A watermark is any marking which appears behind the text of the page and is generally quite light in apprearence. The main text of the page should be legible above it, and the watermark should be visible beneath.
The PostScript for generating a watermark is quite simple. After each %%Page: comment (and before the actual PostScript code for the page, you should insert the code to draw the watermark (safely wrapped between a gsave and grestore pair.
As a concrete example, let us say we want to print the word "Draft" down the page beneath the actual text of the page. Such a watermark would be suitable for printing drafts of documents.
Here is the PostScript code to print the watermark:
gsave
.75 setgray
/Helvetica-Bold findfont 72 scalefont setfont
80 80 800 {
306 exch moveto % move to the center of the line
(Draft) dup
stringwidth pop 2 div neg 0 rmoveto % Center the text horizontally
show % Show the text
} for % and keep doinging it
grestore
The hard part of the job is to find the pages. Fortunately, we can use the same technique we used for the galley proofs. Actually, our requirements are simpler. We do not need to wrap the original page code in a gsave, grestore pair, as we did before.
And here is the PERL script to do the job:
#!/usr/local/bin/perl
$flag = 0;
while (<>) {
if (/^%%Page:/) {
if ($flag) {
print "grestore\n";
}
$flag = 1;
print $_;
print "gsave\n";
print ".75 setgray\n";
print "/Helvetica-Bold findfont 72 scalefont setfont\n";
print "80 80 800 { 306 exch moveto\n";
print "(Draft) dup\n";
print "stringwidth pop 2 div neg 0 rmoveto show } for\n";
print "grestore\n";
} else {
print;
}
}
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