How to make pictures using postscript programs (part 7)
-----------------------------------------------------------------------------
There is one further type of coordinate transformation, beyond translations
and rotations, that we can use: scalings. The command scale has two parameters,
scale factors for the first and second coordinate of the current coordinate 
system. Usually they are the same. If we wrtie 
 0.5 0.5  scale
then in future everything will be drawn at half the size. So if our picture is
too large, we give it a small scale factor, if the picture is too small, we
can blow it up by saying, e.g., 
 2 2 scale
which doubles its size. We can use different scale factors for the axes,
so with 
 0.5 1 scale
the x-axis will be compressed, but not the y-axis, so a circle becomes an 
ellipse. And giving a negative scale factor reverses the direction of the 
axis, so after 
 -1 1 scale
the positive direction of the x-axis is to the left instead of to the right. So
 -1 1 scale    is a reflection on the vertical line x=0,
and
 1 -1 scale    is a reflection on the horizontal line y=0.
---------------------Example Program 15--------------------------------------
%!PS-Adobe-2.0
%%BoundingBox: 0 0 400 410

200 200 translate  2 setlinewidth  
0 0 0 setrgbcolor                    %Black
newpath 0 0 190 0 360 arc stroke
0.8 1 scale    0.5 0.1 0 setrgbcolor %Dark red
newpath 0 0 190 0 360 arc stroke
0.8 1 scale    0.7 0.1 0 setrgbcolor %Brighter Red
newpath 0 0 190 0 360 arc stroke
0.8 1 scale    1.0 0.1 0 setrgbcolor %Full Red
newpath 0 0 190 0 360 arc stroke
1 0.8 scale    1.0 0.4 0 setrgbcolor %Orange
newpath 0 0 190 0 360 arc stroke
1 0.8 scale    1.0 0.8 0 setrgbcolor %Bright Orange
newpath 0 0 190 0 360 arc stroke
1 0.8 scale    1.0 1.0 0 setrgbcolor %Yellow
newpath 0 0 190 0 360 arc stroke
showpage
------------------------------------------------------------------------------
Each scale command modifies the previous coordinate system, so the scale
factors multiply. If you rotated your coordinate system, those scale factors
apply to the rotated axes
------------------------------------------------------------------------------
You can store a coordinate system by gsave and recover it by grestore.
These commands save and restore the entire graphics state, which contains
- the coordinate system
- the current path
- the drawing colors, line thickness, line style, dash pattern etc
- the clipping region
-----------------------------------------------------------------------------
Since it stores your current path, this makes it possible to use the path
again. Because the operations stroke and fill each destroy the current path,
if you want to draw a region, and then draw a line along its boundary,
you can first construct the path, e.g.,
 newpath 100 100 moveto 200 100 lineto 150 186.6 lineto closepath
and then save it, fill it, restore it, and draw (stroke) it.
 gsave 0 0.9 0.2 setrgbcolor fill grestore stroke %fills green, black boundary