You may remember Daniel Jalkut’s blog post about resolution independence, with its demonstration of the superiority in quality of vector graphics over raster graphics (using an EPS file that I created for him ☺).
The problem with using an EPS file, as I pointed out to him when I emailed him the file originally, is that EPS files are very slow on OS X. The current (Tiger) implementation of NSEPSImageRep uses Quartz’s CGPSConverter to convert the EPS data to PDF data, then instantiates an NSPDFImageRep (kept in a private ivar) that it has do all the real work.
That PostScript-to-PDF conversion is the bottleneck. You don’t want that multiple-second delay (yes, really) at runtime. Better to take it before runtime. At the time, I suggested that he use pstopdf to convert to a PDF file, then put the PDF file into his Xcode project to be copied into the app bundle.
But what if you decide later to change the PostScript file? You need to remember to run pstopdf again. EPS files are just PostScript source code, so why not treat them like any other source code file? Or, a better question: How?
The answer is quite simple: Add a custom rule to your target in Xcode that runs pstopdf over EPS files. Then, you add the EPS file — not the PDF file — to the project, and Xcode will exhibit normal build-only-when-necessary behavior on the EPS file and copy the generated PDF file for you. And of course, you can have as many EPS files as you want — they’re source code files just like any others.