# ANN: Displacement Scaling of graphic objects

Jim Hurley jhurley at infostations.com
Wed Mar 15 14:03:36 EST 2006

```Scaling is a very common feature of all graphics applications, e.g.
Illustrator and Freehand. But there is another type of scaling that
is sometimes useful; for lack of a better expression I'll call it
displacement scaling. (Thanks to a suggestion from Scott Rossi for
bringing this up.)

As a simple example, consider a rectangle of width w and height h. If
you magnify this in Illustrator or Freehand by an amount m, you get a
rectangle with sides m*w and m*h. This  preserves the geometrical
features of the rectangle. For example the tangent of the angle
between the diagonal and the base is h/w in both rectangles.

But  suppose you wanted to make a frame by putting two rectangles
together, one inside the other. You would want all the sides of the
expanded rectangle to be at a uniform distance, say "d", from the
original--as in a frame. This expanded rectangle does not preserve
the geometry. The tangent of the diagonal angle becomes:
(h+2d)/(w+2d), which is not the same as h/w. In fact, for large
displacements, the rectangle becomes a square--the tangent approaches
one. (Similarly, an expanded ellipse approaches a circle.)

The stack "ScaleMe" performs this displacement scaling on all
polygons. (It also applies to any polygon with sufficient points that
it approximates a curved figure, for example an ellipse.)

It presents some interesting problems, particularly when the graphic
points are numerous and close together--as in an ellipse. In this
case it is necessary to define the points of the graphic, not by Run
Rev's graphic points (with just 3 significant figures) but with the
full precision of Run Rev's decimal calculations. The calculated
graphic points are stored in a custom property of the graphic. The
points then are stored both as the customary 3 digit graphic points
for purposes of display and as a decimal (8 displayed , 15 total?)
digits for purposes of calculation.  (Scott: This eliminates all the
problems we had with such figures.)

The stack shows how to create some dazzling graphic figures by
repeatedly scaling a simple form and setting each displaced figure to
a different color. It also touches on fractal graphics.

In the message box:

go url "http://home.infostations.net/jhurley/ScaleMe3.rev"

```