Re: [igraph] iGraph plot - labels text-searchable?

[Tamás Nepusz]

> But I'm afraid Adobe Acrobat Professional could not search this pdf.
> Are you sure the actual text is stored?  Maybe Preview on Mac OS is
> doing an OCR search?  It could be that I need to search around for a
> better pdf viewer on Windows....
Preview on Mac OS X is definitely not doing an OCR search (it's too fast for 
that ;)), but there are many possible ways to put text in a PDF file and maybe 
Preview is supporting more of them than Acrobat (which is weird -- after all, 
Acrobat is made by Adobe). These are the possibilities that come to my mind:

1. Writing text with standard PDF text operators and standard fonts
2. Writing text with standard PDF text operators but non-standard fonts
3. Writing text by drawing the glyphs manually without telling the PDF document 
that these are actually letters

#1 is definitely searchable and #3 definitely isn't. I believe that igraph is 
doing #2 -- I'm not sure because the actual drawing is done by the Cairo 
library, and it is entirely up to Cairo's PDF backend. It may also be the case 
that Cairo on my Mac is newer or more clever than Cairo on your computer and 
that's why it is working for me. The bottom line is that it is entirely out of 
igraph's control.

There are at least four different ways to get text into a PDF document (in 
order or likelihood):

        • Place the text with standard text operators and standard fonts
        • Place the text with standard text operators with non-standard fonts
        • Draw one or more images that represent the text
        • Place the text by manually drawing the glyphs with various PDF 
graphics commands

I'd give it a try with Sumatra PDF Reader and/or Foxit Reader. Another option 
is to try saving your plots to SVG files (which is also supported by Cairo) and 
use an SVG viewer that is able to search within text nodes of an SVG file. I 
heard that the Opera web browser is able to do that. Maybe also Chrome, but I'm 
not sure.

Good luck,
-- 
Tamas