PostScript capture issues:

We want to be able to capture PostScript drawing commands and output
them in several formats:

  0. Bounding box
     Just determines the bounding box, don't draw anything. 
     Returns: [llx lly urx ury].

  1. EPS printable PostScript file (for screen dumps)
     images as hex strings

  2. Tokenized NeWS PostScript file (for fast redisplay)
     images as "readcanvas <rasterfile>" or names of images on defined
     on dict stack (what scope?) or usertokens (private to what process?)

  3. Executable array (a PostScript function)
     images as canvases embeded in code

  4. Selection (in what format?)
     Possible formats: any of the above, a file name, an executable
     PostScript array, an executable array "{(filename) run}", an
     executable string, a canvas (the result of rendering the
     PostScript code at some resolution), a DisplayItem, etc...

  5. Structured graphic object
     Capture the drawing commands as a GoodNeWS graphic or some other
     hierarchical structured graphic. Retain some of the semantic
     information about the drawing, inferring the structure from the
     graphics state, grouping paths according to the gsave level and
     transformation matrix. Is there other structural information that
     would be useful to infer while capturing the drawing, to embed in
     the graphic object.


Possible bug in /DoImageCanvas: It writes out the raw bytes of the
canvas via shared memory, and makes a hex string out of that, instead
of writing out rgb values in terms of the canvas's colormap. How does
it look when read back in? Should it just convert 24 bit rgb pseudo
colors to 8 bits of brightness? (lose color) or 24 bit color images?
The server needs to have 24 bit support -- 24 bit input to image
doesn't work!

Should the capture methods and dictionaries be stored in ClassCanvas?
Maybe they should be in systemdict? What happens to ClassDrawable and
ClassRegion objects when they are told to paint? Do any of the
overridden operators depend on the ClassCanvas context?

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Capture bombs is the painting proc leaves something on the stack.
How about forking a process to do the drawing?