1. Page description language from Adobe
Postscript
Page description language from Adobe

2. Copyright 2000, Georgia Tech
Story
History
Basics
Paths
Drawing simple geometric shapes
Working with Coordinate Systems
Drawing ellipses
Ghostscript and GSview
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3. Copyright 2000, Georgia Tech
History
Before Postscript (pre 1984)
Dot matrix printers with poor quality output
High quality printers with proprietary languages
John Warnock at Xerox Parc created Interpress
Couldn’t convince management to sell it
Left Xerox and created Adobe with his old boss
Abode created Postscript (1984)
First used with Apple LaserWriter and Aldus PageMaker
Desktop publishing took off
See for more of the history.
Dot matrix printers are like a computer screen in that the printer has a resolution of dots (pixels) per inch.
John Warnock and Chuck Geschke were the founders of Adobe.
For years the Apple LaserWriters had faster processors than the Macs they were connected to.
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What is Postscript?
A language for printing text and graphics.
Advantages
Device independent
Manufactures license the interpreter
Specifications are freely available
Levels
1 (1985), 2 (1994), and 3 (1998)
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Basics
Interpreted, stack-based language like FORTH
3 4 add
Put 3 on the stack
Put 4 on the stack
add takes the top two items off the stack and adds them and puts the result on the stack
This is also called postfix notation.
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6. Postscript files are Text
Postscript is written in ASCII characters
Use % for comment
% draw a vertical line
newpath
moveto
lineto
stroke
showpage
Using GSView to View
x is 3 inches from left
y is 6 inches from bottom
x is 3 inches from left
y is 4 inches from bottom
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7. Default Coordinate System
Origin is lower left corner of page
X increases to left
Y increases going up
Units are 1/72 inches
So 72 units in an inch
Origin
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Like Drawing by Hand
Start with the current page being empty
Draw things on the page
Things drawn on top of other things will obscure them
When you are done send the page to the printer
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Postscript uses Paths
What is a path?
Set of connected and disconnected points, lines, and curves that describe shapes and their positions
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10. What can you do with a Path?
A path can be
Stroked (like using a pen to draw it)
Filled (like using a paint can to fill it)
Used as a clipping boundary (like using a stencil)
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Defining a Path
Use newpath to start a path
newpath
Use moveto to move the pen to a point on the page (but nothing draws yet)
moveto
Use lineto to create a line from the previous point to the current point
lineto
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12. Disconnected Path Example
This will draw two unconnected lines
newpath
72 72 moveto
rlineto
moveto
0 -72 rlineto
stroke
showpage
Using GSView to View
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Relative Positioning
Using rlineto uses the x and y as relative to the current position
Positive values
X right
Y up
Negative values
X left
Y down
Can use rmoveto as well
To move relative to the current position
-x +y
+x+y
-x -y
+x-y
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Drawing a Rectangle
newpath
moveto
0 72 rlineto
144 0 rlineto
0 -72 rlineto
rlineto
stroke
showpage
second
third
first
The moveto moves the pen to 3.75 inches from left and 5 inches from the bottom of the page. The 0 72 rlineto draws a 1 inch line up from that position in y. The draws the top of the rectangle going 2 inches to the right. The draws the right side of the rectangle by going down 1 inch in y. The draws the bottom of the rectangle by going left in x 2 inches.
fourth
start
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Drawing a Polygon
newpath
moveto
lineto
lineto
lineto
lineto
closepath
stroke
showpage
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Closing the Polygon
Use closepath to go from last point to the last moveto point
does a mitered join
lineto
lineto
lineto
moveto
closepath
lineto
lineto
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17. Working with Coordinates
The default user coordinates are at the bottom left of the current page
But the user coordinates can be
Translated – moves the origin
x y translate
Scaled – change the size of the units
x y scale
Rotated – rotates the axes counterclockwise
angle rotate
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Graphics State
What is in the graphics state?
Current path, gray value, line width, user coordinate system
Save the state to return to it later
gsave
Restore a saved state
grestore
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Using Graphics State
newpath
moveto
0 72 rlineto
144 0 rlineto
0 -72 rlineto
rlineto
gsave
.5 setgray fill
grestore
stroke
showpage
Save current graphics state
The fill command clears the current path. So, we save the current path with gsave and restore it to outline the border of the rectangle.
Clears current path
Restore the saved graphics state including path
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Drawing Arcs
The arc operator draws arcs (and circles)
Center is at centerX and centerY
Radius of radius
Arc drawing starts at beginAngle from x axis and counter clockwise to endAngle
centerX centerY radius beginAngle endAngle arc
Example:
arc
The example starts at 0 degrees from the x axis, so on the x axis and goes counterclockwise to 90 degrees. The center is at 300 in x and 365 in y with a radius of 100 units.
You can also draw arcs clockwise using arcn.
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Drawing a Circle
Use arc with a begin angle of 0 and an end angle of 360
Example
arc
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How to Draw Ellipses?
Use the arc operator
But, first scale the user coordinate system
Example
newpath
1 .75 scale
arc
stroke
showpage
1 .75 scale
1 .5 scale
.5 1 scale
To draw a ellipse you draw a circle but first scale the user coordinate system to match the ratio of the width to the height.
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Defining Variables
Use the def operator to define variables
/ppi 72 def % define the points per inch var
10 ppi mul % multiply 10 * 72
/ppi ppi 1 add def %add 1 to current value
The /ppi means put the literal on the stack and don’t look up the value of it in the dictionary
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24. Postscript Dictionaries
Map keys to values
System dictionary
Maps predefined operators to actions
User dictionary
Maps names to user defined variables and procedures
Looks in user dictionary first then system
You can actually create more dictionaries.
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Procedures
A procedure is a set of operations grouped together with a name
It is stored in the user dictionary with the name as the key and the operations as the value
Example
/inch {72 mul} def
5 inch (results in 5 * 72)
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Creating a Procedure
Create a box procedure
/box
{ 72 0 rlineto
0 72 rlineto
-72 0 rlineto
closepath} def
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Using a Procedure
newpath
moveto box
moveto box
moveto box
stroke
showpage
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Printing Text
Find the font in the font dictionary
Returns a one-point size font
Scale the font to the desired size
Size is specified by the minimum vertical separation needed between lines of text
12 point font needs 12 points between lines of text
A point is 1/72 of an inch
Set the scaled font to the current font
Show the text
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Fonts and Typefaces
What is a font?
A collection of characters with a unified design. An implementation of a typeface.
Typeface
The design used in a font
Typeface families
A set of typefaces designed to work together
Examples: Times-Roman, Helvetica, Courier
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Example with Fonts
% show ‘Hello World’ in times roman
/Times-Roman findfont
24 scalefont
setfont
moveto
(Hello World) show
showpage
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Postscript Operators
Add
3 4 add → 7
Subtract
8 4 sub → 4
Multiply
6 8 mul → 48
Divide
13 8 div → 1.625
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Stack Operators
clear
Removes all items from the stack
6 7 8 clear → nothing on stack
dup
Duplicates the top item on the stack
6 7 8 dup →
pop
Remove the top item from the stack
6 7 8 pop → 6 7
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Painting Operators
fill
Fill the current path with the current color
setgray
Set the current color
.5 setgray (1 is white and 0 is black)
setlinewidth
Set the current line width (x/72 units)
4 setlinewidth % 4/72 units wide
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Ghostscript
What is it?
Ghostscript is an interpreter for the PostScript page description language
Has 3 licenses
Aladdin Free Public License (AFPL) allows free use but not commercial distribution
Where to get it?
There is also a GNU license version of Ghostscript.
Ghostscript was originally created by L. Peter Deutsch, President of Aladdin Enterprises.
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GSview
What is it?
A PostScript previewer based on Ghostscript by Ghostgum Software Pty Ltd
A graphical user interface for Ghostscript
Where to get it?
You must have Ghostscript installed to use GSview.
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