Since Quartz is based on Postscript through PDF, is it possible (or feasible) to render the postscript directly, without converting it to PDF?

PDF's vector-graphics language is derived from PostScript, but isn't PostScript exactly; in particular, flow-control is missing, and many command names are different (abbreviated).

It would be nice to have a subclass of NSView which directly renders the PS.

Indeed it would, but that's possible now. Hint: Start with NSScanner. ☺

Another strange thing I don't understand; why does ps2pdf produce much better looking PDFs than Preview?

I haven't observed that. Both go through the same API, so they should always produce exactly the same results. (Easy way to check would be saving the PDF from Preview, then comparing the PDFs to see if anything is different, and if so, what.)

Another strange thing I don't understand; why does ps2pdf produce much better looking PDFs than Preview?

I will finish it; please be patient.

As it happens, I'm working on the tutorial today. I doubt I'll have it out today, but I am making progress.

%!PS-Adobe
/Times-Roman findfont 80 scalefont setfont
10 600 moveto (Hello World) show

Adobe Illustrator CS2, CS3 are also able to render postscript. I'm planning on using this to do algorithmic drawing with Postscript, and then use the output directly in Illustrator and Flash.

I think reason #8 should be "It's fun". Maybe it's just me but I thought programming in PostScript to be pretty nifty. Something about playing with the stack. In a certain way, PostScript is like Logo for "grown-up" programmers.

Totally. Consider it added.

Is there an interactive PS interpreter available?

Yup: GhostScript. You'll need X11 installed and running to use it. It provides a live interpreter, as well as its own implementation of pstopdf and a few other PostScript-related utilities.

I'll be sure to mention that in the tutorial post.

I think reason #8 should be "It's fun". Maybe it's just me but I thought programming in PostScript to be pretty nifty. Something about playing with the stack. In a certain way, PostScript is like Logo for "grown-up" programmers.

Is there an interactive PS interpreter available? Something like NodeBox? I guess I should start playing with the DPS implementation on X11.

Hmmmm. I haven't actually programmed PS on the Mac. But wasn't one of the main drawbacks (or speed advantages) of PDF and Quartz that they cannot handle the full complexity of PS? Like those tiny files of PS code which will draw a Mandelbrot set, say

Yes; the idea was to make PDF more attractive for embedded systems (mainly printers and PSCs) that probably don't have the processing power to efficiently implement a full interpreted programming language. A Mac is not such a machine: it can handle full PostScript easily.

As for Quartz, that's what CGPSConverter is for.

And I keep being sceptical about the UI scaling argument. Yes, in some situations, like Daniel's example, vector graphics may work well for use in the UI but in other situations, particularly at small sizes, hand-optimised graphics will just look better.

What I want is an NSImage subclass that DTRT for multiple representations. You could have a NSImage with a 24-px raster representation and a 48-pt vector representation, such that it would use the raster representation on low-resolution displays and the vector representation on high-resolution displays. Eventually, when nobody has a low-enough-resolution display to encounter the raster rep anymore, you delete that rep and go vector-only.

I tried writing a category that easily grabs all the representations of a file from a specific bundle and stuffs them into one NSImage, but it didn't work, as NSImage did the exact opposite of the right thing: it used my 48-pt vector rep for the 24-pt image well, and my 24-px raster rep for the 48-pt and 128-pt image wells. (This is with the same NSImage in all three wells.)

I'm open to sharing the code, if anybody wants to hack on it (perhaps by reimplementing -drawInRect:fromRect:operation:fraction:).

Otherwise I guess the question comes down to how much you actually need to draw. I hardly ever needed to draw more than a few lines or shapes which standard NSBezierPaths did just fine (although not too quickly I might add – although I think this may have improved since X.2)

And I keep being sceptical about the UI scaling argument. Yes, in _some_ situations, like Daniel's example, vector graphics may work well for use in the UI but in other situations, particularly at small sizes, hand-optimised graphics will just look better.