Learning PostScript  ~ Part Two ~ By Peter Goed Ed: Check out Part I of this fine series on MD 31.  ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ How did you like the little assignment that I left you to complete last month? Did you solve it? Well here is the result that you should have obtained. 486 396 moveto -180 180 rlineto % Side one -180 -180 rlineto % Side two 180 -180 rlineto % Side Three closepath % Side four stroke showpage Side two is drawn by moving left and and down 180 points each, relative to the current point, therefore both operands are negative. Side three moves right and down 180 points relative to the current point, requiring a negative and positive number, respectively. Side four is constructed using the 'closepath' operator, which completes the diamond. Then the diamond is painted with the 'stroke' operator, and the 'showpage' operator to send it to the printer. As you have by now no doubt determined, PostScript is not really a difficult language to come to terms with. At this stage you should be capable of constructing any type of object comprised of straight lines on any part of your page, so let us move on to text. PostScript uses POSTFIX NOTATION, a system in which operands precede operators. PostScript treats space, tab, and new line (carriage return or line feed) characters - even several in a row - as a single space character. You can use these characteristics to advantage in making your code more readable and understandable, without changing the way that it operates. Remember that all operators are always in lower case and the language is extremely case sensitive. Text as Graphics Although PostScript is best known for graphics drawing, one of the main reasons for choosing PostScript is for its superb font handling capabilities. Using PostScript for text processing provides two primary functions. First, the characters in any PostScript typeface are stored as individual Bezier outlines that can be scaled to form a font of any desired point size on demand. This makes PostScript very versatile and storage efficient, compared to other typographical methods that require pre-formed font bitmaps for each point size. Secondly, the outlines from which the PostScript interpreter generates individual characters are based on the same model used for rendering graphics. Fonts are therefore subject to all types of graphical manipulation, including rotation, scaling, reflection, skewing, and clipping. Thus, in PostScript, text is said to be "fully integrated" with graphics. Elaborate textual designs can be created as easily as other graphics. Bezier curves are one of several ways of representing curved surfaces in computer graphics. Because they define the curves' endpoints and use two other control points to define the shape of the curve, they are ideally suited for use in interactive comp uter graphics, where a pointing device such as a mouse can be used to mould the curve to the desired shape, as happens in most Amiga PostScript programs that let you draw a Bezier curve. Bezier Outlines Bezier outlines are specialized pre-formed graphics that have all the elements of a PostScript page description; an underlying x/y coordinate system with a point of origin in the lower left corner, an initial 'moveto' instruction to begin a path, a series of 'lineto' and 'curveto' instructions necessary to construct the straight and curved line segments that comprise the character shape, and a final 'closepath' instruction to complete the character. Font Selection To select a font in PostScript it is first necessary to identify the desired typeface. /Times-BoldItalic The slash character (/) at the beginning of this instruction is a special PostScript character that always identifies a "literal" name - in this case, "Times-BoldItalic". "Times" identifies the typeface family, of which this particular typeface is a part. Many typeface families used in desktop publishing contain four typefaces: normal, bold, Italic (oblique), and bold-italic, although some of these may be described by other names. findfont PostScript stores the outlines for available typefaces internally. The PostScript 'findfont' operator searches for the requested font, and if it finds it, establishes it as the current font. /Times-BoldItalic findfont PostScript interpreters that are aligned to an Adobe release, contain at least 13 internal typefaces: four typefaces in the Times, Helvetica, and Courier families, plus the Symbol font. Interpreters with 13 typefaces are said to be compatible with the o riginal Apple Laser Writer. Most recent PostScript interpreters have access to the 35 internal typefaces shown in the following list. These interpreters are classed as being compatible with the Apple Laser Writer Plus. The typeface name must be specified exactly as it appears in the list, otherwise the interpreter will be unable to locate the desired typeface and will use the default typeface, which is normally Courier. 35 Standard Typefaces: AvantGarde-Book AvantGarde-BookOblique AvantGarde-Demi AvantGarde-DemiOblique Bookman-Demi Bookman-DemiItalic Bookman-Light Bookman-LightItalic Courier Courier-Bold Courier-BoldOblique Courier-Oblique Helvetica Helvetica-Bold Helvetica-Oblique Helvetica-BoldOblique Helvetica-Narrow Helvetica-Narrow-Bold Helvetica-Narrow-Oblique Helvetica-Narrow-BoldOblique NewCenturySchlbk-Bold NewCenturySchlbk-BoldItalic NewCenturySchlbk-Italic NewCenturySchlbk-Roman Palatino-Bold Palatino-BoldItalic Palatino-Italic Palatino-Roman Symbol (Symbol) Times-Bold Times-BoldItalic Times-Italic Times-Roman ZapfChancery-MediumItalic ZapfDingbats (ZapfDingbats) scalefont Once you've selected a typeface with 'findfont', you can set the size of the type with the 'scalefont' operator. Because characters are scaled uniformly in both the x and y directions, the 'scalefont' operator requires only one operand. (Non uniform scaling of fonts is possible and will be discussed in a future tutorial). /Times-BoldItalic findfont 72 scalefont Bezier outlines are stored internally in the interpreter as 1000 point outlines that 'findfont' factors by .001 to return a 1 point font, this is then scaled to the point size specified by the 'scalefont' operand. setfont The 'setfont' operator establishes the specified typeface and font point size as the current font, to be used for subsequent character operations. /Times-BoldItalic findfont 72 scalefont setfont Character Strings Once you've defined a current font, you're ready to tell the PostScript interpreter what characters to draw in that font. First you establish a new path with an initial 'moveto' instruction, then specify the string of characters you want printed. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) Left and right parentheses are used in PostScript to identify a string of characters. The string may contain one or any number of characters or even no characters. show The character string is now ready to be painted, this is accomplished with a special text operator 'show'. The 'show' operator fills the specified character string with the current colour and moves the current point to the end of the string /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) show showpage % last command needed to print the page ashow There are other PostScript operators beside 'show' that you can use for painting text characters, one of these is 'ashow', which provides the means to modify the distance between the characters in any string, either along the horizontal or vertical axis. The following page description is identical to the previous example, but the 'ashow' operator is substituted for 'show' and firstly used to alter the horizontal and then both the horizontal and vertical spacing between each character in the string. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto 12 0 (Your Text) ashow 72 648 moveto 12 -72 (Your Text) ashow showpage The 'ashow' operator requires three operands - the x and y values of additional spacing (1 point is the standard default) between each character, in either or both the horizontal and vertical directions, and the string of characters to be drawn. As with other x/y values the operands for 'ashow' specify distances in points. The first instance of 'ashow' moves each character 12 points right, the second moves each character 12 points right and 72 points down. charpath When the 'show' operator fills text characters with the current colour, the 'stroke' operator produces character outlines by painting along the character path ('true charpath') of each character. The 'charpath' operator, combined with the operand 'true ', defines the characters' path - the outline of the characters; you can then act on that path as you can any other path. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) true charpath stroke % Produces outline text % Had we used show, filled % characters would have resulted showpage NOTE: The following instructions will accomplish the same result as using the 'show' operator, using 'true charpath fill' is slower than 'show'. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) true charpath fill % Produces filled (solid) text showpage Underlined Text The following instructions will write "Your Text" and then produce a rectangle as a heavy underline below it. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) show 72 612 moveto 288 0 rlineto 0 18 rlineto -288 0 rlineto closepath fill showpage rmoveto In the previous example, the 4 inch underline (that you created in part one of this tutorial) is not really a suitable underline as there is no guarantee that it ends at the end of your character string, hence we use the instruction 'rmoveto' to align the end of the rectangle used as the underline with the end of the text string. This is accomplished by moving to a point directly under the end of the string (the new current point that results when we 'show' the string) and drawing the rectangle from right to left, back to the point of origin for the string, which we know is def ined as 72x. /Times-BoldItalic findfont 72 scalefont setfont 72 648 moveto (Your Text) show 0 -18 moveto % move 18 points below the current point 0 -18 rlineto % draw a line from the current point down 18 points 72 612 lineto % note the use of the absolute 'lineto' 0 18 rlineto % draw a line from the new current point up 18 points closepath % complete the rectangle fill showpage  PostScript String Syntax The following special rules apply to PostScript strings. * Strings are always enclosed in left end right parentheses. * Strings can contain special PostScript characters such as "%". * They can contain ((balanced)) left and right parentheses. * Strings can also be empty or nul, as (). * Within a string the backslash character (\) is a special PostScript "escape" character used to define things such as unbalanced parentheses, or the continuation of a string on a new line. \( unbalanced left parentheses \) unbalanced right parentheses \r carriage return \n line feed \f form feed \t horizontal tab \b backspace \\ backslash \nnn octal character code for accessing ASCII characters The use of octal codes will be covered in a later episode, if we all get that far!  Homework time! That brings us to the end of this month's tutorial. Hopefully you have come to grips with text in this episode and as for last month, it brings us to homework time again. During the next month construct some code that will draw a rectangle having a margin of 1/2 inch all around the outer edges of the page. Within this rectangle, at a point 1 inch below the top of the rectangle and one inch from the left, write the words "Brisbane" giving a space of 3 points between characters and underline it with a 6 point filled rectangle. If you feel confident enough, as an extra, also write the word "Brisbane" going down from the horizontal one, but space the characters half an inch apart vertically, in a direct vertical descent starting with the same "B". A helpful hint is to draw out a full size representation of the figure 1 in last month's tutorial and work out your points on this. Till next time Peter Goed  ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[ ]] 32 [[