@node Aspect, Axis, Arithmetic, Commands

@iftex
@syntax Aspect.
@end iftex
@example
Syntax: ASPECT A
@end example
@pindex Aspect
@findex text plotting, aspect ratio
@findex labels, aspect ratio

   Set the aspect ratio (Y/X) to be A; This is used in drawing
characters and points and is reset when a new DEVICE command is issued.

The current values of the x- and y- dimensions of the current device are
(almost) always available as the variables
@code{$nx} and @code{$ny}, and the current aspect ratio is @code{$aspect}
(they are some of the special variables that are
affected by the @code{DEFINE variable |} command). 
@findex internal variables, aspect
@findex internal variables, nx
@findex internal variables, ny

If A is exactly 0, the current aspect ratio is printed -- this is equivalent
to @code{echo $aspect} and is retained as a curiosity.

   Usually the aspect ratio is calculated by SM to make
characters look right (and to make square points square), but it is
sometimes useful to override this, especially when positioning labels
on graphs that will be plotted on printers of different aspect ratios.

It might be worth going through an example. Suppose that you want to make
a plot that really is square when printed; how should you proceed?

The available plotting area runs from 0--32767 on each axis. So a plot
set up as
@example
location 5000 20000 5000 20000
@end example
@noindent
will have the same aspect ratio as the plotting device, in general rectangular.
We can write this as
@example
define len 15000                # axis length, SCREEN units
location 5000 $(5000 + $len) 5000 $(5000 + $len)
@end example
@noindent
if we feel sophisticated.

The variable @code{$aspect} tells you the Y/X ratio of the current device;
so the location
@example
location 5000 $(5000+$len) 5000 $(5000+int($len/$aspect)) box
@end example
@noindent
will be a square box. Of course, you'd probably really want to say
@example
if($aspect > 1) @{
   location 5000 $(5000+int($aspect*$len)) 5000 $(5000+$len) box
@} else @{
   location 5000 $(5000+$len) 5000 $(5000+int($len/$aspect)) box
@}
@end example
@noindent

There is a problem with this; the sizes of points and labels are varied to
look right with the current aspect ratio. This means that a
@example
putlabel 5 Hello World
@end example
@noindent
command that looks fine on the screen of your workstation will look awful
on the printer. That's where the ASPECT command comes into play: on your
workstation lie to SM and tell it that the aspect ratio is that of the
printer. How do you do that? Well, the slick way is to say
@example
macro aspect_as_device 1 @{
   DEVICE $1
   define 1 $aspect
   ABORT
   DEVICE $device
   ASPECT $1
@}
@end example
@noindent
which assumes that you use a version of the device command that saves the
current device as @code{$device}; the macro @code{dev} does this, and you can
overload @code{device} to mean @code{dev}. Then you can say
@example
aspect_as_device postport
@end example
@noindent
to force the same aspect ratio as the @code{postport device.}; your plots
will look ugly on the screen but beautiful when printed.