n
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