Programming and Graphics

7.2 Getting started withVogle 203

Graphics files

To generate a file containing the graphics, instead of initializing the
graphics device to X11, we initialize it to a different device. Postscript files
are generated by choosing the devices:

postscript ppostscript cps pcps

where the prefix “p” stands for “portrait” and the prefix “c” stands for “color”.
The name of the graphics file is defined by inserting the vogle command:

voutput ("filename");

wherefilenameis a chosen graphics file name. If we do not include this state-
ment, the postscript file will be printed on the screen as a text.

For example, to generate a postscript graphics file namedhello.ps,we
replace the statementvinit("X11")with the two statements:

voutput ("hello.ps");

vinit("pcps");

written in this particular order. After execution, the filehello.pswill appear in
the current directory.

Vogleallows us to initialize the graphics device to one type, and then
change it to a different type, as will be discussed in later sections. This feature
allows us to draw a graph on the screen and, if approved, print it in a graphics
file.

The postscript file can be transformed into an encapsulated postscript
(eps) file using, for example, theps2epsifacility in Unix. The eps file may then
be inserted in a document, as was done in the typesetting of this book.

World coordinates

In the default screen coordinates, the horizontal and vertical variablesx
andyvary in the range (− 1 ,1) over the graphics window. To change the screen
coordinates into world coordinates that vary over a specified range, we use the
ortho2function.

The following code implemented in the fileelaiolado.ccintroduces world
coordinates, and then prints and underlines olive oil in Greek:

/*-------------------------------

PRINT A WORD IN WORLD COORDINATES

-------------------------------*/